Chemistry Paper 1: Topics 1-4 Flashcards
(101 cards)
1
Q
What are chemical equations
A
Show chemical changes. Reactants > products.
2
Q
What are symbol equations
A
Show formulas of reactants and products. Must be same number of atoms of each element on both sides of the symbol equation. You can change the big number in front of the formula
3
Q
In chemical equations involving ions, what do state symbols do?
A
Tell you the physical state of the substance
Aq = aqueous = dissolved in water
4
Q
What are the chemical formulas of these common molecules: Water Carbon dioxide Chlorine Ammonia Hydrogen
A
H2O =water CO2 = carbon dioxide Cl2 = chlorine NH3 = ammonia H2 = hydrogen
5
Q
What’s an ion? How can you work out the charges of ions?
A
Ions form when atoms gain or lose electrons
For single atoms use periodic table to see what charges their ions will form
6
Q
What are the formulas of ions made up of these groups of atoms: Ammonium Hydroxide Nitrate Carbonate Sulfate
A
Ammonium = NH(little4)^+ Hydroxide = OH^- Nitrate = NO(little 3)^- Carbonate = CO(little 3)^2- Sulfate = SO(little 4)^2-
7
Q
What’s an ionic equation
A
Only reacting particles and products are included
Look at the balanced symbols equation and take out aqueous ions present on both sides of the equation. Anything ionic and aqueous will break up into its ions in solution (in equation show all aqueous ions separately)
8
Q
What’s a hazard and whats a risk
A
Hazard = something with the potential to cause harm/damage Risk = probability of being harmed when exposed to hazard
9
Q
What do the following hazard symbols mean: Oxidising Environmental Hazard Toxic Harmful Highly flammable Corrosive
A
Oxidising = provides oxygen allowing other materials to burn
Environmental hazard = harmful to organisms + environment
Toxic = can cause death by swallowing, inhaling etc
Harmful = can caused irritation or blistering of skin
Highly flammable = catches fire easily
Corrosive = destroys materials, including living tissue
10
Q
List the of atom theories over history
A
19th Century - solid spheres. Different spheres make different elements
1897 - Plum pudding model. Atom must contain electrons as has measurements of charge and mass
1909 - positively charged alpha particles at gold sheet. Most went through, some deflected, some sent backwards. Theory of nuclear atom, tiny positively charged nucleus at centre and cloud of negative electrons, rest is empty space.
Refined Bohr model - electrons exist in fixed orbit, each shell has a. Fixed energy
11
Q
Whats the modern conclusion of structure of an atom?
A
3 subatomic particles: protons, neutrons, electrons.
Nucleus in middle of atom, contains neutrons + protons. Positively charged. Whole mass of atom is concentrated around nucleus
Electrons move around nucleus in electron shells. Size of their shell determines size of the atom.
Atoms have an atomic radius of about 10^-10m
Atoms have no overall charge, protons and electrons cancel out charges
12
Q
What’s the atomic number and whats the mass number
A
Atomic number = how many protons (also electrons in neutral atom), every atom of an element has same atomic number
Mass number = total number of neutrons + protons in atom
Biggest number in nuclear symbol is always the mass number
13
Q
What’s an isotope ?
A
Different forms of the same element. Have same number of protons but different numbers of neutrons ie same atomic number but different mass number
Different isotopes of an element appear in different isotopic abundances (quantities)
14
Q
How do isotopes effect relative atomic mass (Ar) of the element
A
Ar of an element is the average mass of one atom of the element, compared to 1/12 of the mass of 1 atom of carbon - 12
On periodic table, Ar is the biggest number next to the element
If element has 1 isotope, Ar is the same as its mass number
Element has more than 1 isotope, Ar is average of mass numbers of all the different isotopes, taking into account how much there is of each one
15
Q
How do you work out Ar of all atoms (isotopes) of an element
A
Multiply each relative atomic mass by its isotopic abundance and add up the results
Divide by sum of the abundances. If abundance’s given as percentages, this will be 100
16
Q
Describe the early periodic table
A
Dmitri Mendeleev arranged about 50 elements to make ‘Table of elements’
Kept elements with similar properties in columns. Elements ordered by atomic mass.
