Chemistry (Cambridge 0620 IGCSE) Flashcards

Question

Balancing equations

Answer 1

Due to CONSERVATION OF MASS, atoms can neither be created or destroyed in a reaction - equations must be BALANCED TIP: start with atoms in a compound: end with elements.

Answer 2

a mixture consists of different substances NOT CHEMICALLY BONDED e.g air

Answer 3

removes large, insoluable particles from a liquid e.g sand from water

Answer 4

leaves behind crystals of a dissolved substance (solute) if heated gently

Answer 5

involves condensing the evaporated solvent and collecting it.

Answer 6

can separate liquids due to their different boiling points

Answer 7

The separating of a mixture to identify its constituent substances e.g pigments in ink, drugs in urine sample. The MOBILE PHASE (sovent e.g water) moves up the STATIONARY PHASE (e.g chromatography/filter paper) due to CAPILLARY ACTION. This pulls the substances in the mixture upwards, with lighter particles being moved further up the stationary phase. The starting line is drawn just above the water line, in pencil (so it won't move). All measrements are made from this. The Rf (retention factor) values can then be compared against that of known substances to identify them. Rf value = distance substance moved ---------------------------- distance mobile phase moved.

Answer 8

have a very specific MELTING/BOILING POINTS, which can be used to test for them.

Answer 9

are MIXTURES of certain quantities of substances designed to fulfil a specific purpose e.g - Paints - Fuels - Alloys - Fertilisers.

Answer 10

the movement of particles in a fluid (gas/liquid) from a high concentration to a low concentration (spreading out)

Answer 11

- particles in regular arrangement (lattic) and vibrate about FIXED POSITIONS - cannot be compressed

Answer 12

- particles have no regular arrangement and are able to move past each other - cannot be compressed

Answer 13

- particles are far apart, move randomly at fast speeds (high energy) - can be compressed

Answer 14

solid -MELTING- liquid liquid -EVAPORATING- gas gas -CONDENSING- liquid liquid -SOLIDIFICATION- solid solid -sublimation- gas

Answer 15

is needed to overcome the (electrostatic) FORCES OF ATTRACTION between particles to melt/evaporate

Answer 16

no new substance is made

Answer 17

can be used in an equation. (aq) indicates the substance is in solution ('aqueous')

Answer 18

e.g NaOH (aq) means its dissolved or in solution

Answer 19

Relative charge: +1 Relative mass: 1

Answer 20

Relative charge: 0 Relative mass: 1

Answer 21

Relative charge: -1 Relative mass: 0 (very small)

Answer 22

is the number of PROTONS in a nucleus. e.g carbon atoms always have 6 protons. An ATOM must also have this number of ELECTRONS in order to be neutral. if not, it is an ION instead.

Answer 23

(or RELATIVE ATOMIC MASS/Ar/RAM) is the number of PROTONS + NEUTRONS in a nucleus.

Answer 24

same element, same proton number, different numbers of neutrons

Answer 25

some mass numbers on the periodic table are not whole numbers - these are an AVARAGE mass of all isotopes for example, the Relative abundance of Chlorine-35 is 75% Chlorine-37 is 25% Avarage Mass (relative abundance equation) avarage mass = total mass of 100 atoms ÷ 100 = (35x75) + (37x25) ÷ 100 = 35.5 (chlorine)

Answer 26

always DONATE electrons to gain an EMPTY OUTER SHELL to form POSITIVE IONS (e.g. Na+) (transitions metals also form positive ions) (HYDROGEN is special as it can basically do both POSITIVE AND NEGATIVE)

Answer 27

always ACCEPT electrons to gain a FULL OUTER SHEEL. they can form NEGATIVE IONS (e.g O²⁻) or can share electrons to do this. (HYDROGEN is special as it can basically do both POSITIVE AND NEGATIVE)

Answer 28

number of electrons in outer shell.

Answer 29

Group 1 are the ALKALI METALS (as they react with water to produce an alkali). they all lose/donate their outer electrons so their ions are all (1)+ They get more REACTIVE down the group as the outer electron is further from the nucleus so its donated more readily (the force of attraction is less)

Answer 30

are the HALOGENS. they form (1)- ions as they accept 1 electron to gain a full outer shell. they get less reactive down the group (and boiling point increases).

Answer 31

are VERY UNREACTIVE as they already have a full outer shell.

Answer 32

can donate different number of electrons e.g an IRON (II) ion is FE²⁺, while IRON (III) is FE³⁺. Usually harder and less reactive than the ALKALI METALS and usually form coloured compounds.

Answer 33

this is how metals bonds to non-metals. Metal atoms donate electrons to non-metals to form IONS. DOT & CROSS DIAGRAMS show the electrons on the outer shells. Metals always end up wih an empty outer shell (no shell), non-metals with 8 electrons (full shell)

Answer 34

this is how metal atoms bond to each other. They form a LATTICE (grid) of IONS surrounded by a 'SEA' OF DELOCALISED ELECTRONS. as the electrons are free to move, metals are good CONDUCTORS of electricity and heat.

Answer 35

Ions are arranged in a LATTICE of repeating units of positive and negative IONS. these form a crystal. Ionic substances have HIGH MELTING/BOILING POINTS due to the STRONG IONIC BONDS. (as the ions have strong electrostatic forces between them). They can conduct electricity when MOLTEN or in SOLUTION (dissolved). this is because the ions are free to move in these states, and they carry charge. ionic compounds are also called SALTS e.g. sodium chloride. - the name order comes from the Postive ions (+) are also known CATIONS while negative ions (-) are called ANIONS = Sodium (+) chloride (-)

Answer 36

e.g hydroxide ions: OH⁻ sulphate ion: SO₄²⁻ carbonate ion: CO₃²⁻ nitrate ion: NO₃⁻ ammonium ion: NH₄⁺

Answer 37

this is how non-metals bond to each other. Atoms SHARE electrons to gain FULL OUTER SHELLS. every covalent bond consists of a PAIR OF SHARED ELECTRONS. we can draw a DOT & CROSS diagram or the STRUCTURAL FORMULA, with a line representing each bond. the number of electrons an atom needs = the number of bonds it makes (e.g H:1 C:4). These are SIMPLE COVALENT STRUCTURES (molecules with a small number of atoms). They have low boiling points due to WEAK INTERMOLECULAR FORCES that need to be overcome.

