Chemistry AS Level Flashcards

Question

What is the trend in 1st I.E across 3rd Period

Answer 1

- I.E of Al lower than Mg: e- removed in Al is from higher energy 3p orbital which is further away from nucleus than 3s electrons being removed from Mg. Nuclear attraction is less for 3p than 3s therefore I.E of Al is lower than Mg - I.E of S lower than P: electron being removed in P is in a half filled, more stable 3p orbital whereas in S, the pairing of electrons in 3p results in increased repulsion therefore less energy need to remove an electrons

Answer 2

Ionic radius describes the size of an ion

Answer 3

- Positive ion: smaller radius than original neutral atom because shell no. decreases, screening effect decreases but the attraction of nucleus increases. - Negative ion: larger ionic radius than neutral atom because electrons added while nuclear charge remains same

Answer 4

- Proton no. and effective nuclear charge increases - Ionic radius decreases

Answer 5

Groups 1 to 3 5 to 7 Ion Positive Negative No. of shells = n − 1, n

Answer 6

Negative ions always larger than positive ions in the same period as they have one more shell

Answer 7

Ionic radius increases down the group since number of electron shells increases

Answer 8

- As negative charge on anion increases, ionic radius increases since the number of electrons gained increases such that the number of electrons exceeds the number of protons - As positive charge on cation increases, number of electrons lost increases, so electrostatic attraction between nucleus and outer electrons increases

Answer 9

Relative atomic mass is the weighted average mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12.

Answer 10

Relative isotopic mass is the mass of an atom of an isotope as compared to 1/12 of the mass of an atom of carbon-12. Isotopic mass is the mass of a particular isotope of an element

Answer 11

Relative molecular mass is the weighted average mass of one molecule of an element or compound compared with 1/12 of the mass of an atom of carbon-12

Answer 12

Relative formula mass is the weighted average mass of one unit of a substance compared with 1/12 of the mass of an atom of carbon-12.

Answer 13

Mole is the amount of substance that has the same number of particles (atoms, ions, molecules or electrons) as there are atoms in exactly 12g of the carbon-12 isotope. One mole of any substance will always contain exactly the same number of particles.

Answer 14

Avogadro’s constant: number of atoms, ions, molecules or electrons in a mole = 6.02×10^23 Number of particles/atoms/molecules = Avogadro’s constant x moles

Answer 15

Relative abundance = (Total abundance/Peak height) ×100% AR =∑ (Mass × Relative Abundance) / 100

Answer 16

Molecular Formula = (Empirical Formula)n Where n = Mass of Empirical Formula / Molecular Mass

Answer 17

1. Divide the mass (or percentage by mass) of each element by its molar mass to calculate the molar ratio. 2. Divide each number in the ratio by the smallest number to get the simplest ratio of elements. 3. If the ratio contains decimal numbers, multiply it as appropriate to obtain whole numbers

Answer 18

1. Divide the mass of CO2 produced during combustion by 44 to find the number of moles of CO2. This is equal to the amount of carbon in the compound. 2. Divide the mass of water produced during combustion by 18 to find the number of moles of water. One mole of H2O contains 2 moles of hydrogen atoms so double the number of moles of water to find the number of moles of hydrogen in the compound. 3. Divide the number of moles of hydrogen and carbon by the smallest value to find the simplest molar ratio. This is the empirical formula

Answer 19

Empirical formula is the simplest whole number ratio of atoms of each element in a compound

Answer 20

Molecular formula gives actual numbers of each type of atom in a molecule. Which can be calculated using the Mr of a compound and its empirical formula.

Answer 21

Calculate the relative formula mass of the empirical formula then divide the relative formula mass of the compound by this calculated value. This will show how many times larger the molecular formula is than the empirical formula.

Answer 22

Calculate the relative formula mass of the empirical formula then divide the relative formula mass of the compound by this calculated value. This will show how many times larger the molecular formula is than the empirical formula.

Answer 23

% Composition = (Atomic Mass × No. of Moles/Molar Mass of Compound) ×100%

Answer 24

Moles = Mass / Molar mass

Answer 25

Volume of a Gas = Moles × 24

Answer 26

Concentration = Moles / Volume Unit of volume is dm^3 and 1000cm^3 =1dm^3 Concentration unit = mol/dm^-3

Answer 27

Molar mass is the mass per mole of a substance and can be calculated by adding the relative atomic masses of all the atoms in a formula.

Answer 28

- At the same temperature and pressure, one mole of any gas will occupy the same volume. At room temperature and pressure, this is 24 dm^3 - This does not mean that these gases will have the same mass. - The number of moles of a gas at room temperature and pressure can be calculated, where V is volume: Moles of gas = Volume (dm^3) /24

Answer 29

Concentration is the amount of solute dissolved in a given volume of solution.

Answer 30

Anhydrous is a compound in which all water molecules are removed

Answer 31

Hydrated is a compound which has a number of water molecules associated with its crystalline structure

Answer 32

Water of Crystallisation are water molecules in a hydrated compound are called water of crystallisation

Answer 33

- Mass spectrometry is an analytical technique which gives information about the abundance of different elements on a mass spectra. - Each line represents a different isotope and the relative heights of the peaks show the relative abundance.

Answer 34

1. Use the mass of carbon dioxide to calculate the number of moles of carbon atoms then use this to calculate the mass of carbon present. 2. Use the mass of water to calculate the number of moles of hydrogen atoms then use this to calculate the mass of hydrogen present. 3. Add the masses of carbon and hydrogen and compare to the initial mass of the compound. If there is no difference, the compound is a hydrocarbon so continue with step 4. If there is a difference, assume that this is due to oxygen (unless otherwise told). Calculate the mass of oxygen present and use this to calculate the number of moles of oxygen atoms. 4. Divide the moles of each element by the smallest value to obtain the empirical formula.

Answer 35

The group number relates to the number of electrons in the outer shell

Answer 36

- We fill 1s, 2s,2p 3s,3p 4s 3d, 4p 4d - We fill orbitals from the lowest energy first - We fill each shell singular first before adding pairs

Answer 37

This is because 3d has a higher energy then 4s

Answer 38

An electron from the 4s orbital moves into the 3d orbital to create a more stable half full or 3d sub-shell respectively

Answer 39

Ionic bond is the electrostatic attraction between oppositely charged ions.

Answer 40

An ionic bond is formed when electrons are transferred from a metal to a non-metal, forming an ionic compound. The compound is held together by the electrostatic attraction between the positively charged metal ions and negatively charged non-metal ions.

Answer 41

It has a giant ionic lattice, crystalline solids. In ionic compounds, ions are surrounded on all sides by oppositely charged ions forming a giant ionic lattice that has high melting and boiling points.

Answer 42

Coordination number is number of oppositely charged ions that surround a particular ion in an ionic solid E.g: NaCl, MgCl2

Answer 43

Dot and cross diagrams are often used to represent ionic bonding. For one species electrons are shown as dots and the other as crosses. Typically only outer shell electrons are shown and charges are shown outside square brackets surrounding the ion.

Answer 44

- For anions, electrons are added to the atom (e.g Chlorine forms Chloride Cl- ions - For cations, electrons are removed from the atom (e.g Sodium forms Na+ ions - Atoms form the same number of bonds as the number of electrons required to be added/removed for maximum stability. (e.g: Chlorine will form 1 bond, Sodium will form 1 bond, but Calcium Ca2+ will form 2 bonds - The central atom may expand its octet to form more bonds if necessary (e.g: S8) - In ionic compounds, electrons are showed to be completely transferred to each of the ions in the compound. - In covalent compounds, electrons are showed to be shared between the atoms in the molecule - Use a legend of different shapes (e.g solid circle, unfilled circle, triangle, cross etc) to show which electrons come from which atom in the same way as colours have been used in the above diagrams

Answer 45

Electronegativity is the ability of an atom to attract a bonding pair of electrons in a covalent bond towards itself

Answer 46

- Radius of atom (atomic size) inversely ∝ electronegativity - Nuclear attraction directly ∝ electronegativity

Answer 47

Electronegativity increases across a period because atomic radius decreases and nuclear attraction increases, so polarity increases Electronegativity increases towards the top right of the periodic table

Answer 48

Electronegativity decreases down a group because atomic radius increases and nuclear attraction decreases, so polarity decreases

Answer 49

Dipole moment is slight charges on atoms in a covalent bond due to differences in electronegativity

Answer 50

The difference between the electronegativity of two atoms in a compound determines the overall dipole moment and overall polarity of the compound

Answer 51

- A polar bond is a bond with a permanent charge difference (or permanent dipole). - Bonds with slight ionic character - Bond formed with atoms of different electronegativity - Polar molecules have dipoles; electric charges of equal magnitude and opposite sign - The greater the difference in electronegativity of the two bonded atoms, the greater is the ionic character

Answer 52

If two atoms in a covalent bond are exactly the same, the electronegativity of both atoms will be the same so the bond will be non-polar. Non-polar molecules have no overall charge

Answer 53

Bonding electrons attracted more towards atom with greater electronegativity therefore unequal sharing of electrons therefore molecule develops slight charges = Polar Molecule

Answer 54

A polar molecule must contain polar bonds and be non-symmetrical. If a polar molecule is symmetrical, the dipoles will cancel each other out.

Answer 55

The oxygen in non-metal oxides is very electronegative. This causes a permanent dipole across the covalent bond so the atom that oxygen is bonded to becomes partially positive. When the oxide is added to water, lone pairs on oxygen in the water are attracted to the partially positive atom in the oxide causing hydrolysis. Below are examples of this reaction: P2O5(s) + 3H2O(l) → 2H3PO4(aq) Cl2O(g) + H2O(l) → 2HClO(aq)

Answer 56

The oxygen in non-metal oxides is very electronegative. This causes a permanent dipole across the covalent bond so the atom that oxygen is bonded to becomes partially positive. When the oxide is added to water, lone pairs on oxygen in the water are attracted to the partially positive atom in the oxide causing hydrolysis. Below are examples of this reaction: P2O5(s) + 3H2O(l) → 2H3PO4(aq) Cl2O(g) + H2O(l) → 2HClO(aq)

Answer 57

A large difference in electronegativity will make the bond more polar (more ionic in nature) but a small difference in electronegativity will make the bond less polar (more covalent in nature)

Answer 58

Strong electrostatic forces of attraction between metal cations and delocalized mobile electrons

Answer 59

In metals, positive metal ions (cations) are fixed in a lattice and surrounded by mobile delocalised electrons. The strong electrostatic attraction between the positive metal ions and negative electrons hold the metal together.

Answer 60

- Increasing positive charge on the ions in the lattice - Decreasing size of metal ions in the lattice - Increasing number of mobile electrons per atom

Answer 61

A covalent bond is a chemical bond where electron pairs are shared between the nuclei of two atoms.

Answer 62

This is because the negative electrons are attracted to the positive protons in the nuclei and this overcome the repulsion between the two nuclei.

Answer 63

Non-bonding electrons or lone pair are pair of valence electrons that are not involved in bond formation

Answer 64

Covalent compounds are made of molecules which are held together by weak intermolecular forces. They have low melting and boiling points

Answer 65

Coordinate bond is a dative covalent bond where both electrons in the bond come from the same atom. Coordinate bond is represented by an “→” drawn from the atom donating to towards the atom accepting. In the dative covalent bond A→B, A donates a pair of electrons to B.

Answer 66

- An atom should have a lone pair of electrons - An atom should be in need of a pair of electrons

Answer 67

- Donor is the atom that supplies the pair of electrons - Acceptor isthe atom that accepts the pair of electrons

Answer 68

- Donor is the atom that supplies the pair of electrons - Acceptor isthe atom that accepts the pair of electrons

Answer 69

For a covalent bond to form, atomic orbitals containing unpaired valence electrons must overlap each other

Answer 70

A sigma bond is a single covalent bond formed when two orbitals overlap end-to-end. The pair of electrons are found between the two nuclei.

Answer 71

- Identical atoms: the electronegativity of both atoms is the same so pair of electron shared equally - Symmetrical polyatomic molecules: dipoles of bond exert equal & opposite effects hence cancel charge

Answer 72

The sigma bond forms when two orbitals from different atoms overlap end-to-end. The process of promoting an electron, hybridisation and formation of the molecular orbitals follows the same pattern in all covalently-bound molecules.

Answer 73

A pi bond is a covalent bond formed when 2 orbitals overlap sideways. The pi bond is the region above and below a sigma bond where this pair of electrons can be found. Orbitals overlap sideways to form a pi bond

Answer 74

- Sigma bond has greater overlap then pi bound therefore sigma > pi - Pi bond cannot exist without a Sigma bond.

Answer 75

Elements in Period 3 can expand their octet by making use of the energetically accessible lower lying d-subshell for bonding. This means that some elements of period 3 can bond with more than 4 electrons at once.

Answer 76

- The number of pairs of electrons around central atom - Whether these pairs are lone pairs or bonded pairs - The arrangement of electrons around the central atom

Answer 77

Electron pairs are regions of negative charge so they repel each other and arrange themselves as far apart as possible.

Answer 78

Valence shell electrons are arranged in pairs to minimize repulsion between themselves

Answer 79

Lone pairs offer more repulsion than bonding pairs Lone pair - lone pair Lone pair - bonding pair

Answer 80

Bonding pair - bonding pair

Answer 81

When drawing the shapes of molecules, a bond in the plane of the paper is a normal line. A bold wedge shows the bond is coming towards you and a dotted wedge shows the bond is going away from you. Dots are used to represent electrons in a lone pair

Answer 82

2 bounded pair 2electrons Linear 180° CO2

Answer 83

3 bounded pair Trigonal planar 120° BF3

Answer 84

4 bounded pair Tetrahedral 109.5° CH4

Answer 85

5 bounded pair Trigonal bipyramidal 90° and 120° PF5

Answer 86

6 bounded pair Octahedral 90° SF6

Answer 87

2 bounded pair, 2 lone pair Non-linear or V-shaped 104.5° H2O

Answer 88

3 bounded pair, 1 lone pair Pyramidal 107° NH3

Answer 89

No, Ions have the same shapes and bond angles as molecules

Answer 90

- Bond energy is the amount of energy needed to break one mole of a given gaseous covalent bond to produce gaseous atoms. Bond energies given in the data book are an average and don’t consider the specific molecule the bond is found in. - Bond length is the distance between two nuclei in a covalent bond. A longer bond means the shared pair of electrons is further from at least one nucleus so the attraction and bond strength decreases with increasing bond length. - Bond polarity. If the electronegativities of the bonding atoms are different, the bond will be polar and the bonding atoms will have partial charges.

Answer 91

The strength of a bond rather than polarity typically determines the rate of a reaction. Polarity may mean molecules are attracted to each other which triggers the reaction.