Used properties of other elements to predict properties of undiscovered elements
17
Q
Describe the modern periodic table
A
Shows elements in order of ascending atomic number
Elements with similar chemical properties form groups (columns)
Group number = number of electrons in outer shell. Group 0 is an exception, all have full outer shells, except helium which has 2 electrons in outer shell
Periods = the rows. Period number corresponds to number of shells
18
Q
What does electronic configuration tell you
A
Electronic configuration 2.5 = 2 electrons in inner shell, 5 electrons in outer shell
19
Q
What are ions. What are anions. What are cations.
A
Ions = charged particles. Can be single atoms or groups of atoms. Anions = negative ions. Forms when atoms gain electrons Cations = positive ions. From when atoms lose electrons
20
Q
What does the charge of an ion tell you. How do charges of ionic compounds work
A
How many more/less electrons than protons
Eg 2 electrons lost, charge is ^2+
Overall charge of any ionic compound is zero. All negative charges balance out all positive charges. Use charges of individual ions present to work out formula of the ionic compound.
21
Q
Why do elements form ions, and which ones are more likely to?
A
Elements in groups 1,2,6,7 are most likely to form ions.
Elements form ions in an attempt to get a stable electronic structure: full outer shell of electrons
22
Q
What does it mean if ions end in ‘ate’ or ‘ide’
A
‘Ate’ = negative ions containing oxygen and at least 1 other element ‘Ide’ = negative ions containing only one element (apart from hydroxide ions which are OH^-)
23
Q
What’s ionic bonding
A
When a metal and non metal react together, the metal atom loses electrons to form a cation and the non metal gains these electrons to form an anion. These oppositely charged ions are strongly attracted to one another by electrostatic forces. This is an ionic bond
24
Q
What can you use to show ionic bonding
A
Dot and cross diagram
Have original atoms, one with electrons represented with dots, the other with crosses. Little arrow to show where electrons will move from and to > the new ions, each has a square bracket around it. Electrons shown in their new places. Charges written outside bracket. Electronic configuration of each ion shown underneath.
25
What are the properties and structure of ionic compounds?
Always have giant ionic lattice structure. Strong electrostatic forces of attraction between oppositely charged ions in all directions. Throughout lattice oppositely charged ions will alternate.
High melting boiling points due to strong attraction between ions. Solid ionic compounds don’t conduct electricity, ions fixed in place. When melted, ions free to move, so will carry electric current.
Many dissolve easily in water, ions free to move in solution.
26
What’s covalent bonding and how does it relate to simple molecular substances
A covalent bond is a strong bond that forms when a pair of electrons is shared by two atoms
Covent bonding forms simple molecular substances and giant covalent structures
Simple molecular substances are made up of molecules containing a few atoms joined by covalent bonds.
27
```
What are the covalent bonds in the following simple molecular substances:
Hydrogen
Hydrogen chloride
Water
Oxygen
Methane
Carbon dioxide
```
Hydrogen = H2 = 2 hydrogen atoms form single covalent bond
Hydrogen chloride = HCl = H+Cl atoms form single covalent bond
Water = H2O = H+H+O, 2 single covalent bonds
Oxygen = O2 = O+O, double covalent bond
Methane = CH4 = C+H+H+H+H, 4 covalent bonds
Carbon dioxide = CO2 = O+C+O, 2 double covalent bonds
28
What’s a double covalent bond
A bond made of 2 shared electron pairs
29
What are the properties of covalently bonded simple molecular substances
Substances containing covalent bonds are usually simple molecular:
- atoms within molecules held together by strong covalent bonds. Forces of attraction between molecules weak.
Melting boiling points low as only need to part molecules
As molecules get bigger, strength of intermolecular forces increases
Don’t conduct electricity, no free electrons or ions
Some are soluble, some aren’t
30
What are polymers
Molecules made of long chains of covalently bonded carbon atoms, formed when many monomers join together
Monomers = lots of small molecules
31
What are the properties of most giant covalent structures
All atoms bonded to each other by strong covalent bonds. Very high melting boiling points due to this.