Answer 38

This results in structures that consists of repeating units of atoms to make what are essentially gian molecules e.g. DIAMOND or SILICON DIOXIDE ('silica'). Very high melting points as you would have to break the covalent bonds. (ALLOYS are mixtures of metals: different size atoms disrupt the LATTICE, so layers cannot slide over each other easily - strong!) Diamond - One of the hardest known substances due to very strong bonds. Graphite - delocalised electrons form weak bonds between layers. - can conduct electricity as these electrons can move. -layers can slide past each other (unlike alloys). (BOTH ARE ALLOTROPES OF CARBON)

Answer 39

(allotropes: structures made of the same element but arranged differently).

Answer 40

Moles are used to compare quantities of substances. 1 MOLE = 6.02x10²³ atoms/molecules. 12g of carbon = 1 mole! Due to CONSERVATION OF MASS, the total mass of reactants must equal the total mass of products, even if a gaseous product leaves (thats why we have to balance equations like earlier). Moles = Mass (g) ÷ Relative atomic mass e.g "how many moles is 96g of oxygen?" 96 ÷ 32 = 3 moles

Answer 41

Example question: "How many grams of water would be made if 64g of methane reacted completely with oxygen?" (Methane= CH₄ + 2O₂ -> CO₂ + 2H₂O) moles = 64 ÷ 16 = 4 mol (stoichiometry: (1)CH₄ : (2)H₂O) 4 x 2 = 8 moles of water. 18 x 8 = 144g of water made (RAM x moles = mass)

Answer 42

the ratio of moles of one substance to another in a reaction.

Answer 43

In order for no reactants to be left over, there must be the correct number of moles both reactants in order to react completely according to their STOICHIOMETRY. e.g. Methane= CH₄ + 2O₂ -> CO₂ + 2H₂O For example, every 1 mole of methane needs 2 moles of oxygen. if there is less than 2 moles of oxygen, there will be methane left unreacted. The oxygen is the LIMITING REACTANT in this case. if there is more than 2 moles of oxygen, there will be unreacted oxygen left behind. The methane is the LIMITING REACTANT now.

Answer 44

When a substance is dissolved in water, it DISSOCIATES into its ions (e.g. H⁺ and OH⁻ ions) CONCENTRATION can be given in g/dm³ or mol/dm³. - HYDROCHLORIC ACID (HCl solution) - if 1 mole dissolved in 1dm³. CONC = 1 mol/dm³ (sometimes just '1 molar') - Converting volume of water: cm³ (or ml) ÷ 1000 = dm³. - Calculating concentration Concentration (mol/dm³) = moles ÷ volume (dm³).

Answer 45

Concentration (mol/dm³) = moles ÷ volume (dm³).

Answer 46

(top = most reactive. bottom = least reactive) Potassium sodium calcium magnesium aluminium carbon* zinc iron tin lead hydrogen* copper silver gold platinum

Answer 47

A DISPLACEMENT REACTION occurs when a MORE reactive metal displaces ('kicks out') a less reactive metal from a compound. e.g. Zn + CuSO₄ -> znSO₄ + Cu Most METALS also react with ACIDS to make a salt and hydrogen e.g. Zn + 2HCl -> ZnCl₂ + H₂ METAL CARBONATES also react with ACIDS to make a salt, carbon dioxide and water. e.g. CaCO₃ + 2HCl -> CaCl₂ + H₂O + CO₂ Group 1 metals are more reactive than hydrogen, so they displace it, to produce hydrogen gas and a metal hydroxide. We can use displacement reactions to obtain metlas from their ores, by displacing with a more reactive, less valuable metal or carbon ('coke'). This happens in a blast furnace: the iron oxide is 'reduced' (opposite of oxidised) to produce iron.

Answer 48

Even if oxygen is not involed in a reaction, we still say that atoms/ions/molecules are OXIDISED or REDUCED. OIL RIG = Oxidation IS Loss Reduction Is Gain (of electrons) For example, iron (Fe) is produced from FeO in a blast furnace - we can show what is happening to just the iron with a HALF/IONIC equation (don't forget state symbols!) EXAMPLES: Na (s) -> Na⁺ (aq) + e⁻ - each Na atoms loses an electron to become an ion: OXIDATION Fe²⁺ (l) + 2e⁻ -> Fe (s) - each Fe²⁺ ion gains 2 electrons to turn back into an atom: REDUCTION

Answer 49

When an acid (pH<7) reacts with an alkali (pH>7), a salt and water (pH=7, neutral) are produced (if reacted completely). ACID + ALKALI -> SALT + WATER e.g. HCl (aq) + NaOH (aq) -> NaCl (aq) + H₂O (l) Using SULPHURIC ACID results in a metal SULPHATE salt formed; NITRIC ACID: metal NITRATE salt. The salt is left in solution. Again, that means that we have a mixture of DISSOCIATED IONS, Na⁺, Cl⁻, H⁺, OH⁻. You can obtain CRYSTALS of the dissolved salt by heating gently so the water EVAPORATES, leaving only the salt behind.

Answer 50

An acid has a pH<7 due to its H⁺ ions. An alkali has a pH>7 due to its OH⁻ ions. Water is neutral, pH of 7 as it always has an equal number of both. pH is dependant on the CONCENTRATION of H⁺ or OH⁻ ions. UNIVERSAL INDICATOR gives you an indication of Ph by changing colour. pH also depends on how STRONG/WEAK an acid is. A strong acid DISSOCIATES more completely. if at the same concentration, it will have a lower pH than a weak acid e.g. STRONG = hydrochloric, sulphuric or nitric acid WEAK = ethanoic, citric or carbonic acid.

Answer 51

Electrolysis involves passing an ELECTRICAL CURRENT through a substance to cause oxidation and reduction at the two ELECTRODES: the ANODE (+) and CATHODE (-). This can only happen if the IONS are free to move to the electrode they're attracted to, so for ionic compounds this can only happen when MOLTEN (melted) or in solution. it can be used to obtain pure metals from a compound/ore e.g. aluminum from aluminum oxide.