Answer 92

- Strength of the bond depends on the length of the bond, which depends on radii of the two bonded atoms; larger the radius, longer the bond length. - A stronger bond means the compound is less reactive

Answer 93

Double bonds are shorter than single bonds because double bonds have a greater negative charge density between the two atomic nuclei hence greater attraction

Answer 94

Hydrogen Bonding

Answer 95

- Molecule having a H atom bonded to F, O or N - Molecule having F, O or N atom with lone pair of electrons

Answer 96

- Molecule having a H atom bonded to F, O or N - Molecule having F, O or N atom with lone pair of electrons

Answer 97

This is because oxygen, nitrogen and fluorine are very electronegative meaning they draw the bonding electrons towards them to create a strong dipole (a charge difference across the bond). .

Answer 98

A hydrogen bond is the attraction between the partially positive hydrogen (Hᵟ+) and a lone pair on Oᵟ-, Nᵟ-, or Fᵟ-.

Answer 99

Intermolecular forces are weak forces present between two covalent neighbouring molecules.

Answer 100

Very weak forces present between non-polar molecules. There are no permanent dipoles but electrons are mobile and in an instant, they may be unevenly distributed.

Answer 101

Due to constant motion of electrons, at an instant, a non-polar molecule develops poles. This creates a temporary dipole, with the side containing more electrons becoming partially negative. The temporary dipole can induce dipoles in neighbouring molecules as the partial negative charge repels electrons. These opposite partial charges will remain attracted to each other.

Answer 102

- increasing number of contact points between molecules; point where molecules come close together - increasing number of electrons (+ protons) in molecule

Answer 103

Permanent dipole-dipole forces are another type of van der Waals forces found between polar molecules, they are weak forces.

Answer 104

- The permanent dipole in these molecules means the partial charges are more strongly attracted to one another. Molecules with permanent dipole-dipole forces usually have higher boiling points than those which only have London forces between them - Molecules always attracted to charged rod, whether positive or negative because molecules have positive and negative charges

Answer 105

- Elements in group 18 exist as single atoms so the only forces between the atoms are London forces. - These forces are relatively weak so require little energy to break meaning group 18 elements have low boiling points. - Boiling point increases down the group because the number of electrons and atomic radius increases meaning there are stronger temporary dipole and stronger London forces between the atoms.

Answer 106

- High melting and boiling points - strong covalent bonds require a large amount of energy to break. - Mostly non-conductors - don’t contain mobile charged particles (except graphite which contains delocalised electrons). - Insoluble - covalent bonds in the lattice are too strong to be broken

Answer 107

- High melting and boiling points - strong electrostatic attraction between oppositely charged ions requires a lot of energy to break. - Electrical conductor - when aqueous or molten, the ions are free to move and conduct electricity. When solid, the ions are fixed in an ionic lattice so can’t conduct electricity. - Soluble in polar solvent - charged parts of the solvent are attracted to the oppositely charged ions.

Answer 108

- High melting and boiling point - the attraction between the ions and delocalised electrons is strong so a lot of energy is needed to overcome the metallic bonding. - Good electrical conductor - contains mobile delocalised electrons which can conduct electricity as a solid. - Malleable and ductile - the regular structure and delocalised electrons allow the uniform layers of ions to slide over one another.

Answer 109

- High boiling point - The melting and boiling points are greater than those of molecule with only van der Waals forces between them because hydrogen bonds are stronger. - Soluble in water - strong permanent dipoles allow the formation of hydrogen bonds with water. - Non-conductors - no mobile charges so are unable to conduct electricity - The hydrogen bonding in water causes water molecules in ice to align in an open lattice structure. This means water expands as it freezes so ice is less dense than water.

Answer 110

- Low boiling point - forces are weak so require little energy to break. Larger molecules have more van der Waals forces so have higher melting and boiling points. - Solubility - unless they react with water, most molecular compounds are insoluble in water because they release too little energy when they dissolve. They are often soluble in organic solvents because they both contain van der Waals forces. - Non-conductors - no mobile charges so are unable to conduct electricity.

Answer 111

An exothermic reaction is a reaction in which energy is released. This is because less energy is required to break bonds than is released when making bonds. Exothermic reactions are involved in bond making. ΔH negative EReactants > EProducts

Answer 112

An endothermic reaction is a reaction which takes in energy. This is because more energy is required to break bonds than is released when making bonds. Endothermic Reactions is a bond breaking reaction that makes the surrounding cooler. ΔH positive EReactants < EProducts

Answer 113

(s) - solid (l) - liquid (aq) - aqueous (g) - gas

Answer 114

these are reactions where a more reactive element takes the place of a less reactive element in a compound

Answer 115

When a solid is produced after two aqueous reactions react

Answer 116

Concentration (gdm-3) = mass of substance (g) / volume (dm-3)

Answer 117

Ideal gas is a gas whose volume varies in proportion to temperature and in inverse proportion to pressure.

Answer 118

- Temperature must be high enough above the boiling point so that there are no intermolecular forces between molecules. - Pressure must be low enough so that the volume of the individual molecules is negligible relative to the volume of the container.

Answer 119

- Molecules are in constant random motion in straight lines. - Molecules are rigid spheres. - Pressure is due to molecules colliding with the walls of the container. - All collisions are elastic (whether between molecules or between molecules and the walls of the container). - Temperature is proportional to the average kinetic energy of the molecules

Answer 120

- High temperature - Low pressure

Answer 121

- Gas molecules move rapidly and randomly - Distance between gas molecules is greater than diameter of molecules therefore volume is negligible - No forces of attraction/repulsion between molecules - All collisions between particles are elastic EK conserved - Temperature of gas related to average EK of molecules

Answer 122

Real gases do not obey kinetic theory in two ways: - There is not zero attraction between molecules - We cannot ignore volume of molecules themselves

Answer 123

- Molecules are close to each other - Volume of molecules not negligible relative to container - Van der Waals forces present, pulling molecules to each other - Pressure is lower than expected from ideal gas - Effective volume is less than expected from ideal gas

Answer 124

The ideal gas equation is: pV = nRT p - pressure (Pa) V - volume (m^3) n - number of moles (mol) R - gas constant (8.31441 J K-1 mol-1) T - temperature (K)

Answer 125

Mole Fraction = Mols of One Gas / Total Mols of Gases

Answer 126

Partial Pressure of a Gas = Mole Fraction × Total Pressure

Answer 127

Standard Conditions: 101KPa and 273K

Answer 128

1 kPa = 1000 Pa

Answer 129

Temperature + 273

Answer 130

Liquids contain randomly arranged particles which are close together with some gaps. The gaps allow the particles to move. The particles in a liquid have enough energy to prevent the intermolecular forces holding them in a fixed arrangement. Most liquids have a slightly lower density than the solid.

Answer 131

- Energy transferred makes liquid particles move faster - Forces of attraction weaken - Highest energy particles escape first - Liquid starts to evaporate – temp. below b.p. - Forces weaken further – particles move faster and spread - Liquid boils – temp. at b.p.

Answer 132

Heat energy causes the particles in a liquid to move fast enough to break all the forces of attraction between them and become a gas

Answer 133

Enthalpy of vaporization is the heat energy required to change 1 mole of liquid into a gas at its boiling point

Answer 134

Enthalpy of fusion is the heat energy required to change 1 mole of solid into a liquid at its melting point

Answer 135

Energy transferred makes solid particles vibrate faster Forces of attraction weaken & solid changes to liquid Heat energy causes the particles in a solid to vibrate. Eventually, the particles have enough energy to disrupt the regular arrangement and become a liquid.

Answer 136

- Constant evaporation from surface - Particles continue to break away from surface but are trapped in space above the liquid - As gaseous particles collide, some of them hit the surface of the liquid again, and become trapped there - An equilibrium is set up in which number of particles leaving surface is balanced by number rejoining it. - Liquid water molecules ⇌ Vapor water molecules - In this equilibrium, there will be a fixed number of the gaseous particles in the space above liquid.

Answer 137

When a liquid evaporates in a closed container, the gaseous particles move around above the liquid. When these particles collide with the walls of the container, they exert a pressure called the vapour pressure.

Answer 138

Finite resource are resources which doesn't get replaced at the same rate that it is used up. A finite resource is used up faster than it is replaced so it will run out if it is continually used. Examples of finite resources are crude oil, copper and aluminium.

Answer 139

Recycling is important to reduce the rate at which resources are used up. It may reduce costs and the environmental impact of materials. Advantage of Recycling: - Saves energy - Reduces environmental issues and what are the conditions for it to occur - Conserves ore supplies - Less wastage - Cheaper than extracting

Answer 140

The 2s and 2p are close in energy to each other. Given the right amount of energy this allows both electrons to move form the 2s orbital to one of the empty 2p orbital fairly easily. For the bonding to occur we must have singly occupied orbital

Answer 141

When the s-orbital is hybridised with two p-orbitals instead of the 3

Answer 142

For solids, generally solubility increases with increasing temperature as the increase in temperature facilitates the overcoming of intermolecular bonds, making it easier for the solid to dissolve

Answer 143

For gases, generally solubility decreases with increasing temperature as the pressure of the gas increases (pressure only affects solubility of gases)

Answer 144

Solids (metals) are generally the best conductors of electricity while gases are the worst conductors

Answer 145

Solids (metals) are generally better conductors of heat than liquids, while liquids are better thermal conductors than gases. This is because of the proximity of molecules in solids allowing heat to be transferred rapidly through vibrations of neighbouring molecules

Answer 146

In a giant ionic lattice the positive and negative ions alternate in a three dimensional structure, held by ionic bonds. - Sodium chloride, Na+ and Cl- ions. - Magnesium oxide, Mg2+ and O2- ions

Answer 147

In a simple molecular (covalent) lattice the molecules held together by van der Waals forces in a cubic structure. - Iodine, face centred cubic structure. - C60 has a ball like structure made up of hexagons and pentagons of carbon atoms with van der Waals forces between molecules. - Nanotubes are a cylinder of graphene (single sheet of carbon atoms covalently bonded together).

Answer 148

Diamond, each carbon shares an electron with 4 other carbon atoms.

Answer 149

- High m.p./b.p. - each carbon forms four covalent bonds - Hard - tetrahedral structure - Doesn’t conduct heat or electricity – no free electrons - Used for cutting as is strongest known substance and has sharp edges

Answer 150

Graphite, hexagons of carbon atoms in layers with each carbon atom covalently bonded to 3 carbon atoms, one delocalised electron per carbon atom so van der Waals forces between layers. Graphene, single layer of graphite.

Answer 151

- Three strong (sp^2) covalent bonds - Fourth electron in p orbital forms a pi bond, forming a cloud of delocalised electron above and below the planes - Layers kept together by weak Van der Waal’s forces - High m.p./b.p. - strong covalent bonds throughout - Soft – forces between layers are weak - Conducts electricity - has delocalized electrons

Answer 152

- Silicon(IV) oxide, similar 3D structure to diamond with oxygen and silicon atoms covalently bonded together. - Each Si is bonded to 4 oxygen atoms, but each oxygen is bonded to 2 Si atoms - Sand is largely SiO2 - Similar properties to diamond

Answer 153

A hydrogen-bonded lattice is an ice, open lattice structure held by hydrogen bonds between partially positive hydrogen and a lone pair of electrons on oxygen.

Answer 154

- In ice form, water molecules slow down and come closer together - Due to polarity, molecules form hydrogen bonds between lone pairs of oxygen and δ+ charge of hydrogens - Each water molecule has 2 H-bonds - They arrange themselves into an open crystalline, hexagonal structure - Due to large spaces, ice is less dense than water

Answer 155

- Relatively high m.p./b.p.: many strong H-bonds - High viscosity: hydrogen bonding reduces ability of water molecules to slide over each other - High surface tension: hydrogen bonds in water exert a downward force on surface of liquid - Ice less dense than water: larger spaces between molecules in hexagonal structure

Answer 156

- Diatomic molecule formed due to covalent bond between individual atoms - Molecules have weak Van der Waals forces of attraction between them

Answer 157

- Dark grey crystalline solid; vaporizes into purple gas - m.p./b.p. are slightly higher than room temp - Slightly soluble in water; dissolves in organic solvents

Answer 158

- C atoms in pentagonal and hexagonal rings - Spherical - C60 molecules held together by Van Der Waals

Answer 159

- Conducts heat and electricity - Very strong and tough - Insoluble in water - High m.p./b.p.

Answer 160

- C atoms in hexagonal rings only - Cylindrical - Structure is rod like due to continuing rings

Answer 161

- Conducts heat and electricity - Very strong and tough - Insoluble in water - High m.p./b.p

Answer 162

1. A high boiling point indicates a giant structure (ionic, metallic or giant covalent) while a low boiling point indicates simple molecules (or atoms for noble gases). 2. Compounds that are soluble in water tend to be ionic. If the compound is soluble and has a low boiling point, it may be a simple molecule that is small and very polar or able to form hydrogen bonds. 3. If the solid compound conducts electricity, it is likely to be a metal, graphite or graphene. If the substance only conducts electricity when molten or dissolved, it is an ionic compound. 4. The appearance of a substance can be used to distinguish between giant structures. A shiny, malleable and ductile substance is a metal whereas ionic and giant covalent structures tend to be brittle.

Answer 163

Enthalpy change, ΔH, is the thermal energy stored in a chemical system. It can’t be measured directly.

Answer 164

If energy is released into the surroundings, the reaction is exothermic and ΔH is negative.

Answer 165

If energy is taken in from the surroundings, the reaction is endothermic and ΔH is positive

Answer 166

Standard molar enthalpy change of combustion ΔHc is enthalpy change when 1 mole of element or compound is completely combusted under standard conditions in their standard states

Answer 167

Standard conditions are the temperature of 298 K (25°C), pressure of 100 kPa (1 bar), solution concentrations of 1 mol dm-3. All products and reactants are in their standard states.

Answer 168

Standard enthalpy change of formation, ΔHӨf, is the enthalpy change that takes place when one mole of a given substance is formed from its elements under standard conditions

Answer 169

Standard enthalpy change of solution, ΔHӨsol, is the enthalpy change that occurs when one mole of a solute is dissolved in a solvent to form an infinitely dilute solution under standard conditions in their standard states

Answer 170

Standard enthalpy change of hydration, ΔHӨhyd is the enthalpy change that takes place when one mole of gaseous ions dissolves in water under standard conditions in their standard states

Answer 171

Standard enthalpy change of atomisation, ΔHӨat is the enthalpy change when one mole of gaseous atoms are formed from its element under standard conditions in their standard states.

Answer 172

Standard enthalpy change of neutralisation ΔHӨneut is the enthalpy change when one mole of water is formed from a neutralisation reaction under standard conditions

Answer 173

Standard enthalpy change of reaction, ΔHӨr is the enthalpy change that occurs when a reaction takes place in the molar quantities given in a chemical equation, all reactants and products in their standard states under standard conditions.