Generally don’t contain charged particles, so don’t conduct electricity (except graphite and Graphene)
Aren’t soluble in water
32
State and describe three carbon based giant covenant structures
Diamond: made of network of carbon atoms, each form 4 covalent bonds. High melting boiling point, atoms held in rigid lattice structure. Doesn’t conduct electricity. Used to strengthen cutting tools
Graphite: each carbon atom forms 3 covalent bonds, creating sheets of carbon atoms arranged in hexagons. No covalent bonds between layers so they’re free to move over each other. Ideal lubricating material. High melting boiling point due to covalent bonds. Each carbon has 1 delocalised electron, so graphite can conduct electricity
Graphene: a type of fullerene, is 1 layer of graphite. Sheet is 1 atom thick, so Graphene is a 2D compound.
33
What does it mean if an electron is delocalised?
It’s free to move
34
What are Fullerenes?
Molecules of carbon shaped like closed tubes or hollow balls. Mainly made of carbon atoms arranged into hexagons. Can contain pentagons or heptagons.
Fullerenes structure forms around an atom or molecule, which is trapped. Could be used to deliver drugs directly to cells.
Have huge surface area, could be used as industrial catalysts, with individual catalyst molecules attached to the fullerenes.
35
Name and describe two examples of fullerenes
Buckminster Fullerenes, C60
- Molecular formula C60, forms hollow sphere of 20 hexagons and 12 pentagons. Stable molecule. Forms soft black crystals
Nanotubes are Fullerenes
- tiny cylinders of Graphene, conduct electricity. High tensile strength (doesn’t break easily when stretched), can be used to strengthen equipment without adding much weight
36
Describe metallic bonding
Metals consist of a giant structure. Electrons in outer shell of metal atoms are delocalised. There are strong forces of electrostatic attraction between positive metal ions and shared negative electrons, these forces hold atoms together in regular structure
Metallic elements and alloys are compounds held together by metallic bonding
All metals have metallic bonding, so similar basic physical properties. Metals usually lose electrons to gain full outer shells.
37
Describe properties of compounds held together by metallic bonding
The delocalised electrons produce all properties of metals
Most compounds with metallic bonds have high melting boiling points. Usually shiny solids at room temperature. Not soluble in water. Denser than non metals, ions in metallic structure packed closely. Layers of atoms in pure metal can solide over each other, meaning metal is malleable (can be shaped)
Delocalised electrons carry electrical current + thermal energy through material, good conductors of electricity + heat
38
What’s Relative Formula Mass
Mr of a compound is the relative atomic masses (Ar) of all atoms in its formula added together
The Mr of compound is equal to mass in grams of 1 mole of the compound
39
What’s empirical formula
Empirical formula of a compound tells you the smallest whole number ratio of atoms in the compound
Work out how many moles of each element there are. Then work out the smallest whole number ratio between the moles of all the elements/atoms to get the empirical formula
40
What’s molecular formula
Molecular formula is the ratio of the elements in a compound given normally, eg glucose is C6H12O6
Use empirical formula and Mr to find molecular formula of a compound
Find Mr of compound. Divide Mr of compound by the Mr of the empirical formula to get Ans. Molecular formula = everything in empirical formula x Ans
41
What’s a mole
A mole is an amount of particles equals to Avogadro’s constant
Avogadro’s constant = 6.02 x 10^23
One mole of atoms or molecules of any substance will have a mass in grams equal to the relative particle mass (Ar (relative atomic mass) or Mr) for that substance
42
What’s equation for number of moles in a certain mass of a compound or element. What’s equation for number of particles something contains
Number of moles = mass in g (of element or compound) / Mr of compound OR Ar of element
Avogadro’s constant (6.02 x 10^23) x number of moles = number of particles (give this in standard form)
43
What’s the equation for concentration
Concentration (g/dm^-3) = mass of solute (g) / volume of solution (dm^3)
1dm^3 = 1 litre = 1000cm^3
44
What’s an experiment to calculate an Empirical Formula?
Calculate empirical formula of a metal oxide: weigh crucible + lid. Weigh crucible + lid with magnesium ribbon inside. Heat. Reweigh crucible + lid + contents.
