Every question since 2022 — with full worked answers

Edexcel GCSE Chemistry Paper 2, Higher Tier (1CH0/2H)Paper 2 — every question, answered

We read the real Higher Tier papers Edexcel has published for Chemistry Paper 2 in June 2022 and June 2023, plus the mark schemes examiners actually used to grade them. June 2019 is no longer published on Pearson's live archive, so we have not included it. Below is what real sub-questions on each recurring topic have asked, what a full mark answer looks like against that year's mark scheme, and what tripped candidates up.

Edexcel 1CH0100 marks, questions marked with an asterisk also assess how logically you structure your answer1 hour 45 minutes for the whole paper2 sittings analysed

Questions © Pearson Education Ltd, quoted for analysis. Diagrams, tables and apparatus described in our own words, not reproduced. Mark scheme content translated into plain English, not copied. PrepWise is independent and not endorsed by Pearson or Edexcel.

The paper is a template

Same 10 question types, every sitting
Q9/Q8Calculating the energy change for a reaction from bond energies4 marksQ9Explaining what a catalyst does using a reaction profile6 marksQ2Explaining why the rate of reaction changes during a reaction3 marksQ9Explaining how the air-hole on a Bunsen burner affects combustion products and harm6 marksQ9Explaining the trend in viscosity of fractions from crude oil2 marksQ10/Q7Completing the equation or repeat unit for an alkene reaction2 marksQ7Describing fermentation and concentrating ethanol by fractional distillation6 marksQ4/Q10Identifying metal ions from flame test results3 marksQ10Describing the test for a named ion using a precipitate3 marksQ5Explaining how impurities in fossil fuels cause acid rain3 marks
Q94 marksAO2, applying bond energy data to calculate an energy change

“Use bond energy data to calculate the overall energy change for a reaction”

Every sitting we have gives you a balanced equation and a table of bond energies, then asks for the overall energy change with the correct sign.

Every Q9 asked — find yours1 question · 2 full worked answers
1×asked

“Hydrogen reacts with fluorine. H2 + F2 -> 2HF. Figure 12 shows the bond energies for the bonds in the three molecules in the equation. Calculate the energy change for this reaction.”

June 2022Bond energies Full worked answer inside

What it’s really asking

You are given the bond energies for H-H, F-F and H-F and asked to work out the overall energy change for the reaction, including whether it is exothermic or endothermic.

Sitting:
What the sources actually showed — June 2022
Figure 12

A small table giving the bond energy in kJ per mole for the H-H bond, the F-F bond and the H-F bond, alongside the balanced equation H2 + F2 -> 2HF printed above the table.

BondBond energy (kJ/mol)
H-H436
F-F158
H-F562
The real data and numbers, recreated in our own layout — never the exam board's own artwork or photos.
The full worked answer — June 2022
Written to: 4/4 full marks. This is question 9(a)(ii) on the June 2022 paper, a four mark calculation with no higher band

Energy to break bonds in reactants = H-H + F-F = 436 + 158 = 594 kJ/mol. Energy released making bonds in products = 2 x H-F = 2 x 562 = 1124 kJ/mol. Overall energy change = 594 - 1124 = -530 kJ/mol. Since the value is negative, the reaction is exothermic.

Why this scoresThis adds the bond energy of every bond broken in the reactants (one H-H bond and one F-F bond), then adds the bond energy of every bond made in the products (two H-F bonds, since the equation shows 2HF), then subtracts bonds made from bonds broken. The four marking points are: energy in reactants, energy in products, the correctly evaluated difference, and the correct negative sign showing the reaction is exothermic.

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 bond energy calculations
Worked answer · PrepWise · prepwise.ukOur own writing — aimed at the real mark scheme, never copied

What the mark scheme rewarded

  • Correctly totalling the bond energies for every bond broken in the reactants, using the correct number of each bond from the balanced equation
  • Correctly totalling the bond energies for every bond made in the products
  • Finding the difference between the two totals (bonds broken minus bonds made)
  • Giving the correct sign, since a negative answer means the reaction is exothermic and a positive answer means it is endothermic
Evidence to deploy — 5 factsScreenshot this
  1. Energy change = total energy to break bonds in reactants minus total energy released making bonds in products
  2. Breaking bonds takes in energy (endothermic), so it is added as a positive value
  3. Making bonds releases energy (exothermic), so it is subtracted from the bonds broken total
  4. A negative overall energy change means the reaction is exothermic, a positive value means it is endothermic
  5. Always check how many of each bond are actually present using the balanced equation, not just the displayed formula of one molecule
PrepWise · prepwise.ukDrill these facts in the app

Traps examiners saw

  • Forgetting to multiply a bond energy by the number of that bond present, for example only using one H-H bond energy when the equation needs three
  • Adding bonds broken and bonds made instead of subtracting them
  • Losing the negative sign, or stating a positive number is exothermic when it is actually endothermic

Full-mark self-check 0 of 4

The method for every Q9 — 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.

  • Adding up the energy needed to break all the bonds in the reactants
  • Adding up the energy released making all the bonds in the products
  • Subtracting bonds made from bonds broken and giving the correct sign for exothermic or endothermic
4 marksCorrect energy change stated with the correct sign, with working shown for bonds broken, bonds made and the difference between them.
3 marksBonds broken and bonds made both correctly calculated and the difference found, but the final sign is wrong or missing.
1 to 2 marksOnly one of bonds broken or bonds made is correctly calculated, or the numbers are combined but not subtracted correctly.

The steps

  1. Use the balanced equation to count how many of each bond are broken in the reactants and add up their bond energies
  2. Count how many of each bond are made in the products and add up their bond energies
  3. Subtract energy released making bonds from energy used breaking bonds
  4. State whether the reaction is exothermic (negative) or endothermic (positive) based on your answer
About 5 minutes for the full calculation, since it usually carries 4 marks
Try one now — from our question bank

Which statement correctly describes the energy change when chemical bonds are broken?

This calculation appears on every paper we analysed, always as a full multi-step calculation worth 4 marks. Learn the method (bonds broken minus bonds made) cold and always check your final sign.

Practise bond energy calculations
Q96 marksAO1, describing and explaining the function of a catalyst

“Discuss what catalysts do and their effect on activation energy, using named examples”

In the sitting we have this question in, you are shown a reaction profile for an uncatalysed exothermic reaction and asked to discuss catalysts in general using named examples from the course.

Every Q9 asked — find yours1 question · 1 full worked answer
1×asked

“The reaction profile for an uncatalysed exothermic reaction is shown in Figure 13. Using some examples of catalysts you have met in chemistry, discuss what catalysts do and their effect on the activation energy of a reaction. You can use Figure 13 to illustrate your answer.”

June 2022Catalysts and reaction profiles Full worked answer inside

What it’s really asking

This is question 9(b) on the June 2022 paper. It wants a general discussion of what catalysts do and why, backed up by named catalysed reactions from the specification, ideally shown on an amended or newly drawn reaction profile.

What the sources actually showed — June 2022
Figure 13

A reaction profile for an uncatalysed exothermic reaction, showing the energy axis against the progress of reaction, with the reactants starting at a lower energy level, a labelled peak in between, and the products ending at a lower energy level than the reactants.