Answer 174

Bond energy is the energy required to break one mole of a given gaseous bond to form atoms. Bond energy is the energy needed to break a specific covalent bond and how much energy is released when a bond forms

Answer 175

ΔH = -mcΔT ΔH - enthalpy change (J) m - mass of surroundings (g) c - specific heat capacity (J g-1 K-1) ΔT - temperature change (K or °C) - When substance dissolved in water use c & m of water - ΔT is change in temp.: add negative or positive to show rise/fall

Answer 176

Hess’ Law states that the total enthalpy change in a chemical reaction is independent of the route by which the chemical reaction takes place as long as the initial and final conditions are the same. This is because the enthalpy of the reactants and products remain the same.

Answer 177

- Standard conditions are hard to maintain (e.g. exo/endo) - Elements don’t always react directly

Answer 178

Method 1: ΔH = total energy needed to break bonds - total energy made when making bonds When totalling the energy released or made, the average bond enthalpies for each bond must be multiplied by the number of that bond present in the equation. Method 2: use an enthalpy cycle

Answer 179

Oxidation numbers are used to show what is being oxidised and reduced in a redox reaction

Answer 180

Oxygen as peroxide; oxidation number = -1 1st group elements & hydrogen; oxidation number = +1 H with highly reactive metal; oxidation number = -1 Following these rules, all other atoms in a covalent bond must balance out the charge

Answer 181

- Atoms in a diatomic molecule; oxidation number = 0 - Oxygen in a compound; oxidation number = -2

Answer 182

- Uncombined elements always have an oxidation state of 0 - In a neutral compound, the sum of the oxidation states of all the atoms or ions is 0. - In an ion, the sum of the oxidation states of all the atoms is equal to the charge of the ion. - More electronegative elements in a substance have a negative oxidation state while less electronegative elements are given a positive oxidation state. - In ionic molecules the group number is equal to the valence electrons

Answer 183

If an oxidation state increases by one unit, one electron is lost from that substance. If an oxidation state decreases by one unit, one electron has been gained. In a reaction, if the oxidation state of one substance decreases, this must be balanced by an increase in the oxidation state of something else.

Answer 184

A redox reaction is a reaction in which oxidation and reduction takes place. Redox reactions can be shown with changes in oxidation numbers of elements from the product side to the reactant side

Answer 185

Oxidation is the loss of electrons, or increase in oxidation number.

Answer 186

Reduction is the gain of electrons, or decrease in oxidation number

Answer 187

Disproportionation Reaction is a reaction when the same species undergoes both oxidation and reduction in a reaction.

Answer 188

Reducing agent is a reaction with a substance which helps to reduce another species by donating electrons to it and itself gets oxidised in the process

Answer 189

Oxidising Agent is a substance which helps to oxidise another species by accepting electrons from it and itself gets reduced in the process

Answer 190

- identifying oxidation number changes - balance oxidation number changes - balance charges - balace atoms

Answer 191

Reversible reaction is a reaction which can go forwards or backwards depending on the conditions.

Answer 192

Dynamic Equilibrium is the state of a reversible reaction carried out in a closed container where the rates of forward and backward reactions are equal and constant

Answer 193

When a chemical system in dynamic equilibrium is disturbed, when conditions changed, it tends to respond in such a way so as to oppose the change and a new equilibrium is set up

Answer 194

- Concentration - Pressure - Temperature - Catalyst

Answer 195

Increasing the concentration of reactants causes the position of equilibrium to shift right in order to reduce the concentration of reactants and form more products. The reverse occurs if concentration is decreased.

Answer 196

Increasing the pressure will cause the position of equilibrium to shift towards the side with the fewest gaseous molecules in order to decrease the pressure. The opposite occurs if pressure is decreased. If there is an equal number of gaseous molecules on both sides of the equation, changing pressure will have no effect on the position of equilibrium.

Answer 197

For an equilibrium where the forward reaction is exothermic, increasing the temperature will cause the position of equilibrium to shift to the left (so more endothermic reactions occur) to take in more heat energy and reduce the temperature. For the same reaction, decreasing the temperature will cause the position of equilibrium to shift to the right (so more exothermic reactions occur) to release more heat energy and increase the temperature. The opposite is true if the forward reaction is endothermic.

Answer 198

A catalyst has no effect on the position of equilibrium because it speeds up the rate of the forward and backward reactions equally, increasing the rate at which dynamic equilibrium is reached.

Answer 199

Homogeneous equilibria have all substances in the same phase. In heterogeneous equilibria, substances are in different phases. For this general equilibrium equation, all substances are (g), (l) or (aq): aA + bB ⇋ cC + dD

Answer 200

Kc = [Product]mols / [Reactant]mols - Only liquids and gases

Answer 201

Kp = p(Product)mols / p(Reactant)mols - Only gases

Answer 202

Large value of Kc/Kp ⇒ equilibrium towards products side Smaller value of Kc/Kp ⇒ equilibrium towards reactants side

Answer 203

Kc/Kp changes only with changes in temperature

Answer 204

The Haber process produces ammonia from nitrogen and hydrogen: N2(g) + 3H2(g) ⇋ 2NH3(g).

Answer 205

Nitrogen is obtained from the air and hydrogen from natural gas. Once the equilibrium is established, gases leaving the reactor are cooled in order to liquify the ammonia and separate it from the unreacted nitrogen and hydrogen. The unreacted nitrogen and hydrogen is recycled back into the reactor.

Answer 206

The forward reaction in the Haber process is exothermic (ΔH = -92 kJ mol-1). Using Le Chatelier’s principle, a low temperature would be favoured in order to shift the position of equilibrium to the right. However, a relatively higher temperature (400 - 450°C) is used to increase the rate of reaction. This temperature is a compromise.

Answer 207

There are more molecules on the left side of the equation, suggesting a high pressure should be used (according to Le Chatelier’s principle) in order to shift the position of equilibrium to the right. However, high pressures are expensive to maintain and they have safety risks, so a lower pressure of 200 atm is used

Answer 208

- Catalyst: The iron catalyst - Temperature: 500 degrees - Pressure: 200 atm

Answer 209

1. How sulfur dioxide is made: sulfur or sulfur ores (e.g. FeS2) are heated in excess air S(s) + O2(g) → SO2(g) 2. Sulfur dioxide to sulfur trioxide: 2SO2(g) + O2(g) ⇋ 2SO3(g) ΔH = -196 kJ mol-1 3. Sulfur trioxide to concentrated sulfuric acid: sulfur trioxide is dissolved in concentrated sulfuric acid (as adding it to water would create a fog of sulfuric acid). H2SO4(l) + SO3(g) → H2S2O7(l). The product (oleum) is then dissolved in water: H2S2O7(l) + H2O(l) → 2H2SO4(l)

Answer 210

The formation of sulfur trioxide is a reversible reaction so changing the conditions will affect the position of equilibrium

Answer 211

The forward reaction in the Contact process is exothermic (ΔH = -196 kJ mol-1). Using Le Chatelier’s principle, a low temperature would be favoured in order to shift the position of equilibrium to the right. However, a higher temperature (400 - 450°C) is used to increase the rate of reaction.

Answer 212

There are more molecules on the left side of the equation, suggesting a high pressure should be used (according to Le Chatelier’s principle) in order to shift the position of equilibrium to the right. However, the conversion of sulfur dioxide to sulfur trioxide at lower pressures (1-2 atm) is 99.5% so the expense and safety risk of using high pressures isn’t worth the slight increase in percentage conversion

Answer 213

- Catalyst: V2O5 catalyst - Temperature: 500 degrees - Pressure: 1 atm

Answer 214

SO3 not dissolved directly into water because reaction explosive and causes H2SO4 to vaporize

Answer 215

Since reaction highly exothermic, gases must be cooled

Answer 216

No impurities otherwise catalyst will be poisoned

Answer 217

Brønsted-Lowry Theory states: - An acid is a proton (H+) donor - A bases is a proton (H+) acceptor

Answer 218

Amphoteric is substances that can act like bases or acids

Answer 219

Strong acids completely dissociate in solution meaning there is a large number of H+ ions in solution. They typically have a pH ranging from 0 - 1

Answer 220

Weak acids partially dissociate in solution and they typically have a pH ranging from 2 - 6. This is typically shown as a reversible reaction using ⇋.

Answer 221

Strong bases completely dissociate in solution meaning there is a large number of OH- ions in solution. They typically have a pH close to 14.

Answer 222

Weak bases partially dissociate in solution and have a lower pH than strong bases but always above pH 7.

Answer 223

- Strong acids/bases react more vigorously than weak acids/bases. - Strong acids have lower pH values than weak acids. - Strong bases have higher pH values than weak bases.

Answer 224

When an acid reacts with a base, salt & water are formed. The pH changes in this neutralisation reaction can be graphed on a titration curve.

Answer 225

A buffer minimises the pH change when a small volume of acid or alkali is added

Answer 226

- An acidic buffer has a pH less than 7 and contains a large amount of weak acid and its conjugate base (from a salt) and relatively few H+ ions in equilibrium. - Adding acid to this buffer solution increases the concentration of hydrogen ions. The position of equilibrium shifts left as CH3COO- reacts with most of the added H+ ions to form CH3COOH in order to reduce the concentration of H+ ions This prevents a large decrease in pH. - Adding alkali to this buffer solution increases the concentration of OH- ions. The small concentration of H+ ions reacts with the added OH- ions to form water: H+ + OH- → H2O. The position of the buffer equilibrium shifts to the right in order to regenerate most of the H+ ion

Answer 227

Rate of a reaction is a change in concentration of reactants or products per unit time

Answer 228

- Orientation of collision. - Energy of collision which must exceed activation energy

Answer 229

Activation energy is the minimum energy colliding particles must possess for a successful collision to take place

Answer 230

Catalysis is the acceleration of a chemical reaction by catalyst

Answer 231

Generally, increasing the concentration of reactants will increase the rate of reaction because there are more particles in the same volume so particles will collide more frequently. This means that there is a greater chance that the particles will collide at the correct orientation with sufficient energy for them to react so there will be more frequent successful collision

Answer 232

- The area under the curve is equal to the total number of particles present. - No particles have no energy. - There is no maximum energy. - Only particles with energy above the activation energy have sufficient energy to react when they collide

Answer 233

Increasing the temperature means the particles have more kinetic energy so there will be more collisions in the same amount of time. Also, a greater proportion of the particles have energy above the activation energy (as seen in the Boltzmann above) meaning more of the collisions will result in a reaction. This means there will be more frequent successful collisions so rate of reaction will increase

Answer 234

A catalyst is a substance which speeds up the rate of a reaction without being chemically changed at the end. A homogeneous catalyst is in the same phase as the reactants while a heterogeneous catalyst is in a different phase to the reactants (e.g. a solid catalyst with liquid or gaseous reactants). In the presence of a catalyst, a reaction has a different mechanism, with a lower activation energy.

Answer 235

- If a precipitate is produced, the rate could be measured by placing the conical flask of reaction mixture over a black cross and timing how long it takes for the cross to disappear. - If the reaction mixture changes colour during the reaction, colorimetry could be used to measure the amount of light absorbed by the mixture. - If hydrogen ions are reacting or are produced, the pH could be measured using a pH probe. This method only works for large changes in the concentration of hydrogen ions. - Electrical conductivity measurements can be taken to work out the rate of reaction. The electrical conductivity of a liquid depends on the concentration of ions so if ions are being used up, the conductivity will decrease. - For a reaction which produces a gas the rate of reaction could be measured using: - A gas syringe to record the volume of gas produced - An upturned measuring cylinder in a trough of water to measure the volume of gas produced - A mass balance to measure the change in mass (mass will be lost as the gas escapes)

Answer 236

- Rate = volume ÷ time - If you want to compare the initial rates of two reactions where the volume of gas collected is the same, it can be said that initial rate is inversely proportional to time: Initial rate ∝ 1/t

Answer 237

- An alkaline buffer has a pH greater than 7 and contains a weak base and its salt. - Adding acid to this buffer solution increases the concentration of H+ ions. Ammonia molecules react with H+ ions to form ammonium ions and remove most of the added H+ ions. - Alternatively, the H+ ions may react with OH- ions which are present in the equilibrium to form water. This causes the position of equilibrium to shift to replace the reacted OH- ions until most of the H+ ions have reacted. - Adding alkali to this buffer solution increases the concentration of OH- ions. The position of equilibrium shifts to the left as NH4+ reacts with the added OH- ions.

Answer 238

An indicator is a weak acid that changes colour when it donates a proton.

Answer 239

Indicator Colour in acid Colour in alkali Methyl orange Red Yellow Phenolphthalein Colourless Pink

Answer 240

Indicator Colour in acid Colour in alkali Methyl orange Red Yellow Phenolphthalein Colourless Pink

Answer 241

- When comparing the atomic radius of period 3 atoms, the metallic radii is used for Na, Mg and Al and the covalent radii is used for Si, P, S and Cl. - Across period three, atomic radius decreases from sodium to chlorine. - The radius of argon can’t be compared as it does not form compounds. - Across the period, atomic number decreases so the nucleus has a higher positive charge. This draws electrons slightly closer to the nucleus meaning the atomic radius decreases.

Answer 242

- Across period 3, the ionic radius decreases from sodium to aluminium (positive ions) then increases from silicon to chlorine (negative ions). - The positive ions have a decreasing ionic radius because, although the ions have the same electron configuration, the number of protons in the nucleus increases so nuclear attraction increases. - The negative ions have an increasing ionic radius because the ions have gained electrons meaning there are now more electrons than protons. As a result, the nuclear attraction to the electrons is weaker so they are not pulled in as strongly

Answer 243

Sodium, magnesium and aluminium are giant metallic structures with metallic bonding. Their melting points increase across the period as the metal-metal bond strength increases. The bond strength increases because the charge of the metal ion increases and the atomic radius decreases.

Answer 244

Silicon is a macromolecule with strong covalent bonds linking all its atoms together. This means it has the highest melting point of all the elements in period 3.

Answer 245

Phosphorus (P4), sulfur (S8) and chlorine (Cl2 ) are all simple covalent molecules. Their melting points are dependent on the strength of their van der Waals/ intermolecular forces. The more atoms/electrons in a molecule mean stronger van der Waals forces so sulfur has the greatest melting point of these three molecules. Chlorine will have the lowest melting point since it is only made up of two atoms

Answer 246

Phosphorus (P4), sulfur (S8) and chlorine (Cl2) are all simple covalent molecules. Their melting points are dependent on the strength of their van der Waals/ intermolecular forces. The more atoms/electrons in a molecule mean stronger van der Waals forces so sulfur has the greatest melting point of these three molecules.Chlorine will have the lowest melting point since it is only made up of two atoms

Answer 247

Argon will have the lowest melting point of period 3 because it exists as single atoms so there are very weak van der Waals intermolecular forces which are easy to overcome.

Answer 248

- Conductivity of a compound relies on the presence of charged particles (such as ions or electrons) which are free to move. - Metallic compounds can conduct electricity due to the sea of delocalised electrons. - Conductivity increases from sodium to aluminium because the number of delocalised electrons increases so more electrons are free to carry charge. - The molecules silicon to chlorine are covalent compounds with no charged particles so they are non-conductors. Similarly argon is monatomic so is unable to conduct electricity.