Reading after - reading of crucible + Iid = mass of magnesium oxide
Work out mass of oxygen, work out number of moles of magnesium and oxygen involved, work out EF
45
What’s a limiting reactant
Reactant is used up, so reaction stops.
| Limiting reactant is the reactant thats used up. The reactant thats not used up is ‘in excess’
46
How do you calculate the amount of product formed from limiting reactant
Write out balanced equation
Work out Mr of reactant + products interested in
Find out how many moles there are of substance you know mass of
Using balanced equation, work out how many moles of the other substance there will be
Use number of moles to calculate the mass
47
How do you work out a balanced symbol equation knowing masses of reactants + products?
Divide mass of each substance by its relative formula mass to find the number of moles
Divide number of moles of each substance by smallest number of moles in the reaction
If needed, multiply all numbers by same amount to make them all integers
Write balanced symbol equation for reaction by putting these numbers in front of the formulas
48
Describe the properties of the three states of matter.
Solids: strong forces hold particles fixed in regular lattice arrangement. Keep definite shape and volume. Particles vibrate around fixed positions
Liquids: free to move past each other, tend to stick together. Keep same volume, not definite shape, will flow to fit a container. Particles constantly move with random motion
Gases: free to move, almost no forces between particles. Travel in straight lines, interact on collision. Don’t keep definite shape or volume, will always fill any container. Move constantly with random motion. When heated, particles expand and pressure increases. When particles bounce of walls of a container, they exert pressure on the walls.
49
How do substances change state
Changing state is a physical process so easy to reverse
By heating: melting, evaporating, subliming (solid to gas)
Particles vibrate until have enough energy to break from their positions/ bonds
By cooling: freezing, condensing
50
What’s a chemical change
Happens during chemical reactions, when bonds between atoms break + atoms change places. Reactants rearranged to form different substances (products). Often hard to reverse
51
What’s a Pure substance,what’s a mixture
Pure substance = made of only one element or compound. Have specific melting boiling points. Test purity by comparing actual melting boiling point with expected value.
Mixture = substances with multiple elements/compounds present. Melts gradually over a range of temperatures. ‘Impure substances’ are mixtures
52
What’s melting point aparatus
Allows heating of small sample of solid very slowly, so can observe and record exact temperature it melts at
53
What’s distillation? What’s the process to get pure water from seawater?
Separates a liquid from a solution
Pour sample of seawater in distillation flask and set up apparatus. Run cold water through condenser. Heat distillation flask, water evaporates, cools in condenser and is collected in beaker. Just salt left in flask.
If heating flammable liquid use an electric heater or water bath
54
What’s fractional distillation? Describe process of separating crude oil at a refinery
Fractional distillation used to separate a mixture of liquids.
Put mixture in flask. Attach fractionating column + condenser. Gradually heat flask. Liquid lowest boiling point evaporates first. When temp on thermometer matches boiling point of this liquid, it will reach top of column. When first liquid collected, raise temp until next one reaches top
55
What’s filtration? Describe the process
Separates insoluble solid from a liquid or solid impurities from a mixture
Put filter paper in funnel, pour mixture in. Liquid runs through paper, leaving the solid residue behind.
56
What’s crystallisation? Describe the process
Separates soluble solids from solution
Pour solution in evaporating disk, gently heat. Solution gets more concentrated as some water begins to evaporate. At point of crystallisation (or once some water evaporates) remove dish from heat and leave solution to cool. Salt forms crystals as becomes insoluble in cold, highly concentrated solution. Filter crystals out of solution, leave in warm place to dry.
57
What’s chromatography?
A method used to separate + identify a mixture of soluble substances. Has two phases:
Mobile phase = where molecules can move. Always liquid or gas.
Stationary phase = where molecules can’t move. A solid or thick liquid
Components in mixture separate out as mobile phase moves over stationary phase. Components end up in different places in stationary phase because each chemical in a mixture will spend different amounts of time dissolved in mobile phase and stuck in stationary phase
58
Describe paper chromatography
Stationary phase is filter paper, mobile phase is solvent.
Draw baseline using pencil. Put spot of mixture on baseline. Did paper in beaker of solvent, baseline must be above solvent. Remove paper before solvent reaches top. Solvent front = distance solvent has moved. Mark this in pencil.