Answer 52

Cryolite lowers the operative temperature in which Aluminium oxid (bauxite) is melted at, lowering expensives. it also increases conductivity, aiding electrolysis.

Answer 53

Electrolysis is the breakdown by the passage of electricity (electrons) of an ionic compound in a molten or ionic state.

Answer 54

Electrolysis can also be carried out on solutions, as the dissolved ions are free to move. EXAMPLE: in an aqueous sodium chloride solution, what reaction will occur at each electrode? ANODE: Halide ions (F, Cl, Br) are always OXIDISED at the ANODE. if the anion isn't a halide, the OXYGEN is oxidised instead, and oxygen gas is produced. CATHODE: If the element is more reactive than HYDROGEN, then the H⁺ ions form. if they are less reactive than hydrogen. that element is formed. in this case, SODIUM is more reactive than the hydrogen, so the hydrogen forms at the CATHODE. The MORE REACTIVE CATION (+) remains in solution, while the less reactive is REDUCED at the cathode

Answer 55

if the solution is DILUTE, and it contains a HALIDE. the rule of halides forming at the ANODE does not apply, as its dilute.

Answer 56

Every chemical reaction involves energy changes: energy is needed to break chemical bonds, while it is released when bonds are made. EXOTHERMIC = If a reaction gets HOT. - there must be a net DECREASE in POTENTIAL ENERGY - which results in a net INCREASE in KINETIC ENERGY. reactants / products ENDOTHERMIC = If a reaction gets COLD. - there must be a net INCREASE in POTENTIAL ENERGY - which results in a net DECREASE in KINETIC ENERGY products / reactants

Answer 57

The rate of forward reaction equals the rate of the reverse reaction, concentrations of reactants and products are constant.

Answer 58

Every bond requires a specific amount of energy to break; it's also the same amount of energy releasesd when the bond is formed (you'll always be given these). In a reaction, we say that all bonds are broken, then the new ones are formed. e.g. In the chemical equation for methane. 2642 KJ/mol into reaction to break all bonds. and 3466 KJ/mol released by bonds being made more energy released than energy needed to break bonds, so this an EXOTHERMIC REACTION. NET ENERGY RELEASED = 3466 - 2642 = 824 KJ/mol. this is also called ENTHALPY CHANGE, ^H, for every mole of methane burned, 824 KJ of energy is released

Answer 59

HYDROGEN: Lit split produces a "squeaky pop" OXYGEN: will relight a glowing splint. CARBON DIOXIDE: causes limewater to turn cloudy when bubbled through it. CHLORINE: bleaches blue litmus paper.

Answer 60

Flame tests (metal ions) LITHIUM = RED SODIUM = YELLOW POTASSIUM = LILAC CALCIUM = ORANGE-RED COPPER = GREEN METALS IONS IN SOLUTION add sodium hydroxide to make metal hydroxide (coloured precipitate). - aluminum/calcium/magnesium: WHITE PRECIPITATE (dissolves/dusappears with excess NaOH) - Copper (ii) ions form BLUE PRECIPITATE - Iron (II) ions form a GREEN PRECIPITATE - IRON (III) ions form a BROWN PRECIPITATE.

Answer 61

CARRBONATES react with acid to produce CARBON DIOXIDE HALIDE IONS will produce a precipitate when mixed with SILVER NITRATE & NITRIC ACID. e.g. (silver) chloride ions form a WHITE precipitate, (silver) bromide form a cream-coloured precipitate and (silver) iodide form as yellow precipitate. SULPHATE IONS produce a WHITE PRECIPITATE WHEN MIXED with BARIUM CHLORIDE & HYDROCHLORIC ACID.

Answer 62

We use a BURETTE to measure what volume of acid/alkali is needed to neutralise, to allow us to calculate an unknown concentration. - Measure e.g. 50cm³ of alkali of known concentration using a glass pipette, put in conical flask with METHYL ORANGE indicator, - Put acid in burette (up to 0cm³ mark), open tap and let it drip into flask while swirling the flask. - Once it goes pink/red, stop, swirl. if it stays, neutralisation has occured. - (rough titration can be done before to give more accurate value.) - Use moles to calculate unknown conectration. (you can also use PHENOLPHTHALEIN indicator, which turns from colourless to pink). (Methyl Orange turns red when a acid is present, but if a base is present it turns yellow) e.g. "determine the concentration of sulphuric acid in a bottle" H₂SO₄ + 2NaOH -> Na₂SO₄ + 2H₂O - 50cm³ of 0.2mol/dm³ NaOH used + 0.050 (50cm³ but in dm³) x 0.2 = 0.01 mol NaOH - as H₂SO₄, half the moles of acid needed to neutralise = 0.005 mol. - lets say that the titration gave a volume of 12.5cm³ (0.0125dm³) of acid to neutralise. - concentration of acid = 0.005 ÷ 0.0125 = 0.4 mol/dm³.

Answer 63

PERCENTAGE YIELD tells you what mass of product is made in a reaction in reality, compared to the MAXIMUM THEORETICAL MASS that could be made (use actual masses). % Yield = total mass of products ÷ total mass of reactants x 100 e.g. "10g of ammonia is made from 20g of reactants. what is the % yield?" = % yield = 10 ÷ 20 x 100 = 50%

Answer 64

Any rate = change in quantity ÷ time (technically MEAN rate_ can use mass/volume of reactant used/product made. Practical test EXAMPLES: - Hydrochloric acid + sodium thiosulphate causes solution to go cloudy (higher turbidity). so place a conical flask containing this solution over a drawn cross. Measure time for cross disappear; repeat at different temperatures. - Measure volume of gas produced by attachingg gas syringge to reaction vessel. In a 'Rate of reaction' graph, to find the rate at any time, you draw a tangent at that point. GRADIENT = rate of reaction (unit: g/s or cm3/s) (any gradient = 'up' ÷ 'across') INCREASING RATE OF REACTION: - increase surface area/concentration/pressure (solids, solutions & gases respectively). particles collide more frequently. - Increase temperature: particles move faster, collide more frequently & with more energy: more leikely to be successful. - Catalysts reduces activation energy: collisions more likely to be successful. 'provides alternative reaction pathway'.