Answer 249

- The first ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions. - First ionisation energy generally increases across period 3. This is because the number of protons increases across the period while electron shielding remains the same. - As a result, across the period, the electrons are attracted more strongly to the nucleus so they are harder to remove, leading to a higher first ionisation energy.

Answer 250

- The first ionisation energy of aluminium is lower than that of magnesium. This is because the electron is being removed from a 3p orbital rather than a 3s orbital. This means there is more electron shielding from the 3s orbital so the electron can be removed more easily. - The first ionisation energy of sulfur is lower than that of phosphorus. Sulfur is the first element to have an electron pair in a 3p orbital so an electron is being removed from a pair. The electrons in the pair repel each other slightly making it easier to remove an electron

Answer 251

- Sodium burns in oxygen with an orange flame to produce a white solid. 4Na + O2 → 2Na2O - Magnesium burns in oxygen with a bright white flame to produce a white solid. 2Mg + O2 → 2MgO - Aluminium burns in oxygen if the aluminium oxide layer on the outside of the metal is removed. This can be done by powdering the aluminium. Sparks can be seen when the powder is burned and a white solid is produced. 4Al + 3O2 → 2Al2O3 - Silicon will only burn in oxygen if it is heated strongly enough. Si + O2 → SiO2 - White phosphorus reacts spontaneously in the air to produce a white solid. P4 + 5O2 → P4O10 - Sulfur burns with a blue flame in oxygen when heated gently. It produces a colourless gas of sulfur dioxide which reacts further with oxygen to form sulfur trioxide. S + O2 → SO2 2SO2 + O2 → 2SO3 - Chlorine does not react with oxygen (directly). - Argon does not react with oxygen.

Answer 252

- Sodium burns in chlorine with a bright orange flame to form sodium chloride (white solid). 2Na + Cl2 → 2NaCl - Magnesium burns in chlorine with a bright white flame to form magnesium chloride (white solid). Mg + Cl2 → MgCl2 - Aluminium burns in a stream of chlorine to produce pale yellow aluminium chloride. 2Al + 3Cl2 → 2AlCl3 At high temperatures, AlCl3 is converted into its molecular form Al2Cl6. - If chlorine is passed over silicon powder, a colourless liquid forms (silicon tetrachloride). Si + 2Cl2 → SiCl4 - White phosphorus burns spontaneously in chlorine to produce phosphorus(V) chloride (off-white solid). P4 + 10Cl2 → 4PCl5

Answer 253

- Sodium undergoes a very exothermic reaction with cold water, producing hydrogen (seen as bubbles) and a colourless solution of sodium hydroxide. 2Na + 2H2O → 2NaOH + H2 - Magnesium reacts slowly with cold water. Bubbles of hydrogen are produced and a thin layer of magnesium hydroxide forms on the magnesium which inhibits further reaction. Mg + H2O → Mg(OH)2 + H2 - Magnesium burns in steam with a bright white flame to produce white magnesium oxide and hydrogen: Mg + H2O → MgO + H2

Answer 254

- The oxidation state of an uncombined element is 0. - The sum of oxidation states in a compound is 0 and the sum of oxidation states in an ion is equal to the overall charge.

Answer 255

- +1 for group one atoms - +2 for group two atoms - -2 for oxygen (except when in a peroxide or F2O) - +1 for hydrogen (except in metal hydrides where it is -1) - -1 for fluorine - -1 for chlorine (except when bonded with fluorine or oxygen)

Answer 256

Na2O +1 MgO +2 Al2O3 +3 SiO2 +2 P4O10 +5 SO2 +6 SO3 +4 In each of the cases above, the oxidation state has the same value as the number of valence shell electrons (the number of electrons in the outer energy level of the atom)

Answer 257

NaCl +1 MgCl2 +2 AlCl3 +3 SiCl4 +4 PCl4 +5 In each of the cases above, the oxidation state has the same value as the number of valence shell electrons (the number of electrons in the outer energy level of the atom)

Answer 258

- Sodium oxide is a strongly basic oxide which reacts exothermically with water to form a solution of sodium hydroxide (around pH 14). Na2O + H2O → 2NaOH - Magnesium oxide undergoes a slight reaction with water, forming some magnesium hydroxide ions. As these are only partially soluble, the pH of the resulting solution is about 9 since not many hydroxide ions are released into the solution. MgO + H2O → Mg(OH)2 - Aluminium oxide does not react with water. - Silicon dioxide does not react with water because it is difficult to break up the macromolecule. - Phosphorus(V) oxide reacts violently with water to form phosphoric acid. P4O10 + 6H2O → 4H3PO4 - Sulfur dioxide reacts with water to form an acidic solution of sulfurous acid. SO2 + H2O → H2SO3 - Sulfur trioxide reacts violently with water to produce sulfuric acid. SO3 + H2O → H2SO4

Answer 259

- Sodium oxide is a strong base which reacts with acid to form a salt and water. Na2O + 2HCl → 2NaCl + H2O - Magnesium oxide reacts with warm dilute hydrochloric acid to form a salt and water. MgO + HCl → MgCl2 + H2O - Aluminium oxide is amphoteric so reacts with acids and bases. It reacts with warm dilute hydrochloric in the same way as magnesium and sodium: Al2O3 + 6HCl → 2AlCl3 + 3H2O - Aluminium oxide also reacts with bases: Al2O3 + 2NaOH + 3H2O → 2NaAl(OH)4 - Silicon dioxide reacts with hot concentrated sodium hydroxide solution. A colourless solution is formed. SiO2 + NaOH → Na2SiO3 + H2O - Phosphorus(V) oxide can form a range of salts when reacted with a base. Here is one example: P4O10 + 12NaOH →4Na3PO4 + 6H2O - Sulfur dioxide will react with a base when bubbled through it: SO2 + NaOH → Na2SO3 + H2O - Sulfur trioxide reacts with a base to form sulfuric acid and water. SO3 + 2NaOH → Na2SO4 + H2O

Answer 260

- Sodium and magnesium hydroxides are both simple basic hydroxides. NaOH + HCl → NaCl + H2O Mg(OH)2 + 2HCl → MgCl2 + 2H2O - Aluminium hydroxide is amphoteric so will react with acids and bases: Al(OH)3 + 3HCl → AlCl3 + 3H2O Al(OH)3 + NaOH → NaAl(OH)4 - The other period three hydroxides each act as acids since the OH group is covalently bonded to the element.

Answer 261

- The ionic chlorides of sodium do not react with water, but the polar water molecules of magnesium chlorides are attracted to the ions the white solids dissolve to form colourless solution - The simple molecular chlorides aluminum, silicon, phosphorus and sulfur react with water, giving off white fumes of hydrogen chloride gas

Answer 262

- Generally, the Group 2 metals burn in oxygen to form a metal oxide. - Beryllium is coated in a thin layer of beryllium oxide which inhibits the reaction meaning it only reacts in a powder form. 2Be + O2 → 2BeO - Magnesium burns in oxygen with a bright white flame. 2Mg + O2 → 2MgO - Calcium burns with an orange/red flame. 2Ca + O2 → 2CaO - Strontium is reluctant to start burning but burns intensely with a red flame. 2Sr + O2 → 2SrO - Barium burns in oxygen with green flame. 2Ba + O2 → 2BaO

Answer 263

- The reactions of the Group 2 metals with water or steam can be used to see the trend in reactivity down the group. - Beryllium reacts with steam only at very high temperatures. Be + H2O → BeO + H2 - Magnesium has a very slight reaction with cold water. The reaction stops due to the production of an insoluble coat of magnesium hydroxide. Mg + 2H2O → Mg(OH)2 + H2 - Magnesium burns in steam more readily than cold water: Mg + H2O → MgO + H2 - Calcium, strontium and barium all react in cold water to produce their hydroxide and hydrogen gas. The reactions become increasingly vigorous down the group. E.g. Ca + 2H2O → Ca(OH)2 + H2 - Beryllium only reacts with steam at high temperatures but, going down Group 2, the metals react more readily and rapidly with cold water, with barium reacting the fastest. This shows that reactivity increases down the group.

Answer 264

- The reactions of the Group 2 metals with water or steam can be used to see the trend in reactivity down the group. - Beryllium reacts with steam only at very high temperatures. Be + H2O → BeO + H2 - Magnesium has a very slight reaction with cold water. The reaction stops due to the production of an insoluble coat of magnesium hydroxide. Mg + 2H2O → Mg(OH)2 + H2 - Magnesium burns in steam more readily than cold water: Mg + H2O → MgO + H2 - Calcium, strontium and barium all react in cold water to produce their hydroxide and hydrogen gas. The reactions become increasingly vigorous down the group. E.g. Ca + 2H2O → Ca(OH)2 + H2 - Beryllium only reacts with steam at high temperatures but, going down Group 2, the metals react more readily and rapidly with cold water, with barium reacting the fastest. This shows that reactivity increases down the group.

Answer 265

All Group 2 metals react with dilute hydrochloric acid to produce a metal chloride and hydrogen gas. The reactions get more vigorous as you go down the group. The general equation for this reaction is: X + 2HCl → XCl2 + H2 (where X is a Group 2 metal). E.g. Ca + 2HCl → CaCl2 + H2

Answer 266

- Dilute sulfuric acid reacts with Group 2 metals to produce a metal sulfate and hydrogen. The general equation for this reaction is: X + H2SO4 → XSO4 + H2 (where X is a Group 2 metal). E.g. Mg + H2SO4 → MgSO4 + H2 - The reactions with dilute sulfuric acid do not get more vigorous down the group due to the solubility of the sulfates produced. - Beryllium and magnesium produce soluble sulfates so their reactions with sulfuric acid are similar to their reactions with hydrochloric acid. Calcium produces a sparingly soluble sulfate. Strontium and barium produce insoluble sulfates. This means calcium, strontium and barium will only react with sulfuric acid for a short period of time because the reaction will stop once the insoluble sulfate forms on the metal.

Answer 267

- Apart from beryllium, all Group 2 oxides react with water to produce hydroxides. - Magnesium oxide produces a solution that is around pH 9. This is because the magnesium hydroxide is only sparingly soluble so not many OH- ions are released into the solution. MgO + H2O → Mg(OH)2 - Calcium oxide (quicklime) undergoes an exothermic reaction to produce calcium hydroxide (also known as slaked lime or lime water). Calcium hydroxide is partially soluble so the resulting solution is pH 12. CaO + H2O → Ca(OH)2 - Strontium oxide and barium oxide produce hydroxides which are increasingly soluble. They react in the same way as calcium but produce solutions with a higher pH as more OH- ions get released into the solution.

Answer 268

- All Group 2 oxides react with dilute acids to produce salt and water. - The general equations for these reactions (where X is a Group 2 metal) are: XO + 2HCl → XCl2 + H2O XO + 2HNO3 → X(NO3)2 + H2O XO + H2SO4 → XSO4 + H2O - The reactions with hydrochloric and nitric acid are standard and reactivity increases down the group. - The reactions with sulfuric acid are different due to the different solubilities of the products. Magnesium and beryllium oxides react as expected. Calcium, barium and strontium oxides react differently because their sulfates are increasingly insoluble. The sulfate formed during the reaction coats the metal oxide, slowing or stopping the reaction.

Answer 269

The Group 2 hydroxides do not react with water.

Answer 270

- The Group 2 hydroxides react with dilute acids in the same way as the metal oxides. The only difference is that two water molecules are produced rather than one. E.g. Sr(OH)2 + 2HCl → SrCl2 + 2H2O

Answer 271

The Group 2 metal carbonates are insoluble so they do not react with water.

Answer 272

- Group 2 carbonates react with dilute acids to produce a salt, water and carbon dioxide. The general equations for these reactions (where X is a Group 2 metal) are: XCO3 + 2HCl → XCl2 + H2O + CO2 XCO3 + 2HNO3 → X(NO3)2 + H2O + CO2 XCO3 + H2SO4 → XSO4 + H2O + CO2 - The reactions with hydrochloric and nitric acid are standard and reactivity increases down the group. - The reactions with sulfuric acid are different due to the different solubilities of the products. Magnesium and beryllium carbonates react as expected. Calcium, barium and strontium carbonates react differently because their sulfates are increasingly insoluble. The sulfate formed during the reaction coats the metal carbonate, slowing or stopping the reaction.

Answer 273

- All Group 2 nitrates undergo thermal decomposition to produce a metal oxide, oxygen and nitrogen dioxide. - The nitrates are heated more strongly as you go down the group because they become more stable. The general equation for this reaction (where X is the Group 2 metal) is: 2X(NO3)2 → 2XO + 4NO2 + O2 - Observations: The nitrate and the oxide are both white solids. Nitrogen dioxide is a brown gas.

Answer 274

- All Group 2 carbonates undergo thermal decomposition to produce a metal oxide and carbon dioxide. The carbonates are heated more strongly as you go down the group because they become more stable - The general equation for this reaction (where X is the Group 2 metal) is: XCO3 → XO + CO2 - Observations: The carbonate and the oxide are both white solids. Carbon dioxide is a colourless gas.

Answer 275

- The solubilities of the Group 2 metal hydroxides and sulfates show trends in the group. - The trend in the solubility of sulfates is opposite to the trend in the hydroxides: Group 2 element Hydroxide - X(OH)2 Sulfate-XSO4 Magnesium Least soluble Most soluble Calcium Beryllium Barium Most soluble Least soluble -Compounds with very low solubilities, like magnesium hydroxide, are often said to be sparingly soluble. Most sulfates are soluble in warm water except barium sulfate which is insoluble.

Answer 276

- Calcium hydroxide and calcium carbonate are both compounds used in agriculture. - Calcium carbonate is powdered limestone. Calcium hydroxide is formed when calcium oxide is added to water. - Calcium oxide and calcium hydroxide are often referred to as lime and slaked lime, respectively. - Crops grow best in soil around pH 6. If soil becomes too acidic, calcium carbonate or calcium hydroxide can be added to raise the pH. This is because both compounds react with and neutralise acids. - Calcium carbonate reacts more slowly than calcium hydroxide since it is not water soluble, however it is used more often as it is cheaper and easier to handle.

Answer 277

- At room temperature, the colours of the halogens get darker down the group. The boiling points also increase due to the increasing strength of the intermolecular forces. - Fluorine - pale yellow gas - Chlorine - green gas - Bromine - red-brown liquid - Iodine - grey solid

Answer 278

- Fluorine has the lowest melting and boiling points in group 17 and is therefore the most volatile. This is because it has the weakest van der Waals (intermolecular) forces. - The number of electrons in each molecule and the size of the molecules increases down group 17. This means that the temporary dipoles get stronger so there are more van der Waals forces between molecules. - More energy is needed to overcome these forces so volatility decreases down Group 17.

Answer 279

The covalent bonds are weaker moving down the group because the halogen atoms get larger, their atomic radius increases. This means that the bonding pair gets further away from the nucleus and shielding increases so the attraction gets weaker. This means the bonds get easier to break.