Different solvents may separates components differently
59
What’s a chromatogram? What’s Rf values?
Piece of paper you get at end of paper chromatography. If have colourless chemicals in mixture, spray chromatogram with locating agent
Rf value is ratio between distance travelled by solute and solvent
Rf = distance travelled by solute / distance travelled by solvent
Solute = the dissolved substance
60
What’s ‘controlled reference materials’
Sample with a controlled concentration + purities, to be compared against
61
What’s surface water? Whats ground water? What does potable mean? What’s waste water?
Surface water = lakes, rivers, reservoirs.
Ground water = from aquifers (rocks which trap water underground)
Waste water= water contaminated by human processes. Can be treated to make it potable
Potable = drinkable
62
What are the three stages of water purification
1) filtration: wire mesh screens out large debris, gravel + sand beds filter out other solids
2) sedimentation: iron Sulfate or Aluminium Sulfate added, makes fine particles clump together and settle at bottom
3) chlorination: chlorine gas bubbled through, kills harmful bacteria
Sea water can be distilled to be made potable, but that’s expensive
Experiments should use deionised water, as ions can interfere with reactions
63
What’s an acid?
A substance with a pH below 7. Forms H^+ ions in water. Higher concentration hydrogen ions means more acidic means lower pH
64
What’s a base?
A substance that reacts with an acid to form a salt and water
65
What’s an alkali?
A base which is soluble in water. PH higher than 7, form OH^- ions (hydroxide ions) in water. Higher concentration of hydroxide ions means higher pH
66
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What’s an indicator? When in acid, neutral or alkali, what colours to the following indicators turn:
Universal indicator
Litmus paper
Methylorange
Phenolphthalein
```
Indicator = dye, changes colour depending on pH
Universal indicator = red acid, green neutral, purple alkali
Litmus = red acid, purple neutral, blue alkali
Methylorange = red acid, purple neutral, blue alkali
Phenolphthalein = colourless acidic + neutral, pink alkaline
67
What’s a neutralisation reaction. What’s it in terms of hydroxide and hydrogen ions?
Acid + base > salt + water
H^+ (aq) + OH^- (aq) > H2O (l)
68
How do you investigate a neutralisation reaction?
Base and dilute hydrochloric acid
1 measure set volume of dilute hydrochloric acid into conical flask
2 measure fixed mass of calcium oxide using mass balance, add the calcium oxide to the hydrochloric acid
3 wait for base to completely react. Find out pH of solution.
4 repeat steps 2-3 until all acid has reacted (get excess base)
5 plots graph to see how pH changes with mass of base added. PH first changes slowly, then suddenly as approaches neutral
69
What do acids do in solution
All acids ionise (dissociate) in solution, meaning they split up to produce hydrogen ion and another ion.
Strong acids ionise almost completely in water
Weak acids do not fully ionise in solution
Ionisation of a weak acid is a reversible reaction, so sets up an equilibrium. Only a few acid particles release H^+ ions so equilibrium lies to the left
70
What’s acid strength and what’s acid concentration
Acid strength = what proportion of the acid molecules ionise in water
Acid concentration = measures how much acid there is in a litre (1dm^3) of water
If concentration of H^+ ions increases by factor of 100 (10x10), pH decreases by 2 (1+1)
71
what salt (an ionic compound) do the following produce in neutralisation reactions:
Hydrochloric acid
Sulphuric acid
Nitric acid
Hydrochloric acid produces chloride salts
Sulphuric acid produces Sulfate salts
Nitric acid produces Nitrate salts
72
```
Acids react with things to make what:
Acid + metal oxide > ?
Acid + metal hydroxide > ?
Acid + metal > ?
Acid + metal carbonate > ?
```
Acid + metal oxide > salt + water
Acid + metal hydroxide > salt + water
Acid + metal > salt + hydrogen
Acid + metal carbonate > salt + water + carbon dioxide
73
How do you test for CO2, how do you test for hydrogen
To see if gas is carbon dioxide, bubble it through limewater. It should turn cloudy.
