QCE Chemistry: equilibrium, redox and organic chemistry, and how the external exam is built

How QCE Chemistry is marked

Details are from the QCAA Chemistry syllabus (2025 version 1.3, January 2026), checked on 11 November 2026. Units 1 and 2 are reported only as satisfactory or unsatisfactory.

Internal marks and the external result are added to give a mark out of 100. QCAA subject experts then set the A to E cut-offs, and the exam does not change your internal marks. Chemistry is one of the subjects where the external exam counts for half the result, whereas in most other General subjects it counts for a quarter.

The external exam and the 2026 changes

The two papers both assess Units 3 and 4, with multiple choice, short answers, extended responses, calculations and unseen stimulus such as graphs and data tables. The QCAA formula and data book is supplied. The QCAA lists four changes that matter for 2026: perusal time is down from 10 to 5 minutes; the calculator conditions are clarified; the reaction pathway diagram is now in the formula and data book, which has been updated; and green chemistry principles, atom economy and molecular manufacturing are now assessed in the internal assessments, not the external exam.

The 2026 external assessments run from Monday 26 October to Tuesday 17 November 2026. No 2027 timetable was on the QCAA site when this page was checked. Past external assessments and marking guides for each year since 2020 are on the Chemistry syllabus page.

What Units 3 and 4 cover

• Unit 3, Equilibrium, acids and redox reactions. Chemical equilibrium (25 hours): the factors that shift equilibrium, equilibrium constants, properties of acids and bases, dissociation constants, indicators and volumetric analysis. Oxidation and reduction (20 hours): redox reactions, galvanic cells, standard electrode potentials and electrolytic cells.
• Unit 4, Structure, synthesis and design. Properties and structure of organic materials (30 hours): the structure of organic compounds, physical properties, reactions and reaction pathways, analytical techniques. Chemical synthesis and design (15 hours).

Our Organic Chemistry course and Reaction Kinetics course support Unit 4 and the rates ideas behind equilibrium, and the pH Calculator and Titration Lab suit the acid and base work.

Worked examples

An equilibrium constant

At equilibrium in a rigid vessel the concentrations in 2SO₂ + O₂ ⇌ 2SO₃ are [SO₂] = 0.20, [O₂] = 0.10 and [SO₃] = 0.40 mol L⁻¹. Products go on top, raised to their coefficients:

The constant has units, here L mol⁻¹, and it only changes with temperature. Adding more O₂ shifts the position to the right but leaves K_(c) at 40.

A titration

A 25.00 mL sample of NaOH needs a mean titre of 18.40 mL of 0.100 mol L⁻¹ HCl to reach the endpoint. The 1 : 1 reaction gives n(HCl) = 0.100 × 0.01840 = 1.84 × 10⁻³ mol, so:

Mean titre means concordant titres only: discard any outlier more than 0.10 mL away from the others.

A weak acid and a cell

For 0.10 mol L⁻¹ ethanoic acid with Kₐ = 1.8 × 10⁻⁵, assuming little dissociation, [H⁺] = √(Kₐ × c) = 1.3 × 10⁻³ mol L⁻¹ and the pH is about 2.87. For a zinc and copper galvanic cell, the standard cell potential is E°(cathode) − E°(anode) = 0.34 − (−0.76) = 1.10 V, taking both values from the data book.

Now name or write an organic formula, then press Mark:

Using the daily papers as a practice exam

Each daily paper is 8 original questions worth 25 to 35 marks, a short timed paper of 35 to 45 minutes, not a QCAA external exam. Queensland has no state trials, so full-length practice means the QCAA's past exams.

• On the Year 12 Chemistry paper, acids, bases and buffers, electrode potentials, organic synthesis, carbonyl compounds and NMR and spectroscopy fit Units 3 and 4.
• On the Year 11 paper, chemical equilibria, redox, alcohols, and alkanes and alkenes are a good match.
• Skip transition metals, Born-Haber cycles and entropy, and Kp questions: they go beyond the QCE subject matter.

Grades, results and ATAR

Each result is reported as A to E alongside the mark out of 100. The 2026 results are released from 9:00 am on Wednesday 16 December 2026, and QTAC releases ATARs on 18 December 2026. The ATAR uses your five best scaled results.

Exam answers

Answers and a worked mark scheme for the daily paper come with today's paper once it's marked. The QCAA publishes its own marking guides for its past exams; we do not reproduce them.

Common mistakes in QCE Chemistry

• Writing K_(c) with the reactants on top. Products over reactants, each to the power of its coefficient.
• Using total volume wrongly in titrations. Convert mL to L before dividing, and use the aliquot volume for the unknown.
• Reversing the cell. The more positive electrode potential is the cathode in a galvanic cell; in an electrolytic cell it is reversed by the power supply.
• Naming from the wrong chain. Find the longest chain containing the functional group before numbering.

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