AQA GCSE Chemistry Paper 2 (Higher Tier)Paper 2 — every question, answered
We analysed every real Chemistry Paper 2 Higher Tier sitting AQA has made public since the pandemic disruption, including the actual questions students saw and the mark schemes examiners used. Below is what each recurring question type has asked, what the real data and diagrams showed, and a complete worked answer for each sitting we have. This is the closest you can get to seeing exactly what a full mark answer looks like without a real exam paper in front of you.
Questions © AQA, quoted for analysis. Diagrams and data described in our own words, not reproduced. Mark scheme content translated into plain English, not copied. PrepWise is independent and not endorsed by AQA.
The paper is a template
Same 18 question types, every sitting“What flame colour or test result identifies a metal ion?”
Every sitting we checked asks you to name a flame test result or a chemical test result for a metal ion. The ions tested change, but the method (clean wire, blue Bunsen flame, observe colour) stays the same.
1×asked“What flame colour is produced by copper sulfate solution?”
“What flame colour is produced by copper sulfate solution?”
What it’s really asking
It wants the specific flame colour copper ions produce, not just 'coloured' or a vague description.
The full worked answer — June 2020
Copper sulfate solution produces a blue-green flame colour.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise flame tests and ion identificationWhat the mark scheme rewarded
- Naming the colour blue-green (or blue) precisely, not a vague description like 'coloured' or 'bright'
- Lithium: crimson/red flame
- Sodium: yellow flame
- Potassium: lilac flame
- Calcium: orange-red flame
- Copper: blue-green flame
- Barium: green flame
Traps examiners saw
- Confusing copper's blue-green with barium's green
- Writing 'blue' only when the mark scheme wants 'blue-green'
Full-mark self-check 0 of 2
1×asked“Give a test to identify the Group 1 metal ion in potash alum, and give the result of the test.”
“Give a test to identify the Group 1 metal ion in potash alum, and give the result of the test.”
What it’s really asking
It wants both the method (flame test) and the specific result (lilac flame) for the Group 1 metal ion in potash alum, which is potassium.
The full worked answer — June 2021
The test is a flame test: dip a clean metal wire in a sample of the compound and hold it in a blue Bunsen burner flame. The result is a lilac flame colour, which shows the Group 1 metal ion present is potassium.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise flame tests and ion identificationWhat the mark scheme rewarded
- Naming the test as a flame test
- Stating the lilac flame result specifically for potassium
- Potash alum has the formula KAl(SO4)2, so its Group 1 metal ion is potassium
- Potassium produces a lilac flame colour in a flame test
Traps examiners saw
- Confusing potassium's lilac with sodium's yellow
- Naming the test but forgetting the result, or vice versa
Full-mark self-check 0 of 2
1×asked“Give a method the scientist could use to show that a sample of medicine contains potassium ions and bromide ions, giving the results of the tests.”
“Give a method the scientist could use to show that a sample of medicine contains potassium ions and bromide ions, giving the results of the tests.”
What it’s really asking
It wants a full planned method combining a flame test for potassium ions with a silver nitrate and nitric acid test for bromide ions, with both results stated.
The full worked answer — June 2023
To test for potassium ions, place a sample of the medicine on a clean metal wire and introduce it into a blue, non-luminous Bunsen burner flame. Observe a lilac flame colour, which shows potassium ions are present.
To test for bromide ions, dissolve a sample of the medicine in distilled water in a test tube, then add a few drops of dilute nitric acid followed by silver nitrate solution using a dropping pipette. Observe a cream precipitate forming, which shows bromide ions are present.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise flame tests and ion identificationWhat the mark scheme rewarded
- Logically sequencing both tests (potassium flame test, then bromide precipitate test)
- Naming the correct precipitate colour cream specifically for bromide, not white or yellow
- Using dilute nitric acid before silver nitrate to remove other interfering ions
- Chloride ions give a white precipitate with silver nitrate
- Bromide ions give a cream precipitate with silver nitrate
- Iodide ions give a yellow precipitate with silver nitrate
- Dilute nitric acid is added first to remove carbonate ions that would also give a precipitate
Traps examiners saw
- Naming the bromide precipitate as white (that is chloride) or yellow (that is iodide)
- Forgetting to acidify with nitric acid before adding silver nitrate
Full-mark self-check 0 of 3
The method for every Q01/Q07 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Naming the exact flame colour for the metal ion asked about
- Describing the correct test method when asked to describe rather than just name a colour
- Knowing that some colours (lilac potassium, crimson lithium) are easily confused with others and must be named precisely
The steps
- Identify which metal ion the question is asking about
- Recall its flame test colour from the standard list (lithium crimson, sodium yellow, potassium lilac, calcium orange-red, copper blue-green, barium green)
- If asked for a test rather than just a colour, describe dipping a clean wire in the sample and holding it in a blue Bunsen flame
- State the result precisely, since 'green' alone is not enough when barium and copper are both possible answers
Which type of wire is used to carry out a flame test?
Flame test colours and ion tests come up almost every sitting. Learn the exact colour for each metal ion cold, since 'close' answers do not score.
Practise flame tests and ion identification“Which solution and result shows the presence of sulfate ions, or a halide ion, in a sample?”
Sulfate testing (add acidified barium chloride, look for a white precipitate) and halide testing (add acidified silver nitrate, check the precipitate colour) both come up as short, precisely worded point-marked questions.
1×asked“Name the solution that would show the presence of sulfate ions when added to this mixture, after dilute hydrochloric acid has been added to copper sulfate solution.”
“Name the solution that would show the presence of sulfate ions when added to this mixture, after dilute hydrochloric acid has been added to copper sulfate solution.”
What it’s really asking
It wants the specific reagent that confirms sulfate ions once dilute hydrochloric acid has already been added, which is barium chloride (or barium nitrate) solution.
The full worked answer — June 2020
Barium chloride solution would show the presence of sulfate ions, since it produces a white precipitate of barium sulfate with sulfate ions present.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise ion identification testsWhat the mark scheme rewarded
- Naming barium chloride solution (barium nitrate solution also accepted)
- Dilute hydrochloric acid is added first to remove carbonate ions, which would otherwise also give a precipitate with barium chloride
- Barium sulfate is an insoluble white precipitate
Traps examiners saw
- Naming silver nitrate, which tests for halides not sulfates
- Forgetting the acid step is needed before barium chloride to rule out carbonates
Full-mark self-check 0 of 1
1×asked“Describe a test to identify the presence of sulfate ions in a solution of potash alum, and give the result of the test.”
“Describe a test to identify the presence of sulfate ions in a solution of potash alum, and give the result of the test.”
What it’s really asking
It wants the full test method (acidify then add barium chloride) plus the precipitate colour, not just the reagent name.
The full worked answer — June 2021
Add dilute hydrochloric acid to the solution of potash alum, then add barium chloride solution. A white precipitate forms, which shows sulfate ions are present.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise ion identification testsWhat the mark scheme rewarded
- Adding dilute hydrochloric acid before the barium chloride
- Naming barium chloride (or barium nitrate) solution
- Stating a white precipitate forms
- Potash alum, KAl(SO4)2, contains sulfate ions
- The acid step removes carbonate ions that would otherwise give a false positive precipitate
Traps examiners saw
- Skipping the acid step, which loses a mark even if barium chloride and the white precipitate are both correct
- Naming the precipitate as a generic 'solid' instead of specifically white
Full-mark self-check 0 of 3
1×asked“Describe a test to show the presence of copper(II) ions in a solution of copper(II) sulfate, and give the result of the test.”
“Describe a test to show the presence of copper(II) ions in a solution of copper(II) sulfate, and give the result of the test.”
What it’s really asking
It wants sodium hydroxide solution added to the copper(II) sulfate solution, with the specific blue precipitate colour that identifies copper(II) ions.
The full worked answer — June 2023
Add sodium hydroxide solution to the copper(II) sulfate solution. A blue precipitate forms, which shows the presence of copper(II) ions.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise ion identification testsWhat the mark scheme rewarded
- Naming sodium hydroxide solution
- Stating the precipitate colour is blue, specific to copper(II) ions
- Iron(II) ions give a green precipitate with sodium hydroxide
- Iron(III) ions give a brown precipitate with sodium hydroxide
- Copper(II) ions give a blue precipitate with sodium hydroxide
Traps examiners saw
- Confusing the blue copper(II) precipitate with the green iron(II) precipitate
Full-mark self-check 0 of 2
The method for every Q01/Q05 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Naming the correct reagent (barium chloride for sulfate, silver nitrate for halides)
- Stating both results are dependent: acid must be mentioned first
- Naming the exact precipitate colour
The steps
- Identify whether the ion being tested is a sulfate or a halide
- For sulfate: add dilute hydrochloric acid, then barium chloride solution, and look for a white precipitate
- For a halide: add dilute nitric acid, then silver nitrate solution, and check the precipitate colour (white for chloride, cream for bromide, yellow for iodide)
- Always state which specific colour of precipitate is expected
Which reagents are used to test for carbonate ions in a solution?
The sulfate test and the metal hydroxide precipitate tests are short, precisely worded questions. Learn each reagent and each exact precipitate colour so you never mix up copper, iron(II) and iron(III).
