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: 111
Time: 180 min
Authority: QCAA
Updated: 2026-10-07

Open the official PDF Official marking notes

Key fact

This paper was set on the 2019 QCAA syllabus. From the 2026 external assessments the 2025 syllabus applies, so some content and the exam format have changed. It is still useful practice, but check the current QCAA Chemistry syllabus and QCAA's 2026 key changes before relying on it. The total marks at the top of this page are QCAA's published total for this year's papers (check the marking guide), and the time shown is two papers of 90 minutes working time. Marks and question types vary, so use QCAA's own paper.

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

QCAA sets the external assessment as more than one paper, and the number of marks, the sections and the question types differ from year to year. Open the official paper for the exact structure of this year; the marks and time shown at the top of this page are a guide only.

Pace by marks. Share your working time in proportion to the marks on offer, so a 6-mark item gets about three times the time of a 2-mark item. Flag any multiple choice item that runs long and return to it.
Use perusal time. Scan for the data-heavy items and the longest calculations or extended responses so you can plan them early.
Subject habits. Use the QCAA data booklet rather than recalling constants. For any calculation chain, label the quantity at each step so method marks are visible even if the final number is wrong, and keep a few minutes at the end to check state symbols, balancing, units and significant figures.

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.

Worked example

Question 3 (4 marks): Identify the oxidising and reducing agents in the reaction $Zn(s) + Cu^{2+}(aq) \rightarrow Zn^{2+}(aq) + Cu(s)$ , and write the two half-equations.

Oxidation half-equation: zinc loses electrons (oxidation number $0 \to +2$ ):
$Zn(s) \rightarrow Zn^{2+}(aq) + 2e^-$
Reduction half-equation: copper ions gain electrons ( $+2 \to 0$ ):
$Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)$
The species that is oxidised ( $Zn$ ) is the reducing agent; the species that is reduced ( $Cu^{2+}$ ) is the oxidising agent.

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

The 2023 sitting was two papers of 90 minutes working time each, with 10 minutes of perusal in the booklets. QCAA's 2026 timetable has two papers, each with 5 minutes of perusal and 90 minutes of working time (check the current QCAA syllabus for your sitting). Sit one paper at a time under timed conditions, pacing each by marks. Mark against the QCAA marking guide and published assessment report (linked at the top of this page), 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.

What this paper assessed

Structure and timing

Worked practice questions (exam-style)

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.

Question 3 (4 marks): Identify the oxidising and reducing agents in the reaction Zn(s)+Cu2+(aq)→Zn2+(aq)+Cu(s)Zn(s) + Cu^{2+}(aq) \rightarrow Zn^{2+}(aq) + Cu(s)Zn(s)+Cu2+(aq)→Zn2+(aq)+Cu(s), and write the two half-equations.

Common errors students made

How to use this paper

Keep going

Question 3 (4 marks): Identify the oxidising and reducing agents in the reaction $Zn(s) + Cu^{2+}(aq) \rightarrow Zn^{2+}(aq) + Cu(s)$ , and write the two half-equations.