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2026 QCE Chemistry exam: What to learn from last year's mistakes
Hi all, in preparation for the upcoming exam, here's what to learn from last year's mistakes.
2025 exam median and average: not stated in QCAA's report.
9,335 students completed Units 3 and 4. The external exam was worth 110 raw marks and contributed 50% of the subject result.
The lowest multiple-choice result was 30.65% correct on protein structure. I've gone through last year's report and marking guide. These are the questions I'd redo.
The percentages are published results. QCAA doesn't give written-question averages, so those sections explain where an answer misses the marking criteria, not how many students made each mistake.
Paper 1, Q9: Protein structure
1 mark. 30.65% correct.
Where students went wrong: 36.34% chose secondary structure and 27.20% chose tertiary structure.
What they should have done: Choose quaternary structure. The question described multiple polypeptide chains. Secondary structure is local folding, such as alpha helices. Tertiary structure is the overall shape of one chain. Quaternary structure involves multiple chains associating.
Paper 1, Q12: Dichromate colour change
1 mark. 32.42% correct.
Where students went wrong: 27.79% chose red to yellow and 24.99% chose pink to colourless.
What they should have done: Choose orange to green. The reagent was acidified potassium dichromate(VI), used to oxidise 1-propanol to propanoic acid. Orange dichromate(VI) is reduced to green chromium(III). Check the reagent before using a colour change you've memorised.
Paper 1, Q27: Aqueous versus molten NaCl
4 marks.
Where an answer loses marks: Giving the same cathode product for concentrated aqueous sodium chloride and molten sodium chloride. QCAA specifically flagged electrolysis under different conditions for improvement.
What you needed: Hydrogen gas at the cathode in concentrated aqueous NaCl, but liquid sodium in molten NaCl. Water can be reduced in the aqueous solution. There is no water in the molten salt.
The oxidation half-equations are:
Concentrated solution: 2Cl⁻(aq) → Cl₂(g) + 2e⁻
Molten salt: 2Cl⁻(l) → Cl₂(g) + 2e⁻
Each cathode product and each half-equation earned one mark. Include the charges and states.
Paper 1, Q28c: Stronger base, same acid volume
4 marks.
Where an answer loses marks: Assuming a stronger base needs more acid when the amount of base being neutralised hasn't changed.
What you needed: The equivalence-point pH increases to 7 for the strong acid–strong base titration in the question. The HCl volume stays the same because the moles of base are unchanged. Each prediction and its explanation earned a separate mark.
Paper 2, Q4a: Acid dissociation
2 marks.
Where an answer loses marks: Showing both acids dissociating completely. QCAA specifically flagged incorrect reaction arrows.
What you needed:
HOCl(aq) ⇌ H⁺(aq) + OCl⁻(aq)
HCl(aq) → H⁺(aq) + Cl⁻(aq)
HOCl is weak and only partially dissociates. HCl is strong and dissociates essentially completely in water. The arrows show the difference being assessed.
For 2026, green chemistry principles, atom economy and molecular manufacturing have moved to internal assessment. Don't make the old green chemistry question an external revision priority. Perusal time is five minutes, and the updated formula booklet includes the reaction pathway diagram.
Use the 2025 report alongside the official marking guide. 2026 syllabus changes.
Figures and criteria: QCAA. Explanations paraphrased from its materials, © State of Queensland (QCAA) 2025–2026, CC BY 4.0.
Use the Chemistry hub and past papers and marking guides alongside this.
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