Practise ion identification tests“Explain how potable water is produced from fresh water, or from a different water source.”
Both sittings we checked with a water question ask you to explain the standard fresh-water treatment steps (filter beds then sterilisation) as a logically linked account.
1×asked“In the UK, potable (drinking) water is produced from different sources of fresh water. Explain how potable water is produced from fresh water.”
“In the UK, potable (drinking) water is produced from different sources of fresh water. Explain how potable water is produced from fresh water.”
What it’s really asking
It wants the two-stage UK fresh-water treatment process explained as a logical account, not just a list of two words.
The full worked answer — June 2020
An appropriate source of fresh water is chosen, such as a river, stream, lake or borehole. The water is passed through filter beds, which removes undissolved solids from it. The filtered water is then sterilised, using chlorine, ozone or ultraviolet light, which destroys harmful microbes in the water so that it is safe to drink.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise water treatment questionsWhat the mark scheme rewarded
- Naming an appropriate fresh water source
- Filtration to remove undissolved solids
- Sterilisation using a named method (chlorine, ozone or UV light)
- Linking sterilisation to destroying harmful microbes
- Fresh water sources include rivers, streams, lakes and boreholes
- Filter beds remove solid particles
- Chlorine, ozone and UV light are all accepted sterilising methods
Traps examiners saw
- Naming only one stage (just filtration, or just sterilising) instead of both
- Listing steps without explaining what each one removes or destroys
Full-mark self-check 0 of 3
1×asked“Explain why the ground water requires Process 2 before the water is safe to drink.”
“Explain why the ground water requires Process 2 before the water is safe to drink.”
What it’s really asking
It wants an explanation of why sterilisation (Process 2) is still needed even after ground water has already been filtered, because filtration alone does not remove harmful microbes.
What the sources actually showed — June 2022
A table comparing sea water and ground water treatment, showing filtration as Process 1 for ground water and UV light exposure as Process 2, alongside sodium and chloride ion concentrations before and after each process.
| Sea water | Ground water | |
|---|---|---|
| Concentration of Na+ and Cl- ions before Process 1 | Na+: 0.5 mol/dm3, Cl-: 0.5 mol/dm3 | Na+: 0.001 mol/dm3, Cl-: 0.001 mol/dm3 |
| Process 1 | Reverse osmosis | Filtration |
| Concentration of Na+ and Cl- ions after Process 1 | X | Na+: 0.001 mol/dm3, Cl-: 0.001 mol/dm3 |
| Process 2 | Add ozone | Expose to ultraviolet light |
The full worked answer — June 2022
The ground water contains microbes which are harmful to health. Process 2, exposure to ultraviolet light, sterilises the water so that the harmful microbes are destroyed.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise water treatment questionsWhat the mark scheme rewarded
- Stating the ground water contains harmful microbes
- Explaining that Process 2 sterilises the water or destroys the microbes
- Filtration removes solid particles but does not kill microbes
- UV light, chlorine and ozone all sterilise water by destroying microbes
Traps examiners saw
- Assuming filtration alone makes water safe, when sterilisation is still required
- Not naming what Process 2 actually removes (microbes, not solids)
Full-mark self-check 0 of 2
The method for every Q02/Q05 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Naming both stages: filtration to remove solids, then sterilisation to kill microbes
- Naming a specific sterilising agent (chlorine, ozone or UV light)
- Linking each step to why it is needed, not just listing steps
The steps
- Choose an appropriate source of fresh water (rivers, streams, lakes, boreholes)
- Pass the water through filter beds to remove undissolved solids
- Sterilise the water using chlorine, ozone or UV light
- State that sterilising destroys harmful microbes
What does the term 'potable water' mean?
Water treatment questions reward the two-stage process explained as a logical account: filtration removes solids, sterilisation destroys microbes. Practise linking each step to its purpose.
Practise water treatment questions“Suggest one process a country with little rainfall could use to obtain most of its potable water.”
This short suggest question rewards naming a desalination process (distillation or reverse osmosis) when a country cannot rely on fresh water sources.
1×asked“A different country has very little rainfall, a long coastline, and plentiful energy supplies. Suggest one process this country could use to obtain most of its potable water.”
“A different country has very little rainfall, a long coastline, and plentiful energy supplies. Suggest one process this country could use to obtain most of its potable water.”
What it’s really asking
It wants a named desalination process appropriate for a coastal country with plentiful energy but little fresh water, since desalination is energy-intensive.
The full worked answer — June 2020
This country could use distillation, or reverse osmosis, to desalinate sea water and obtain potable water.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise water resource questionsWhat the mark scheme rewarded
- Naming distillation or reverse osmosis (desalination in general is also accepted)
- Distillation and reverse osmosis are the two standard desalination methods on the specification
- Desalination requires large amounts of energy, matching the country's plentiful energy supply
Traps examiners saw
- Naming filtration or sterilisation alone, which do not remove dissolved salt
Full-mark self-check 0 of 1
The method for every Q02/Q05 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Naming distillation or reverse osmosis specifically, since a coastal country with sea water access needs desalination, not fresh water treatment
The steps
- Recognise the country described has a long coastline and little rainfall, meaning sea water is the available source
- Name distillation or reverse osmosis as the desalination method
What does the term 'potable water' mean?
When a country lacks fresh water but has sea water and energy, desalination (distillation or reverse osmosis) is the answer. Keep this distinction from ordinary water treatment clear.
Practise water resource questions“Evaluate the use of two different materials for the same product, using features of life cycle assessments (LCAs).”
This extended question always gives you a data table comparing two or three materials for the same product (food plates, milk bottles) and asks for a judgement built from raw materials, manufacturing, use and disposal stages.
1×asked“Evaluate the use of these materials for making food plates. You should use features of life cycle assessments (LCAs). Use Table 2.”
“Evaluate the use of these materials for making food plates. You should use features of life cycle assessments (LCAs). Use Table 2.”
What it’s really asking
It wants a judgement comparing paper, polymer and ceramic food plates across every LCA stage, using the actual figures given for raw materials, packaging, reuse and disposal.
What the sources actually showed — June 2020
A table comparing paper, polymer and ceramic food plates of equal diameter, showing raw material (wood, crude oil, mined clay), number packaged in a fixed box volume, average number of times used, and whether each is biodegradable and recyclable.
| Material | Raw material | Plates fitting in a 10 dm3 box | Average number of times used | Biodegradable | Recyclable |
|---|---|---|---|---|---|
| Paper | Wood | 500 | 1 | Yes | Yes |
| Polymer | Crude oil | 100 | 400 | No | Yes |
| Ceramic | Mined clay | 50 | 1000 | No | No |
The full worked answer — June 2020
Looking at raw materials, wood used for paper plates is a renewable resource, while crude oil for polymer plates and mined clay for ceramic plates are both finite resources that will eventually run out, so paper plates score better here.
For manufacturing and packaging, 500 paper plates fit in the same 10 dm cubed box as only 100 polymer plates or 50 ceramic plates, so paper plates need the least packaging per plate and less transport energy overall, conserving raw materials used in packaging and fuel used in transport.
For use and operation, paper plates are used only once on average, while polymer plates are used 400 times and ceramic plates 1000 times, meaning far fewer polymer and ceramic plates need to be manufactured over their working lives, which reduces raw material and energy use overall despite each plate individually requiring more resources to make.
For disposal, paper plates are biodegradable and recyclable, so they do not build up in landfill, while ceramic plates are neither biodegradable nor recyclable and will sit in landfill permanently, and polymer plates, though not biodegradable, can at least be recycled into different polymer products.
Overall I judge paper plates are the most sustainable for single or occasional use because they use the least packaging, are biodegradable and are recyclable, even though each individual plate is used only once; but for a setting where plates are reused many times, such as a canteen, ceramic plates become more sustainable overall because their very high reuse figure of 1000 outweighs the fact that clay is a finite raw material and that ceramic cannot be recycled.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise life cycle assessment questionsWhat the mark scheme rewarded
- Comparing raw materials (renewable wood versus finite crude oil and clay)
- Using the manufacturing and packaging figures from the table
- Using the reuse figures from the table
- Comparing biodegradability and recyclability at disposal
- A reasoned judgement supported by the points above
- Trees are a renewable resource; crude oil and mined clay are finite
- 500 paper plates fit a 10 dm cubed box versus 100 polymer or 50 ceramic
- Paper plates are used once on average; polymer plates 400 times; ceramic plates 1000 times
- Paper is biodegradable and recyclable; polymer is recyclable but not biodegradable; ceramic is neither
Traps examiners saw
- Only discussing raw materials without moving on to manufacturing, use and disposal
- Giving a judgement with no supporting reasons ('paper is best' with nothing else)
- Ignoring the actual numbers in the given table and writing generic LCA theory instead
Full-mark self-check 0 of 3
1×asked“Milk bottles can be made from glass or from a polymer. Evaluate the use of glass for milk bottles compared with the use of a polymer for milk bottles. Use features of life cycle assessments (LCAs) in your answer. Use Table 2.”
“Milk bottles can be made from glass or from a polymer. Evaluate the use of glass for milk bottles compared with the use of a polymer for milk bottles. Use features of life cycle assessments (LCAs) in your answer. Use Table 2.”