Answer 65

Products ⇌ reactants Both the forward and reverse reaction will coninuously take place. LE CHATELIER'S PRINCIPLE: if a system at equilibrium is subjected to a change, the system will adjust to counteract the change. Eventually the rate of these will be equal. EQUILIBRIUM is reached: the overall quantity of both sides will not change, unless... INCREASING PRESSURE will favour the reaction that produces fewer moles (forward in this case). The rate of this reaction will increase to produce ammonia until equilibrium is again reached. "The position of the equilibrium has been shifted to the right" e.g. N₂ + 3H₂ ⇌ 2NH₃ 4 moles ⇌ 2 moles (the HABER PROCESS) CONCENTRATION of solutions follows the same principle. REMOVING product form one side shifts the position of equilibrium in that direction. e.g. removing ammonia (NH₃) would result in more being made. INCREASING TEMPERATURE favores the ENDOTHERMIC reaction (as heat is needed for it), One direction is always ENDOTHERMIC, while the other is EXOTHERMIC.

Answer 66

makes AMMONIA N₂ + 3H₂ ⇌ 2NH₃ NITROGEN is obtained from the air its reacted with, while the HYDROGEN can be obtained through the electrolysis of water. They're passed over a CATALYST at a temperature of 450°C and a pressure of 200 atm (atmospheres) The high pressure favours the FORWARD reaction, while a higher temperature increases the RATE of reaction (good) but it also favours the REVERSE reaction (not good!) so 400°C is a COMPROMISE temperature. This is to maximise the YIELD of ammonia produced, while ensuring the reacton also happens at a reasonable RATE. the AMMONIA then produced is condensed and pumped out through the bottom of the machine, while the un-reacted Hydrogen and ammonia is recycled to produce more ammonia.

Answer 67

PLANTS NEED NITROGEN, PHOSPHORUS & POTASSIUM, so we make ferilisers made from their salts. Ammonia is used to make AMMONIUM SALTS. POTASSIUM CHLORIDE & POTASSIUM SULPHATE are obtained by mining. PHOSPHATE rock is also mined, but is treated with an acid before being added to the feriliser.

Answer 68

We can choose the density of the polymers, depending on the condition used when making. HDPE: High Density Polyethene LDPE: Low Density Polyethene Thermosoftening polymers melt when heated Thermosetting polymers do not, due to CROSSLINKS between polymers increasing the attractive forces between the layers.

Answer 69

MIXTURES OF METLAS TO FULFIL A SPECIFIC NEED BRONZE: copper + tin BRASS: copper + zinc JEWELLERY GOLD: gold + silver + copper + zinc STEEL: iron + carbon STAINLESS STEEL: STEEL + chromium/nickel. Alloys are STRONGER than pure metlas due to different size atoms disrupting the lattice, so layers cannot slide over each other as easily. ALUMINUM is used to make LIGHT/LOW DENSITY alloys.

Answer 70

THE DESTRUCTION OF METALSS OVER TIME DUE TO CHEMICAL REACTIONS. We say iron RUSTS when it corrodes due to it reaction with OXYGEN + WATER (steel too, as it contains iron) COPPER corrodes when it reacts with oxygen to make COPPER OXIDE (green) We can cover materials with SACRIFICIAL METALS that will corrode before the important metal underneath does. Covering another metal in ZINC is called GALVANISING (e.g. most cars nowadays)

Answer 71

Hydrolysis is a chemical reaction where a substance reacts with water and breaks down into smaller parts. In chemistry, hydrolysis often happens when acids or alkalis help water to break apart substances like salts, esters, or proteins. For example, when an ester reacts with water, it splits into an alcohol and an acid. Hydrolysis usually needs heat and sometimes a catalyst like an acid or a base to happen faster.

Answer 72

The composition of clean, dry air as approximately 78% nitrogen, N2 , 21% oxygen, O2 and the remainder as a mixture of noble gases and carbon dioxide, CO2. The source of each of these air pollutants: limited to: - CARBON DIOXIDE from the complete combustion of carbon-containing fuels - CARBON MONOXIDE and particulates from the incomplete combustion of carbon-containing fuels - METHANE from the decomposition of vegetation and waste gases from digestion in animals - NITROGEN OXIDES from car engines - SULFUR DIOXIDES from the combustion of fossil fuels which contain sulfur compounds The adverse effect of these air pollutants: limited to: - Carbon dioxide: higher levels of carbon dioxide leading to increased global warming, which leads to climate change - Carbon monoxide: toxic gas - Particulates: increased risk of respiratory problems and cancer - Methane: higher levels of methane leading to increased global warming, which leads to climate change - Oxides of nitrogen: acid rain, photochemical smog and respiratory problems - Sulfur dioxide: acid rain

Answer 73

THE GREENHOUSE EFFECT is what keeps the Earth warm - greenhouse gases absorb long wavelength radiation reflected off the surface of the Earth. the GREENHOUSE GASES include WATER VAPOUR, CARBON DIOXIDE & METHANE

Answer 74

Distillation is a process used to separate a liquid from a mixture by heating it until it turns into a gas and then cooling the gas back into a liquid. It works because different substances have different boiling points. The substance with the lower boiling point evaporates first, and when the gas is cooled, it condenses back into pure liquid. Distillation is often used to purify water or to separate liquids like alcohol from a mixture.