A reaction profile for an uncatalysed exothermic reaction, showing the energy axis against the progress of reaction, with the reactants starting at a lower energy level, a labelled peak in between, and the products ending at a lower energy level than the reactants.
The real data and numbers, recreated in our own layout — never the exam board's own artwork or photos.
The full worked answer — June 2022
Written to: Level 3, 6/6 full marks. Covers description, function, a diagram amendment and two named examples

A catalyst is a substance that increases the rate of a reaction without being used up or changing chemically itself, and without changing the products formed, so its own mass stays the same at the end of the reaction as at the start.

Why this scoresThis is the description strand of Level 1 to 2: it states clearly that a catalyst speeds up the reaction, is chemically unchanged, is not used up, and does not alter the products.

For a reaction to happen, particles must collide with at least a minimum amount of energy called the activation energy. A catalyst works by providing an alternative reaction pathway that has a lower activation energy than the uncatalysed route, so a greater proportion of collisions between particles have enough energy to be successful and go on to form products.

Why this scoresThis is the function strand the mark scheme requires: minimum energy needed (activation energy), an alternative route, a lower activation energy, and the consequence that more collisions succeed. This is what separates Level 2 from a simple description.

On the reaction profile in Figure 13, the catalysed version of this reaction would start and finish at exactly the same energy levels as the uncatalysed profile, since the reactants and products are chemically identical either way, but the new profile would show a lower peak in the middle, representing the lower activation energy of the catalysed pathway.

Why this scoresThis addresses the diagram strand directly, describing exactly what changes (a lower peak) and what stays the same (start and end energy), which is the labelled reaction profile requirement for the top level.

Two examples of catalysts I have met in chemistry are the iron catalyst used in the Haber process to make ammonia from nitrogen and hydrogen, and the enzymes contained in yeast that catalyse the fermentation of glucose to produce ethanol. Both increase the rate of their reaction without being consumed by it.

Why this scoresThis satisfies the named-example requirement with two genuinely different catalysed reactions from the specification (an industrial inorganic catalyst and a biological enzyme catalyst), which is what Level 3 asks for to move beyond a single vague example.

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 reaction profile questions
Worked answer · PrepWise · prepwise.ukOur own writing — aimed at the real mark scheme, never copied

What the mark scheme rewarded

  • A correct description that a catalyst increases rate without being used up and without changing the products
  • A correct explanation of activation energy and how a catalyst provides an alternative route with a lower activation energy
  • Reference to or amendment of a reaction profile, showing the same start and end energy but a lower peak
  • At least one named catalysed reaction from the specification, such as the Haber process, cracking, fermentation, hydrogen peroxide decomposition, catalytic converters, or biological enzymes
Evidence to deploy — 8 factsScreenshot this
  1. A catalyst increases the rate of reaction without being used up and without being chemically changed
  2. Activation energy is the minimum energy particles need for a collision to result in a reaction
  3. A catalyst provides an alternative reaction pathway with a lower activation energy
  4. This means a greater proportion of collisions have enough energy to be successful
  5. The Haber process uses an iron catalyst to make ammonia from nitrogen and hydrogen
  6. Cracking uses a catalyst to break down long-chain hydrocarbons into smaller, more useful molecules
  7. Fermentation uses enzymes in yeast as a biological catalyst to convert glucose into ethanol
  8. Catalytic converters in cars use catalysts to convert harmful exhaust gases into less harmful ones
PrepWise · prepwise.ukDrill these facts in the app

Traps examiners saw

  • Saying a catalyst 'speeds up the reaction' without explaining activation energy or the alternative pathway, which limits you to the lower level
  • Forgetting to state that the start and end energy levels stay the same on a catalysed profile, only the peak changes
  • Naming only one example, or naming something that is not actually a catalyst from the specification
  • Confusing a catalyst with a reactant, implying it gets used up or changes the products

Full-mark self-check 0 of 4

The method for every Q9 — 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.

  • Describing that a catalyst increases the rate of reaction without being used up or changing the products
  • Explaining that a catalyst provides an alternative reaction pathway with a lower activation energy, so a greater proportion of collisions are successful
  • Illustrating this with a reaction profile showing a lower peak but the same start and end energy
  • Naming specific catalysed reactions from the course, such as the Haber process or cracking
Level 3, 5 to 6 marksIdentifies at least one catalysed reaction, gives a good description of the role of a catalyst, and describes the function of a catalyst or draws a labelled reaction profile.
Level 2, 3 to 4 marksCovers two of: identifying a catalysed reaction, describing the role of a catalyst, or describing its function/reaction profile, but not all three in full detail.
Level 1, 1 to 2 marksIdentifies a catalysed reaction or gives a simple description of the role of a catalyst or a simply labelled activation energy on the diagram.

The steps

  1. State what a catalyst does: increases the rate of reaction, is not used up, and does not change the products
  2. Explain the function: particles need a minimum amount of energy (activation energy) to react; a catalyst provides an alternative pathway with a lower activation energy, so a greater proportion of collisions have enough energy to be successful
  3. Add to or amend the reaction profile: a catalysed profile has the same reactant and product energy levels, but a lower peak
  4. Give at least one named example, such as the iron catalyst in the Haber process, or an enzyme catalyst in fermentation
6 marks, aim for about 8 to 10 minutes since you need to cover description, function, a diagram and named examples
Try one now — from our question bank

What does activation energy represent on a reaction profile?

This extended response wants named examples, not just a generic definition of a catalyst. Learn the Haber process, cracking and fermentation as your go-to catalysed reactions.

Practise reaction profile questions
Q23 marksAO3, interpreting data to explain a change in rate

“Explain why the rate of reaction changes as the reaction proceeds”

Both sittings we have give you a rate-of-reaction investigation with a metal or marble chips reacting with acid, then ask you to explain why the rate falls away over time in terms of particles being used up.

Every Q2 asked — find yours1 question · 2 full worked answers
1×asked

“State and explain what happens to the rate of reaction as the acid reacts with the marble chips in this experiment.”

June 2023Rate of reaction, collision theory Full worked answer inside

What it’s really asking

This is question 2(b)(ii) on the June 2023 paper. Using the gas volume against time data given, you need to explain why the reaction rate falls as marble chips react with hydrochloric acid, in terms of reactants being used up and collision frequency.

Sitting:
What the sources actually showed — June 2023
Figure 4

A table of the volume of gas produced each minute for six minutes as marble chips react with dilute hydrochloric acid.

time in minutes0123456
volume of gas in cm3052789197100100
Figure 5

A second table showing the rate of reaction calculated for each one-minute time interval from the Figure 4 results, which decreases steadily from the first interval to the last. The rate for the 2 to 3 minute interval is the value you are asked to calculate, so it is left blank here exactly as it is on the real exam paper.

time interval0 to 1 minute1 to 2 minutes2 to 3 minutes3 to 4 minutes4 to 5 minutes
rate of reaction in cm3/min5226?63
The real data and numbers, recreated in our own layout — never the exam board's own artwork or photos.
The full worked answer — June 2023
Written to: 3/3 full marks

The rate of reaction decreases as the reaction proceeds. This is because the reactants, the acid and the marble chips, are gradually used up as the reaction happens, so there are fewer acid particles and less marble chip surface available over time. With fewer reactant particles present, collisions between them become less frequent, so the rate of reaction falls.