Answer 280

- Halogens have high electron affinity (they gain electrons easily) hence they are good oxidising agents - Oxidising ability decreases down the group because electron affinity decreases as atomic size increases.

Answer 281

- When the halogens react, they gain an electron to form negative ions. - Reactivity of the halogen decreases down the group. This is because it becomes harder to gain an electron as electron shielding and atomic radius increase down the group so there is weaker attraction between the incoming electron and the protons in the nucleus

Answer 282

Oxidising agents are elements/compounds that gain electrons to oxidise another element/compound. -

Answer 283

Halogens act as oxidising agents and they become less oxidising down the group due to the decreasing reactivity. The relative oxidising strengths of the halogens can be seen by their displacement reactions with other halide ions. Between chlorine, bromine and iodine. Chlorine is the strongest oxidising agent and iodine is the weakest:

Answer 284

Chlorine (Cl2) will displace bromide and iodide ions. Cl2 + 2Br- → 2Cl- + Br2 Cl2 + 2I- → 2Cl- + I2

Answer 285

Bromine (Br2) will displace iodide ions. Br2 + 2I- → 2Br- + I2

Answer 286

Iodine (I2) will not react with chloride or bromide ions No reactions take place

Answer 287

A halogen will displace a halide from a solution if the halide ion is below it in the periodic table.

Answer 288

- Chlorine solution - colourless - Bromine solution - orange - Iodine solution - brown

Answer 289

- The halogens react with hydrogen to form hydrogen halides. These reactions show that reactivity decreases down Group 17. - The standard reaction equation for the reaction with hydrogen (where X is the halogen) is: X2 + H2 → 2HX

Answer 290

- Fluorine reacts explosively with hydrogen to form hydrogen fluoride gas. This reaction occurs even in a cold atmosphere. - Chlorine reacts with hydrogen if lightly heated or exposed to sunlight. - Bromine reacts with hydrogen if heated with a flame. - Iodine only partially reacts with hydrogen when constantly heated. There is a partial reaction because an equilibrium is set up: I2 + H2 ⇌ 2HI

Answer 291

Thermal stability of the hydrides decreases down Group 17.This is because further down the group, the covalent bonds are weaker so they can be broken more easily upon heating. The bonds are weaker further down the group because the halogen atoms get larger. This means that the bonding pair gets further away from the nucleus so the attraction gets weaker and the bond is easier to break.

Answer 292

- The thermal stability of a hydride is how easy a hydrogen halide is broken up into its constituent elements when heated. - Hydrogen fluoride and hydrogen chloride are very thermally stable. They will not split into hydrogen and the halogen if heated under laboratory conditions. - Hydrogen bromide will split into hydrogen and bromine when heated. - Hydrogen iodide will split into hydrogen and iodine more easily than hydrogen bromide.

Answer 293

The thermal stability of the halogens decreases down the group. This can be explained in terms of bond energies. Bond enthalpies of the hydrogen halides decrease down Group 17 because the size of the halogen increases. This means less energy is required to break the covalent bond between hydrogen and halogen

Answer 294

The bond enthalpies of the halogen molecules decrease from Cl2 to I2. This is because the size of the molecules increases so the bonding pair is further from the nucleus. In the same way as the hydrogen halides, the bonding pair is less attracted to the nucleus in larger molecules so the covalent bond is more easily broken.

Answer 295

- When the halide ions react, they lose an electron. Reactivity of the halide ions increases down the group. This is because it becomes easier to lose an electron as electron shielding and atomic radius increase down the group so there is weaker attraction between the outer electrons and the protons in the nucleus. - Reducing agents are elements/compounds that lose electrons to reduce another element/compound. - Halide ions act as reducing agents and they become more reducing down the group due to the increasing reactivity

Answer 296

1. Add nitric acid to the halide ion solution to remove any ions which may produce a false positive for the test (e.g. carbonate ions). 2. Add a few drops of silver nitrate solution (AgNO3). 3. Observe the precipitate formed. - The standard equation for this reaction (where X is the halide ion) is: Ag+(aq) + X-(aq) → AgX(s)

Answer 297

- Fluoride ions - no precipitate. - Chloride ions - white precipitate. - Bromide ions - cream precipitate. - Iodide ions - yellow precipitate.

Answer 298

To ensure the precipitates have been correctly identified, aqueous ammonia can be added: - Chloride precipitate - soluble in dilute NH3 - Bromide precipitate - soluble in concentrated NH3 - Iodide precipitate - insoluble in dilute and concentrated NH3

Answer 299

All halide ions react with concentrated sulfuric acid to produce a hydrogen halide. A secondary reaction then takes place, which differs depending on which halide

Answer 300

NaF + H2SO4 → NaHSO4 + HF NaCl + H2SO4 → NaHSO4 + HCl For both of these reactions, HF and HCl can be identified as misty fumes. HF and HCl are not strong enough reducing agents so no further reactions occur

Answer 301

NaBr + H2SO4 → NaHSO4 + HBr Misty fumes of HBr are produced. HBr is a strong enough reducing agent to react with H2SO4. This second reaction produced the choking gas SO2 and brown fumes of Br2 in a redox reaction: 2HBr + H2SO4 → Br2 + SO2 + 2H2O

Answer 302

NaI + H2SO4 → NaHSO4 + HI Misty fumes of HI are produced. HI is a strong enough reducing agent to react with the H2SO4. Similarly to the reaction above, SO2 is produced. Since HI is a very strong reducing agent, the SO2 is further reduced to H2S - which smells of rotten eggs. 2HI + H2SO4 → I2 + SO2 + 2H2O 6HI + SO2 → H2S + 3I2 + 2H2O

Answer 303

Chlorine is used in water purification because it kills bacteria. Chlorine reacts with water in a disproportionation reaction, producing chloride and chlorate ions. The reaction produces HCl so an alkali is usually added to the water to reduce the acidity. Cl2 + H2O ⇌ 2H+ + Cl- + ClO Chlorate ions kill bacteria so treating water with chlorine or chlorate ions makes it safe to drink or swim in

Answer 304

- Kills dangerous microorganisms which could cause diseases. - Some chlorine persists in the water which prevents reinfection in the long term. - Prevents the growth of algae. - Removes bad tastes and smells. - Removes discolouration.

Answer 305

- A disproportionation reaction is a reaction in which an element is both oxidised and reduced. - Chlorine reacts with cold dilute sodium hydroxide: 2NaOH(aq) + Cl2 (g) → NaClO(aq) + NaCl(aq) + H2O(l) - This is a disproportionation reaction because chlorine has been reduced from 0 in Cl2 to -1 in NaCl and oxidised from 0 in Cl2 to +1 in NaClO. NaClO (also known as sodium chlorate(I) solution) is bleach. It is used in water treatment, to bleach textiles and paper, and for cleaning because it kills bacteria.

Answer 306

6NaOH(aq) + 3Cl2(g) → 5NaCl(aq) + NaClO3(aq) + 3H2O(l) This is a disproportionation reaction because chlorine has been reduced from 0 in Cl2 to -1 in NaCl and oxidised from 0 in Cl2 to +5 in NaClO3

Answer 307

- Nitrogen, has a low reactivity due to its bonding. - A nitrogen molecule, has a triple covalent bond between two nitrogen atoms. - Nitrogen is very unreactive as a large amount of energy is required to break the strong triple covalent bond. - Nitrogen molecules are also unreactive since the bonds in nitrogen molecules are nonpolar and are not easily polarisable. This means electrophiles and nucleophiles are not attracted to nitrogen molecules, making the molecules less likely to be involved in reactions - It reacts only under extreme temperature or pressure or in presence of catalyst.

Answer 308

- Ammonia is a weak base as it only partially dissociates (ionises) in water: NH3 + H2O ⇌ NH4+ + OH - Ammonia is a Bronsted-Lowry base because it accepts hydrogen ions. The hydrogen ion bonds to the ammonia molecule by forming a coordinate bond. This produces an ammonium ion. The production of the hydroxide ions are what gives ammonia its basic character.

Answer 309

- Ammonium ions are produced during acid-base reactions. - The ammonium ion has a tetrahedral shape -Lone pair of e-s of nitrogen forms a coordinate bond with the H+ ion - Formation: NH3(g) + H+ NH4+ - Shape: tetrahedral - Bond angle: 109.5 - Bond length: equal lengths

Answer 310

- Ammonia can be displaced from its salts by heating an ammonium salt with an alkali. The ionic equation for the reaction that takes place is: NH4+ + OH- → NH3 + H2O - This is a common laboratory method of obtaining ammonia. - Any Ammonium Salt + Any Base → Ammonia Gas + salt + water

Answer 311

- Oxides of nitrogen, such as nitrogen monoxide, can be formed as a result of combustion reactions in car engines. - Nitrogen oxides are also produced naturally by the occurrence of lightning. The reaction between oxygen and nitrogen takes place at high pressures and temperatures which occur in car engines. - The reaction that takes place for the formation of nitrogen monoxide is: N2 + O2 → 2NO - Exhaust gases passed through catalytic convertors containing a catalyst (platinum/ palladium/nickel) helping to reduce oxides to nitrogen. - Catalytic role in oxidation of sulphur dioxide

Answer 312

- Catalytic converters can be used to remove oxides of nitrogen from car exhaust fumes. - Catalytic converters contain a ceramic honeycomb structure which is coated in a thin layer of metal catalysts like rhodium and platinum. The honeycomb creates a larger surface area of metal. - Catalytic converters catalyse the reaction between carbon monoxide with nitrogen monoxide (harmful gases) to produce nitrogen and carbon dioxide: 2NO + 2CO → N2 + 2CO2 - If atmospheric oxides of nitrogen (NO and NO2) are not removed from the air, they can react with unburned hydrocarbons to form peroxyacetyl nitrate (PAN). -PAN is a component of photochemical smog - a type of air pollution which causes various respiratory problems.

Answer 313

- Nitrogen dioxide catalyses the reaction for the formation of sulfur trioxide from sulfur dioxide: SO2 + NO2 → SO3 + NO - Nitrogen monoxide reacts with oxygen to reform the nitrogen dioxide catalyst: 2NO + O2 → 2NO2

Answer 314

- Used in the production of nitric acid - Used in the production of inorganic fertilizers - Used in the production of nylon - Used in the production of explosives

Answer 315

- Sulfur dioxide reacts with oxygen in the atmosphere to form sulfur trioxide. Sulfur trioxide is a pollutant because it reacts with water vapour in clouds to form acid rain which causes various environmental problems: - Acid Rain: SO3 + H2O → H2SO4 - 2NO2 + H2O → HNO3 + HNO2 or NO2 + H2O + ½O2→ HNO3 - Acid rain causes environmental damage such as: - Corrosion of limestone buildings and statues. - Acidification of lakes and rivers, damaging the ecosystems in the water. - Damage to vegetation.

Answer 316

Sulfur dioxide is formed when fossil fuels, containing sulfur impurities, are burnt in oxygen. S + O2 → SO2

Answer 317

- Nitrogen oxide (NO): formed by reaction of N2 and O2 in the engine, forms acid rain and respiratory problems - Atmospheric oxides of nitrogen (NO & NO2) can react with unburned hydrocarbons to form peroxyacetyl nitrate (PAN) which is a component of photochemical smog - Carbon monoxide (CO): source: incomplete combustion of hydrocarbon fuel, toxic effect on haemoglobin

Answer 318

- SO2 is used by itself or as a sulphite to preserve food SO2 + H2O→ H2SO3(aq) - SO2 & sulphites inhibit growth of bacteria, yeasts and are reducing agents, so reduce rate of oxidation of food. - Used to prevent spoilage of dried fruit, dehydrated vegetables and fruit juices

Answer 319

Organic chemistry is the study of hydrocarbons and their derivative

Answer 320

- Carbon is tetravalent - Carbon-carbon bonds can be single, double or triple - Atoms can be arranged in chains, branches and rings

Answer 321

- Is a series of compounds of similar structures - contain the same functional group - all share same general formula - formula of homologue differs from neighbour by CH2 - similar chemical properties - gradual change in physical properties as Mr increases

Answer 322

Functional group is an atom or group of atoms in an organic molecule that determine the characteristic reactions of a homologous series.

Answer 323

- Molecular formula - actual number of atoms of each element in a molecule. - Structural formula - shows the structure carbon by carbon with hydrogens and functional groups attached. - Skeletal formula - only shows the bonds on the carbon skeleton. The carbon and hydrogen atoms are not shown but any functional groups are. It can be used to simplify large complicated structures. - Displayed formula - shows how all the atoms are arranged and shows every bond between them.

Answer 324

Hybridisation is mixing up of different atomic orbitals resulting in new orbitals of equal energy.

Answer 325

- Carbon has the electron configuration 1s2 ,2s2 ,2p2. However, if the right amount of energy is provided, an electron can be promoted from one of the s orbitals to a p orbital. - The configuration would now be 1s2, 2s1, 2p3. This is a favourable process due to the fact that the electrons are unpaired so there is less repulsion and more stability

Answer 326

One s orbital and one p orbital hybridise (combine) to form two equivalent orbitals. The new orbitals are called sp orbitals and they repel to give a linear shape with a 180 bond angle

Answer 327

One s orbital and two p orbitals hybridise to form three equivalent orbitals. The remaining 2p orbital is left unchanged. The three new sp2 orbitals all repel to give a trigonal planar arrangement with a bond angle of 120. The unchanged 2p orbital lies perpendicular to this planar arrangement.

Answer 328

One s orbital and three p orbitals hybridise to form four equivalent orbitals. The new orbitals are called sp3 orbitals and they all repel to give a tetrahedral arrangement. This means the molecule has bond angles of 109.5

Answer 329

1. Identify the longest carbon chain that contains the functional group. 2. Identify the functional group on the chain. This gives you the suffix or prefix of the compound. 3. Count along the carbon chain so that the functional group has the lowest number. 4. If there are any side chains, add these as prefixes (e.g. methyl-) to the beginning of the name. Do the same if there are other (less important) functional groups. Put these at the start of the name in alphabetical order. 5. If there are two or more identical functional groups or side chains use the prefixes di-, tri- and tetra- before that section of the name.

