Skill Align QCE Chemistry - Free Online Pack 0 Paper 2
An independently authored QCE Chemistry practice paper with worked answers and question-specific marking guidance.
- Paper
- Paper 2 Question and Response Book
- Reading
- 5 minutes perusal
- Writing
- 90 minutes
- Assessment
- 55 marks
The official QCAA Chemistry 2025 formula and data book is supplied separately as “snr_chemistry_25_formula_data_book.pdf”. A QCAA-approved scientific or graphics calculator may be used.
Short-response questions
Questions 1-9 are short response. Answer all parts, show calculations and justify conclusions using the supplied chemical evidence.
Question 1
8 marksFor N₂O₄(g) ⇌ 2NO₂(g), Kc = 0.212 at a stated temperature. An equilibrium mixture contains [N₂O₄] = 0.180 mol L⁻¹ and [NO₂] = 0.195 mol L⁻¹. A separate mixture at the same temperature is prepared with [N₂O₄] = 0.250 mol L⁻¹ and [NO₂] = 0.100 mol L⁻¹.
Question 2
3 marksA buffer contains H₂PO₄⁻ and HPO₄²⁻ at 25 °C.
Question 3
5 marksA cell is assembled from Fe(s)/Fe²⁺(1.0 mol L⁻¹) and Ag⁺(1.0 mol L⁻¹)/Ag(s). E°(Fe²⁺/Fe) = −0.44 V and E°(Ag⁺/Ag) = +0.80 V.
Question 4
5 marksAn unknown compound has a molecular-ion peak at m/z 102. Its IR spectrum has a strong absorption at 1740 cm⁻¹ and a band at 1200 cm⁻¹, with no broad O–H absorption. Hydrolysis produces methanol and butanoic acid.
Question 5
6 marksA polyester is made from ethane-1,2-diol and hexanedioic acid. The monomers are HO–CH₂–CH₂–OH and HOOC–(CH₂)₄–COOH.
Question 6
10 marksA pilot ammonia plant compares two settings. Setting L: 380 °C, 18 MPa, single-pass equilibrium NH₃ 36%, gas processed 82 kmol h⁻¹, compressor energy 7.2 GJ t⁻¹ NH₃. Setting H: 470 °C, 28 MPa, single-pass equilibrium NH₃ 31%, gas processed 126 kmol h⁻¹, compressor energy 11.8 GJ t⁻¹ NH₃. Both use the same iron catalyst and recycle unreacted gas. The forward reaction is exothermic and reduces four gas moles to two.
Question 7
4 marksAt pH 6.0, amino acid A has net charge +1 and amino acid B has net charge −1. Equal amounts are placed at the centre of an electrophoresis gel between a positive electrode and a negative electrode. An electric field is applied.
Question 8
9 marksA 25.00 mL reef-water sample is treated so that all acid capacity reacts 1:1 with NaOH. Standardisation gives c(NaOH) = 0.09876 mol L⁻¹. Titres are 12.42, 12.38, 12.40 and 13.06 mL. A procedural blank requires 0.20 mL NaOH.
Question 9
5 marksGlucose ferments according to C₆H₁₂O₆(aq) → 2C₂H₅OH(aq) + 2CO₂(g). A batch begins with 18.0 kg glucose and produces 7.36 kg ethanol. Use M(glucose) = 180.0 g mol⁻¹ and M(ethanol) = 46.0 g mol⁻¹.
Worked Solutions And Marking Guide
General marking principles
- Award each listed mark independently when the required chemical evidence is demonstrated.
- Accept chemically accurate equivalent wording, balanced equations and logically equivalent calculations.
- Apply follow-through where a prior numerical error is used consistently and the subsequent chemical method is correct.
- Do not award conclusions that contradict the supplied data or rely on unstated evidence.
Question 1
(a) - Uses Kc = [NO₂]²/[N₂O₄]. - Substitutes the equilibrium concentrations. - Obtains Kc ≈ 0.211, consistent with 0.212.
(b) - Calculates Qc = 0.100²/0.250 = 0.0400. - Compares Qc < Kc. - Predicts net forward reaction towards NO₂.
(c) - Recognises one gas mole on the left and two on the right. - Predicts a shift towards N₂O₄, while Kc remains unchanged.
Detailed marking criteria
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Uses Kc = [NO₂]²/[N₂O₄].