Why this scoresThis gives the full three-point chain the mark scheme rewards: the rate decreases, this is because the reactants are being used up, and this means collisions are less frequent. All three points are linked into one explanation rather than stated as isolated facts.

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 questions
Worked answer · PrepWise · prepwise.ukOur own writing — aimed at the real mark scheme, never copied

What the mark scheme rewarded

  • Stating the rate of reaction decreases or the reaction slows down as it proceeds
  • Linking the decrease to the reactants (acid or marble chips) being used up
  • Explaining that fewer reactant particles present leads to less frequent collisions
Evidence to deploy — 4 factsScreenshot this
  1. Rate of reaction depends on how frequently particles collide with enough energy to react
  2. As a reaction proceeds, reactants are converted into products, so there is less reactant available over time
  3. Fewer reactant particles in the same volume means collisions happen less often
  4. A rate-time graph that levels off (reaches zero gradient) shows the reaction has stopped, usually because a reactant has been fully used up
PrepWise · prepwise.ukDrill these facts in the app

Traps examiners saw

  • Describing the rate speeding up at the very start of the reaction instead of addressing the overall slowing trend the question asks about
  • Stating reactants 'run out' without explaining the collision-frequency consequence
  • Confusing a levelling-off graph with the reaction becoming faster

Full-mark self-check 0 of 3

The method for every Q2 — 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 that the rate of reaction decreases as the reaction proceeds
  • Linking this to reactants (acid or marble chips) being used up
  • Explaining that fewer particles present means less frequent collisions
3 marksA full chain linking decreasing rate, reactants being used up, and fewer frequent collisions.
1 to 2 marksOnly part of the chain is given, for example stating the rate decreases without explaining why, or stating reactants are used up without linking this to collision frequency.

The steps

  1. State that the rate of reaction decreases (slows down) as the reaction proceeds
  2. Explain that this is because the reactants are being used up as the reaction happens
  3. Link this to particles: fewer reactant particles present means less frequent collisions between them
  4. Do not describe the rate speeding up at the very start, since this question is about the whole reaction slowing overall
About 4 minutes for a 3-mark explanation
Try one now — from our question bank

Which of the following factors does NOT affect the rate of a chemical reaction?

This is really a collision theory question wearing a graph-reading disguise. Always link decreasing rate back to fewer particles colliding less often as reactants are used up.

Practise rate of reaction questions
Q96 marksAO1/AO2, describing combustion products and explaining harm

“Explain the effect of opening and closing a Bunsen burner air-hole on the products of combustion and the harm large quantities of the fuel can cause”

In the sitting we have this question in, you are shown a Bunsen burner and asked to link the air-hole setting to complete or incomplete combustion, and then to the harmful effects of burning large quantities of methane.

Every Q9 asked — find yours1 question · 1 full worked answer
1×asked

“Large quantities of methane are used as a fuel. Figure 16 shows a Bunsen burner. Methane can be used as fuel for the Bunsen burner. The air-hole on the chimney of the Bunsen burner can be opened and closed. Explain the effect of opening and closing the air-hole of the Bunsen burner on the products of combustion of methane and the harm that using large quantities of methane as a fuel can cause.”

June 2023Combustion of hydrocarbons and greenhouse gases Full worked answer inside

What it’s really asking

This is question 9(c) on the June 2023 paper. It wants you to connect the air-hole setting to complete versus incomplete combustion, name the different products in each case, and explain the harm both carbon monoxide and greenhouse gases can cause.

What the sources actually showed — June 2023
Figure 16

A diagram of a Bunsen burner, with the chimney and the air-hole on the chimney both labelled, showing where air enters to mix with the gas fuel before combustion.

A diagram of a Bunsen burner, with the chimney and the air-hole on the chimney both labelled, showing where air enters to mix with the gas fuel before combustion.
The real data and numbers, recreated in our own layout — never the exam board's own artwork or photos.
The full worked answer — June 2023
Written to: Level 3, 6/6 full marks. Covers open air-hole, closed air-hole and two harmful effects with named equations

When the air-hole is open, a large amount of oxygen can mix with the methane gas, so complete combustion takes place: CH4 + 2O2 -> CO2 + 2H2O. Only carbon dioxide and water are produced.

Why this scoresThis covers the open air-hole strand with the correctly balanced equation for complete combustion and correctly names both products, which is required for the top level.

When the air-hole is closed, less oxygen is able to mix with the methane, so incomplete combustion takes place instead, for example 2CH4 + 3O2 -> 2CO + 4H2O. This time carbon monoxide is produced instead of carbon dioxide, and soot (carbon) can also form if there is very little oxygen available.

Why this scoresThis covers the closed air-hole strand, giving a correctly balanced incomplete combustion equation and naming carbon monoxide (and soot) as the different products, completing the second of the three required aspects.

Carbon monoxide from incomplete combustion is harmful because it is a colourless and odourless gas, so people cannot detect it, and it combines with haemoglobin in red blood cells in place of oxygen, which reduces the blood's capacity to carry oxygen around the body and makes it toxic. Separately, both carbon dioxide and water vapour from complete combustion are greenhouse gases: they absorb heat energy radiated from the Earth's surface and re-radiate it, which increases the greenhouse effect, raises global temperatures, and contributes to climate change, including melting polar ice and rising sea levels.

Why this scoresThis gives two distinct harmful effects (the toxicity of carbon monoxide via haemoglobin binding, and the greenhouse/climate consequence of carbon dioxide and water vapour), fully completing the third required aspect and reaching the level 3 requirement to cover all three parts of the question.

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 combustion questions
Worked answer · PrepWise · prepwise.ukOur own writing — aimed at the real mark scheme, never copied

What the mark scheme rewarded

  • Correctly explaining that an open air-hole gives complete combustion, producing carbon dioxide and water
  • Correctly explaining that a closed air-hole gives incomplete combustion, producing carbon monoxide and/or soot
  • Explaining carbon monoxide's toxicity through binding to haemoglobin in place of oxygen
  • Explaining that carbon dioxide and water vapour are greenhouse gases that increase the greenhouse effect and contribute to global warming and climate change
Evidence to deploy — 6 factsScreenshot this
  1. Complete combustion needs plenty of oxygen and produces only carbon dioxide and water
  2. Incomplete combustion happens with a limited oxygen supply and can produce carbon monoxide, carbon (soot), and water
  3. Carbon monoxide is toxic because it binds to haemoglobin in red blood cells more readily than oxygen does, reducing the blood's capacity to transport oxygen
  4. Soot can aggravate respiratory problems and makes buildings dirty
  5. Carbon dioxide and water vapour are greenhouse gases that absorb and re-radiate heat energy from the Earth
  6. Increased greenhouse gas levels increase the greenhouse effect, contributing to global warming and climate change
PrepWise · prepwise.ukDrill these facts in the app