Answer 75

- Describe chemical tests for the presence of water using anhydrous cobalt(II) chloride and anhydrous copper(II) sulfate - Describe how to test for the purity of water using melting point and boiling point - Explain that distilled water is used in practical chemistry rather than tap water because it contains fewer chemical impurities - Water from natural sources may contain substances, including: (a) dissolved oxygen (b) metal compounds (c) plastics (d) sewage (e) harmful microbes (f) nitrates from fertilisers (g) phosphates from fertilisers and detergents - State that some of these substances are beneficial, including: (a) dissolved oxygen for aquatic life (b) some metal compounds provide essential minerals for life - State that some of these substances are potentially harmful, including: (a) some metal compounds are toxic (b) some plastics harm aquatic life (c) sewage contains harmful microbes which cause disease (d) nitrates and phosphates lead to deoxygenation of water and damage to aquatic life Details of the eutrophication process are not required - Describe the treatment of the domestic water supply in terms of: (a) sedimentation and filtration to remove solids (b) use of carbon to remove tastes and odours (c) chlorination to kill microbes

Answer 76

CRUDE OIL is made from PLANKTON buried underwater and compressed over a long time. It consits mainly of HYDROCARBONS: molecules made from ONLY CARBON & HYDROGEN. There are two types: ALKANES & ALKENES. ALKANES are made from single-covalently bonded CARBON atoms surrounded by HYDROGEN atoms We say alkanes are SATURATED since they dont have a C=C double bond. While ALKENES are unsaturated as they do contain C=C bonds. General formula for ALKANES: C₂H₂ₙ ₊ ₂ METH- 1 CARBON ETH- 2 CARBONS PROP- 3 CARBONS BUT- 4 CARBONS e.g. METHANE = CH₄

Answer 77

A homologous series is a group of organic compounds that have the same general formula, similar chemical properties, and show a gradual change in physical properties like boiling point. Each member differs from the next by a CH₂ group. - Alkanes are a homologous series with the general formula CₙH₂ₙ₊₂. They are saturated hydrocarbons (only single bonds between carbon atoms). - Alkenes are a homologous series with the general formula CₙH₂ₙ. They are unsaturated hydrocarbons (they have at least one double bond between carbon atoms). - Alcohols are a homologous series with the general formula CₙH₂ₙ₊₁OH. They contain an -OH (hydroxyl) group. - Carboxylic acids are a homologous series with the general formula CₙH₂ₙ₊₁COOH. They contain a -COOH (carboxyl) group.

Answer 78

A functional group is the part of a molecule that is responsible for its chemical reactions. It is like the "reactive part" of the molecule that gives the compound its specific chemical properties. - Alkanes: Functional group: None special (they just have single C–C bonds). - Alkenes: Functional group: C=C double bond (carbon-carbon double bond). - Alcohols: Functional group: –OH group (hydroxyl group). - Carboxylic acids: Functional group: –COOH group (carboxyl group).

Answer 79

Fractional distillation is the process of separating a mixture of liquids into individual components by boiling and condensing, based on their different boiling points.

Answer 80

The hydrocarbons in crude oil must be separated into FRACTIONS before they can be used. They're evaporated and they rise up the fractionating column where they recondense at different heights: higher = colder. Longer alkanes have higher boiling points due to more energy needed to overcome the stronger intermolecular forces, so they recondense lower down the column. (in order of condensation in the fractional distillation tower, top to bottom) - LPG (liquid petroleum gases) - Petrol (cars) - Kerosene (jetts) - Diesel oil (car or trucks) - Heavy fuel oil (ships or other large machines) - Bitumen (roads)

Answer 81

COMPLETE COMBUSTIONS: fuel + oxygen -> carbon dioxide + water INCOMPLETE COMBUSTIONS: fuel + oxygen -> carbon monoxide + water Longer alkanes have higher VISCOSITY Shorter alkanes are more FLAMMABLE Hydrocarbons can also be used to make SOLVENTS, LUBRICANTS, DETERGENTS and... POLYMERS (used to make plastics) can be made from ALKENES but not alkanes An ALKENE is a hydrocarbon with at least one DOUBLE COVALENT BONDT -- Their names end with -ene. Alkenes are UNSATURATED (formula CₙH₂ₙ)

Answer 82

Alkenes will turn BROMINE WATER from orange to COLOURLESS. This is due to the bromine atoms bonding to the alkene by breaking the double bond. the molecule has been SATURATED. CHLORINE and IODINE react in a similar way, while WATER can react with an alkene to make an ALCOHOL.

Answer 83

There is more demand for SHORTER alkanes compared to longer ones. We use CRACKING to breaking longer alkanes into shorter ALKANE and a ALKENE to meet these demands. CATALYTIC CRACKING uses a ZEOLITE CATALYST at 550°C STEAM CRACKING uses no catalyst and a higher temperature at >800°C.

Answer 84

An ALCOHOL is an organic molecule with an -OH (hydroxyl) functional group. Their names end with -ol. COMPLETE COMBUSTION: alcohol + oxygen -> carbon dioxide + water INCOMPLETE COMBUSTION: alcohol + oxygen -> carbon monoxide + water Alcohols can produce a solution with WATER, but this becomes more difficult the longer the alcohol. An ALCOHOL can be OXIDISED to produce a CARBOXYLIC ACID (-COOH).

Answer 85

POLYMERS are long chained organic molecules of repeating sections made from MONOMERS (POLY = many. MONO = one) Monomers joined together by ADDITION POLYMERISATION must contain a DOUBLE BOND, which breaks in order to produce a SINGLE BOND to bond to the next monomer ETHENE (monomer) -> POLYTHENE (polymer) h h Displayed formula -> (-c-c-)n h h

Answer 86

The polymerisation of different monomers that have TWO FUNCTIONAL GROUPS on the ends of the molecules. Reacting an alcohol with -OH on both ends with a carboxylic acid with -COOH on both ends make a POLYESTER, while WATER is also produced carboxylic acid + alcohol -> ester + water = ethanoic acid + ethanol -> ethyl ethanoate (PLEASE WHEN YOU READ THIS FLASHCARD WATCH A VIDEO ABOUT THIS) (ITS HARD TO EXPLAIN WITHOUT A PICTURE).