What it’s really asking
It wants a judgement comparing glass and polymer milk bottles across raw materials, manufacturing energy, mass, reuse and disposal, using the exact energy and reuse figures given.
What the sources actually showed — June 2022
A table comparing glass and polymer milk bottles of equal volume, showing raw materials, energy needed to process raw materials in kilojoules, energy needed to manufacture the bottle in kilojoules, mass of the bottle, mean number of times used, and one disposal method for each.
| Material | Raw materials | Energy to process raw materials (kJ) | Energy to manufacture bottle (kJ) | Mean number of times used | Disposal method |
|---|---|---|---|---|---|
| Glass | Limestone, sand, sodium carbonate | 6750 | 750 | 25 | Recycled into different products of the same type |
| Polymer | Crude oil | 1710 | 90 | 1 | Recycled into different products of the same type |
The full worked answer — June 2022
Glass is made from limestone, sand and sodium carbonate, while the polymer is made from crude oil. Since crude oil is finite, relying on it for single bottles is less sustainable in raw material terms than glass, though glass's raw materials still require quarrying, which has its own environmental impact.
The energy figures make the biggest difference at the processing and manufacturing stages: processing raw materials for glass takes 6750 kJ against only 1710 kJ for the polymer, and manufacturing the bottle itself takes 750 kJ for glass against 90 kJ for the polymer, so producing one glass bottle from scratch uses roughly four times more total energy than one polymer bottle.
However, glass bottles are reused on average 25 times each, while polymer bottles are used only once, and the glass bottle has ten times the mass of the polymer bottle, meaning the huge one-off energy cost of making a glass bottle is spread across 25 uses rather than one, which changes the overall energy picture in glass's favour once reuse is accounted for.
At disposal, both materials can be recycled into different products of the same type, so this stage does not distinguish them strongly, though the polymer's lower mass means less material enters the recycling or landfill stream per bottle even before accounting for reuse.
Overall I judge glass is the more sustainable choice for milk bottles specifically because of its high reuse figure of 25, which offsets its much higher raw material and manufacturing energy demand; if the polymer bottle were also reused many times rather than once, this judgement would likely reverse, since the polymer's much lower energy cost per bottle would then dominate.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise life cycle assessment questionsWhat the mark scheme rewarded
- Comparing raw materials for both bottles
- Using the quoted energy figures for processing and manufacturing
- Using the quoted reuse and mass figures
- Comparing disposal methods
- A reasoned judgement weighing energy against reuse
- Glass raw materials: limestone, sand, sodium carbonate; polymer raw material: crude oil
- Glass: 6750 kJ to process raw materials, 750 kJ to manufacture, mass 200 g, reused 25 times
- Polymer: 1710 kJ to process raw materials, 90 kJ to manufacture, mass 20 g, reused 1 time
- Both materials in the table are recycled to make different products of the same type
Traps examiners saw
- Treating glass's raw materials as automatically 'more natural' and therefore better, without checking the actual energy figures
- Not connecting the reuse figures back to the manufacturing energy figures
- Giving only a one-sided judgement that ignores what would happen if the polymer bottle's usage changed
Full-mark self-check 0 of 5
The method for every Q05/Q03 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Using every stage of an LCA: raw materials, manufacturing and packaging, use and operation, and disposal
- Quoting specific figures from the given table to support each point
- Reaching a reasoned overall judgement, not just listing pros and cons
The steps
- State whether each raw material is finite (crude oil, mined clay) or renewable (wood)
- Compare energy used in processing raw materials and manufacturing, quoting the actual kJ figures given
- Compare use and operation: how many times each product can be reused before disposal
- Compare disposal: which materials are biodegradable, recyclable, or go to landfill
- Finish with an overall judgement on which material is more sustainable, supported by the reasons above
What does LCA stand for in the context of environmental science?
LCA evaluation questions always give you a data table. The top band comes from quoting the actual figures and weighing conflicting factors (like high energy cost against high reuse), not from generic LCA theory.
Practise life cycle assessment questions“Compare an alkane with an alkene, referring to their structure and bonding, and their reactions.”
This extended comparison question always gives you two displayed structural formulae and asks for both structural differences and reaction differences.
1×asked“Ethane is an alkane and ethene is an alkene. Compare ethane with ethene. You should refer to their structure and bonding, and their reactions.”
“Ethane is an alkane and ethene is an alkene. Compare ethane with ethene. You should refer to their structure and bonding, and their reactions.”
What it’s really asking
It wants a structured comparison of ethane and ethene covering bonding differences and reaction differences, since the two compounds have almost identical formulae but very different chemical behaviour.
What the sources actually showed — June 2020
The displayed structural formulae of ethane and ethene, showing ethane with a single carbon-carbon bond and six hydrogen atoms, and ethene with a double carbon-carbon bond and four hydrogen atoms.
The full worked answer — June 2020
Both ethane and ethene are hydrocarbons containing two carbon atoms per molecule and small molecules held together by covalent bonds, but ethane contains six hydrogen atoms per molecule while ethene contains only four, because ethane's carbon atoms are joined by a single C-C bond, whereas ethene's carbon atoms are joined by a double C=C bond, which uses up bonding positions that would otherwise hold two more hydrogen atoms.
In terms of reactions, both undergo complete combustion in oxygen to produce carbon dioxide and water, and both can undergo incomplete combustion to produce carbon monoxide and water if oxygen is limited, though incomplete combustion is more likely with ethene because of its higher carbon to hydrogen ratio.
The biggest reaction difference is that ethene decolourises bromine water, turning it from orange to colourless, while ethane does not decolourise bromine water at all, because ethene's C=C double bond can open up to add the bromine atoms across it in an addition reaction, a reaction ethane cannot do since it has no double bond to react across.
Because of its reactive double bond, ethene is more reactive overall than ethane and can also react with hydrogen to produce ethane, with water to produce ethanol, with halogens, and can polymerise to form poly(ethene), none of which ethane can do since its single bonds are much less reactive.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise alkane and alkene comparison questionsWhat the mark scheme rewarded
- Both are hydrocarbons and small molecules with covalent bonds
- Ethane has six hydrogen atoms, ethene has four
- Ethane has a single C-C bond, ethene has a double C=C bond
- Both combust completely and incompletely, but incomplete combustion is more likely for ethene
- Ethene decolourises bromine water, ethane does not
- Ethene is more reactive and undergoes addition reactions ethane cannot
- Ethane: C2H6, single C-C bond
- Ethene: C2H4, double C=C bond
- Bromine water test: orange to colourless confirms a C=C double bond
- Addition reactions of alkenes: with hydrogen (to form the alkane), with water (to form an alcohol), with halogens, and polymerisation
Traps examiners saw
- Only discussing structure without moving on to reactions, or vice versa
- Forgetting to state the specific hydrogen atom counts (six versus four)
- Naming that ethene reacts with bromine water without explaining the colour change or the underlying reason (the C=C bond)
Full-mark self-check 0 of 4
The method for every Q03/Q02/Q06 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Naming both compounds as hydrocarbons with the correct number of carbon and hydrogen atoms
- Correctly identifying the single C-C bond in the alkane versus the double C=C bond in the alkene
- Naming distinct reaction differences: the alkene decolourises bromine water and can undergo addition reactions, the alkane cannot
The steps
- State both are hydrocarbons made of carbon and hydrogen only
- Compare the number of hydrogen atoms for the same number of carbon atoms
- State the alkane has only single covalent bonds, while the alkene has one C=C double bond
- Compare their reactions: alkenes decolourise bromine water and undergo addition reactions (with hydrogen, water, halogens, or polymerisation); alkanes do not
What is the general formula for alkenes?
Comparison questions reward specific numbers (atom counts, bond types) linked to specific reaction outcomes, not two separate lists. Practise linking structure to reactivity.
Practise alkane and alkene comparison questions“Plan an investigation to determine the Rf value for a dye, or spot the mistakes in a chromatography method already set up.”
This question type either asks you to plan the full chromatography method from scratch, or gives you a diagram of an already-set-up experiment and asks you to spot what is wrong with it.
1×asked“A food colouring contains a dye. Plan an investigation to determine the Rf value for the dye in this food colouring. Your plan should include the use of a beaker, a solvent, and chromatography paper.”
“A food colouring contains a dye. Plan an investigation to determine the Rf value for the dye in this food colouring. Your plan should include the use of a beaker, a solvent, and chromatography paper.”
What it’s really asking
It wants the complete, correctly sequenced chromatography method, from drawing the start line to calculating the Rf value using both distance measurements.
The full worked answer — June 2021
Draw a pencil start line near the bottom of a piece of chromatography paper, then place a small spot of the food colouring on the start line and allow it to dry. Place the paper into a beaker containing a suitable solvent, making sure the solvent level is below the start line so the spot of dye does not dissolve straight into the solvent.
Wait for the solvent to travel up the paper, near to the top, then remove the paper and immediately mark the position of the solvent front in pencil before it evaporates and dries.