Traps examiners saw

  • Only describing one air-hole setting instead of contrasting both open and closed
  • Naming carbon monoxide as a greenhouse gas, when the greenhouse gas point applies to carbon dioxide and water vapour from complete combustion
  • Forgetting to explain WHY carbon monoxide is harmful (the haemoglobin link), rather than just stating it is toxic
  • Missing the connection between opening the air-hole and the amount of oxygen mixing with the fuel

Full-mark self-check 0 of 4

The method for every Q9 — 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 an open air-hole allows complete combustion, producing carbon dioxide and water
  • Explaining that a closed air-hole starves the flame of oxygen, causing incomplete combustion and producing carbon monoxide (and/or soot)
  • Explaining the harm caused: carbon monoxide is toxic because it binds to haemoglobin, and carbon dioxide/water vapour are greenhouse gases that increase the greenhouse effect and contribute to global warming
Level 3, 5 to 6 marksDescribes all three of: what happens with the air-hole open, what happens with it closed, and at least one harmful effect, connecting them logically.
Level 2, 3 to 4 marksDescribes two of the three aspects (open air-hole, closed air-hole, harmful effect) in reasonable detail.
Level 1, 1 to 2 marksDescribes only one aspect, for example that a closed air-hole gives less oxygen, or a simple statement of one harmful effect.

The steps

  1. State that with the air-hole open, plenty of oxygen mixes with the methane, so complete combustion occurs, producing carbon dioxide and water only
  2. State that with the air-hole closed, less oxygen is available, so incomplete combustion occurs, producing carbon monoxide (and/or carbon, as soot) as well as water
  3. Explain that carbon monoxide is toxic because it combines with haemoglobin in the blood in place of oxygen, reducing the blood's capacity to carry oxygen
  4. Explain that carbon dioxide and water vapour are greenhouse gases that absorb and re-radiate heat energy from the Earth, increasing the greenhouse effect and contributing to global warming and climate change
6 marks, aim for about 8 to 10 minutes since this question needs both combustion equations and a harm explanation
Try one now — from our question bank

What are the only products formed during the complete combustion of a hydrocarbon?

This question wants both combustion equations AND the harm they cause. Learn complete and incomplete combustion equations for methane cold, and know exactly why carbon monoxide is dangerous.

Practise combustion questions
Q92 marksAO1, explaining a trend using knowledge of hydrocarbon structure

“Explain why the viscosity of fractions from crude oil changes with fraction position”

In the sitting we have this question in, you are shown a fractionating column and told the fractions get more viscous further down the column, then asked to explain why.

Every Q9 asked — find yours1 question · 1 full worked answer
1×asked

“Figure 15 shows a fractionating column, the fractions obtained and the trend in viscosity of the fractions. Explain the trend in the viscosity of the fractions.”

June 2023Crude oil and fractional distillation Full worked answer inside

What it’s really asking

This is question 9(a)(ii) on the June 2023 paper. It wants an explanation linking the size of hydrocarbon molecules in each fraction to the strength of intermolecular forces and therefore viscosity.

What the sources actually showed — June 2023
Figure 15

A diagram of a fractionating column with crude oil entering at the bottom, and six labelled outlet pipes for gases, petrol, kerosene, diesel oil, fuel oil and bitumen going from top to bottom, alongside an arrow showing viscosity increases going down the column.

A diagram of a fractionating column with crude oil entering at the bottom, and six labelled outlet pipes for gases, petrol, kerosene, diesel oil, fuel oil and bitumen going from top to bottom, alongside an arrow showing viscosity increases going down the column.
The real data and numbers, recreated in our own layout — never the exam board's own artwork or photos.
The full worked answer — June 2023
Written to: 2/2 full marks

Viscosity increases down the column because the hydrocarbon molecules in each fraction get larger, containing more carbon atoms, the further down the column the fraction is collected. Larger molecules have stronger intermolecular forces of attraction between them, which makes the liquid flow less easily, so the fraction is more viscous.

Why this scoresThis gives both required marking points: the molecules getting larger (more carbons/longer chains) further down the column, and the correct explanation that larger molecules have stronger intermolecular forces, which is what actually causes the higher viscosity.

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 questions
Worked answer · PrepWise · prepwise.ukOur own writing — aimed at the real mark scheme, never copied

What the mark scheme rewarded

  • Stating that molecules get larger, longer or contain more carbons further down the fractionating column
  • Linking this to stronger intermolecular forces (or forces of attraction) between the larger molecules, which increases viscosity
Evidence to deploy — 4 factsScreenshot this
  1. Crude oil is separated by fractional distillation, based on the different boiling points of hydrocarbons of different chain length
  2. Fractions collected further down the column contain longer hydrocarbon chains with higher boiling points
  3. Larger hydrocarbon molecules have greater surface area of contact and stronger intermolecular forces of attraction
  4. Stronger intermolecular forces mean a liquid resists flowing, making it more viscous
PrepWise · prepwise.ukDrill these facts in the app

Traps examiners saw

  • Explaining boiling point trends instead of the viscosity trend the question actually asks about
  • Saying molecules are 'bigger' without explaining why bigger molecules are more viscous (the intermolecular force link)
  • Confusing intermolecular forces between molecules with the covalent bonds within a molecule

Full-mark self-check 0 of 3

The method for every Q9 — 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 that molecules get larger (more carbon atoms/longer chains) further down the column
  • Linking larger molecules to stronger intermolecular forces of attraction and higher viscosity
2 marksBoth the size/length trend AND the intermolecular force explanation are given and linked together.
1 markOnly one of the two points is given, for example stating molecules get larger without explaining the intermolecular force consequence.

The steps

  1. State that viscosity increases down the column because the hydrocarbon molecules in each fraction get larger (more carbon atoms) further down
  2. Explain that larger molecules have stronger intermolecular forces of attraction between them
  3. Link this to viscosity: stronger intermolecular forces make the liquid flow less easily, so it is more viscous
About 3 minutes for a 2-mark explanation
Try one now — from our question bank

A hydrocarbon is a compound that contains only:

Trend questions like this always want the size-of-molecule link to intermolecular forces, not just a restated observation. Learn this two-step chain for viscosity and boiling point trends alike.

Practise crude oil questions
Q10/Q72 marksAO2, applying knowledge of alkenes to complete an equation or repeating unit

“Complete the equation for an alkene reacting with bromine, or draw the repeating unit of its addition polymer”

Both sittings we have give you a displayed alkene structure and ask you to either complete an addition reaction with bromine or draw the polymer repeating unit it forms.

Every Q10/Q7 asked — find yours2 questions · 4 full worked answers
1×asked

“Figure 14 shows the structure of a molecule of hydrocarbon Z, C4H8. Complete the balanced equation for the reaction of hydrocarbon Z, C4H8, with bromine.”

June 2022Alkenes, addition reactions Full worked answer inside

What it’s really asking

This is question 10(a)(ii) on the June 2022 paper. You need to add the formula for bromine and the correct product formula to complete the equation for the addition reaction of but-2-ene with bromine.

Sitting:
What the sources actually showed — June 2022
Figure 14

A displayed structural formula of but-2-ene, C4H8, showing a central C=C double bond with a CH3 group and an H atom attached to each of the two double-bonded carbons.