Answer 330

Alkanes general formula CnH2n+2 Suffix: -ane i.e Propane C3H8. Structural formula CH3CH2CH3

Answer 331

Alkenes functional group : CnH2n Suffix: -ene i.e Ethene C2H4. Structural formula CH2CH2

Answer 332

- Halogenoalkanes general formula is CnH2n+1X - X is F, Cl, Br, l Prefex: Fluoro-, Chloro-, Bromo-, Iodo- i.e Chloroethane C2H5Cl. structural formula CH3CH2Cl

Answer 333

Alcohols general formula is CnH2n+1OH suffix: -ol i.e Ethanol C2H6O. Structural formula CH3CH2OH

Answer 334

Aldehydes general formula is CnH2n+1CHO suffix: -al i.e Ethanal C2H4O. structural formula CH3CHO

Answer 335

Ketones general formula CnH2n+1COCmH2m+1 suffix: -one i.e Propanone C3H6O. Structural formula CH3COCH3

Answer 336

Carboxylic acids general formula CnH2n+1COOH suffix: -oic acid i.e Ethanoic acid C2H4O2. Structural formula CH3COOH

Answer 337

Esters general formula CnH2n+1COOCmH2m+1 prefix: Alkyl- suffix: -oate i.e Methyl ethanoate C3H6O2. Structural formula CH3COOCH3

Answer 338

Amines general formula CnH2n+1NH2 suffix: -amine i.e methylamine CH5N. Structural formula CH3NH

Answer 339

Nitriles general formula CnH2n+1CN suffix: -nitrile i.e Ethane nitrile C2H3N. Structural formula ChH3CN

Answer 340

Number of carbons Stem 1 meth- 2 eth- 3 prop- 4 but- 5 pent- 6 hex- 7 hept- 8 oct- 9 non- 10 dec-

Answer 341

Organic compounds can be described as being straight-chained, branched or cyclic, depending on how the carbon atoms are arranged.

Answer 342

- Two atoms sharing electron pair of similar electro-tivity -When bond breaks, each atom takes one electron from pair of electrons forming free radicals

Answer 343

- A free radical an uncharged molecule with unpaired electrons that are very reactive - Free radical reaction catalysed by heat or light

Answer 344

- The splitting of a covalent bond where one atom retains both electrons from the bonding pair - Results in the formation of positive ad negative ions - if positive charge on C its called carbocation or carbonium - If negative charge on C its called carbanion

Answer 345

- A molecule or substance that donates electrons - Must have lone pair of electrons - Attack centre of a positive charge - Reaction with nucleophile called nucleophilic reactions - i.e CH-, Cl-, H2O, CN-

Answer 346

- Electrophile is a molecule or substance that acts as an electron pair acceptor - positive ions or electrons deficient molecules - Attack regions of high electron density - i.e Br+, CH3+, AlCl3

Answer 347

- A reaction where two or more molecules react together to form a larger molecule - Electrophilic addition (alkenes) - Free radical (carbonyl compounds)

Answer 348

- A reaction where an atom or group is replaced by another atom or group. - Nucleophilic substitution (halogenoalkanes) - Free radical substitution (alkanes)

Answer 349

A reaction in which two substituents are removed from a molecule in a mechanism with one or two steps.

Answer 350

- The splitting up of a compound or molecule using water. - Breaking down of molecule by water, sped up by acid or alkali (ester and alkenes)

Answer 351

The formation of a compound with the release of water.

Answer 352

- An sp3 orbital overlaps with another sp3 orbital to form a C-C covalent bond. - The other three orbitals overlap with the s orbital of a hydrogen atom to form more covalent bonds. - These bonds between each atom are sigma (𝜎) bonds. - The shape of an ethane molecule is tetrahedral, with bond angles of 109.5 - Rotation can occur around sigma bonds because they are formed when two orbitals overlap end-to-end

Answer 353

- Two sp2 orbitals overlap to form a single sigma C-C bond. - The unhybridized 2p orbitals at 90 degrees to this also overlap with each other to form a second bond called a pi bond. - Ethene molecules have a trigonal planar shape with bond angles of 120. - These molecules contain both sigma and pi bonds - The molecule is planar because there is restricted rotation around the C=C pi (π) bond. - Rotation is restricted around this pi bond because the bond is formed when orbitals overlap below and above the plane of atoms.

Answer 354

Structural isomers are molecules with the same molecular formula but a different structural formula. The different types of structural isomerism Chain isomerism, Functional group isomerism, Positional isomerism.

Answer 355

Structural isomers are molecules with the same molecular formula but a different structural formula. The different types of structural isomerism Chain isomerism, Functional group isomerism, Positional isomerism.

Answer 356

- This occurs when there is branching on the carbon chain. - Isomers have different carbon chain length - Same chemical properties but slightly different physical

Answer 357

- The functional groups on the carbon chain changes. - Isomers have different functional groups, belong to different homologous series - Have different physical and chemical properties

Answer 358

- The carbon chain backbone remains the same but the groups attached to the chain move around and change position. - Isomers differ in position of substituent atoms or groups or the functional group - Chemical properties but slightly different physical

Answer 359

- Stereoisomers are molecules with the same molecular and structural formula but a different arrangement of atoms in space. - Geometrical (cis-trans) isomerism and optical isomerism are both types of stereoisomerism

Answer 360

- Stereoisomers are molecules with the same molecular and structural formula but a different arrangement of atoms in space. - Geometrical (cis-trans) isomerism and optical isomerism are both types of stereoisomerism

Answer 361

- Geometrical isomerism is a branch of stereoisomerism. - It can also be called cis-trans or E/Z isomerism. - This type of isomerism occurs due to a pi bond which restricted rotation around the C=C double bond. - Since there is restricted rotation around this bond, the various groups attached to the carbon are fixed in position meaning different isomers can form. - cis isomers have higher dipole - trans isomers of symmetrical alkene has zero dipole - cis-trans isomers have different boiling point

Answer 362

- Geometrical isomerism is the type of isomerism that occurs in alkenes because it relies on a C=C double bond due to its restricted rotation. - The cis isomer has both of the highest priority groups on the same end (either both above or below the C=C bond). - The trans isomer the highest priority groups diagonally across from each other, on opposite sides of the double bond. - The priority of a group is decided by atomic number

Answer 363

- Optical isomerism is another branch of stereoisomerism. - It occurs when there is a chiral center - Optical isomers have the same molecular and structural formula but they are mirror images of one another since the atoms are arranged differently in space.

Answer 364

- A chiral centre is an atom with four different groups bonded to it. - This arrangement creates compounds which are non-superimposable mirror images of each other. - If a compound has a chiral centre, it will display optical isomerism. - It is possible for compounds to have more than one chiral centre.

Answer 365

Chiral centres can be identified in organic compounds by spotting a carbon atom which is bonded to four different groups.

Answer 366

- All C–C bonds single; alkanes = saturated hydrocarbons - Non-polar therefore no centre of charge to act as either nucleophile or electrophile therefore cannot attract polar reagents like acids, bases, metals or oxidizing agents - Alkanes are generally unreactive. This is because alkanes are largely made up of C-C and C-H covalent bonds which require a lot of energy to break. - This means alkanes are also generally not very reactive with polar reagents.

Answer 367

- The volatility of the alkanes decreases and melting point or boiling point increases as number of carbon atoms increases - Reason: increasing Van der Waals forces

Answer 368

- Alkanes make good fuels because they release huge amounts of energy when burnt. - They are also relatively readily available and are easy to transport. Complete combustion occurs in excess oxygen. Complete combustion of alkanes produces water and carbon dioxide. Examples of balanced combustion equations: C3H8 + 5O2 → 3CO2 + 4H2O 2C6H14 + 19O2 → 12CO2 + 14H2O - Incomplete combustion of alkanes occurs when there is insufficient oxygen. This leads to the formation of water and various other products and pollutants including, carbon particulates, C, carbon monoxide, CO, and some carbon dioxide, CO2 Examples of these reactions: 2C3H8 + 7O2 → 6CO + 8H2O 2C2H6 + 3O2 → 4C + 6H2O 4CH4 + 5O2 → 2CO + 8H2O + 2C - Carbon monoxide is a toxic colourless and odourless gas. It binds haemoglobin molecules in red blood cells (to the same sites as oxygen), preventing oxygen being transported around the body. - Carbon particulates are also produced, they are small fragments of unburned hydrocarbon. - Unless removed from the waste products in industry, these can cause serious respiratory problems as they pollute the air.

Answer 369

- Alkanes can undergo substitution reactions with halogens. This reaction only occurs in the presence of ultraviolet light. - A substitution takes place when a hydrogen atom is replaced by a halogen atom from a halogen molecule (Cl2 or Br2). - When this reaction takes place, a halogenoalkane is produced. For example: CH4 + Br2 → CH3Br + HBr CH3CH3 + Cl2 → CH3CH2Cl + HCl

Answer 370

- Shorter alkane chains are more in demand and useful than the heavier fractions. Large fractions can be cracked (broken down) into smaller alkanes and alkenes. There are two types of cracking thermal and catalytic

Answer 371

- High temperatures (around 1000C). - High pressures (around 70 atm) - Produces lots of alkenes

Answer 372

- Zeolite catalyst - Slight pressure - High temperature (around 450oC) - Produces mostly aromatic hydrocarbons and motor fuels

Answer 373

- Crude oil is unrefined petroleum found in the ground. It contains a mixture of hydrocarbons. - Crude oil isn’t very useful unless it is separated into the different hydrocarbon fractions by fractional distillation. - Crude oil is a source of aliphatic and aromatic hydrocarbons. - Aliphatic hydrocarbons are straight chain hydrocarbons (e.g. alkanes and alkenes). - Aromatic hydrocarbons contain at least one benzene ring.

Answer 374

1. The crude oil is vaporised. 2. The crude oil vapours are placed into the fractionating column. The column has a temperature gradient where it is hotter at the bottom and cooler at the top. 3. The vapours rise up the column. Different hydrocarbon vapours have different boiling points so they condense at different temperatures. The separated liquid hydrocarbons leave the column. 4. The largest hydrocarbons have higher boiling points, so they are rarely vaporised. They run off the bottom as a sticky residue.

Answer 375

- Unsaturated hydrocarbons - Contain at least one C=C double bond - General formula: CnH2n (like cycloalkanes) - Source of alkenes: - Cracking alkanes - Dehydration of alcohols - More reactive than alkanes due to presence of double bond; pi electrons loosely and more susceptible to attacks by electrons deficient groups like electrophiles - Alkenes combust completely carbon dioxide + water - Give energy but not used as fuels; have other uses

Answer 376

- To identify alkenes aqueous bromine is added, the bromine will turn from a brown solution to a colourless solution if alkenes are present. - KMnO4 changes from pink to colourless

Answer 377

- Electrophile forms by heterolytic fission - Electrophile attacks double bond - Pair of electrons from double bond migrate to electrophile and pi bond breaks - Carbocation formed which attacks the nucleophile

Answer 378

Markovnikov’s principle is when an electrophile adds to an unsymmetrical alkene so that the most stable carbocation is formed as an intermediate

Answer 379

- Hydrogen binds to carbon with more hydrogens - Alkyl groups donate electron to the ring - Producing a positive inductive effect - A larger alkyl group has a weaker inductive effect - When a hydrogen halide bonds to an unsymmetrical alkene, there are two possible products. - The quantities of each product produced depends on how stable the carbocation intermediate is. - Carbocations with more alkyl groups are more stable. This is because alkyl groups have a positive inductive effect on the carbon atom and feed electrons towards the positive charge. - The more stable carbocation is more likely to form so there will be higher quantities of this product. It is often referred to as the major product.

Answer 380

- Alkenes undergo addition reactions because they contain at least one C=C double bond. - This is when two compounds combine to form a larger compound. - Alkenes can undergo addition with different compounds: - Halogens - Hydrogen halides - Hydrogen(g) and Pt/Ni - Water (in the form of steam)

Answer 381

- Hydrogenation (Alkene + H2 Alkane) - Reagent: H2(g) - Catalyst: Nickel - Temperature: 100C - Press.: 2 atm. - Use: convert liquid oils to saturated solid fats - Alkenes undergo hydrogenation when they react with hydrogen. The C=C double bond opens up to form covalent bonds with the new hydrogen atoms. CH2CH2 + H2 → CH3CH3

Answer 382

- Halogenation (Alkene + X2 Dihaloalkane) - Reagent: Halogen(aq) - Condition: room temperature and pressure or in the dark - When alkenes react with halogens, covalent bonds form between the halogen atoms and the carbons on either side of the double bond, producing a di-halogenoalkane. - The mechanism is called electrophilic addition

Answer 383

- Halogenation (Alkene + Hydrohalogen Halogenoalkane) - Reagent: Hydrohalogen (g) - Condition: room temperature and pressure - A hydrogen halide is polar due to the difference in electronegativity between hydrogen and the much more electronegative halogen atom. - This polarity means both the hydrogen and the halide bond to carbon atoms in the alkene, forming a halogenoalkane.

Answer 384

- Hydration (Alkene + H2O(g) Alcohol) - Reagent: steam - Catalyst: H3PO4 – phosphoric acid - Temperature: 300oC - Pressure: 70atm - Alkenes are hydrated when they react with steam to form alcohols. This requires an acid catalyst such as phosphorus acid or sulfuric acid. - CH2CH2 + H2O → CH3CH2OH - When steam reacts with propene, according to Markovnikov’s rule of addition, the OH group joins to the carbon atom in the double bond which is directly bonded to the most carbons atoms. This can be seen in the equation - CH3CHCH2 + H2O → CH3C(OH)CH3 - Using Markovnikov’s rule, propan-2-ol is the major product and propan-1-ol is the minor product. The reaction will mostly produce propan-2-ol.

Answer 385

- Potassium manganate(VII) contains manganate(VII) ions meaning it is a strong oxidising agent. - Manganate(VII) ions can oxidise alkenes to form diols (alkane with two alcohol groups). - For this reaction to take place, the manganate ions must be cold, dilute and acidified. - In the reaction below, [O] denotes the oxidising agent: CH2CH2 + H2O + [O] → CH2(OH)CH2(OH) - During this reaction, the purple solution will decolouris - Diol is formed

Answer 386

- When an alkene reacts with hot, concentrated, acidified manganate(VII) ions the C=C double bond, ruptures. - The manganate(VII) ions oxidise the alkene by breaking the C=C bond and replacing it with a C=O double bond on each new molecule. - Further reactions then take place, depending on the groups attached to the carbons: - If both the R groups in the product are alkyl groups then a ketone will form. Ketones are not easily oxidised so no further oxidation takes place. - If a product has one alkyl group and one hydrogen then an aldehyde will be produced. Aldehydes are easily oxidised to carboxylic acids meaning that the final product will be a carboxylic acid. - If both R groups in the product are hydrogen atoms, methanal will be formed. This is oxidised to methanoic acid which is then oxidised to water and carbon dioxide - Leads to the rupture of the double bond - Two compounds are formed - Products formed depend on alkene

Answer 387

- Alkenes can undergo addition polymerisation. In this reaction, many alkene monomers join together to form a polymer. - Alkenes are able to react and form polymers because their C=C double bonds can open up, allowing the carbons to join together. - The polymers produced are saturated because they do not contain any carbon-carbon double bonds. - Addition polymers are very unreactive. This is because the polyalkene chains are saturated and the main carbon chain is non-polar. - Repeated addition of 1000s of alkene molecules (monomer) to each other forming a macromolecule - General conditions: high pressure, high temperature and catalyst

Answer 388

- Non-biodegradable: does not break down so increases amount of volume needed for landfill sites - Combustion produces harmful gases which contribute to global warming e.g. SO2, CO2 and HCl from PVCs

Answer 389

- Recycle existing plastic - Make polymers biodegradable by adding starch units

Answer 390

Polyethene: - LDPE: cling wrap - HDPE: water pipes, wire insulation Polychloroethene (PVC): - Water pipes - Insulation of wires

Answer 391

Halogenoalkanes are alkanes which contain a halogen atom covalently bonded to a carbon atom.

