OCR AS Level · Analysis & Prediction

2025 OCR AS Level Chemistry B (Salters) - H033 Past Paper: Analysis & Answers

June 2025 AS Chemistry B (Salters) H033: two 70-mark, 90-minute papers (Foundations of chemistry; Chemistry in depth). Heavy on quantitative work (amount of substance, energetics, equilibrium constants) and practical skills (about 17 marks), with a balanced mix of organic, inorganic and physical chemistry. Two 6-mark level-of-response questions carry the highest-tariff reasoning.

Updated: 11 Nov 2026

Analysis Sample paper

Difficulty 3.0/5

Total marks

140

Duration

180 mins

Most tested

Practical skills and amount-of-substance calculations

Paper breakdown

H033/01 Foundations of chemistry: 70 marks · 90 minsH033/02 Chemistry in depth: 70 marks · 90 mins

Top chapters

Development of practical skills in chemistry · 17 marksFormulae, equations and amount of substance (Developing fuels (DF)) · 11 marksRedox · 11 marks

Difficulty verdict

Taken together, the two June 2025 papers sit at a medium level. Paper 1 opens with 20 accessible multiple-choice marks and then moves through short structured questions. Paper 2 is deeper, with two 6-mark level-of-response questions and a long equilibrium question that rewards careful, multi-step calculation. Most marks are available to a candidate who has secure fundamentals and writes clear working.

Where the marks are

Practical skills and data handling (about 17 marks): recrystallisation, preparing a salt, graph plotting with an anomaly, titration technique and justifying apparatus choices. This is the single largest block.
Amount of substance (about 28 marks across three chapters): atom economy, gas volumes, titrations, percentage composition, empirical formula of a hydrate and relative atomic mass.
Redox and halogen chemistry (about 11 marks): electrolysis, half-equations, oxidation states and displacement.
Energetics, kinetics and equilibria (about 25 marks): calorimetry, catalysis with an energy profile and Boltzmann distribution, and a full Kc calculation with a Le Chatelier argument.

Pitfalls to avoid

The mark scheme repeatedly signals where candidates slip. These points are inferred from the marking guidance, because no examiner report was supplied.

Saying that more bonds are made than broken, or that energy is needed to make bonds, instead of comparing the energy released with the energy absorbed.
Writing that equilibrium means the reactions have stopped, instead of equal rates.
Giving too many significant figures where an appropriate number is requested, or leaving out the minus sign on an enthalpy change.
Putting the acid in excess when preparing a salt from a carbonate, which loses the filtration mark.
Drawing curly arrows that do not start on a bond or end on an atom.

Strategy

Do the multiple-choice section quickly (about 25 minutes) so that the calculations get proper time. Always write out each step: most calculation questions award method marks, and ECF protects you after an early slip. For level-of-response questions, plan both parts (for example, a calculation and an explanation of an error) before writing, because the level is set by coverage and the communication quality sets the mark within the level. For comment-on-a-statement questions, say explicitly whether the statement is right, wrong or partly right, and then give the correct chemistry.

Prediction

Topics that appeared lightly this series but have historically carried more marks, such as polymers, modern analytical techniques (IR, NMR, mass spectrometry) and inorganic chemistry from the sea, are good candidates to return. Energetics, equilibria and amount of substance are reliable high-mark topics, so keep them as your core revision.

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Charts

Marks by chapter

See where the marks were concentrated so revision time goes to the highest-value topics.

Question type mix

Compare the mark share of each paper section and question type.

Multiple choice20 marks · 20 questions
Calculation23 marks · 10 questions
Level-of-response extended answer12 marks · 2 questions
Diagram, graph, mechanism or structure drawing16 marks · 5 questions
Describe, explain or comment (short/medium)31 marks · 14 questions
Short recall, naming or equation writing38 marks · 30 questions

Mark accessibility

Estimate which marks were basic, mid-level, or high-difficulty.

71%within easy or medium reach

easy: 45 marksmedium: 55 markshard: 40 marks

Difficulty trend

Compare difficulty across recent years.

Command word frequency

Spot common command words so answers match the expected response style.

Skill weighting

Shows the skill mix this paper tested most heavily.

Study ROI

Higher bubbles carry more marks; bubbles further left are easier. Start with the topics that sit high and to the left.