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Substitutes the equilibrium concentrations.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Obtains Kc ≈ 0.211, consistent with 0.212.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: Calculates Qc = 0.100²/0.250 = 0.0400.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: Compares Qc < Kc.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: Predicts net forward reaction towards NO₂.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part c (1 mark)
Awards one mark for accurately establishing this question-specific point: Recognises one gas mole on the left and two on the right.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part c (1 mark)
Awards one mark for accurately establishing this question-specific point: Predicts a shift towards N₂O₄, while Kc remains unchanged.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Question 2
(a) - States that H₂PO₄⁻ donates a proton to added OH⁻, forming HPO₄²⁻ and water. - Explains that removal of much of the added OH⁻ limits the pH increase.
(b) - States that consuming most of either conjugate component exceeds the buffer capacity.
Detailed marking criteria
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: States that H₂PO₄⁻ donates a proton to added OH⁻, forming HPO₄²⁻ and water.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Explains that removal of much of the added OH⁻ limits the pH increase.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: States that consuming most of either conjugate component exceeds the buffer capacity.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Question 3
(a) - Writes Fe(s) → Fe²⁺ + 2e⁻. - Writes Ag⁺ + e⁻ → Ag(s).
(b) - Writes Fe(s) + 2Ag⁺(aq) → Fe²⁺(aq) + 2Ag(s).
(c) - Calculates E°cell = 0.80 − (−0.44) = +1.24 V. - Uses the positive potential to identify the written reaction as spontaneous under standard conditions.
Detailed marking criteria
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Writes Fe(s) → Fe²⁺ + 2e⁻.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Writes Ag⁺ + e⁻ → Ag(s).
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: Writes Fe(s) + 2Ag⁺(aq) → Fe²⁺(aq) + 2Ag(s).
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part c (1 mark)
Awards one mark for accurately establishing this question-specific point: Calculates E°cell = 0.80 − (−0.44) = +1.24 V.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part c (1 mark)
Awards one mark for accurately establishing this question-specific point: Uses the positive potential to identify the written reaction as spontaneous under standard conditions.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Question 4
(a) - Identifies an ester functional group from C=O and C–O absorptions without O–H.
(b) - Identifies methyl butanoate. - Writes CH₃CH₂CH₂COOCH₃.
(c) - Relates the methanol product to the –OCH₃ side. - Relates butanoic acid to the four-carbon acyl side.
Detailed marking criteria
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Identifies an ester functional group from C=O and C–O absorptions without O–H.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: Identifies methyl butanoate.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: Writes CH₃CH₂CH₂COOCH₃.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part c (1 mark)
Awards one mark for accurately establishing this question-specific point: Relates the methanol product to the –OCH₃ side.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part c (1 mark)
Awards one mark for accurately establishing this question-specific point: Relates butanoic acid to the four-carbon acyl side.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Question 5
(a) - Gives repeat unit [–O–CH₂–CH₂–O–CO–(CH₂)₄–CO–]n. - Identifies condensation polymerisation.
(b) - States that water forms when hydroxyl and carboxyl groups form ester links. - For n of each bifunctional monomer in a linear chain, accepts approximately (2n−1) water molecules or an end-group-aware equivalent.
(c) - Links polar ester groups to dipole interactions between chains. - Relates those interactions to greater cohesion or higher softening temperature than a comparable non-polar chain.
Detailed marking criteria
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Gives repeat unit [–O–CH₂–CH₂–O–CO–(CH₂)₄–CO–]n.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Identifies condensation polymerisation.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: States that water forms when hydroxyl and carboxyl groups form ester links.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: For n of each bifunctional monomer in a linear chain, accepts approximately (2n−1) water molecules or an end-group-aware equivalent.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part c (1 mark)
Awards one mark for accurately establishing this question-specific point: Links polar ester groups to dipole interactions between chains.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part c (1 mark)
Awards one mark for accurately establishing this question-specific point: Relates those interactions to greater cohesion or higher softening temperature than a comparable non-polar chain.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Question 6
(a) - Explains that lower temperature favours exothermic ammonia formation. - Explains that higher temperature increases reaction rate. - Explains that higher pressure favours the side with fewer gas moles.
(b) - Compares 36% with 31% single-pass equilibrium NH₃. - Compares the higher 126 kmol h⁻¹ throughput with 82 kmol h⁻¹. - Compares compressor energy of 11.8 with 7.2 GJ t⁻¹ NH₃.
(c) - States that the catalyst increases rate without changing equilibrium composition. - States that recycle improves overall reactant utilisation after product removal.
(d) - Recommends Setting L for the stated energy constraint. - Justifies the recommendation using its lower compression energy together with its higher single-pass equilibrium percentage, while acknowledging lower throughput.