Answer 392

When naming halogenoalkanes, the prefix of the halogen (fluoro-/chloro-/bromo-/iodo-) is put before the alkane name with a number to indicate which carbon the halogen is bonded to. For example 1-bromopropane, 3-chlorohexane and 2-iodopentane

Answer 393

- This is a nucleophilic substitution. In these reactions, a nucleophile replaces a leaving group. - These reactions are two step mechanisms. This type of reaction takes place in tertiary and some secondary halogenoalkanes. - If the nucleophile is unable to attack the back of the carbon atom (for example if it is blocked by larger atoms / groups such as -CH3) a carbocation intermediate is formed. - The first step in the process is generating the carbocation intermediate and the second step is the attack of the nucleophile on the carbocation to form the product. - Unimolecular – only one molecule involved in 1st step - Tertiary halogenoalkanes

Answer 394

- This is a nucleophilic substitution. In these reactions, a nucleophile replaces a leaving group. - These reactions are a one step mechanism. - The nucleophile attacks the substrate at the same time as the leaving group leaves the substrate. - The nucleophile attacks the carbon atom from the back side, causing an inversion of the groups in the product. - The nucleophile attacks from the backside because the large halogen atom prevents the attack from the other direction. - Bimolecular – two molecules involved in 1st step - Primary and secondary halogenoalkanes

Answer 395

- The reactivity of a halogenoalkane depends on the strength of the carbon-halogen bond. For a reaction to take place, the carbon-halogen bond needs to be broken. The weaker the carbon-halogen bond is, the more reactive the halogenoalkane. - C-F has the highest bond enthalpy and so is the strongest carbon-halogen bond. This makes fluoroalkanes the least reactive of halogenoalkanes so they react slowest. - C-I has the lowest bond enthalpy so is the weakest carbon-halogen bond. This makes iodoalkanes the most reactive of halogenoalkanes so they will react fastest. - Carbon-halogen bond enthalpy decreases down the group, so reactivity increases

Answer 396

- The halogenoalkane reactivity trend for SN1 is: tertiary > secondary > primary. - This is because alkyl groups have a positive inductive effect which helps stabilise the carbocation. - This makes the tertiary carbocation most stable and therefore the most likely to form.

Answer 397

- The halogenoalkane reactivity trend for SN2 is: primary > secondary > tertiary - This is due to steric hindrance which is caused by side chains on the molecule preventing a reaction occurring. - Tertiary halogenoalkanes are less reactive because the alkyl groups prevent the nucleophile attacking the back side of the carbon so substitution doesn’t occur.

Answer 398

- Hydrolysis occurs when a halogenoalkane undergoes nucleophilic substitution with a hydroxide. Hydrolysis (R – X + OH- R – OH + X-) - Reagent: strong alkali; NaOH(aq) or KOH(aq) - Condition: heat/reflux - Fluoroalkanes are not hydrolysed because the C – F bond is too strong - Ease of hydrolysis increases: Primary < Secondary < Tertiary - Tertiary halogenoalkanes can be hydrolysed without alkali - If any Cl- or Br- ions present in NaOH(aq), these ions will interfere with reaction

Answer 399

- Nitrile (cyanide) (R – X + CN- RCN + X-) - Reagent: KCN or NaCN in ethanol - Condition: Heat/Reflux - Solvent: Ethanol - Nitriles are formed when a halogenoalkane reacts with cyanide. The reaction requires warm, ethanolic potassium cyanide (ethanolic means dissolved in ethanol). - Reaction forms a C – C bond therefore no. of C increases; name has one more carbon

Answer 400

- Primary Amines (R – X + NH3 RNH2(l) + HX(g)) - Reagent: Ammonia (NH3) - Condition: ammonia in alcohol under pressure in sealed container - Primary amines are formed when a halogenoalkane is warmed with excess ethanolic ammonia under pressure. - lf excess concentration ammonia used, HX reacts with it forming NH4X

Answer 401

- Halogenoalkanes can also undergo an elimination reaction when they are heated under reflux with ethanolic hydroxide ions. - The hydroxide ions can’t be dissolved in water as this would cause hydrolysis would occur. - R – X + OH- Alkene + X- + H2O - Reagent: ethanolic NaOH or KOH Conditions: temperature 60C, reflux - OH- acts as a proton acceptor; it accepts the H+ loss from the halogenoalkanes during elimination - Elimination become progressively easier - Primary < Secondary < Tertiary - The carbon atom adjacent to carbon with halide must have at least one hydrogen attached to it.

Answer 402

- CFCs are inert and can be liquefied easily: Strength of C – X bond is very high, hence do not decompose easily and are not flammable. Uses: - As propellants in aerosol cans - As solvents in dry-cleaning - As refrigerant for freezers and fridges - Fire extinguishers, insecticides and pesticides

Answer 403

CFCs Effect on Ozone Layer - Causes the destruction of the ozone layer - CFCs escape in atmosphere and because of their inertness, remain without further reaction until they reach the stratosphere and ozone layer. - In stratosphere, high energy U.V causes Cl atom to split of CFC molecule forming Cl free radical which reacts with ozone

Answer 404

alternative is using HCFCs (replace Cl with H or more F atoms) as they break down more easily and do not release Cl → less effect on ozone layer

Answer 405

- CFCs escape in atmosphere and because of their inertness, remain without further reaction until they reach the stratosphere and ozone layer. - In stratosphere, high energy U.V causes Cl atom to split of CFC molecule forming Cl⋅ which reacts with ozone - This is a catalytic cycle where one Cl⋅ can react with many O3 thus causing destruction of ozone layer: Cl⋅ + O3(g) ⋅OCl(g) + O2(g)⋅OCl(g) + O(g) Cl⋅ + O2(g) - Can react and breakdown another O3 molecule

Answer 406

- Fluoroalkanes contain carbon and fluorine only. - Fluorohalogenoalkanes contain carbon, fluorine and hydrogen only. - Fluoroalkanes and fluorohalogenoalkanes are chemically inert. - The C-F bond is very strong and requires a lot of energy to break, making the compounds very unreactive. - Uses of fluoroalkanes and fluorohalogenoalkanes: - Refrigerants - Propellants for aerosols - Solvents for dry cleaning - Making expanded polystyrene

Answer 407

- This mechanism requires a free radical (a particle with an unpaired electron). A free radical is denoted by having a dot next to the chemical symbol, e.g. Cl⠂. - There are three stages to free radical substitution: initiation, propagation and termination - Initiation - Free radicals are produced. UV light is required to split the covalent bond and to form two separate atoms with an unpaired electron (free radicals) - Propagation - The free radicals are used up and recreated in chain reactions - Termination - All the free radicals are completely used up. When two radicals react, they form a covalent bond.

Answer 408

- The electron dense double bond in an alkene is susceptible to attack from electrophiles. This leads to electrophilic addition reactions which can lead to the formation of halogenoalkanes. - When alkenes react with halogens, covalent bonds form between the halogen atoms and the carbons on either side of the double bond, producing a di-halogenoalkane.

Answer 409

- The electron dense double bond in an alkene is susceptible to attack from electrophiles. This leads to electrophilic addition reactions which can lead to the formation of halogenoalkanes. - A hydrogen halide is polar due to the difference in electronegativity between hydrogen and the much more electronegative halogen atom. This polarity means both the hydrogen and the halide bond to carbon atoms in the alkene, forming a halogenoalkane.

Answer 410

- Primary and secondary alcohols react very, very slowly with hydrogen chloride, HCl. - Tertiary alcohols react rapidly with concentrated hydrochloric acid at room temperature: (CH3)3COH + HCl → (CH3)3CCl + H2O

Answer 411

- Hydrogen bromide reacts with alcohols. - Typically the alcohol is treated with potassium bromide and concentrated sulfuric acid as these two reactants will produce hydrogen bromide: CH3CH2OH + HBr → CH3CH2Br + H2O

Answer 412

- Hydrogen iodide reacts with alcohols. Typically the alcohol is treated with potassium iodide and phosphoric(V) acid. - Phosphoric(V) acid is used in this reaction instead of sulfuric acid as sulfuric acid will readily oxidise the iodide ions to iodine. CH3CH2OH + HI → CH3CH2I + H2O

Answer 413

Alcohols are organic compounds which contain a hydroxyl group, -OH. Alcohols can be separated into three different classifications primary, secondary and tertiary alcohols

Answer 414

- Alkenes are hydrated when they react with steam to form alcohols. This requires an acid catalyst such as phosphorus acid or sulfuric acid. CH2CH2 + H2O → CH3CH2OH - When steam reacts with propene, according to Markovnikov’s rule of addition, the OH group joins to the carbon atom in the double bond which is directly bonded to the most carbons atoms. This can be seen in the equation below: CH3CHCH2 + H2O → CH3C(OH)CH3 - Using Markovnikov’s rule, propan-2-ol is the major product and propan-1-ol is the minor product. The reaction will mostly produce propan-2-ol.

Answer 415

- Potassium manganate(VII) contains manganate(VII) ions meaning it is a strong oxidising agent. -Manganate(VII) ions can oxidise alkenes to form diols (alkane with two alcohol groups). - For this reaction to take place, the manganate ions must be cold, dilute and acidified. - In the reaction below, [O] denotes the oxidising agent: CH2CH2 + H2O + [O] → CH2(OH)CH2(OH) - During this reaction, the purple solution will decolourise.

Answer 416

An alcohol is produced when a halogenoalkane undergoes nucleophilic substitution with a hydroxide ion.

Answer 417

The symbol [H] is used in equations to represent the reducing agent- LiAlH4. RCHO + 2[H] →RCH2OH

Answer 418

The symbol [H] is used in equations to represent the reducing agent- LiAlH4 RCHO + 2[H] →RCH2OH

Answer 419

The reducing agent is LiAlH4 R1COR2 + 2[H] →RC(OH)HR2

Answer 420

- Carboxylic acids can be reduced to primary alcohols using LiAlH4. - The reduction process occurs in two stages because the carboxylic acid is converted into an aldehyde before becoming a primary alcohol. - The overall equation for this reaction is: RCOOH + 4[H] → RCH2OH + H2O

Answer 421

- When esters react with water an acid catalyst is required. This reaction is reversible so excess water must be used to ensure the position of equilibrium is shifted as far towards the products as possible. - This reaction can occur when the ester is mixed with dilute acid. CH3CH2COOCH3 + H2O ⇌ CH3CH2COOH + CH3O

Answer 422

- Colourless liquids at room temperature and pressure - b.p. and density increases with increasing C atoms and also with increasing OH groups

Answer 423

boiling point decreases : primary> secondary> tertiary - Because branching increases and van der waals forces decreases - b.p. of alcohols > alkenes as they have hydrogen bonds

Answer 424

- Smaller alcohols mix completely with water since strong hydrogen bonds occur between alcohols and water - As hydrocarbon nature increase (i.e. more C-C… bonds), the non-polar character outweighs the ability of the OH to form hydrogen bonds and therefore solubility decreases - Small alcohols (e.g. ethanol) are good solvents for both polar and non-polar compounds as they have polar and non-polar components

Answer 425

- When sodium reacts with an alcohol, a salt and bubbles of hydrogen gas are produced. - Reaction with Sodium R – OH + Na(l) RO- Na+ + ½ H2(g) - Type of reaction: acid-base - Reagent used: liquid sodium metal - Reactivity of alcohols decreases with increasing chain lengths of hydrocarbon - Reaction less vigorous than that of Na and water which shows water is a stronger acid than alcohol - This reaction can be used to remove alcohol groups from a compound or to safely dispose of small amounts of sodium (as sodium reacts explosively with water).

Answer 426

- Alcohols undergo oxidation when reacted with potassium or sodium dichromate(VI). - During this reaction, the orange potassium dichromate(VI) turns green. - The products of this reaction varies depending on the classification of the alcohol (primary, secondary or tertiary). - When writing an equation, [O] is used to denote the oxidising agent.

Answer 427

- Alcohol(l) Alkene + H2O(l) Condition: - Conc. H2SO4 OR - H3PO4 at 180C OR - Al2O3 at 300oC - Type of reaction: Elimination - Adjacent carbon to carbon with OH must have at least one hydrogen (tertiary cannot undergo dehydration) - Alcohols can be dehydrated to form alkenes. This can be carried out using aluminium oxide or an acid as a catalyst.

Answer 428

Alcohols can react with halides to form halogenoalkanes. During this substitution reaction, the hydroxyl group is replaced by a halogen atom. Reactions with Hydrogen Halides ● Primary and secondary alcohols react very, very slowly with hydrogen chloride, HCl. Tertiary alcohols react rapidly with concentrated hydrochloric acid at room temperature: (CH3)3COH + HCl → (CH3)3CCl + H2O ● Hydrogen bromide reacts with alcohols. Typically the alcohol is treated with potassium bromide and concentrated sulfuric acid as these two reactants will produce hydrogen bromide: CH3CH2OH + HBr → CH3CH2Br + H2O ● Hydrogen iodide reacts with alcohols. Typically the alcohol is treated with potassium iodide and phosphoric(V) acid. Phosphoric(V) acid is used in this reaction instead of sulfuric acid as sulfuric acid will readily oxidise the iodide ions to iodine. CH3CH2OH + HI → CH3CH2I + H2O

Answer 429

- Alcohols can react with halides to form halogenoalkanes. During this substitution reaction, the hydroxyl group is replaced by a halogen atom. - Alcohols react with phosphorus(III) halides to produce halogenoalkanes: 3CH3CH2OH + PCl3 → 3CH3CH2Cl + H3PO3 3CH3OH + PBr3 → 3CH3Br + H3PO3 3CH3CH2CH2OH + PI3 → 3CH3CH2CH2I + H3PO3 - Phosphorus(V) chloride will react violently with alcohols to produce steamy fumes of hydrogen chloride. CH3CH2OH + PCl5 → CH3CH2Cl + HCl + POCl3

Answer 430

- Alcohols can react with halides to form halogenoalkanes. During this substitution reaction, the hydroxyl group is replaced by a halogen atom - Sulfur dichloride oxide reacts with alcohols at room temperature to produce chloroalkanes. CH3CH2OH + SOCl2 → CH3CH2Cl + SO2 + HCl

Answer 431

- Primary alcohols can be partially oxidised to aldehydes. CH3CH2OH + [O] → CH3CHO + H2O - With further oxidation, aldehydes become carboxylic acids. CH3CHO + [O] → CH3COOH + H2O - The full oxidation reaction can be written as: CH3CH2OH + 2[O] → CH3COOH + 2H2O

Answer 432

- Secondary alcohols are oxidised to ketones. No further oxidation can take place. CH3C(OH)HCH3 + [O] → CH3COCH3 + H2O

Answer 433

Tertiary alcohols not oxidised because no hydrogens attached to carbon with OH group so oxidising agent colour does not change

Answer 434

- Esters can be formed when an alcohol and a carboxylic acid are heated together in the presence of an acid catalyst (commonly sulfuric acid). The process is known as esterification. - The left side of this compound is derived from the carboxylic acid and the right side from the alcohol. - This ester was formed from ethanoic acid and ethanol and it is called ethyl ethanoate. ‘Ethyl’ comes from the alcohol and ‘ethanoate’ from the carboxylic acid.

