§-Past paper

QLDChemistry2022

QCE Chemistry 2022

Walkthrough of the 2022 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 QCAA Chemistry external assessment (worth 50% of the subject) covers Units 3 and 4. The 2022 paper assessed:

Unit 3 - Equilibrium, acids and redox reactions: chemical equilibrium and $K_{eq}$ , Le Chatelier's principle, acid-base reactions (pH, $K_a$ , buffers, titrations), and oxidation-reduction including electrochemical cells and $E^\circ$ values.
Unit 4 - Structure, synthesis and design: properties of organic compounds, functional groups and reaction pathways, organic synthesis, polymers, and macromolecules/materials design.

Items required balanced equations with state symbols, worked calculations that show the chosen relationship before the arithmetic, and the ability to link practical technique to chemical theory. The paper rewarded clearly set-out multi-step reasoning over unsupported final answers.

Structure and timing

60 marks in 120 minutes (about 2 min/mark), with perusal time and the QCAA data booklet (periodic table, constants, $E^\circ$ table) available:

Section 1 - Multiple choice: about 20 marks. Budget ~30 minutes.
Section 2 - Short and extended response: about 40 marks. Budget ~85 minutes, leaving ~5 minutes to check.

Use the 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 check significant figures against the data given.

Worked practice questions (exam-style)

Worked example

Question 1 (5 marks): Titration calculation

A $20.00\ \text{mL}$ sample of hydrochloric acid is titrated against $0.150\ \text{mol L}^{-1}$ NaOH, requiring $24.60\ \text{mL}$ to reach the endpoint. Calculate the concentration of the HCl.

Solution. The neutralisation is $\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}$ (1 mark), a 1:1 mole ratio.

n(\text{NaOH}) = c \times V = 0.150 \times 0.02460 = 3.69 \times 10^{-3}\ \text{mol}

So $n(\text{HCl}) = 3.69 \times 10^{-3}\ \text{mol}$ (1 mark).

c(\text{HCl}) = \frac{n}{V} = \frac{3.69 \times 10^{-3}}{0.02000} = 0.1845\ \text{mol L}^{-1} \approx 0.185\ \text{mol L}^{-1}

(2 marks for working, 1 mark for the answer to 3 significant figures with units.)

Worked example

Question 2 (4 marks): Le Chatelier's principle

For the equilibrium $2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g)$ , $\Delta H < 0$ . Predict and explain the effect on the equilibrium yield of $\text{SO}_3$ of (a) increasing pressure and (b) increasing temperature.

Solution.
(a) Increasing pressure shifts the system toward the side with fewer gas moles. There are 3 mol of gas on the left and 2 mol on the right, so the equilibrium shifts right, increasing the yield of $\text{SO}_3$ , to partially oppose the increase in pressure (2 marks).
(b) The forward reaction is exothermic. Increasing temperature favours the endothermic (reverse) direction to oppose the added thermal energy, shifting the equilibrium left and decreasing the $\text{SO}_3$ yield (2 marks). Full marks require naming the driver (opposing the imposed change), not just stating the direction.

Worked example

Question 3 (6 marks): Redox and electrochemical cells

A galvanic cell is constructed from a zinc half-cell and a copper half-cell. Given $E^\circ(\text{Cu}^{2+}/\text{Cu}) = +0.34\ \text{V}$ and $E^\circ(\text{Zn}^{2+}/\text{Zn}) = -0.76\ \text{V}$ , identify the anode and cathode, write the half-equations and overall equation, and calculate the cell potential.

Solution. The half-cell with the lower (more negative) reduction potential is oxidised, so zinc is the anode (oxidation) and copper is the cathode (reduction) - 1 mark.

Half-equations:

\text{Anode (oxidation): } \text{Zn}(s) \rightarrow \text{Zn}^{2+}(aq) + 2e^-

\text{Cathode (reduction): } \text{Cu}^{2+}(aq) + 2e^- \rightarrow \text{Cu}(s)

(2 marks for both, with state symbols.) Overall:

\text{Zn}(s) + \text{Cu}^{2+}(aq) \rightarrow \text{Zn}^{2+}(aq) + \text{Cu}(s)

(1 mark.) Cell potential:

E^\circ_{\text{cell}} = E^\circ_{\text{cathode}} - E^\circ_{\text{anode}} = 0.34 - (-0.76) = +1.10\ \text{V}

(2 marks.) The positive value confirms the reaction is spontaneous as written.

Common errors students made

The 2022 QCAA marker report flagged that students lost marks by omitting state symbols, mixing up oxidising and reducing agents, and quoting Le Chatelier shifts without naming the driver; energy diagrams were often unlabelled or drawn without an activation-energy marker. Add these recurring traps:

Significant figures and units dropped at the final step or carried inconsistently through a calculation chain.
Mole-ratio errors - assuming 1:1 when the balanced equation is not (e.g. diprotic acids, or the $2:1:2$ ratio in the $\text{SO}_2$ equilibrium).
Sign errors in $E^\circ_{\text{cell}}$ - reversing cathode/anode or mishandling the negative anode potential.
Ambiguous organic structures - missing hydrogens, unclear bonds, or drawing an ester where a carboxylic acid is required.

How to use this paper

Sit Section 1 in 30 minutes, then Section 2 in ~85 minutes with only the QCAA data booklet. Mark against the official QCAA marking guide and marker report (linked in the frontmatter above) to see exactly where method marks fall. Rebuild every multi-step calculation that lost more than half its marks, writing one labelled line per quantity. Drill the functional-group/reaction-pathway map and the $E^\circ$ procedure until cell potentials and half-equations are automatic, then practise stating the Le Chatelier driver explicitly in words.

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.

What this paper assessed

Structure and timing

Worked practice questions (exam-style)

Common errors students made

How to use this paper

Use this paper well

Keep going