A displayed structural formula of but-2-ene, C4H8, showing a central C=C double bond with a CH3 group and an H atom attached to each of the two double-bonded carbons.
The real data and numbers, recreated in our own layout — never the exam board's own artwork or photos.
The full worked answer — June 2022
Written to: 2/2 full marks

C4H8 + Br2 -> C4H8Br2. Bromine's formula, Br2, is added on the left, and the double bond in but-2-ene opens up so that one bromine atom attaches to each of the two carbons that were double bonded, giving C4H8Br2 as the single addition product.

Why this scoresThis correctly identifies bromine as Br2 and gives the correct molecular formula of the addition product, matching the mark scheme's requirement for a fully correct equation with the C=C double bond having reacted with both bromine atoms.

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 alkene and polymer questions
Worked answer · PrepWise · prepwise.ukOur own writing — aimed at the real mark scheme, never copied

What the mark scheme rewarded

  • Correctly identifying bromine as Br2 or drawing it as Br-Br
  • Showing the C=C double bond becoming a single bond in the product
  • Attaching one bromine atom to each of the two carbons that were part of the double bond
  • Keeping every other atom in the structure unchanged
Evidence to deploy — 4 factsScreenshot this
  1. Alkenes contain a carbon-carbon double bond (C=C), which is more reactive than the single bonds in alkanes
  2. In an addition reaction, atoms are added across the double bond, turning it into a single bond
  3. Bromine water is used as a test for alkenes: it turns from orange to colourless as bromine adds across the double bond
  4. The general rule: one atom (or group) is added to each of the two carbons that were part of the C=C double bond
PrepWise · prepwise.ukDrill these facts in the app

Traps examiners saw

  • Forgetting to change the C=C double bond to a single bond in the product structure
  • Adding bromine to the wrong carbons, rather than the two that were part of the double bond
  • Missing the second bromine atom, only showing addition of one Br

Full-mark self-check 0 of 3

1×asked

“Draw the repeating unit of the addition polymer formed when hydrocarbon Z undergoes polymerisation.”

June 2022Addition polymers Full worked answer inside

What it’s really asking

This is question 10(a)(iii) on the June 2022 paper. You need to draw the repeating unit of poly(but-2-ene), showing the double bond opened to a single bond with continuation bonds on either side.

Sitting:
What the sources actually showed — June 2022
Figure 14

The same displayed structural formula of but-2-ene, C4H8, used in the earlier part of the question, showing the C=C double bond with a CH3 group and an H atom on each double-bonded carbon.

The same displayed structural formula of but-2-ene, C4H8, used in the earlier part of the question, showing the C=C double bond with a CH3 group and an H atom on each double-bonded carbon.
The real data and numbers, recreated in our own layout — never the exam board's own artwork or photos.
The full worked answer — June 2022
Written to: 2/2 full marks

The repeating unit shows two neighbouring carbon atoms joined by a single bond, each with a CH3 group and a hydrogen atom attached exactly as in the original but-2-ene structure, with continuation bonds extending outward from each carbon to show the unit repeats indefinitely, and crucially no C=C double bond remaining anywhere in the unit.

Why this scoresThis correctly converts the double bond to a single bond (the first mark) and correctly keeps the rest of the structure intact with continuation bonds shown on both sides (the second mark), matching exactly what the mark scheme credits for a repeating unit.

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 alkene and polymer questions
Worked answer · PrepWise · prepwise.ukOur own writing — aimed at the real mark scheme, never copied

What the mark scheme rewarded

  • Showing the C=C double bond has become a single bond in the repeating unit
  • Keeping the rest of the monomer's atoms and bonds unchanged in the repeating unit
  • Adding continuation bonds on both sides of the repeating unit to show it repeats
Evidence to deploy — 4 factsScreenshot this
  1. Addition polymerisation joins many alkene monomers together by opening their C=C double bonds
  2. The repeating unit of an addition polymer contains the same atoms as the monomer, but with a single bond instead of a double bond
  3. Continuation bonds (short lines extending beyond the unit) show that the unit repeats many times in the full polymer
  4. The general name pattern is poly(monomer name), for example poly(ethene) from ethene
PrepWise · prepwise.ukDrill these facts in the app

Traps examiners saw

  • Leaving the C=C double bond in the repeating unit, which is not allowed since polymerisation opens it up
  • Forgetting the continuation bonds, which are needed to show the structure repeats
  • Changing the side groups on the carbons instead of keeping them exactly as they were in the monomer

Full-mark self-check 0 of 3

The method for every Q10/Q7 — 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 showing the C=C double bond becoming a single bond with the added atoms attached
  • Drawing the repeating unit with continuation bonds and no C=C double bond remaining
2 marksFully correct structure or equation, including correct bonds and correct atoms added.
1 markPartially correct, for example the correct formula given without full structural detail, or one part of the structure correct.

The steps

  1. Identify the C=C double bond in the alkene, since this is the reactive site
  2. For an addition reaction, break the double bond to a single bond and attach the new atoms (for example Br to each carbon)
  3. For a polymer repeating unit, break the double bond to a single bond and add continuation bonds either side, keeping all other atoms the same
  4. Check the total number of bonds around each carbon is still four
About 3 minutes for a 2-mark structural question
Try one now — from our question bank

What is the general formula for alkenes?

Alkene structural questions always come down to one move: open the C=C double bond. Practise both the addition-reaction version and the polymer-repeating-unit version of this move.

Practise alkene and polymer questions
Q76 marksAO1, describing a practical process in a logical sequence

“Describe how glucose is fermented to ethanol and how the dilute ethanol produced is concentrated by fractional distillation”

In the sitting we have this question in, you are given the formula of glucose and asked to describe both the fermentation process and the fractional distillation process used to concentrate the ethanol produced.

Every Q7 asked — find yours1 question · 1 full worked answer
1×asked

“Glucose, C6H12O6, is a carbohydrate. A dilute solution of ethanol can be produced from glucose by fermentation. The dilute solution of ethanol can then be processed to form a concentrated solution of ethanol. Describe how the fermentation of glucose is carried out and how the dilute solution of ethanol produced can then be processed to form a concentrated solution of ethanol. You may include diagrams in your answer.”

June 2023Fermentation and fractional distillation of ethanol Full worked answer inside

What it’s really asking

This is question 7(b) on the June 2023 paper. It wants a full method for both fermenting glucose into dilute ethanol and then concentrating that ethanol using fractional distillation, in a clear logical order.

What the sources actually showed — June 2023
Question stem

The question text itself, stating glucose is a carbohydrate with the formula C6H12O6, and that a dilute ethanol solution made by fermenting it is later processed to become more concentrated, with no additional diagram or apparatus provided.