Once the paper has dried, measure the distance from the start line to the centre of the dye spot, and separately measure the distance from the start line to the solvent front. Then calculate the Rf value by dividing the distance moved by the dye by the distance moved by the solvent.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise chromatography planning and analysisWhat the mark scheme rewarded
- Drawing a pencil start line
- Placing a spot of food colouring on the start line
- Using a suitable solvent with the level below the start line
- Marking the solvent front once it has travelled up the paper
- Measuring both distances
- Using the measurements to determine the Rf value
- Rf = distance moved by substance / distance moved by solvent
- The start line must be drawn in pencil, since ink would dissolve and mix with the sample
- A lid on the beaker prevents the solvent evaporating before it has fully travelled
Traps examiners saw
- Forgetting to state the solvent level must be below the start line
- Forgetting the final calculation step, describing only the practical setup
Full-mark self-check 0 of 3
1×asked“The student made two mistakes when setting up the apparatus. Give two mistakes the student made.”
“The student made two mistakes when setting up the apparatus. Give two mistakes the student made.”
What it’s really asking
It wants two specific, correctly identified errors from the diagram shown: comparing what the student did against the standard correct method.
What the sources actually showed — June 2023
A diagram showing a student's chromatography set-up with a beaker, a lid, chromatography paper, and a start line marked in ink positioned below the level of water in the beaker.
The full worked answer — June 2023
The first mistake is that the start line was drawn in ink rather than in pencil, which risks the ink itself dissolving and mixing with the food colouring being tested, making the results unreliable.
The second mistake is that the start line was drawn below the level of the water in the beaker, meaning the orange food colouring spot would dissolve directly into the water rather than being carried up the paper by it, ruining the separation.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise chromatography planning and analysisWhat the mark scheme rewarded
- Identifying the start line was drawn in ink instead of pencil
- Identifying the start line was below the water level
- Pencil is used for the start line because ink is itself a mixture of dyes that would move during chromatography
- The start line and spot must stay above the solvent level or the sample dissolves straight into the solvent
Traps examiners saw
- Naming a vague error like 'the paper was the wrong size' when the two real errors shown are the ink line and its position below the water
- Only naming one error when two are asked for and available
Full-mark self-check 0 of 2
The method for every Q04/Q03/Q06 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Drawing the start line in pencil, near the bottom of the paper but above the level of the solvent
- Adding a small spot of the substance being tested on the start line
- Using measurements of the distance travelled by the substance and by the solvent to calculate Rf
The steps
- Draw a pencil start line on chromatography paper and place a spot of the substance on it
- Place the paper in a beaker containing a suitable solvent, with the solvent level below the start line
- Use a lid on the beaker and wait for the solvent to travel up the paper, then mark the solvent front and dry the paper
- Measure the distance from the start line to the centre of the spot, and the distance from the start line to the solvent front, then calculate Rf as distance moved by substance divided by distance moved by solvent
What is the purpose of chromatography?
Chromatography questions test the full standard method: pencil start line above the solvent, correct measurements, correct Rf formula. Learn the standard errors examiners plant in diagrams too.
Practise chromatography planning and analysis“Calculate a missing distance or Rf value from given chromatography data.”
This calculation always rearranges the Rf formula (Rf = distance moved by substance / distance moved by solvent) to find a missing value.
1×asked“The Rf value of the yellow dye = 0.60. The distance moved by the yellow dye = 5.7 cm. Calculate the distance moved by the solvent.”
“The Rf value of the yellow dye = 0.60. The distance moved by the yellow dye = 5.7 cm. Calculate the distance moved by the solvent.”
What it’s really asking
It wants the Rf formula rearranged to find the distance moved by the solvent, given the Rf value and the distance moved by the dye.
What the sources actually showed — June 2020
A diagram of a chromatogram showing a start line, two dye spots (yellow and blue) close together, and a solvent front, with the diagram marked as not to scale.
The full worked answer — June 2020
Rf = distance moved by substance divided by distance moved by solvent, so 0.60 = 5.7 divided by the distance moved by the solvent. Rearranging gives distance moved by solvent = 5.7 divided by 0.60, which equals 9.5 cm.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise Rf value calculationsWhat the mark scheme rewarded
- Substituting 0.60 = 5.7 / distance moved by solvent
- Rearranging to 5.7 / 0.60
- Calculating 9.5 (cm)
- Rf = distance moved by substance / distance moved by solvent
- 9.5 cm is the correct rearranged answer
Traps examiners saw
- Dividing the wrong way round (0.60 divided by 5.7)
- Forgetting the unit cm in the final answer
Full-mark self-check 0 of 3
1×asked“Determine value X in Table 3, the distance moved by the yellow dye on Type B chromatography paper.”
“Determine value X in Table 3, the distance moved by the yellow dye on Type B chromatography paper.”
What it’s really asking
It wants the Rf formula rearranged to find the missing distance moved by the yellow dye, using the given Rf value of 0.60 and the given solvent distance of 12.0 cm.
What the sources actually showed — June 2023
A table comparing type A and type B chromatography paper for red and yellow dye, showing distance moved by dye, distance moved by water, and Rf value for each combination, with one distance value missing and marked X.
| Type A: Red dye | Type A: Yellow dye | Type B: Red dye | Type B: Yellow dye | |
|---|---|---|---|---|
| Distance moved by dye in cm | 4.8 | 6.6 | 5.4 | X |
| Distance moved by water in cm | 12 | 12 | 12 | 12 |
| Rf value | 0.4 | 0.55 | 0.45 | 0.6 |
The full worked answer — June 2023
0.60 = distance moved by dye divided by 12.0, so distance moved by dye = 0.60 multiplied by 12.0, which equals 7.2 cm. This is the value of X.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise Rf value calculationsWhat the mark scheme rewarded
- Substituting 0.60 = distance moved by dye / 12.0
- Rearranging to 0.60 x 12.0
- Calculating 7.2 (cm)
- Rf = distance moved by substance / distance moved by solvent
- When the unknown is the numerator, rearranging means multiplying rather than dividing
Traps examiners saw
- Dividing 12.0 by 0.60 instead of multiplying, a rearrangement error caused by not checking which value is missing
Full-mark self-check 0 of 2
The method for every Q04/Q06 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Correctly rearranging the Rf formula
- Substituting the given numbers correctly
- Giving the final answer to the correct number of significant figures
The steps
- Write the Rf formula with the known Rf value and known distance substituted in
- Rearrange to make the unknown distance the subject
- Calculate and round appropriately
What is the purpose of chromatography?
Rf calculations are simple rearrangement practice, but the direction of rearrangement changes depending on which value is missing. Practise both directions.
Practise Rf value calculations“Draw a tangent to a curve at a given point and use it to calculate the rate of reaction at that instant.”
Every sitting we checked includes a tangent-to-curve rate calculation, always following the same method: draw the tangent, find the gradient, then convert using a given conversion factor if the y-axis is not already in moles.
1×asked“Determine the rate of reaction for 0.05 mol/dm3 sulfuric acid at 80 seconds. Show your working on Figure 9. Give your answer to 2 significant figures.”
“Determine the rate of reaction for 0.05 mol/dm3 sulfuric acid at 80 seconds. Show your working on Figure 9. Give your answer to 2 significant figures.”
What it’s really asking
It wants a tangent drawn at 80 seconds on the given curve, then the gradient calculated and rounded to 2 significant figures, using cm3 of gas per second as the unit.
What the sources actually showed — June 2021
A graph of volume of gas produced (cm3) against time (seconds) for the reaction of zinc powder with two different concentrations of sulfuric acid, showing two curves that both level off, with the 0.05 mol/dm3 curve reaching a lower final volume than the 0.10 mol/dm3 curve.
The full worked answer — June 2021
Draw a tangent to the 0.05 mol/dm3 curve at 80 seconds. Reading from the tangent, take a convenient x-step, for example from 60 to 100 seconds (an x-step of 40 seconds), and read the corresponding y-step over that range, for example from about 50 cm3 to about 60 cm3 (a y-step of 10 cm3).
Rate = y-step divided by x-step = 10 divided by 40 = 0.25 cm3 per second.
To 2 significant figures, the rate of reaction at 80 seconds is 0.25 cm3/s.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise rate of reaction graph questionsWhat the mark scheme rewarded
- Drawing a tangent at 80 seconds
- Reading a correct x-step and y-step from that tangent
- Calculating the rate as y-step / x-step
- Rounding to 2 significant figures with the correct unit
- Rate of reaction = gradient of the tangent at a specific point on a volume-time graph
- The steeper the tangent, the faster the reaction is happening at that instant
Traps examiners saw
- Drawing the tangent to the wrong curve, since two curves are shown
- Reading the x-step and y-step from different, inconsistent points on the tangent
- Forgetting to round to the specified number of significant figures
Full-mark self-check 0 of 3
1×asked“The percentage of light reaching the light sensor decreases by 1% when 7.1 x 10-5 moles of sulfur is produced. Determine the rate of reaction in mol/s for the production of sulfur at 30 seconds. You should draw a tangent on Figure 7.”
“The percentage of light reaching the light sensor decreases by 1% when 7.1 x 10-5 moles of sulfur is produced. Determine the rate of reaction in mol/s for the production of sulfur at 30 seconds. You should draw a tangent on Figure 7.”