Answer 435

Tests for Alcohols Reagent Result with: Primary Secondary Tertiary Na metal Bubble of H2 Gas K2Cr2O4/H+ Green X KMnO4/H+ Colourless X

Answer 436

boiling point increases: Alkanes

Answer 437

- Smaller carbonyl compounds: completely soluble as they form hydrogen bonds with water molecules; are good solvents for polar & non-polar solutes - Larger carbonyl compounds: polar nature decreases, and non-polar nature increases; ability to form hydrogen bonds decreases

Answer 438

- Reagent: HCN - Condition: HCN w/alkali or HCN w/KCN - Since HCN added, carbon chain increases - Hydrogen cyanide reacts with aldehydes and ketones to produce hydroxynitrile compounds by removing the C=O double bond. The reaction is called nucleophilic addition - Product formed is hydroxynitrile or cyanohydrine - Aldehydes are more susceptible to nucleophilic attacks than ketones - Smaller carbonyl compounds more reactive - Product has a chiral carbon \therefore∴ exhibits optical isomerism - Addition of KCN and dilute H2SO4 can provide HCN and more CN- ions

Answer 439

- Type of Reaction: nucleophilic addition (H- ions) - Reducing agents: - NaBH4 – sodium tetrahydrioborate - LiAlH4 – lithium aluminium hydride - H2/Pt or Ni - Ketones ⟹ 2 Alcohols - R-CO-R + 2[H] R-CH(OH)-R - A reducing agent can be used to reverse the reactions above and convert aldehydes and ketones back to primary and secondary alcohols.

Answer 440

- Type of Reaction: nucleophilic addition (H- ions) - Reducing agents: - NaBH4 – sodium tetrahydrioborate - LiAlH4 – lithium aluminium hydride - H2/Pt or Ni - Aldehydes ⟹ 1o Alcohols - R-CHO + 2[H] RCH2OH - A reducing agent can be used to reverse the reactions above and convert aldehydes and ketones back to primary and secondary alcohols.

Answer 441

When naming a hydroxynitrile, the carbon in the nitrile group (C≡N) is referred to as the first carbon so the position of groups (including the alcohol group) is counted from there

Answer 442

- Aldehydes and ketones both contain the carbonyl group, C=O. - The position of the carbonyl group in the carbon chain is different in aldehydes and ketones. - The carbonyl group is at the end of the carbon chain in aldehydes and in the middle in ketones. - The suffix for aldehydes is -al and the suffix for ketones is -one.

Answer 443

- Aldehydes and ketones are formed when alcohols are oxidised using acidified potassium dichromate(VI) (Cr2O72-/H+). - Aldehydes are formed from primary alcohols, whereas ketones are formed from secondary alcohols. - Secondary alcohols are oxidised to ketones. No further oxidation can take place. CH3C(OH)HCH3 + [O] → CH3COCH3 + H2O

Answer 444

- Aldehydes and ketones are formed when alcohols are oxidised using acidified potassium dichromate(VI) (Cr2O72-/H+). - Aldehydes are formed from primary alcohols, whereas ketones are formed from secondary alcohols - Primary alcohols can be partially oxidised to aldehydes. CH3CH2OH + [O] → CH3CHO + H2O - If the aldehyde undergoes further oxidation, carboxylic acids are produced. CH3CHO + [O] → CH3COOH + H2O - The full oxidation reaction can be written as: CH3CH2OH + 2[O] → CH3COOH + 2H2O - If you are only collecting the aldehyde, carry out the reaction with excess alcohol and distill off the aldehyde as soon as it forms to prevent further oxidation.

Answer 445

- When aldehydes and ketones react with HCN to form hydroxynitriles, a nucleophilic addition reaction occurs. A nucleophile is an electron pair donor. The Mechanism: - The carbonyl bond (C=O) is highly polar. The negative cyanide ion acts as a nucleophile and attacks the slightly positive carbon atom. The C=O bond breaks, leaving only a single bond between the carbon and oxygen atoms. - The negatively charged oxygen then bonds to a hydrogen ion (from HCN or any added acid)

Answer 446

- The carbonyl group can be detected using 2,4-dinitrophenylhydrazine (2,4-DNPH). - When 2,4-DNPH is added to a solution of aldehyde or ketone, a yellow/ orange precipitate is produced. The formation of this coloured precipitate indicates the presence of a C=O carbonyl group. - After identifying a solution as a carbonyl using 2,4-DNPH, certain reactions can be carried out using oxidising agents. A positive result indicates that an aldehyde is present while a negative result suggests a ketone is present. - Forms: red/orange ppt. - The m.p. of the ppt. can be used to identify individual aldehydes and ketones

Answer 447

- A CH3CO- group can be detected using alkaline aqueous iodine, I2 - Iodine is added to the carbonyl, followed by sodium hydroxide (to make the solution alkaline). If the CH3CO- group is present, a yellow precipitate of tri-iodomethane (CHI3) will form. CH3COR + 3I2 + 4NaOH → RCOONa + CHI3 + 3NaI + 3H2O

Answer 448

Aldehyde - orange solution turns green. Ketone - no visible change / solution remains orange.

Answer 449

Aldehyde - silver mirror forms on the walls of the test tube. Ketone - no visible change.

Answer 450

Aldehyde - blue solution gives a brick red precipitate. Ketone - no visible change / solution remains blue

Answer 451

- Weak acids; don’t dissociate completely - Carboxylic acids are organic compounds with the functional group -COOH. - Carboxylic acids can be produced from alcohols, aldehydes and nitriles - Forms hydrogen bonds: - High m.p./b.p. - High solubility of smaller carboxylic acids - Forms hydrogen bonded dimers when pure vapour, liquid or solid & when dissolved in non-polar organic solvents

Answer 452

- Primary alcohols are oxidised to aldehydes. - Aldehydes are further oxidised to carboxylic acids. - Acidified potassium dichromate(VI) is used as an oxidising agent when producing carboxylic acids from alcohols and aldehydes. - During oxidation, potassium dichromate(VI) changes colour from orange to green. In the following equations, [O] denotes the oxidising agent. - Primary alcohols are partially oxidised to aldehydes: RCH2OH + [O] → RCHO + H2O - If the aldehyde undergoes further oxidation, carboxylic acids are produced: RCHO + [O] → RCOOH + H2O - The full oxidation reaction can be written as: RCH2OH + 2[O] → RCOOH + 2H2O - For oxidation to occur, the alcohol or aldehyde is heated under reflux with acidified potassium dichromate(VI)

Answer 453

- Nitriles can undergo hydrolysis to form carboxylic acids. The C≡N nitrile bond reacts with water to produce the carboxylic acid. - Acid hydrolysis The nitrile is heated under reflux with a dilute acid (such as hydrochloric acid). A carboxylic acid and a salt are produced. The reaction of propanenitrile with a dilute acid:CH3CH2CN + 2H2O + HCl → CH3CH2COOH + NH4Cl - Alkaline hydrolysis The nitrile is heated under reflux with an alkali (such as sodium hydroxide). This produces a carboxylic acid and ammonia. The reaction takes place in two stages. First, carboxylate ions are produced (e.g. sodium carboxylate forms if sodium hydroxide is used). A strong acid must then be added to provide hydrogen ions to liberate the carboxylic acid. Hydrochloric acid is commonly used.

Answer 454

- Nitriles can undergo hydrolysis to form carboxylic acids. The C≡N nitrile bond reacts with water to produce the carboxylic acid. - Acid hydrolysis The nitrile is heated under reflux with a dilute acid (such as hydrochloric acid). A carboxylic acid and a salt are produced. The reaction of propanenitrile with a dilute acid: CH3CH2CN + 2H2O + HCl → CH3CH2COOH + NH4Cl - Alkaline hydrolysis The nitrile is heated under reflux with an alkali (such as sodium hydroxide). This produces a carboxylic acid and ammonia. The reaction takes place in two stages. First, carboxylate ions are produced (e.g. sodium carboxylate forms if sodium hydroxide is used). A strong acid must then be added to provide hydrogen ions to liberate the carboxylic acid. Hydrochloric acid is commonly used.

Answer 455

- A salt is produced when carboxylic acids react with metals, alkalis or carbonates. - Reactions with metals: Carboxylic acids react with reactive metals to produce a salt and bubbles of hydrogen gas. Since carboxylic acids are weak acids, the reaction rates are a lot slower than the reactions involving strong acids like hydrochloric acid. Remember salts are ionic compounds so the charges of each ion must balance when writing equations and formulae.

Answer 456

- Esters are produced when carboxylic acids and alcohols are heated in the presence of an acid catalyst (typically concentrated sulfuric acid). The process is known as esterification. - The left side of the compound is derived from the carboxylic acid and the right side from the alcohol. - This compound has been formed from ethanoic acid and ethanol and is called ethyl ethanoate. - ‘Ethyl’ from the alcohol and ‘ethanoate’ from the carboxylic acid.

Answer 457

- Carboxylic acids can be reduced to primary alcohols using LiAlH4. - The reduction process occurs in two stages because the carboxylic acid is converted into an aldehyde before becoming a primary alcohol. - The symbol [H] is used in equations to represent the reducing agent. The overall equation for this reaction is: RCOOH + 4[H] → RCH2OH + H2O

Answer 458

When carboxylic acids react with alkalis, a simple neutralisation reaction takes place, since carboxylic acids are weak acids. The ionic equation is: H+ + OH- → H2O CH3COOH + NaOH → CH3COONa + H2O 2HCOOH + Mg(OH)2 → (HCOO)2Mg + 2H2O

Answer 459

When carboxylic acids react with carbonates, a salt, carbon dioxide and water are formed. 2CH3COOH + Na2CO3 → 2CH3COONa + CO2 + H2O

Answer 460

- When esters react with water an acid catalyst is required. - This reaction is reversible so excess water must be used to ensure the position of equilibrium is shifted as far towards the products as possible. - This reaction can occur when the ester is mixed with dilute acid. CH3CH2COOCH3 + H2O ⇌ CH3CH2COOH + CH3OH

Answer 461

- An ester can be hydrolysed by heating it under reflux with a dilute alkali (such as sodium hydroxide). - These reactions are not reversible so the products are easier to separate. CH3CH2COOCH3 + NaOH → CH3CH2COONa + CH3OH - To convert the carboxylate salt product into a carboxylic acid, excess strong dilute acid can be added to the salt (after the alcohol has been removed from the products by distillation).

Answer 462

Esters are commonly used commercially as solvents, perfumes and flavourings. Many foods contain esters to artificially create the smell and taste of fruit

Answer 463

Primary amines have the formula RNH2 where R is an alkyl group

Answer 464

- Alkyl amines can be made from halogenoalkanes: - Heat the halogenoalkane in a sealed tube with concentrated ammonia in an ethanol solvent (reflux cannot be used as ammonia is too volatile). -To ensure that a primary amine is formed, rather than an ammonium salt, an excess of ammonia must be used.

Answer 465

Nitriles are formed when a halogenoalkane reacts with cyanide. The reaction requires warm, ethanolic potassium cyanide (ethanolic means dissolved in ethanol).

Answer 466

- When aldehydes and ketones react with HCN to form hydroxynitriles, a nucleophilic addition reaction occurs. - The carbonyl bond (C=O) is highly polar. The negative cyanide ion acts as a nucleophile and attacks the slightly positive carbon atom. - The C=O bond breaks, leaving only a single bond between the carbon and oxygen atoms. - The negatively charged oxygen then bonds to a hydrogen ion (from HCN or any added acid).

Answer 467

When synthesising an organic compound, several factors are considered before deciding which synthetic route to use: - Type of reaction - addition reactions are more sustainable than substitution or elimination reactions as there are no waste products. - Reagents - renewable reagents with few safety concerns are preferred. - By-products - less harmful by-products are favoured as there would be fewer safety and environmental concerns. If the by-products can be used in another industry, the process is more sustainable. - Conditions - choose the reaction with the most energy efficient and safe conditions

Answer 468

- Synthetic routes are the routes which can be used to produce a certain product from a starting organic compound. - It is important that you understand the different methods and conditions required to convert compounds to other products.

Answer 469

Some organic molecules can be prepared using a multi-stage synthesis. Typically, this involves two stages: reactant → intermediate → product

Answer 470

- This is when a sample being analysed is irradiated with electromagnetic waves in the infra-red region of the electromagnetic spectrum. - Machine used is spectrophotometer and it detects intensity of wavelengths of infra-red that pass through the sample - The energy absorbed corresponds to changes in vibration of bonds leading to the bond being to stretch, bend and twist - At a specific frequency, the resonance frequency, the largest vibrations are obtained - Each type of vibration will absorb characteristic wavelengths of infra-red radiation - We can hence identify the presence (or absence) of different functional groups from the absorbance pattern on an infra-red spectrum

Answer 471

- IR spectroscopy identifies particular bonds in a molecule, and so each pollutant will show a different pattern of absorptions – this allows the identification of the pollution - It is also possible to measure the concentration of each pollutant with the different amounts of absorption

Answer 472

- Chlorides that dissolve in water to form a solution with a pH close to 7 are ionic whereas chlorides that react with water to form an acidic solution and hydrogen chloride gas are covalent. - If a Period 3 oxide forms an acidic solution when it dissolves in water, it is covalent. - If it is ionic, it may react with water to form an alkaline solution or it may not react with water.

Answer 473

Base ---> yellow Acid ---> red

Answer 474

Base ---> pink Acid ---> colorless

Answer 475

Base ---> yellow Acid ----> red

Answer 476

Base ---> blue Acid ---> yellow

Answer 477

Base ---> blue Acid ---> yellow/ green

Answer 478

Base --->purple Acid ---> yellow

Answer 479

The clonal flask solution goes from colorless to pink. The potassium solution is purple, it changes color when oxidized

Answer 480

1. Identify the central atom 2. Count its valence electrons 3. Add one electron for each bonding atom 4. Add or subtract electrons for charge (If its positive add if negative subtract) 5. Divide the total of these by 2 to find the total number of electron pairs 6. Use this number to predict the shape

Answer 481

1. Count the number of valence electrons. 2. Count the number of atoms that bond to the central atom and multiply by 8 (except for hydrogen, which requires 2). 3. Find the number of lone pairs on the central atom by subtracting the number of valence electrons on bonded atoms (Step 2) from the total number of valence electrons (Step 1). 3. Divide the number of VEs not in bonds (from Step 3) by 2 to find the number of LP

Chemistry AS Level Flashcards

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