The real data and numbers, recreated in our own layout — never the exam board's own artwork or photos.
The full worked answer — June 2023
Written to: Level 3, 6/6 full marks. Describes fermentation in detail and fractional distillation in detail

To ferment the glucose, first dissolve the glucose in water to make a glucose solution, then place this solution into a suitable flask and add yeast. The flask is kept warm, at a temperature of around 25 to 35 degrees Celsius, since yeast enzymes work best in this range, and an air lock is fitted into the neck of the flask to let carbon dioxide escape while keeping oxygen out, since oxygen would allow the yeast to respire aerobically instead of fermenting the glucose anaerobically. The reaction is left until bubbles of carbon dioxide stop being produced, showing fermentation has finished, and then the dilute ethanol solution is decanted away from the solid yeast, or the yeast is filtered out.

Why this scoresThis gives a detailed, logically ordered description of fermentation covering every marking point: dissolving glucose, adding yeast, the correct warm temperature range, the purpose of the air lock, recognising when the reaction has finished, and separating the ethanol from the yeast, which is what the mark scheme credits for a detailed description of one process.

To concentrate the dilute ethanol solution, fractional distillation is used. The dilute ethanol is placed in a round bottomed flask connected to a fractionating column, with a thermometer positioned at the top of the column, and the column is connected to a condenser with water running through its outer jacket. The flask is heated to a temperature above the boiling point of ethanol but below the boiling point of water, so mostly ethanol vapour rises up the fractionating column, is cooled and condensed back to a liquid in the condenser, and concentrated ethanol is collected as it drips out from the end of the condenser, leaving most of the water behind in the original flask.

Why this scoresThis gives an equally detailed description of the second process, covering the apparatus (round bottomed flask, fractionating column, thermometer, condenser), the key temperature control step (heating between the two boiling points), and the outcome (concentrated ethanol collected, water left behind), which is exactly what Level 3 requires for both processes to be described, with at least one in detail.

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 alcohol and fermentation questions
Worked answer · PrepWise · prepwise.ukOur own writing — aimed at the real mark scheme, never copied

What the mark scheme rewarded

  • Dissolving glucose in water and adding yeast to start fermentation
  • Keeping the mixture warm, ideally specifying a temperature range around 25 to 40 degrees Celsius
  • Fitting an air lock (or equivalent) to exclude oxygen while letting carbon dioxide escape
  • Recognising the reaction is complete when bubbling stops, then decanting or filtering to remove yeast
  • Using fractional distillation with a fractionating column, thermometer and condenser
  • Heating to a temperature between the boiling points of ethanol and water, and collecting the concentrated ethanol from the condenser
Evidence to deploy — 5 factsScreenshot this
  1. Fermentation is the anaerobic respiration of glucose by yeast, producing ethanol and carbon dioxide
  2. An air lock allows carbon dioxide to escape while preventing oxygen from entering, since oxygen would allow aerobic respiration instead
  3. Yeast fermentation works best at a warm temperature, typically 25 to 40 degrees Celsius; too hot and the enzymes are denatured
  4. Fractional distillation separates liquids with different boiling points using a fractionating column
  5. Ethanol boils at a lower temperature than water, so it evaporates first and is collected separately when the mixture is heated within the right temperature range
PrepWise · prepwise.ukDrill these facts in the app

Traps examiners saw

  • Describing only fermentation or only fractional distillation, missing the marks available for the other half of the process
  • Forgetting the air lock and its purpose, which is a commonly missed marking point
  • Giving a temperature for distillation without specifying it must be between the two boiling points
  • Confusing fractional distillation with simple distillation, missing the fractionating column

Full-mark self-check 0 of 4

The method for every Q7 — 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.

  • Describing fermentation: glucose solution, yeast added, warm temperature, an air lock to keep oxygen out, reaction stops when bubbles stop, then decanting or filtering
  • Describing fractional distillation: the dilute ethanol placed in a flask with a fractionating column and thermometer, heated to a temperature between the boiling points of ethanol and water, then concentrated ethanol collected from the condenser
  • Presenting both processes in a clear, logically ordered sequence
Level 3, 5 to 6 marksBoth processes are described, with at least one described in detail.
Level 2, 3 to 4 marksA detailed description of one process, or a basic description of both processes.
Level 1, 1 to 2 marksA basic description of either process, or a very basic description of both.

The steps

  1. Dissolve glucose in water to form a solution and add yeast
  2. Keep the mixture warm (around 25 to 40 degrees Celsius) and fit an air lock to the flask to exclude oxygen
  3. Leave until bubbles of carbon dioxide stop, then decant the ethanol solution away from the yeast
  4. Place the dilute ethanol in a flask with a fractionating column and thermometer at the top, connected to a condenser
  5. Heat above the boiling point of ethanol but below the boiling point of water, so ethanol vapour rises and is condensed and collected, leaving most of the water behind
6 marks, aim for about 8 to 10 minutes, ideally with a labelled diagram for at least one process
Try one now — from our question bank

What is the functional group present in all alcohols?

This question rewards a genuinely detailed method for at least one of the two processes, not a vague summary of both. Learn the air lock's purpose and the exact apparatus for fractional distillation.

Practise alcohol and fermentation questions
Q4/Q103 marksAO3, interpreting flame test data and evaluating a method

“Identify metal ions from flame test colours, and explain how to improve an invalid flame test method”

Both sittings we have use a flame test, either asking you to identify unknown compounds from their flame colours or to spot and fix a flaw in the method that makes a conclusion invalid.

Every Q4/Q10 asked — find yours2 questions · 2 full worked answers
1×asked

“Figure 7 shows the results of the flame tests on three compounds, P, Q and R. Use Figure 7 to identify the metal ions in compounds P, Q and R.”

June 2022Flame tests Full worked answer inside

What it’s really asking

This is question 4(b)(ii) on the June 2022 paper. You are given the flame colours (red, lilac, blue-green) for three unknown compounds and need to name the correct metal ion for each based on standard flame test colours.

What the sources actually showed — June 2022
Figure 7

A small table listing three compounds, P, Q and R, alongside the flame colour observed for each: red for P, lilac for Q, and blue-green for R.

CompoundFlame colour observed
Pred
Qlilac
Rblue-green
The real data and numbers, recreated in our own layout — never the exam board's own artwork or photos.
The full worked answer — June 2022
Written to: 3/3 full marks

P contains lithium ions, since lithium compounds produce a red flame colour. Q contains potassium ions, since potassium compounds produce a lilac flame colour. R contains copper ions, since copper compounds produce a blue-green flame colour.

Why this scoresThis correctly matches each of the three named flame colours to its standard metal ion identity, one mark for each of the three correct identifications, based on memorised flame test colours rather than any calculation.

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 test questions
Worked answer · PrepWise · prepwise.ukOur own writing — aimed at the real mark scheme, never copied

What the mark scheme rewarded

  • Correctly identifying lithium from a red flame colour
  • Correctly identifying potassium from a lilac flame colour
  • Correctly identifying copper from a blue-green flame colour
Evidence to deploy — 5 factsScreenshot this
  1. Lithium compounds produce a red flame
  2. Sodium compounds produce a yellow-orange flame
  3. Potassium compounds produce a lilac flame
  4. Calcium compounds produce an orange-red (brick red) flame
  5. Copper compounds produce a blue-green flame
PrepWise · prepwise.ukDrill these facts in the app

Traps examiners saw

  • Confusing lithium's red flame with calcium's orange-red flame
  • Confusing sodium's yellow-orange flame with potassium's lilac flame
  • Giving the compound's full name instead of just identifying the metal ion, which is what the question actually asks for

Full-mark self-check 0 of 2

1×asked

“A student carried out a flame test on a sample of solid potassium chloride. The student made the following observation and conclusion: 'I saw that the flame colour was yellow so the sample must contain sodium ions.' Due to the way the student carried out the experiment, this is not a valid conclusion. Explain one improvement that the student could make to their method to obtain a valid conclusion.”