Answer 87

The Contact Process is used to make sulfuric acid by first burning sulfur to get sulfur dioxide, then reacting it with oxygen under controlled conditions (450°C, 2 atm, vanadium(V) oxide catalyst) to form sulfur trioxide. Careful control of temperature and pressure ensures a good balance between yield, cost, and speed. Finally, sulfur trioxide is safely converted into sulfuric acid via oleum to avoid producing a dangerous mist. The Contact Process - Sulfur dioxide gas is produced by burning sulfur in air. Sulfur, a cheap raw material, is burned in oxygen to make sulfur dioxide, the essential starting gas for the next steps. - Sulfur dioxide reacts with oxygen to form sulfur trioxide under controlled conditions. This reversible reaction needs the right conditions (temperature, pressure, catalyst) to maximize sulfur trioxide production without wasting energy or material. - Temperature is set at about 450°C as a balance between yield and speed. Lower temperatures would give better yield but make the reaction too slow. Higher temperatures speed it up but reduce the amount of sulfur trioxide made. So, 450°C is a compromise for good speed and acceptable yield. - Pressure is kept at around 2 atmospheres to avoid high costs. Higher pressure would slightly improve the yield because fewer gas molecules are formed, but it’s not used much because building strong, high-pressure equipment is very expensive. A moderate pressure is enough. - A catalyst (vanadium(V) oxide) is used to speed up reaching equilibrium. The catalyst increases the reaction speed but doesn’t change how much sulfur trioxide is eventually made. It helps save time and energy. - Sulfur trioxide is absorbed into concentrated sulfuric acid to form oleum, then diluted with water. Direct absorption into water is dangerous, so oleum is made first, then safely mixed with water to produce concentrated sulfuric acid.

Answer 88

Conc = Moles ÷ Vol Moles = mass (g) ÷ RAM Moles = Vol (r.t.p) ÷ 24dm³

Answer 89

(the substance) has water molecules built into its crystal structure

Answer 90

(a) Effect of heat on hydrated compounds (using copper(II) sulfate and cobalt(II) chloride): • Heating removes water (dehydration). • For copper(II) sulfate: • Blue hydrated crystals become white anhydrous copper(II) sulfate CuSO₄.5H₂O -> CuSO₄ • For cobalt(II) chloride: • Pink hydrated crystals become blue anhydrous cobalt(II) chloride CoCl₂.6H₂O -> CoCl₂ (b) Addition of water to anhydrous compounds: • Adding water reverses the reaction (hydration). • For copper(II) sulfate: • White anhydrous copper(II) sulfate turns blue again. • For cobalt(II) chloride: • Blue anhydrous cobalt(II) chloride turns pink again.

Answer 91

Contains no water molecules in its crystal structure

Answer 92

Crystallization (method to obtain crystals from a solution): • Dissolve the solid in a solvent (usually water) to make a solution. • Warm the solution gently to evaporate some of the solvent. • Stop heating when the solution becomes saturated (no more solid can dissolve). • Allow the hot, saturated solution to cool slowly. • Crystals form as the solution cools. • Filter the crystals from the remaining solution. • Dry the crystals between sheets of filter paper or in a warm place.

Answer 93

Oxidation number (also called oxidation state) is a number that shows how many electrons an atom has gained, lost, or shared during a chemical reaction. It helps you keep track of which atoms are oxidized or reduced in a reaction. - Elements that are not combined with anything (like O₂, H₂, Cl₂) always have an oxidation number of 0. - Simple ions (like Na⁺, Cl⁻) have an oxidation number equal to their charge. (Example: Na⁺ is +1, Cl⁻ is -1.) - Group 1 elements (e.g., Na, K) always have oxidation number +1 in compounds. - Group 2 elements (e.g., Mg, Ca) always have oxidation number +2 in compounds. - Hydrogen usually has oxidation number +1 (except in metal hydrides like NaH, where it is -1). - Oxygen usually has oxidation number -2 (except in peroxides like H₂O₂, where it is -1). - halogens usually have a oxidation of -1 - flourine is always -1 - The sum of oxidation numbers in: - a neutral compound must be 0. - a polyatomic ion must equal the ion’s charge. *How to Use Oxidation Numbers:* - To decide which element is oxidized and which is reduced: - Oxidation means the oxidation number increases (loses electrons). - Reduction means the oxidation number decreases (gains electrons). - To check if a reaction is a redox reaction: - If any oxidation numbers change, it is a redox reaction. - To balance complex redox reactions, use oxidation numbers to match how many electrons are gained and lost.

Answer 94

A hydrogen-oxygen fuel cell is a device that converts chemical energy directly into electrical energy by reacting hydrogen and oxygen together. Instead of burning hydrogen, the fuel cell allows hydrogen and oxygen to react electrochemically (in a controlled way) to produce electricity, water (H₂O), and heat as the only products. Key Points to Understand: - Hydrogen gas is supplied to the anode (negative electrode). - Oxygen gas (from air) is supplied to the cathode (positive electrode). - At the anode, hydrogen loses electrons (oxidation) and produces H⁺ ions. - At the cathode, oxygen gains electrons (reduction) and reacts with H⁺ ions to form water. - Electrons flow through an external circuit from anode to cathode — this flow of electrons is the electric current we use. Key Advantages: - Produces only water as waste — no carbon dioxide or air pollution. - Efficient — more energy is converted into electricity compared to burning fuels. - Quiet and can be used in vehicles like hydrogen-powered cars. Key Disadvantages: - Hydrogen gas is hard to store and transport — it needs special, high-pressure tanks. - Hydrogen is often made from fossil fuels, which can still cause pollution indirectly. - Expensive technology — fuel cells and hydrogen storage systems are costly.

Answer 95

An acid is a substance that produces hydrogen ions (H⁺) when dissolved in water. Acids have a sour taste, can corrode metals, and turn blue litmus paper red. In reactions, acids act as proton donors — they give away H⁺ ions to other substances. Common examples are hydrochloric acid, sulfuric acid, and nitric acid. Acids are important in many chemical processes such as neutralization reactions and manufacturing.

Answer 96

A base is a substance that reacts with an acid to form a salt and water only. Some bases are soluble in water and are called alkalis, producing hydroxide ions (OH⁻) when dissolved. Bases are usually bitter in taste, feel soapy, and turn red litmus paper blue. They act as proton acceptors — meaning they take H⁺ ions from acids during reactions. Common examples include sodium hydroxide, potassium hydroxide, and ammonia.

Answer 97

Chromatography is a technique used to separate mixtures and identify substances based on how they move through a material (like paper). It works because different substances travel at different speeds depending on how strongly they are attracted to the stationary phase (paper) and the mobile phase (solvent). It is often used to separate colored substances like inks or food dyes, but can also be used for colorless substances using locating agents. - Stationary phase: The material substances move across (e.g., chromatography paper). - Mobile phase: The solvent that carries the substances (e.g., water or ethanol). - Separation happens because different substances travel at different speeds — some are more soluble in the solvent or more attracted to the paper. - Rf value is used to identify substances: - Rf = distance moved by substance ÷ distance moved by solvent - Colorless substances can be made visible by spraying with a locating agent. - A pure substance will produce only one spot; a mixture will show more than one spot.