Hydrogen. Stick a lit splint in the hydrogen, it’ll make a noise which comes from hydrogen burning with the oxygen in the air to form water
74
How do insoluble salt and soluble salt form?
Insoluble salt will form as a precipitate
| Soluble salt will form in a solution
75
Are the following soluble or insoluble in water:
1 Common salts of sodium, potassium and ammonium
2 nitrates
3 common chlorides
4 common Sulfates
5 common carbonates + hydroxides
1 soluble
2 soluble
3 soluble except silver chloride + lead chloride
4 soluble except lead, barium + calcium Sulfate
5 insoluble except sodium, potassium and ammonium ones
76
What’s a precipitation reaction?
Reaction which gives a pure, dry sample of insoluble salt. Add 2 correct soluble salts together to achieve this, eg lead nitrate and sodium chloride
77
How do you make any soluble salt?
Use an acid and an insoluble base. React acid continuing 1 of the ions you want in the salt with an insoluble base (sometimes a metal) that contains the other ion you need (usually a metal oxide or metal hydroxide)
OR use an acid alkali reaction using titration
Slowly add alkali to acid using a burette, until reach end point = acid has been exactly neutralised. Repeat with same measurements without indicator
78
What’s electrolysis
The breaking down of a substance using electricity. A d.c electric current is passed through an electrolyte, causing it to decompose. Cations in electrolyte move towards cathode and are reduced. Anions in electrolyte move towards anode and are oxidised. This creates a flow of charge through the electrolyte. As ions gain/lose electrons, they form uncharged substances and are discharged from the electrolyte
79
What’s an electrolyte?
| What’s reduction? What’s oxidation?
```
Electrolyte = A molten or dissolved ionic compound
Reduction = gain of electrons OR the removal of oxygen
Oxidation = loss of electrons OR a reaction with or the addition of oxygen
```
80
What’s a cathode? What’s an anode?
| What’s an electrochemical cell?
Cathode = negative electrode
Anode = positive electrode
Electrochemical cell = a circuit made of the anode,cathode, electrode, a powert course and wires that connect the two electrodes
81
What’s a half equation
Shows how electrons are transferred during reactions.
Put things being oxidised/reduced on one side, thing it gets oxidised/reduced into on the other side
Balance number of atoms
Add electrons (written e^-) on one side to balance the charges
82
What’s the method for electrolysis if the electrolytes a solution
1 get two inert (unreactive) electrodes
2 clean electrodes using emery paper
3 place electrodes in beaker filled with electrolyte
4 connect electrodes to power supply. Current will flow through cell. Voltage of cell decreases as electrolysis continues
In aqueous solutions theres ions from the ionic compound + hydrogen ions and hydroxide ions from the water
83
What’s the method for electrolysis if the electrolytes a solid ionic substance
1 put solid ionic substance in crucible
2 heat until solid molten
3 dip 2 clean, inert electrodes into electrolyte
4 connect electrodes to power supply. Current flows through cell
Positive Metall ions are reduced to metal atoms at cathode
Negative ions oxidised to atoms or molecules at anode
84
In electrolysis, what happens at cathode if H^+ ions and metal ions are present. In electrolysis, what happens at anode if OH^- ions are present
1 if metal more reactive than hydrogen, hydrogen gas produced
If metal less reactive than hydrogen, solid layer of pure metal produced
2 if halide ions present, molecules of chlorine, bromine or iodine formed
If no halide ions present, oxygen formed
Halide ions = Cl^-, Br^-, I^-
85
List products of electrolysis of copper Sulfate with inert electrodes
Produces copper metal at cathode (Cu^2+ +2e^- > Cu)
| oxygen and water at anode (4OH^- > O2 + 2H2O + 4e^-)
86
Describe electrolysis of copper Sulfate using copper electrodes
Used to purify impure copper extracted from ore
Anode is lump of impure copper, cathode is thin pice of pure copper, electrolyte is copper (II) Sulfate solution (contains Cu^2+ ions)
1 impure copper anode is oxidised, dissolving into electrolyte to form copper ions
2 copper ions are reduced at pure copper cathode, and add to it as a layer of pure copper
3 any impurities from impure copper anode sink to bottom of cell
87
What are combustion reactions
Involve oxidisation and are always exothermic
88
What do a metal’s position in the reactivity series in comparison to the position of hydrogen or carbon tell you?