What it’s really asking
It wants a tangent drawn at 30 seconds, the gradient read as a percentage-per-second rate, then converted into mol/s using the given conversion factor.
What the sources actually showed — June 2022
A graph of the percentage of light from a light source reaching a light sensor, plotted against time in seconds, for the reaction of sodium thiosulfate solution with hydrochloric acid, showing a decreasing curve that levels off at around 24%.
The full worked answer — June 2022
Draw a tangent to the curve at 30 seconds. Reading from the tangent, take an x-step of 20 seconds, for example from 20 to 40 seconds, and the corresponding y-step, for example a decrease of about 24% in that time.
The ratio of y-step to x-step is 24 divided by 20, which equals 1.2 (percent per second).
Since a 1% decrease corresponds to 7.1 x 10 to the power minus 5 moles of sulfur produced, the rate in mol/s is 1.2 multiplied by 7.1 x 10 to the power minus 5, which equals about 8.5 x 10 to the power minus 5 mol/s.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise rate of reaction graph questionsWhat the mark scheme rewarded
- Drawing a tangent at 30 seconds
- Reading correct x-step and y-step values
- Calculating the ratio before conversion
- Applying the given conversion factor to reach a rate in mol/s
- The gradient of the tangent gives the rate of change of light percentage per second
- The given conversion factor (7.1 x 10-5 mol per 1% change) turns this into a molar rate
Traps examiners saw
- Forgetting to apply the conversion factor and leaving the answer in percent per second
- Reading the tangent inaccurately by not using two points far enough apart on the tangent line
Full-mark self-check 0 of 3
The method for every Q08/Q09/Q01/Q07 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Drawing an accurate tangent to the curve at the specified point
- Correctly reading the x-step and y-step from that tangent
- Applying any given conversion factor and rounding to the specified significant figures
The steps
- Draw a straight tangent line that just touches the curve at the specified point
- Read off a clear x-step and the corresponding y-step from that tangent line
- Calculate the gradient as y-step divided by x-step
- If the y-axis is not already in moles, multiply by the given conversion factor
- Round the final answer to the number of significant figures asked for
According to collision theory, which of the following must happen for a chemical reaction to take place?
Tangent-to-curve rate questions are pure technique: an accurate tangent, a clean x-step and y-step, and the correct conversion factor if one is given. Practise drawing tangents on real exam graphs.
Practise rate of reaction graph questions“Explain why the rate of reaction changes over time or between two different concentrations, using a given graph.”
This short question always asks you to link a changing or different rate directly to a changing or different concentration, referencing the graph given.
1×asked“Explain why the rate of reaction changes between 0 and 60 seconds. Answer in terms of concentration. Use Figure 7.”
“Explain why the rate of reaction changes between 0 and 60 seconds. Answer in terms of concentration. Use Figure 7.”
What it’s really asking
It wants the rate change (fastest at the start, slowing down) explained specifically in terms of the falling concentration of a reactant as the reaction proceeds.
What the sources actually showed — June 2022
A graph of the percentage of light reaching a light sensor plotted against time, showing a curve that falls steeply at first and then levels off as the reaction between sodium thiosulfate and hydrochloric acid proceeds.
The full worked answer — June 2022
The rate of reaction is greatest at the start because the concentration of the reactants is at its highest. As the reaction proceeds, the concentration of the reactants decreases, so the rate of reaction decreases too, which is why the curve becomes less steep over time.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise rate and concentration questionsWhat the mark scheme rewarded
- Stating rate decreases (or is greatest at the start)
- Stating this is because concentration of reactants decreases
- Higher concentration means more particles per unit volume, so more frequent collisions and a faster rate
- As reactants are used up, concentration falls, so collision frequency and rate both fall
Traps examiners saw
- Describing the shape of the graph without explaining why it happens in terms of concentration
- Confusing rate decreasing with the reaction stopping completely before it actually has
Full-mark self-check 0 of 2
The method for every Q08/Q01 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Stating the rate decreases (or is lower) because concentration decreases (or is lower)
- Linking this to fewer particles per unit volume and therefore fewer frequent collisions
The steps
- Identify what the graph shows about the changing steepness of the curve
- State that concentration of the reactant decreases as the reaction proceeds (or is lower for one curve than the other)
- Link lower concentration to a lower rate
Which of the following factors does NOT affect the rate of a chemical reaction?
Rate-concentration explanation questions want a direct cause-and-effect link: concentration falls, so collisions become less frequent, so rate falls. Practise stating this chain precisely.
Practise rate and concentration questions“Explain why specific temperature and pressure conditions are chosen for an industrial equilibrium reaction, referring to rate and yield.”
This extended question always covers the same reasoning pattern: the chosen conditions balance a faster rate of reaction against a better position of equilibrium (yield), while also considering cost.
1×asked“The Haber process uses a temperature of 450 degrees Celsius and a pressure of 200 atmospheres. The forward reaction is exothermic. Explain why these conditions are chosen for economical production of ammonia in the Haber process. You should include references to the rate of reaction and the position of equilibrium.”
“The Haber process uses a temperature of 450 degrees Celsius and a pressure of 200 atmospheres. The forward reaction is exothermic. Explain why these conditions are chosen for economical production of ammonia in the Haber process. You should include references to the rate of reaction and the position of equilibrium.”
What it’s really asking
It wants an explanation of why 450 degrees Celsius and 200 atmospheres are a compromise for the Haber process, covering both rate and yield effects and the cost of using more extreme conditions.
What the sources actually showed — June 2022
A table showing the percentage yield of ammonia at 450 degrees Celsius across a range of pressures from 60 to 420 atmospheres, with yield increasing with pressure but by a smaller amount at higher pressures.
| Pressure in atmospheres | Percentage (%) yield of ammonia |
|---|---|
| 60 | 9 |
| 120 | 18 |
| 180 | 25 |
| 240 | 31 |
| 300 | 36 |
| 360 | 40 |
| 420 | 43 |
The full worked answer — June 2022
A higher temperature gives a higher rate of reaction because particles collide more frequently and more particles have the activation energy needed to react, so ammonia is produced faster at 450 degrees Celsius than at a lower temperature.
However, since the forward reaction is exothermic, a higher temperature shifts the position of equilibrium to the left, towards the reactants, reducing the percentage yield of ammonia. This means 450 degrees Celsius is a compromise: high enough to give a reasonably fast rate, but not so high that the equilibrium yield of ammonia becomes too low.
A higher pressure also gives a higher rate of reaction because particles collide more frequently when they are more concentrated in a smaller space, and higher pressure shifts the position of equilibrium to the right, towards ammonia, because there are fewer gas molecules on the right-hand side of the equation (two moles of ammonia compared to four moles of nitrogen and hydrogen combined), increasing the yield.
Even though a higher pressure than 200 atmospheres would increase the yield further, as shown by the data continuing to rise beyond 420 atmospheres, higher pressures need more energy to generate and stronger, more expensive reaction vessels to contain safely, so 200 atmospheres is chosen as a compromise between yield and cost, in the same way 450 degrees Celsius is chosen as a compromise between rate and yield.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise Haber process and equilibrium conditions questionsWhat the mark scheme rewarded
- Higher temperature gives higher rate (more frequent collisions, more particles with activation energy)
- Higher temperature shifts equilibrium left because the reaction is exothermic, reducing yield
- Higher pressure gives higher rate (more frequent collisions) and higher pressure shifts equilibrium right (fewer molecules on that side)
- Higher temperature or pressure increases costs
- The chosen conditions are a compromise between rate, yield and cost
- N2(g) + 3H2(g) reversible reaction 2NH3(g), an exothermic forward reaction
- 4 moles of gas on the reactant side, 2 moles on the product side
- 450 degrees Celsius and 200 atmospheres are the standard Haber process conditions
- An iron catalyst speeds up the reaction without affecting the position of equilibrium
Traps examiners saw
- Explaining rate and yield without ever using the word 'compromise' or making the trade-off explicit
- Forgetting that pressure increases both rate and yield in the same direction, unlike temperature where rate and yield pull in opposite directions
- Not linking the mole counts on each side of the equation to the pressure effect on equilibrium
Full-mark self-check 0 of 4
The method for every Q07/Q10 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Explaining that higher temperature increases rate (more frequent collisions, more particles with activation energy)
- Explaining the effect of temperature and pressure on the position of equilibrium, linked correctly to whether the forward reaction is exothermic or endothermic and to the number of gas molecules on each side
- Reaching a compromise conclusion that names cost as well as rate and yield
The steps
- State that a higher temperature increases the rate of reaction because particles collide more frequently and more particles have the activation energy needed
- State the effect of temperature on the position of equilibrium, using whether the forward reaction is exothermic or endothermic
- State the effect of pressure on both rate (more frequent collisions) and the position of equilibrium (based on the number of gas molecules on each side)
- Note that more extreme temperature and pressure increase costs, so the actual conditions used are a compromise
Industrial equilibrium questions always reward the same structure: rate effect, equilibrium effect, then a cost-based compromise. Learn this template and apply it to any reversible industrial reaction.
Practise Haber process and equilibrium conditions questions“Explain how a colour change in an equilibrium mixture shows the position of equilibrium has shifted, when a condition changes.”