Amount of substance calculations (moles, gas volume, titration, empirical formula)

28 marks · Difficulty 2.5

Organic functional groups, reactions and isomerism

22 marks · Difficulty 2.5

Practical skills (purification, salt preparation, graphs, titration)

17 marks · Difficulty 2.5

Redox and halogens

11 marks · Difficulty 2.5

Equilibria and Kc calculations

9 marks · Difficulty 3

Energetics and calorimetry

8 marks · Difficulty 3

Kinetics and catalysis (energy profile, Boltzmann)

8 marks · Difficulty 3.5

Radical substitution and ozone depletion

8 marks · Difficulty 2.5

Atomic structure and ionisation enthalpy

7 marks · Difficulty 2

Time vs marks

Compare marks with suggested time allocation to plan exam pacing.

marksmins

Next-year prediction

Topics worth watching next year, and why. These are informed guesses from past papers, not a forecast.

Formulae, equations and amount of substance

It is the largest recurring block of marks across all series and underpins every calculation question.

Energetics (enthalpy changes, Hess cycles, bond enthalpies)

It is a consistent high-mark topic every year; only calorimetry appeared this time, so cycle and bond enthalpy calculations are still to come.

Equilibria and Kc

It is regularly worth 6 to 13 marks and is a core quantitative topic. Expect Le Chatelier and Kc again.

Modern analytical techniques (IR, NMR, mass spectrometry)

Earlier series gave 8 to 13 marks, but only 1 mark appeared this time, so a larger spectroscopy question is likely to return.

Kinetics (rate, Arrhenius, Boltzmann)

Catalysis was tested this series. Rate equation and Arrhenius analysis have not appeared recently.

Polymers

There were no polymer marks this series after 1 to 6 marks in earlier ones, so addition and condensation polymers are due.

Inorganic chemistry and the periodic table (Elements from the sea)

Only 2 marks this series, against 14 to 15 marks in the two previous summers, so halogens and halide tests could carry more marks next time.

Bonding and structure

Marks fell to 4 after 14 in a previous series, so shapes, polarity and intermolecular forces are due to rise.

Cumulative marks ladder

The line is your running mark total question by question; dashed lines are the estimated grade boundaries, taken from the table below when this year's are known. See which question the line crosses your target grade at, so you know how far you must answer cleanly and which questions decide a band.

Topic-year heatmap

Compare topic weight by year to spot recurring and returning areas.

Jun 2022

Jun 2023

Jun 2024

Jun 2025

Energetics

Formulae, equations and amount of substance (Elements of life (EL))

Formulae, equations and amount of substance (Developing fuels (DF))

Equilibria

Inorganic chemistry and the periodic table (Elements from the sea (ES))

Modern analytical techniques (What’s in a medicine? (WM))

Inorganic chemistry and the periodic table (Elements of life (EL))

Bonding and structure (Developing fuels (DF))

Kinetics (Developing fuels (DF))

Atomic structure

Examiner insights

AI-inferred

Common pitfalls

Stating that more bonds are made than broken, or that energy is required to make bonds, instead of comparing energy released on bond making with energy absorbed on bond breaking.
Giving an answer to the wrong number of significant figures, or omitting the negative sign for an exothermic enthalpy change, where the mark scheme demands them.
Using excess acid rather than excess solid when preparing a salt from a carbonate, and evaporating to dryness instead of to the crystallisation point.
Curly arrows that do not begin on a bond or end on an atom, and missing charges on intermediates.
Quoting atomic size or electronegativity instead of the number of electrons when explaining intermolecular forces in the halogenoalkanes.

Misconceptions

At equilibrium the forward and backward reactions have stopped (they continue at equal rates).
Hydrogen ions are discharged at the cathode in electrolysis of a neutral solution, rather than water being reduced to hydrogen and hydroxide ions.
Concentrated sulfuric acid gives pure hydrogen iodide with an iodide, rather than being reduced further to give impurities such as H2S and I2.
Ozone breakdown is linked to respiratory problems or photochemical smog, rather than to increased UV reaching the surface.

Where marks are lost

Extended calculation plus explanation questions (the two 6-mark level-of-response items), where structure and the second explanatory strand are often missing.
Method marks in multi-step calculations when working is not shown, and ECF cannot be awarded.
Evaluating experimental results and statements (comment on a student's claim) without saying clearly whether it is correct.
Practical procedure details such as where soluble and insoluble impurities are removed, and the justification for apparatus choice.

Estimated grade boundary

Updated: 11 Nov 2026

Source: OCR

Grade	Mark	Percentage
A	94/140	67%
B	79/140	56%
C	65/140	46%
D	51/140	36%
E	37/140	26%

Official grade boundaries published by OCR.

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