Answer 98

- In a redox reaction, there is always an oxidizing agent and a reducing agent. They are responsible for transferring electrons between substances. - Oxidizing agent: A substance that causes oxidation by accepting electrons. It itself gets reduced. - Reducing agent: A substance that causes reduction by donating electrons. It itself gets oxidized. In simple words: - Oxidizing agent = takes electrons (gets reduced). - Reducing agent = gives electrons (gets oxidized). *Key Points to Identify Them:* - If a substance’s oxidation number decreases, it is an oxidizing agent. - If a substance’s oxidation number increases, it is a reducing agent. - Oxidizing agents are often substances rich in oxygen or electronegative elements (like chlorine). - Reducing agents are often metals or substances rich in hydrogen.

Answer 99

AMPHOTERIC OXIDES - Amphoteric oxides react with acids just like bases do. - Amphoteric oxides react with bases just like acids do. - They usually come from metals that are not very reactive (middle of the reactivity series). EXAMPLES - Aluminium oxide (Al₂O₃) - Zinc oxide (ZnO) NEUTRAL OXIDES Neutral oxides are oxides that do not react with acids or bases. They are chemically unreactive towards acids and bases. They are often gases at room temperature. - They are formed by elements that are not metals (non-metals). - Common examples: - Carbon monoxide (CO) - Nitrous oxide (N₂O) - Water (H₂O — sometimes treated as a neutral oxide) BASIC OXIDES Basic oxides are oxides that react with acids to form a salt and water. They are usually made from metals, especially metals from Group 1 and Group 2 of the Periodic Table. - Made by metals (mostly reactive metals like sodium, magnesium, calcium). - React with acids but not with bases. - Form a salt and water during the reaction (neutralization reaction). - Ionic bonding is common in basic oxides. ACIDIC OXIDES Acidic oxides are oxides that react with bases to form a salt and water. They are usually made from non-metals, especially from elements like carbon, sulfur, and nitrogen. - Made by non-metals (especially carbon, sulfur, phosphorus). - React with bases but not with acids. - Form a salt and water during the reaction. - Often covalent bonding is found in acidic oxides.

Answer 100

SATURATED A saturated solution is a solution in which the maximum amount of solute has been dissolved in a given amount of solvent at a specific temperature. If more solute is added to a saturated solution, it will not dissolve and will remain as a solid at the bottom of the container. - Contains the maximum amount of solute that can dissolve at that temperature. - If you add more solute, it won’t dissolve. - The solution is in equilibrium, meaning the rate at which solute dissolves equals the rate at which it comes out of solution. - If the solution is cooled, some solute may precipitate out. UNSATURATED An unsaturated solution is a solution in which less than the maximum amount of solute has been dissolved. This means that the solution can still dissolve more solute at that temperature. - Contains less than the maximum amount of solute that can dissolve at a given temperature. - More solute can still dissolve in the solution. - No undissolved solute is present at the bottom of the container. *How to Know Which is Which:* - Saturated solution: When you add more solute, it does not dissolve and collects at the bottom. - Unsaturated solution: When you add more solute, it continues to dissolve without any solute collecting at the bottom.

Answer 101

Crystallization is a process used to separate a solid solute from a solution by forming crystals as the solvent evaporates or cools down. It occurs when a saturated solution is cooled or when the solvent evaporates, causing the solute to come out of the solution and form solid crystals. WHY DO THEY FORM? - Saturation: A solution becomes saturated when it cannot hold any more solute at a given temperature. When the solution cools or the solvent evaporates, the solute reaches its limit and begins to form solid crystals. - Decrease in solubility: As temperature decreases or the solvent evaporates, the solubility of the solute also decreases, making it more likely to form crystals as it can no longer stay dissolved in the solution. - Crystals form to reach equilibrium: The process of crystallization allows the system to reach a more stable state by removing excess solute from the solution and forming solid structures.

Answer 102

To determine if a compound is aqueous (aq) in a chemical equation, you need to know if it dissolves in water. A compound is written as aqueous if it dissolves and dissociates into ions (for ionic compounds) or molecules (for covalent compounds) in water. Ionic compounds like salts (e.g., sodium chloride, NaCl) are aqueous when they dissolve in water, because they separate into ions. Strong acids (e.g., hydrochloric acid, HCl) and strong bases (e.g., sodium hydroxide, NaOH) also form aqueous solutions in water. Covalent compounds like sugar (C₆H₁₂O₆) may also be aqueous if they dissolve in water. If a substance does not dissolve in water (like insoluble salts or solids), it is written as solid (s), not aqueous.

Answer 103

When metal salts are heated in a flame, their electrons get excited to higher energy levels. As they return to their normal state, they release energy in the form of visible light, which we see as different colors. The color of the flame depends on the energy released by the metal ion, and this is a key feature in identifying the metal. Key Flame Colors and How to Identify Them: - Lithium (Li⁺): Crimson red flame Common salt: Lithium chloride (LiCl). - Sodium (Na⁺): Yellow flame Common salt: Sodium chloride (NaCl). - Potassium (K⁺): Lilac or light purple flame Common salt: Potassium chloride (KCl). - Calcium (Ca²⁺): Orange-red flame Common salt: Calcium chloride (CaCl₂). - Copper(II) (Cu²⁺): Green flame (may appear blue-green depending on the compound) Common salt: Copper(II) chloride (CuCl₂) or Copper(II) sulfate (CuSO₄). - Barium (Ba²⁺): Green flame Common salt: Barium chloride (BaCl₂). - Strontium (Sr²⁺): Crimson red flame Common salt: Strontium nitrate (Sr(NO₃)₂) or Strontium chloride (SrCl₂). HOW TO PREFORM A FLAME TEST. - add the salt you are testing onto a wooden splint. - hover it over a bunsen burner - observe the flame it gives off