This question gives you a coloured reversible reaction and asks you to explain a specific colour change caused by adding a reagent, changing temperature, or changing pressure.
1×asked“A few drops of a colourless solution containing a high concentration of thiocyanate ions are added to the orange equilibrium mixture. Explain the colour change observed.”
“A few drops of a colourless solution containing a high concentration of thiocyanate ions are added to the orange equilibrium mixture. Explain the colour change observed.”
What it’s really asking
It wants the colour change (towards red) explained as the equilibrium position shifting right because more thiocyanate ions were added, in line with Le Chatelier's principle.
What the sources actually showed — June 2020
The ionic equation for the reversible reaction between iron(III) ions (yellow) and thiocyanate ions (colourless) forming FeSCN2+ ions (red), with the equilibrium mixture described as orange at room temperature.
The full worked answer — June 2020
The mixture becomes more red because the position of equilibrium moves to the right. Adding more thiocyanate ions increases the concentration of thiocyanate ions in the mixture, so the equilibrium shifts to counteract this increase, favouring the forward reaction that uses up thiocyanate ions to produce more of the red FeSCN2+ ion.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise equilibrium and Le Chatelier's principle questionsWhat the mark scheme rewarded
- Stating the mixture becomes more red
- Stating this is because the position of equilibrium moves to the right
- Linking this to reducing the increase in thiocyanate ion concentration
- Fe3+(aq) + SCN-(aq) reversible reaction FeSCN2+(aq): yellow + colourless reversible reaction red
- Le Chatelier's principle: a system at equilibrium responds to a change by shifting to partially counteract it
Traps examiners saw
- Stating the colour becomes red without explaining the direction of the shift or the reason for it
- Confusing which ion's concentration increased (thiocyanate, not iron)
Full-mark self-check 0 of 3
1×asked“The teacher pushes the syringe piston in. This increases the pressure in the gas syringe. What is the colour of the mixture when a new equilibrium position is reached?”
“The teacher pushes the syringe piston in. This increases the pressure in the gas syringe. What is the colour of the mixture when a new equilibrium position is reached?”
What it’s really asking
It wants the correct colour outcome identified from increasing pressure on the NO2/N2O4 equilibrium, based on which side of the equation has fewer gas molecules.
What the sources actually showed — June 2023
A diagram of a sealed gas syringe containing a brown-coloured mixture of nitrogen dioxide (brown) and dinitrogen tetroxide (colourless), with the balanced equation 2NO2(g) reversible reaction N2O4(g) shown, and the forward reaction stated as exothermic.
The full worked answer — June 2023
The mixture becomes a lighter shade of brown. Increasing the pressure shifts the position of equilibrium towards the side with fewer gas molecules, which is the N2O4 side (one mole of gas, compared to two moles of NO2 on the other side), and since N2O4 is colourless while NO2 is brown, more N2O4 forming makes the mixture a lighter shade of brown overall.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise equilibrium and Le Chatelier's principle questionsWhat the mark scheme rewarded
- Identifying that the mixture becomes a lighter shade of brown
- 2NO2(g) reversible reaction N2O4(g): brown reversible reaction colourless
- Increasing pressure shifts equilibrium towards the side with fewer gas molecules
- N2O4 has fewer gas molecules (one mole) than 2NO2 (two moles)
Traps examiners saw
- Assuming increased pressure always means a darker colour, without checking which side has fewer gas molecules
- Confusing this with the effect of increasing temperature, which is a different variable entirely
Full-mark self-check 0 of 2
The method for every Q10/Q09 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Stating the correct direction the colour change indicates the equilibrium has shifted
- Explaining why, using the change applied (added reagent, temperature or pressure change)
- Linking the shift to Le Chatelier's principle: the system counteracts the change
The steps
- State which colour becomes dominant, and which direction the equilibrium has shifted
- Explain why, using the specific change applied
- Link this to Le Chatelier's principle: the shift counteracts the applied change
At dynamic equilibrium, which of the following is true?
Le Chatelier colour-change questions always want you to name the shift direction and the specific reason (concentration, temperature or pressure change), not just describe the colour.
Practise equilibrium and Le Chatelier's principle questions“Explain how fractions are obtained from crude oil by fractional distillation, or explain the temperature gradient effect on where a fraction condenses.”
Both fractional distillation questions we checked test the same underlying model: crude oil is heated to vaporise, then fractions condense at different heights in a temperature gradient depending on their boiling point.
1×asked“Explain how these fractions are obtained from crude oil by fractional distillation. Use Table 3.”
“Explain how these fractions are obtained from crude oil by fractional distillation. Use Table 3.”
What it’s really asking
It wants the fractional distillation process explained, linking the different boiling point ranges given in the table to where each fraction condenses in the column.
What the sources actually showed — June 2022
A table showing three fractions obtained from crude oil (lubricating oil, naphtha, petroleum gases) alongside their boiling point range in degrees Celsius, with lubricating oil having the highest range and petroleum gases the lowest.
| Fraction | Boiling point range (degrees Celsius) |
|---|---|
| Lubricating oil | 300 to 350 |
| Naphtha | 90 to 200 |
| Petroleum gases | below 25 |
The full worked answer — June 2022
Crude oil is heated to vaporise the hydrocarbons it contains. There is a temperature gradient in the fractionating column, cooler at the top than at the bottom, so the vaporised hydrocarbons condense at different levels depending on their boiling point.
Lubricating oil, with the highest boiling point range of 300 to 350 degrees Celsius, condenses lower down the column where it is still hot, naphtha, with a boiling point range of 90 to 200 degrees Celsius, condenses higher up where it is cooler, and petroleum gases, with a boiling point below 25 degrees Celsius, do not condense at all inside the column and are collected as a gas at the very top, all because of their different boiling points.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise crude oil and fractional distillation questionsWhat the mark scheme rewarded
- Crude oil is heated to vaporise the hydrocarbons
- A temperature gradient exists in the column, cooler going up
- Fractions condense at different levels because of their different boiling points
- Linking specific fractions to specific heights using the given boiling point data
- Fractional distillation separates crude oil hydrocarbons by boiling point
- Longer hydrocarbon chains have higher boiling points and condense lower in the column; shorter chains have lower boiling points and stay gaseous or condense near the top
Traps examiners saw
- Describing the column as having one uniform temperature rather than a gradient
- Not linking the specific data in the table to specific condensing positions
Full-mark self-check 0 of 3
The method for every Q02/Q04 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Stating crude oil is heated to vaporise the hydrocarbons
- Explaining the temperature gradient in the fractionating column
- Linking each fraction's boiling point to where it condenses
The steps
- State crude oil is heated so the hydrocarbons vaporise
- State the fractionating column has a temperature gradient, cooler towards the top
- Explain that different fractions have different boiling points because their molecules are different sizes
- Link each fraction condensing at the height where the column temperature matches its boiling point
A hydrocarbon is a compound that contains only:
Fractional distillation questions want the temperature gradient explicitly linked to the specific boiling point data given, not a generic textbook description.
Practise crude oil and fractional distillation questions“Explain how the conditions for producing ethanol from ethene and steam should be chosen to produce ethanol as economically as possible.”
This is the same rate-versus-yield-versus-cost reasoning template as the Haber process question, applied to the industrial production of ethanol from ethene and steam.
1×asked“Ethanol can be produced from ethene and steam. The forward reaction is exothermic. Explain how the conditions for this reaction should be chosen to produce ethanol as economically as possible.”
“Ethanol can be produced from ethene and steam. The forward reaction is exothermic. Explain how the conditions for this reaction should be chosen to produce ethanol as economically as possible.”
What it’s really asking
It wants the same rate-yield-cost compromise reasoning as the Haber process, applied to the reversible reaction between ethene and steam that produces ethanol.
What the sources actually showed — June 2021
The equation C2H4(g) + H2O(g) reversible reaction C2H5OH(g), with the forward reaction stated as exothermic.
The full worked answer — June 2021
A higher temperature gives a higher rate of reaction because particles collide more frequently and more particles have enough energy to react. However, since the forward reaction is exothermic, a higher temperature shifts the position of equilibrium to the left, away from ethanol, reducing the yield.
A higher pressure gives a higher rate of reaction because particles collide more frequently, and higher pressure also shifts the position of equilibrium to the right, towards ethanol, because there are fewer gas molecules on the product side (one mole of ethanol) than on the reactant side (two moles combined, ethene and steam), increasing the yield of ethanol.