June 2023Flame tests, practical technique Full worked answer inside

What it’s really asking

This is question 10(a)(i) on the June 2023 paper. You need to spot that the student's method (dipping a wooden splint into water then the solid, then into a Bunsen flame) risks contamination or an unreliable colour, and suggest a specific fix.

What the sources actually showed — June 2023
Question stem and method steps

A student's stated method for a flame test on potassium chloride using a wooden splint dipped first in water, then in the solid sample, then held in a roaring Bunsen burner flame, alongside the student's observation of a yellow flame and their (incorrect) conclusion that this shows sodium ions.

The real data and numbers, recreated in our own layout — never the exam board's own artwork or photos.
The full worked answer — June 2023
Written to: 2/2 full marks

The student should use a (nichrome) metal wire instead of a wooden splint, because a wooden splint itself burns in the flame, and the flame produced by the burning wood can interfere with or mask the true flame colour of the metal ions being tested, making the yellow colour unreliable evidence for sodium.

Why this scoresThis gives a specific, workable improvement (a metal or nichrome wire loop) linked to the correct reason the original method was invalid (the wooden splint burning and affecting the flame colour), matching what the real mark scheme credits.

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 test questions
Worked answer · PrepWise · prepwise.ukOur own writing — aimed at the real mark scheme, never copied

What the mark scheme rewarded

  • Suggesting a specific improvement, such as using a metal (nichrome) wire instead of a wooden splint
  • Linking the improvement to the correct reason: the wood itself burning interferes with the flame colour observed
Evidence to deploy — 3 factsScreenshot this
  1. A flame test uses a clean wire (traditionally nichrome or platinum) dipped in acid, then in the sample, then held in a roaring Bunsen flame
  2. A wooden splint can burn and produce its own flame colour, contaminating the observation
  3. Contamination between samples (using the same unclean wire for different substances) is another common source of invalid flame test conclusions
PrepWise · prepwise.ukDrill these facts in the app

Traps examiners saw

  • Suggesting an unrelated improvement, such as changing the Bunsen burner setting, without addressing the wooden splint issue
  • Giving an improvement without explaining why it fixes the specific flaw in the described method

Full-mark self-check 0 of 2

The method for every Q4/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.

  • Matching flame colours to the correct metal ions from memory (lithium red, sodium yellow-orange, potassium lilac, calcium orange-red/brick red, copper blue-green)
  • Identifying a genuine flaw in a described method (for example, contamination or the wrong part of the flame used) and explaining a specific fix
3 marks (identification question)All three (or more) unknown compounds correctly matched to their metal ions from the flame colours given.
2 marks (method improvement question)A specific, workable improvement is given, linked to a correct reason why the original method was invalid.

The steps

  1. Learn the standard flame colours: lithium (red), sodium (yellow-orange), potassium (lilac), calcium (orange-red/brick red), copper (blue-green)
  2. Match each compound in the data to its ion based on the flame colour observed
  3. If asked to evaluate a method, check for contamination risks (for example testing multiple samples with the same wire without cleaning it) or technique errors (holding the wire in the wrong part of the flame)
  4. Suggest a specific fix, such as cleaning the wire between tests or using a different piece of equipment, and explain why this removes the flaw
About 2 to 4 minutes depending on whether it is a straightforward identification or an evaluation question
Try one now — from our question bank

Which type of wire is used to carry out a flame test?

Flame test questions test two different skills: memorising the standard colours, and spotting practical flaws in a described method. Practise both versions.

Practise flame test questions
Q103 marksAO1, describing a chemical test in a logical sequence

“Describe how to test a solution for a named ion using a precipitate reaction”

In the sitting we have this question in, you are asked to describe the standard test for chloride ions, which uses acidified silver nitrate solution and a colour-coded precipitate.

Every Q10 asked — find yours1 question · 1 full worked answer
1×asked

“A sample of the potassium chloride was also tested for chloride ions. Describe the test for chloride ions.”

June 2023Testing for halide ions Full worked answer inside

What it’s really asking

This is question 10(b) on the June 2023 paper. It wants the full standard method for testing halide ions: acidifying with nitric acid, adding silver nitrate, and stating the correct precipitate colour for chloride specifically.

What the sources actually showed — June 2023
Question stem

The question text stating a sample of potassium chloride, already used in the flame test earlier in the question, was also tested for chloride ions, with no additional apparatus diagram provided.

The real data and numbers, recreated in our own layout — never the exam board's own artwork or photos.
The full worked answer — June 2023
Written to: 3/3 full marks

Add a few drops of dilute nitric acid to the sample of potassium chloride solution, then add silver nitrate solution. A white precipitate forms, which confirms the presence of chloride ions.

Why this scoresThis gives all three marking points in the correct logical order: acidifying with dilute nitric acid first, adding silver nitrate second, and correctly stating a white precipitate as the result specific to chloride 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 test questions
Worked answer · PrepWise · prepwise.ukOur own writing — aimed at the real mark scheme, never copied

What the mark scheme rewarded

  • Adding dilute nitric acid to the sample before testing
  • Adding silver nitrate solution
  • Stating that a white precipitate forms, confirming chloride ions
Evidence to deploy — 5 factsScreenshot this
  1. Dilute nitric acid is added first to remove other ions (such as carbonate) that could otherwise produce a false positive precipitate
  2. Silver nitrate solution reacts with halide ions to form an insoluble silver halide precipitate
  3. Chloride ions give a white precipitate (silver chloride)
  4. Bromide ions give a cream precipitate (silver bromide)
  5. Iodide ions give a yellow precipitate (silver iodide)
PrepWise · prepwise.ukDrill these facts in the app

Traps examiners saw

  • Forgetting to acidify with nitric acid before adding silver nitrate
  • Stating the wrong precipitate colour, for example cream (bromide) or yellow (iodide) instead of white for chloride
  • Testing with sulfuric or hydrochloric acid instead of nitric acid, which would introduce more of the ion you are trying to identify

Full-mark self-check 0 of 3

The method for every 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.

  • Adding the correct acid (dilute nitric acid) before testing
  • Adding silver nitrate solution
  • Correctly stating the precipitate colour produced for the ion being tested
3 marksAll three steps given in a logical order: acidify with nitric acid, add silver nitrate, correct precipitate colour stated.
1 to 2 marksOnly some of the three steps are given, for example silver nitrate and the precipitate colour but missing the acidification step.

The steps

  1. Add a few drops of dilute nitric acid to the sample first, to remove other ions that could interfere with the test
  2. Add silver nitrate solution to the acidified sample
  3. Observe the precipitate: chloride ions give a white precipitate, bromide ions give a cream precipitate, and iodide ions give a yellow precipitate
About 3 to 4 minutes for a 3-mark descriptive test
Try one now — from our question bank

Which reagents are used to test for carbonate ions in a solution?