Metals position in reactivity series compared to carbon dictates how it’s extracted from its ore.
Hydrogen shows reactivity with dilute hydrochloric acid. If the metals below hydrogen, it wont react with dilute acids
89
List and describe the reactivity series
```
Potassium (most reactive, easily lose electrons to form cations. Least resistant to oxidation, corrodes more easily)
Sodium
Lithium
Calcium
Magnesium
Aluminium
Carbon
Zinc
Iron
Tin
Hydrogen
Copper
Silver
Gold (least reactive, most resistant to oxidation)
```
90
Metal + water > ?
| Less reactive metal + steam > ?
Metal + water > metal hydroxide + hydrogen
| Less reactive metal + steam > metal oxide + hydrogen
91
What are displacement reactions
Redox reactions: oxidation and reduction both happen. A more reactive element reacts to take the place of a less reactive element in a compound.
In metal displacement reactions the more reactive metal loses electrons (is oxidised) and the less reactive metal gains electrons (is reduced)
If put reactive metal in a solution of a less reactive metal salt, the reactive metal will replace the less reactive metal in the salt
92
Whats a metal ore
A rock containing enough metal to make it economically worthwhile to extract the metal. The ore is usually an oxide of the metal. Metal can be extracted from ore chemically by reduction using carbon if below carbon in reactivity series. If above, extracted using electrolysis of molten compounds, metal discharged at cathode.
Some unreactive metals found as uncombined elements that are mined out of ground and then refined
93
What are biological ways of extracting metals
Use living organisms
Bioleaching (bacterial method) = bacteria gets energy from bonds between atoms in ores, separates metal from ore. Produces leachate, contains metal ions which can be extracted
Phytoextraction: grow plants in soil containing metal compounds. Metal builds up in leaves. Plant harvested, dried and burnt in a furnace. Ash contains metal compounds, metal extracted.
94
What’s recycling do?
Saves energy as uses less energy than energy needed to extract and refine the material.
Conserves rare materials
Less rubbish to be sent to landfill
Creates jobs
95
What’s a life cycle assessment
Company carries out life cycle assessment when they want to manufacture a new product. It looks at the environmental impact of each stage of products life:
Choice of material, manufacture, product use, disposal
96
What does reversible reaction mean
Products can react with each other to produce the original reactants
97
Describe the Haber Process
Nitrogen and hydrogen react to form ammonia in the equation N2 + 3H2 (reversible equation sign) 2NH3
Nitrogen is obtained from air, hydrogen extracted from hydrogen extracted from hydrocarbons from sources like natural gas and crude oil.
Carried out at 450*C, with a pressure of 200 atmospheres and an iron catalyst
98
Describe how equilibrium works
As reactants react, concentration falls, > reaction falls down
As products form, concentration rises, < reaction speeds up
Equilibrium is the point they reach where both reactions are happening but theres no overall effect. Reactant and products won’t change. This is called ‘dynamic equilibrium’
99
What does it mean if equilibrium lies to the left? Right?
```
Left = concentration of products is greater than reactants
Right = concentration reactants greater than products
```
position depends on reaction + conditions: temperature, pressure (in gases), concentration or reactants and products
Can change conditions to shift position to the right (towards products) to increase yield
100
What’s Le Chateliers Principle
If theres a change in concentration, pressure or temperature in a reversible reaction, the equilibrium position will move to help counteract that change
101
How do the conditions temperature, pressure and concentration affect equilibrium position?
Decrease temp: equilibrium moves in exothermic reaction to produce more heat
Increase temp: equilibrium moves in endothermic reaction to absorb extra heat
(All reactions are exothermic in one direction and endothermic in another)
increase pressure: equilibrium moves side that has fewer moles of gas, to decrease pressure
Decrease pressure: equilibrium moves side that has more moles of gas, to increase pressure
Increase concentration of reactants: equilibrium moves to right to use up reactants and make more product
Increase concentration of products: equilibrium moves to left to use up products, making more reactant
(Decreasing has opposite effect)