Because higher temperatures and higher pressures both use more energy and require stronger, more expensive equipment, the chosen temperature is a compromise between a fast enough rate and a high enough yield, and the chosen pressure is a compromise between yield and the cost of generating and containing that pressure.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise industrial equilibrium reaction questionsWhat the mark scheme rewarded
- Higher temperature gives higher rate
- Higher temperature shifts equilibrium left because the reaction is exothermic, reducing yield
- Higher pressure gives higher rate and shifts equilibrium right because of fewer gas molecules on the product side
- Higher temperature or pressure increases costs, so the conditions used are a compromise
- C2H4(g) + H2O(g) reversible reaction C2H5OH(g), an exothermic forward reaction
- 2 moles of gas on the reactant side, 1 mole on the product side
- Costs increase with more extreme temperature and pressure, needing more energy and stronger equipment
Traps examiners saw
- Forgetting the forward reaction here is exothermic and applying the wrong direction of equilibrium shift
- Not naming the specific mole counts (2 versus 1) when explaining the pressure effect
Full-mark self-check 0 of 3
The method for every Q10/Q02 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Explaining temperature's effect on rate and on the position of equilibrium, given the forward reaction is exothermic
- Explaining pressure's effect on rate and equilibrium, using the mole counts of gas on each side
- Reaching a compromise conclusion that names cost
The steps
- State that higher temperature increases rate due to more frequent collisions and more particles with activation energy
- State that since the forward reaction is exothermic, higher temperature shifts equilibrium away from ethanol, reducing yield
- State that higher pressure increases rate and shifts equilibrium towards ethanol because there are fewer gas molecules on that side
- Note higher temperature and pressure increase costs, so a compromise is used
What is the functional group present in all alcohols?
This is the exact same rate-yield-cost template as the Haber process, just applied to ethanol production. Learn the template once and it applies to any industrial reversible reaction question.
Practise industrial equilibrium reaction questions“Complete or draw the displayed structural formula of an addition polymer, or its monomer, and identify the functional group involved.”
Every sitting we checked with a polymers question asks you to move between a monomer's structure and its polymer's structure, or to circle the functional group responsible for addition polymerisation.
1×asked“The addition polymer poly(butene) is produced from the monomer butene. Complete Figure 2 to show the displayed structural formula of butene.”
“The addition polymer poly(butene) is produced from the monomer butene. Complete Figure 2 to show the displayed structural formula of butene.”
What it’s really asking
It wants the monomer's structure derived by reversing the polymer's repeat unit: replacing the C-C single bond between the two repeat-unit carbons with a C=C double bond.
What the sources actually showed — June 2022
Figure 1 shows the displayed structural formula of poly(butene) as a repeating unit in brackets with a methyl group on each of the two backbone carbons. Figure 2 shows a partially completed monomer diagram with the same methyl and hydrogen groups but the bond between the two carbons left unlabelled.
The full worked answer — June 2022
The bond between the two carbon atoms shown in Figure 2 should be a double bond (C=C), since a polymer's repeating unit always has a single C-C bond where the monomer originally had a C=C double bond. The remaining bonds to the methyl group and hydrogen atom on each carbon stay as single bonds, unchanged from the polymer diagram.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise addition polymer structure questionsWhat the mark scheme rewarded
- Drawing the C=C double bond between the two backbone carbons
- Keeping the correct substituent bonds (2x C-H and 2x C-CH3) unchanged
- Addition polymerisation opens up a C=C double bond in the monomer, forming a single C-C bond in the polymer chain
- The repeat unit in brackets shows only a single bond because the double bond has already reacted
Traps examiners saw
- Drawing a single bond in the monomer, the same as shown in the polymer, forgetting the whole point of the question is to reverse this change
- Adding extra bonds through the position where brackets would be, which is only correct for the polymer, not the monomer
Full-mark self-check 0 of 2
1×asked“Draw a circle around the functional group on the displayed structural formula of chloroethene that allows chloroethene to produce an addition polymer.”
“Draw a circle around the functional group on the displayed structural formula of chloroethene that allows chloroethene to produce an addition polymer.”
What it’s really asking
It wants the C=C double bond specifically circled, since this is the functional group that opens up to allow addition polymerisation, not any other part of the molecule.
What the sources actually showed — June 2023
The displayed structural formula of chloroethene, showing two carbon atoms joined by a double bond, with one carbon bonded to two hydrogen atoms and the other bonded to one hydrogen atom and one chlorine atom.
The full worked answer — June 2023
The circle should be drawn around the C=C double bond between the two carbon atoms, since this double bond is the functional group that opens up during addition polymerisation to link monomer units together.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise addition polymer structure questionsWhat the mark scheme rewarded
- Circling the C=C double bond specifically, not any other bond in the molecule
- All alkenes contain a C=C double bond, which is the functional group that enables addition polymerisation
- The chlorine atom in chloroethene ends up as a substituent on the polymer chain but is not itself the reactive group
Traps examiners saw
- Circling the C-Cl bond instead of the C=C bond
- Circling the whole molecule rather than just the specific double bond
Full-mark self-check 0 of 1
The method for every Q04/Q01/Q08 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Correctly drawing single bonds either side of the repeat unit through the brackets, with the C=C bond in the monomer replaced by a C-C bond in the polymer
- Correctly identifying the C=C double bond as the functional group that enables addition polymerisation
The steps
- Identify the C=C double bond in the monomer as the functional group involved
- When drawing the polymer, replace the double bond with a single C-C bond and extend single bonds through the brackets on each side
- When drawing the monomer from the polymer, reverse this: put back the C=C double bond and remove the extending bonds and brackets
What type of monomers are needed for addition polymerisation?
Polymer structure questions reward knowing exactly which bond changes (the C=C double bond becomes a single bond) and which stays the same. Practise moving between monomer and polymer diagrams in both directions.
Practise addition polymer structure questions“Explain how an equation shows that a carboxylic acid is a weak acid, or how one carboxylic acid ionises more than another.”
Carboxylic acid weak-acid reasoning always comes back to the reversible arrow in the ionisation equation, and to comparing pH or reaction rate as evidence of relative acid strength.
1×asked“Ethanoic acid ionises in water. The equation for the reaction is CH3COOH(aq) reversible reaction CH3COO-(aq) + H+(aq). Explain how the equation shows that ethanoic acid is a weak acid.”
“Ethanoic acid ionises in water. The equation for the reaction is CH3COOH(aq) reversible reaction CH3COO-(aq) + H+(aq). Explain how the equation shows that ethanoic acid is a weak acid.”
What it’s really asking
It wants the reversible arrow in the given equation identified as evidence of incomplete ionisation, which is the defining feature of a weak acid.
What the sources actually showed — June 2020
The equation CH3COOH(aq) reversible reaction CH3COO-(aq) + H+(aq), showing a reversible arrow rather than a single forward arrow.
The full worked answer — June 2020
The reversible arrow in the equation shows that ionisation is incomplete or partial, because the reaction is reversible, meaning not all of the ethanoic acid molecules split up into ions; some remain as CH3COOH molecules while others ionise. This partial ionisation is what defines a weak acid, unlike a strong acid which ionises completely, shown with a single forward arrow.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise carboxylic acids and weak acid questionsWhat the mark scheme rewarded
- Stating the ionisation is incomplete or partial
- Stating this is because the reaction is reversible (or in equilibrium)
- A strong acid's ionisation equation uses a single forward arrow, since it ionises completely
- A weak acid's ionisation equation uses a reversible arrow, since only some molecules ionise at any one time
Traps examiners saw
- Describing the equation without mentioning the reversible arrow specifically
- Confusing 'weak acid' with 'dilute acid', which are different concepts
Full-mark self-check 0 of 2
1×asked“The rate of the reaction with methanoic acid is greater than the rate of the reaction with ethanoic acid, at the same concentration. Explain why. You should refer to ions in your answer. Use Table 3.”
“The rate of the reaction with methanoic acid is greater than the rate of the reaction with ethanoic acid, at the same concentration. Explain why. You should refer to ions in your answer. Use Table 3.”
What it’s really asking
It wants the faster reaction rate of methanoic acid explained using its lower pH (from the given table) as evidence of a higher concentration of hydrogen ions, leading to more frequent collisions.
What the sources actually showed — June 2020
A table showing methanoic, ethanoic and propanoic acid, their formulae, and the pH of a 0.01 mol/dm3 solution of each, with methanoic acid having the lowest pH of 2.91.
| Name | Formula | pH of a 0.01 mol/dm3 solution |
|---|---|---|
| Methanoic acid | ? | 2.91 |
| Ethanoic acid | CH3COOH | 3.39 |
| ? | CH3CH2COOH | 3.44 |
The full worked answer — June 2020
Table 3 shows that 0.01 mol/dm3 methanoic acid has a lower pH than 0.01 mol/dm3 ethanoic acid, so methanoic acid has a higher concentration of hydrogen ions in solution at the same overall concentration. This means methanoic acid ionises to a greater extent than ethanoic acid, making it a (relatively) stronger weak acid.
Because there is a higher concentration of hydrogen ions in the methanoic acid solution, there are more frequent collisions between hydrogen ions and the zinc carbonate per unit time, which is why the rate of reaction with methanoic acid is greater than with ethanoic acid at the same overall concentration.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise carboxylic acids and weak acid questionsWhat the mark scheme rewarded
- Using the pH data to establish methanoic acid has a higher hydrogen ion concentration
- Linking higher hydrogen ion concentration to more frequent collisions
- Concluding this is why the rate is greater for methanoic acid
- Lower pH means a higher concentration of hydrogen ions in solution
- Collision theory: a higher concentration of reacting ions causes more frequent collisions and a faster rate
Traps examiners saw
- Stating methanoic acid 'is a stronger acid' without connecting this back to hydrogen ion concentration and collision frequency
- Not referring to ions at all, despite the question specifically asking for this
Full-mark self-check 0 of 3
The method for every Q09/Q02 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Recognising the reversible arrow in an ionisation equation as evidence of incomplete ionisation
- Linking incomplete ionisation to the definition of a weak acid
The steps
- Note the equation uses a reversible arrow rather than a single forward arrow
- State this shows the acid only partially or incompletely ionises in water
- Link this to the definition of a weak acid: not all molecules release their hydrogen ions
What is the functional group present in all carboxylic acids?