Ion test questions want the full sequence in order, not just the final colour. Learn nitric acid first, then silver nitrate, then the specific colour for each halide.

Practise ion test questions
Q53 marksAO1, explaining a chain of chemical events

“Explain how impurities in fossil fuels can result in acid rain”

In the sitting we have this question in, you are asked to explain the full chain from a sulfur impurity in a fossil fuel to acid rain forming.

Every Q5 asked — find yours1 question · 1 full worked answer
1×asked

“Acid rain is caused by some pollutant gases present in the atmosphere. Explain how impurities in fossil fuels can result in acid rain.”

June 2023Atmospheric pollution and acid rain Full worked answer inside

What it’s really asking

This is question 5(c) on the June 2023 paper. It wants the full chain of reasoning from a sulfur impurity in fossil fuel, through combustion to sulfur dioxide, to that gas dissolving in water to form acid rain.

What the sources actually showed — June 2023
Question stem

The question text alone, stating that acid rain is caused by pollutant gases present in the atmosphere, with no additional diagram or data provided.

The real data and numbers, recreated in our own layout — never the exam board's own artwork or photos.
The full worked answer — June 2023
Written to: 3/3 full marks

Some fossil fuels contain sulfur as an impurity. When the fuel is burned, this sulfur impurity is also burned, reacting with oxygen in the air to form sulfur dioxide gas. Sulfur dioxide then dissolves in water in rain or clouds, forming an acidic solution, which falls to the ground as acid rain.

Why this scoresThis correctly links all three marking points in order: sulfur present as an impurity, sulfur being oxidised to sulfur dioxide during combustion, and sulfur dioxide dissolving in water to form the acidic solution that is acid rain.

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 atmospheric pollution questions
Worked answer · PrepWise · prepwise.ukOur own writing — aimed at the real mark scheme, never copied

What the mark scheme rewarded

  • Identifying sulfur as the impurity present in the fossil fuel
  • Explaining that the impurity is burned (oxidised/combusted) to form sulfur dioxide
  • Explaining that sulfur dioxide dissolves in rain or cloud water to form an acidic solution
Evidence to deploy — 4 factsScreenshot this
  1. Fossil fuels such as coal and oil often contain sulfur as a natural impurity
  2. When the fuel is burned, sulfur reacts with oxygen: S + O2 -> SO2
  3. Sulfur dioxide is a pollutant gas that dissolves in atmospheric water
  4. Dissolved sulfur dioxide forms sulfurous or sulfuric acid, making rain more acidic than normal, causing damage to buildings, plants and aquatic life
PrepWise · prepwise.ukDrill these facts in the app

Traps examiners saw

  • Mentioning nitrogen oxides instead of sulfur, which is a different pollutant with a different formation route (from high engine temperatures, not fuel impurities)
  • Stopping the explanation at 'sulfur dioxide is formed' without explaining how this actually becomes acid rain
  • Saying sulfur dioxide 'mixes with' rain instead of the more precise chemistry of dissolving to form an acidic solution

Full-mark self-check 0 of 3

The method for every Q5 — 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.

  • Identifying sulfur as the impurity present in the fuel
  • Explaining that the sulfur burns (reacts with oxygen) to form sulfur dioxide
  • Explaining that sulfur dioxide dissolves in rain/cloud water to form an acidic solution (acid rain)
3 marksA complete chain: sulfur impurity, combustion to sulfur dioxide, and dissolving in water to form acid rain.
1 to 2 marksOnly part of the chain given, for example identifying sulfur dioxide is formed without explaining how it becomes acidic.

The steps

  1. State that sulfur is present as an impurity in some fossil fuels
  2. Explain that when the fuel is burned, the sulfur impurity also burns (reacts with oxygen) to form sulfur dioxide
  3. Explain that sulfur dioxide dissolves in rain water (or moisture in clouds), forming an acidic solution, which falls as acid rain
About 4 minutes for a 3-mark explanation chain
Try one now — from our question bank

Which of these gases is NOT a greenhouse gas?

This is a three-step chain question: name the impurity, explain the combustion reaction, then explain how the gas becomes acidic. Miss any one link and you lose a mark.

Practise atmospheric pollution questions
Across the sittings we analysed

The topics that keep coming up

Across the 2 sittings we have full papers for (June 2019 is no longer publicly available), these are the recurring question types and marks at stake on Paper 2.

Bond energy calculation for the energy change of a reaction2 out of 2 sittings, both times a full 4-mark multi-step calculation4 marks per sessionVery highPractise
Explaining why the rate of reaction changes as a reaction proceeds2 out of 2 sittings1 to 3 marks depending on the sittingVery highPractise
Flame tests, either identifying ions or evaluating the method2 out of 2 sittings2 to 3 marks per sessionHighPractise
Alkene addition reactions and addition polymer repeating units2 out of 2 sittings2 marks per structure, several structures per sessionHighPractise
Catalysts and reaction profiles as a 6-mark extended response1 out of 2 sittings, worth 6 marks6 marks in that sessionHighPractise
Bunsen burner combustion products and harm as a 6-mark extended response1 out of 2 sittings, worth 6 marks6 marks in that sessionHighPractise
Fermentation and fractional distillation of ethanol as a 6-mark extended response1 out of 2 sittings, worth 6 marks6 marks in that sessionHighPractise
Testing for a named ion using a precipitate (silver nitrate test)1 out of 2 sittings3 marks in that sessionMediumPractise
Explaining the viscosity trend of fractions from crude oil1 out of 2 sittings2 marks in that sessionMediumPractise
Explaining how impurities in fossil fuels cause acid rain1 out of 2 sittings3 marks in that sessionMediumPractise
0

Not the primary focus in the 2 sittings we have full papers for

The Haber process as a standalone extended response topic in these two papers · Chromatography and Rf value calculations as a standalone question in these two papers · Water treatment and life cycle assessment as standalone extended response topics in these two papers

These topics have not carried a full extended response question in the papers we analysed, but can still appear as shorter structured questions, so do not skip them entirely.

Common questions

Before you revise

Are these real mark scheme answers?

The data, tables and apparatus are described in our own words, not reproduced, and the worked answers are written entirely by us, aimed at the actual level descriptors and mark points of the real Edexcel mark schemes for each sitting. They are not copied from Edexcel'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 Pearson and Edexcel and not endorsed by them.

Why is June 2019 missing from this page?

We only build these pages from real past papers we can verify directly against Pearson's own published mark scheme. June 2019 is no longer available on Pearson's live public archive, so rather than guess at its content we have left it out entirely. We will add it if Pearson republishes it.

Will the exact same questions come up again this year?

Bond energy calculations, rate of reaction explanations, flame tests and alkene structures return in some form in every single sitting we analysed, and the 6-mark extended response often falls on catalysts, combustion or fermentation. But you cannot rely on repeats alone, since the exact substance, numbers and context change every time even when the question type is similar. Use this page to see which QUESTION TYPES keep returning and make sure you know the underlying chemistry cold, whatever the exact wording turns out to be.

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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