QCE Chemistry 2023

Walkthrough of the 2023 QCE chemistry exam: what it assessed, strategy tips, and the common errors flagged in the official marker report.

Marks: 60
Time: 120 min
Authority: QCAA
Updated: 2026-05-29

Open the official PDF ->Official marking notes

What this paper assessed

The QCE Chemistry external assessment (Paper, worth 50% of the Unit 3 & 4 result) covered the Unit 3 and Unit 4 content of the QCAA syllabus:

Unit 3 - Equilibrium, acids and redox reactions: chemical equilibrium and $K_{eq}$ , Le Chatelier's principle, acid-base concepts ( $pH$ , $pK_a$ , buffers, titration), and oxidation-reduction (half-equations, electrochemical cells, $E^\circ$ ).
Unit 4 - Structure, synthesis and design: properties and reactions of organic functional groups, reaction pathways and synthesis, polymers, and instrumental analysis (IR, NMR, mass spectrometry).

The 2023 paper was calculation-heavy, with items blending theory and practical technique. Markers expected balanced equations with state symbols, the chosen relationship stated before the arithmetic, and answers reported to appropriate significant figures.

Structure and timing

The paper is 60 marks in 120 minutes, plus 5 minutes perusal time.

Section 1 - multiple choice (~20 marks): target ~30 minutes (about 1.5 min/question).
Section 2 - short response (~40 marks): target ~90 minutes at roughly 2.25 minutes per mark.

A 4-mark calculation deserves ~9 minutes; a 6-mark explain/evaluate ~13 minutes. Reserve ~10 minutes at the end to check units, significant figures and state symbols. Use perusal time to scan the data-based and multi-step calculation items.

Worked practice questions (exam-style)

Worked example

Question 1 (5 marks): A 20.0 mL sample of hydrochloric acid is exactly neutralised by 18.5 mL of 0.100 mol/L sodium carbonate solution. Calculate the concentration of the hydrochloric acid.

Balanced equation (with state symbols):

2HCl(aq) + Na_2CO_3(aq) \rightarrow 2NaCl(aq) + H_2O(l) + CO_2(g)

Moles of sodium carbonate:

n(Na_2CO_3) = c \times V = 0.100 \times 0.0185 = 1.85 \times 10^{-3}\ \text{mol}

Mole ratio is $2\,HCl : 1\,Na_2CO_3$ , so:

n(HCl) = 2 \times 1.85 \times 10^{-3} = 3.70 \times 10^{-3}\ \text{mol}

Concentration:

c(HCl) = \frac{n}{V} = \frac{3.70 \times 10^{-3}}{0.0200} = 0.185\ \text{mol/L}\ (3\ \text{s.f.})

Worked example

Question 2 (5 marks): For the equilibrium $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$ , $\Delta H = -198\ \text{kJ/mol}$ . Predict and explain, using Le Chatelier's principle, the effect on the yield of $SO_3$ of (a) increasing pressure and (b) increasing temperature.

(a) Increasing pressure: there are 3 mol of gas on the left and 2 mol on the right. The system partially opposes the disturbance by shifting toward fewer gas moles - to the right - increasing the yield of $SO_3$ .
(b) Increasing temperature: the forward reaction is exothermic, so adding heat favours the reverse (endothermic) direction. The system shifts left, decreasing the yield of $SO_3$ and decreasing $K_{eq}$ for the forward reaction.
Synthesis link: industrially (Contact process) this is a compromise - moderate temperature keeps the rate workable despite reducing equilibrium yield, with a catalyst ( $V_2O_5$ ) used to raise the rate without shifting the position of equilibrium.

Common errors students made

Recurring errors in QCE Chemistry responses include:

Omitting state symbols, especially in ionic and redox equations.
Mixing up the oxidising and reducing agents (the agent that is oxidised is the reducing agent).
Quoting a Le Chatelier shift without naming the driver (concentration, pressure or temperature) and direction.
Drawing energy profile diagrams without labelling the activation energy or $\Delta H$ .

Add these subject-specific traps:

Careless mole-ratio errors and failing to identify the limiting reagent in multi-step stoichiometry.
Reporting answers to the wrong number of significant figures - match the least precise datum.
Confusing acid strength (degree of ionisation) with concentration.
Misreading the QCAA cognition verb - giving a description where "evaluate" or "predict and justify" is required.

How to use this paper

Sit Section 1 in 30 minutes and Section 2 in 90 minutes under timed conditions. Mark against the QCAA marking guide and published assessment report (linked in the frontmatter), which show where method and reasoning marks sit. Re-attempt every integrated calculation after a 48-hour gap, writing the balanced equation and stated relationship before any arithmetic. Build a one-page checklist of recurring errors (state symbols, significant figures, mole ratios, redox agent identification) and tick it against every numerical item in your next sitting.

Use this paper well

Sit the paper under exam conditions (120 minutes, 60 marks).
Mark yourself against the official QCAA marking notes.
Compare against the Chemistry hub to find the syllabus dot points this paper tested.