Weak acid questions want the reversible arrow linked explicitly to incomplete ionisation, and rate comparisons linked through pH to ion concentration to collision frequency. Practise the full reasoning chain.
Practise carboxylic acids and weak acid questions“Give the sources of the raw materials for an industrial process, and explain how the product is separated from unreacted materials.”
This shorter Haber process question asks about where the nitrogen and hydrogen come from, and how ammonia is separated from the unreacted gases that get recycled.
1×asked“Give the sources of the nitrogen and of the hydrogen used in the Haber process.”
“Give the sources of the nitrogen and of the hydrogen used in the Haber process.”
What it’s really asking
It wants the two named raw material sources: air for nitrogen and natural gas for hydrogen.
The full worked answer — June 2022
Nitrogen is obtained from the air. Hydrogen is obtained from natural gas.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise Haber process raw materials and separation questionsWhat the mark scheme rewarded
- Nitrogen from air or the atmosphere
- Hydrogen from natural gas or methane
- Air is roughly 78% nitrogen, making it a practical industrial nitrogen source
- Natural gas (mostly methane) reacts with steam to produce hydrogen for the Haber process
Traps examiners saw
- Reversing the two sources
- Naming water as the source of hydrogen instead of natural gas
Full-mark self-check 0 of 2
1×asked“Explain how the ammonia produced is separated from the unreacted nitrogen and hydrogen in X.”
“Explain how the ammonia produced is separated from the unreacted nitrogen and hydrogen in X.”
What it’s really asking
It wants the cooling and condensing step explained, showing that ammonia liquefies while nitrogen and hydrogen remain as gases and are recycled back to the reactor.
What the sources actually showed — June 2022
A flow diagram of the Haber process showing nitrogen and hydrogen entering a reactor, the mixture of nitrogen, hydrogen and ammonia passing to a box labelled X, unreacted nitrogen and hydrogen being recycled back to the reactor, and ammonia leaving as the final product.
The full worked answer — June 2022
The mixture is cooled, so that only the ammonia liquefies. The unreacted nitrogen and hydrogen remain as gases and are recycled back into the reactor to react again.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise Haber process raw materials and separation questionsWhat the mark scheme rewarded
- Stating the mixture is cooled
- Stating this causes only ammonia to liquefy (or condense)
- Ammonia has a higher boiling point than nitrogen or hydrogen, so it condenses first as the mixture cools
- Unreacted nitrogen and hydrogen gases are recycled back into the reactor rather than wasted
Traps examiners saw
- Describing 'filtering' or another separation technique that does not apply to a gas mixture
- Not stating that only ammonia specifically liquefies, leaving the answer vague
Full-mark self-check 0 of 2
The method for every Q06 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Naming air as the source of nitrogen and natural gas as the source of hydrogen
- Explaining that the mixture is cooled so that only ammonia liquefies, since it has a higher boiling point than nitrogen or hydrogen
The steps
- State nitrogen comes from the air
- State hydrogen comes from natural gas
- For separation: state the mixture is cooled so that only ammonia liquefies and can be removed, while unreacted nitrogen and hydrogen remain gases and are recycled
The Haber process raw materials and separation steps are short, precise recall questions. Learn the sources (air, natural gas) and the separation method (cooling to liquefy only ammonia) exactly.
Practise Haber process raw materials and separation questions“Describe how copper is extracted from low-grade ores using phytomining or bioleaching.”
Both alternative copper extraction methods come up as description questions: phytomining (grow plants, burn them, dissolve the ash) and bioleaching (using bacteria to produce a leachate solution).
1×asked“Copper is extracted from low-grade ores by phytomining. Describe how copper is extracted from low-grade ores by phytomining.”
“Copper is extracted from low-grade ores by phytomining. Describe how copper is extracted from low-grade ores by phytomining.”
What it’s really asking
It wants the full phytomining sequence described: growing plants, burning them, dissolving the ash, then extracting the copper from solution.
The full worked answer — June 2021
Plants are grown on land containing copper ore, and they absorb copper compounds from the soil as they grow. The plants are then burnt, which produces ash containing copper compounds. This ash is dissolved in acid to produce a solution containing a copper compound. Finally, copper is extracted from this solution either by electrolysis, or by displacement using scrap iron added to the solution.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise copper extraction and resource questionsWhat the mark scheme rewarded
- Growing plants on land containing copper ores
- Burning the plants to produce ash
- Dissolving the ash in acid to produce a solution of a copper compound
- Extracting copper from the solution by electrolysis or displacement with scrap iron
- Phytomining is used for low-grade ores where traditional mining is not economical
- Electrolysis and displacement using a more reactive metal (like iron) are both standard ways to extract a metal from a compound in solution
Traps examiners saw
- Missing a step in the sequence (for example, going straight from burning to extraction without mentioning dissolving the ash in acid)
- Naming only one extraction method when either is accepted, so naming one correctly is enough, but omitting it entirely loses the mark
Full-mark self-check 0 of 2
1×asked“Copper can be extracted from low-grade ores by bioleaching. Describe what is meant by bioleaching.”
“Copper can be extracted from low-grade ores by bioleaching. Describe what is meant by bioleaching.”
What it’s really asking
It wants bioleaching defined as the use of bacteria to produce a leachate solution containing copper compounds extracted from a low-grade ore.
The full worked answer — June 2023
Bioleaching is the use of bacteria to produce a leachate solution that contains metal compounds, such as copper compounds, extracted from a low-grade ore.
Could you have written this? Every fact in this answer is drilled in our quizzes — the writing is the easy part once the evidence is automatic.
Practise copper extraction and resource questionsWhat the mark scheme rewarded
- Stating bacteria are used
- Stating this produces leachate solutions containing metal or copper compounds
- Bioleaching, like phytomining, is used for low-grade ores that would not be economical to mine and process conventionally
- The leachate solution produced by bioleaching can then have its copper extracted by displacement or electrolysis, the same as with phytomining
Traps examiners saw
- Confusing bioleaching with phytomining, which uses plants rather than bacteria
- Not naming what the resulting solution actually contains
Full-mark self-check 0 of 2
The method for every Q06/Q02/Q05 — same every sittingMark bands, steps, timing
What this question type rewards
The topic changes by sitting — the mark scheme never does. Learn this once, then open your question above for that sitting’s sources and a full worked answer.
- Correctly sequencing the phytomining steps: growing plants, burning them to ash, dissolving the ash in acid, then extracting copper from the resulting solution
- For bioleaching, naming bacteria as the agent that produces a leachate solution containing copper compounds
The steps
- For phytomining: grow plants on land containing low-grade copper ore, burn the plants to produce ash, dissolve the ash in acid to produce a solution containing a copper compound, then extract copper by electrolysis or displacement using scrap iron
- For bioleaching: state bacteria are used to produce a leachate solution containing copper compounds from the ore
Which of the following best describes a finite resource?
Phytomining and bioleaching are both alternative copper extraction methods for low-grade ores. Keep the sequence of steps for phytomining and the bacteria-based definition of bioleaching clearly separate.
Practise copper extraction and resource questionsThe topics that keep coming up
Across the 4 sittings we have full papers for, these are the topics with the most exam appearances and marks at stake on Paper 2.
Not the primary focus in the 4 sittings we have full papers for
Greenhouse effect and climate change as a standalone extended question (it appeared as short factual recall questions in one sitting rather than a full extended question) · Instrumental methods of analysis as a full standalone question (it has appeared only as short 1-mark recall questions) · Recycling as a standalone extended question separate from life cycle assessment
These topics have not been the main focus of a question in the papers we analysed, but can still support your revision, so do not skip them entirely.
Before you revise
Are these real mark-scheme answers?
The diagrams and data are described in our own words, not reproduced, and the worked answers are written entirely by us, aimed at the top level descriptors of the real AQA mark schemes for each sitting. They are not copied from AQA's own exemplar materials, since that would breach copyright, but they are built to hit exactly what the real mark scheme rewarded that year. PrepWise is independent of AQA and not endorsed by them.
Will the exact same questions come up again this year?
Sometimes stems repeat closely, but you cannot rely on repeats alone, since the actual data, diagrams and numbers change every time even when the topic and question style repeat. Use this page to see which TOPICS and question TYPES keep returning (like tangent-to-curve rate calculations, or the rate-versus-yield-versus-cost equilibrium template) and make sure you know the method cold, whatever the exact numbers turn out to be.
How many marks do I lose if I run out of time on the extended 6-mark questions?
Extended questions like the LCA evaluation or the equilibrium conditions question are worth up to 6 marks each and are marked using levels, not individual points. If you are short on time, still write a short concluding judgement, even a brief one, rather than leaving the answer unfinished, since a partial answer with a clear structure usually scores better than an unfinished list of facts.
Is PrepWise free to use for this?
Yes, PrepWise is free during alpha. You can practise every topic on this page without paying anything right now.
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