Answer 104

1. Test for Oxygen (O₂) Test: Insert a glowing splint into a test tube containing oxygen gas. Observation: The splint will relight, showing that oxygen is present. 2. Test for Carbon Dioxide (CO₂) Test: Bubble the gas through limewater (a dilute solution of calcium hydroxide, Ca(OH)₂). Observation: Limewater turns cloudy or milky due to the formation of calcium carbonate (CaCO₃). Equation: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O 3. Test for Hydrogen (H₂) Test: Ignite a small amount of the gas with a lighted splint. Observation: A “pop” sound will be heard, indicating the presence of hydrogen gas. 4. Test for Nitrogen (N₂) Test: Nitrogen is usually tested indirectly as it is an inert gas and does not support combustion or react easily. However, it can be tested by showing that it does not support the burning of a glowing splint. Observation: A glowing splint does not relight in nitrogen, indicating it does not support combustion. 5. Test for Ammonia (NH₃) Test: Use damp red litmus paper. Observation: The red litmus paper turns blue, indicating the presence of ammonia gas. This is because ammonia is a basic (alkaline) gas. 6. Test for Chlorine (Cl₂) Test: Use damp litmus paper (red or blue). Observation: The litmus paper is first bleached (turns white), then it will be red (because chlorine is acidic), and then blue (indicating that it can be neutralized). 7. Test for Sulfur Dioxide (SO₂) Test: Pass the gas through a solution of potassium dichromate (K₂Cr₂O₇) or potassium permanganate (KMnO₄). Observation: Potassium dichromate turns from orange to green, or potassium permanganate turns from purple to colorless, indicating the presence of sulfur dioxide. This is due to the reduction of the dichromate or permanganate ions. 8. Test for Carbon Monoxide (CO) Test: Carbon monoxide is a colorless, odorless, and non-reactive gas under normal conditions. It is often detected by its lack of reactivity. No obvious change is observed in a simple test. 9. Test for Hydrogen Chloride (HCl) Test: Hold a glass rod dipped in ammonia solution near the gas. Observation: White fumes of ammonium chloride (NH₄Cl) form, showing the presence of hydrogen chloride gas. This occurs due to the reaction of ammonia with hydrogen chloride. 10. Test for Nitrogen Dioxide (NO₂) Test: Pass the gas through an alkaline solution of potassium iodide (KI). Observation: Brown fumes of iodine gas will form, indicating the presence of nitrogen dioxide.

Answer 105

Soluble A substance is soluble if it can dissolve in a solvent, forming a homogeneous solution. For example, salt (sodium chloride) is soluble in water because it dissolves completely when mixed with water. Example: Sugar is soluble in water because it dissolves to form a clear solution. Insoluble A substance is insoluble if it cannot dissolve in a solvent, and it remains as a separate solid when mixed with the solvent. For example, sand is insoluble in water because it does not dissolve and stays as a solid when added to water. Example: Chalk is insoluble in water because it does not dissolve and remains as a solid. In summary: Soluble: Dissolves in a solvent (e.g., sugar in water). Insoluble: Does not dissolve in a solvent (e.g., sand in water).

Answer 106

Structural isomers are compounds that have the same molecular formula (same number and types of atoms) but differ in the way those atoms are connected or arranged in the molecule. This means they have different structural arrangements, resulting in distinct compounds with potentially different chemical and physical properties. Key Points about Structural Isomers: Same Molecular Formula: They contain the same number of atoms of each element. Different Connectivity: The atoms are bonded together in a different way, leading to different structures. Distinct Properties: Due to their different arrangements, structural isomers can have different boiling points, melting points, and reactivity. Example: C₄H₁₀ (butane) has two structural isomers: n-butane: A straight chain of four carbon atoms. isobutane (methylpropane): A branched chain with three carbon atoms in a straight chain and one carbon attached as a branch.

Answer 107

Anion Tests 1. Carbonate (CO₃²⁻) • Add dilute acid → bubbles form • Test gas with limewater → turns milky = CO₂ present 2. Halides (Cl⁻, Br⁻, I⁻) • Add dilute nitric acid then aqueous silver nitrate • Chloride: white ppt • Bromide: cream ppt • Iodide: yellow ppt 3. Nitrate (NO₃⁻) • Add aluminium foil and sodium hydroxide, heat • Test gas with damp red litmus → turns blue = ammonia released 4. Sulfate (SO₄²⁻) • Add dilute nitric acid then aqueous barium nitrate • White ppt = barium sulfate 5. Sulphite (SO₃²⁻) • Add acidified potassium manganate(VII) • Purple color decolorizes = SO₃²⁻ present

Answer 108

Cation Tests 1. Aluminium (Al³⁺) • With NaOH: White precipitate forms, dissolves in excess • With NH₃: White precipitate, insoluble in excess 2. Ammonium (NH₄⁺) • With NaOH: No precipitate, on warming produces ammonia gas (turns red litmus blue) 3. Calcium (Ca²⁺) • With NaOH: White precipitate, insoluble in excess • With NH₃: No or very slight precipitate 4. Chromium(III) (Cr³⁺) • With NaOH: Grey-green precipitate, dissolves in excess to give green solution • With NH₃: Grey-green precipitate, insoluble in excess 5. Copper(II) (Cu²⁺) • With NaOH: Light blue precipitate, insoluble in excess • With NH₃: Light blue precipitate, dissolves in excess to give deep blue solution 6. Iron(II) (Fe²⁺) • With NaOH: Green precipitate, turns brown on standing • With NH₃: Green precipitate 7. Iron(III) (Fe³⁺) • With NaOH: Reddish-brown precipitate • With NH₃: Reddish-brown precipitate 8. Zinc (Zn²⁺) • With NaOH: White precipitate, dissolves in excess • With NH₃: White precipitate, dissolves in excess

Answer 109

When a substance contains impurities: - its melting point falls, and its boiling point rises - it melts and boils over a range of temperatures, not sharply. The more impurity there is in a substance: - The bigger the change in melting and boiling points - the wider the temperature range over which it changes state

Answer 110

Activation energy is the minimum amount of energy that must be available to reactants for a chemical reaction to occur.

Answer 111

the difference in the amounts of stored chemical energy between the products and the reactants