Detailed marking criteria
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Explains that lower temperature favours exothermic ammonia formation.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Explains that higher temperature increases reaction rate.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Explains that higher pressure favours the side with fewer gas moles.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: Compares 36% with 31% single-pass equilibrium NH₃.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: Compares the higher 126 kmol h⁻¹ throughput with 82 kmol h⁻¹.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: Compares compressor energy of 11.8 with 7.2 GJ t⁻¹ NH₃.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part c (1 mark)
Awards one mark for accurately establishing this question-specific point: States that the catalyst increases rate without changing equilibrium composition.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part c (1 mark)
Awards one mark for accurately establishing this question-specific point: States that recycle improves overall reactant utilisation after product removal.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part d (1 mark)
Awards one mark for accurately establishing this question-specific point: Recommends Setting L for the stated energy constraint.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part d (1 mark)
Awards one mark for accurately establishing this question-specific point: Justifies the recommendation using its lower compression energy together with its higher single-pass equilibrium percentage, while acknowledging lower throughput.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Question 7
(a) - Predicts A migrates towards the negative electrode. - Predicts B migrates towards the positive electrode.
(b) - Relates direction to attraction between opposite charges. - Recognises that the stated pH produces different net ionic forms.
Detailed marking criteria
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Predicts A migrates towards the negative electrode.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Predicts B migrates towards the positive electrode.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: Relates direction to attraction between opposite charges.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: Recognises that the stated pH produces different net ionic forms.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Question 8
(a) - Rejects 13.06 mL as discordant. - Calculates mean concordant titre = 12.40 mL.
(b) - Subtracts the 0.20 mL blank to obtain 12.20 mL. - Calculates n = 0.09876 × 0.01220 = 1.205 × 10⁻³ mol.
(c) - Divides by 0.02500 L. - Obtains 0.04820 mol L⁻¹.
(d) - Explains that the blank corrects titrant consumed by reagents/apparatus rather than sample acid. - Explains that concordance supports precision and identifies an anomalous titre.
(e) - Explains that the titration measures combined acid-neutralising capacity and does not identify individual acid species.
Detailed marking criteria
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Rejects 13.06 mL as discordant.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Calculates mean concordant titre = 12.40 mL.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: Subtracts the 0.20 mL blank to obtain 12.20 mL.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: Calculates n = 0.09876 × 0.01220 = 1.205 × 10⁻³ mol.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part c (1 mark)
Awards one mark for accurately establishing this question-specific point: Divides by 0.02500 L.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part c (1 mark)
Awards one mark for accurately establishing this question-specific point: Obtains 0.04820 mol L⁻¹.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part d (1 mark)
Awards one mark for accurately establishing this question-specific point: Explains that the blank corrects titrant consumed by reagents/apparatus rather than sample acid.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part d (1 mark)
Awards one mark for accurately establishing this question-specific point: Explains that concordance supports precision and identifies an anomalous titre.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part e (1 mark)
Awards one mark for accurately establishing this question-specific point: Explains that the titration measures combined acid-neutralising capacity and does not identify individual acid species.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Question 9
(a) - Calculates 100 mol glucose. - Uses the 1:2 ratio to obtain 200 mol ethanol. - Obtains 9.20 kg theoretical ethanol.
(b) - Calculates 7.36/9.20 × 100 = 80.0%.
(c) - Identifies incomplete fermentation, competing microbial reactions or ethanol loss during separation as a plausible cause.
Detailed marking criteria
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Calculates 100 mol glucose.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Uses the 1:2 ratio to obtain 200 mol ethanol.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part a (1 mark)
Awards one mark for accurately establishing this question-specific point: Obtains 9.20 kg theoretical ethanol.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part b (1 mark)
Awards one mark for accurately establishing this question-specific point: Calculates 7.36/9.20 × 100 = 80.0%.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Part c (1 mark)
Awards one mark for accurately establishing this question-specific point: Identifies incomplete fermentation, competing microbial reactions or ethanol loss during separation as a plausible cause.
Acceptable alternatives: Accept chemically equivalent wording or a logically equivalent calculation.
Do not credit by itself: Do not award an unsupported conclusion or a response that contradicts the supplied stimulus.
Diagnostic Checklist
| Topic | Questions | Marks | Marks Lost | Action |
|---|---|---|---|---|
| Unit 3 Topic 1 - Chemical equilibrium systems | Q1, Q2, Q8 | 20 | ___ | Review equilibrium, Kc, Q, Ksp, acids, bases, buffers, indicators and volumetric analysis. |
| Unit 3 Topic 2 - Oxidation and reduction | Q3 | 5 | ___ | Review oxidation states, half-equations, galvanic and electrolytic cells, cell potentials and electrolysis calculations. |
| Unit 4 Topic 1 - Properties and structure of organic materials | Q4, Q7 | 9 | ___ | Review organic structure, nomenclature, isomerism, reactions, properties, spectra, chromatography and electrophoresis. |
| Unit 4 Topic 2 - Chemical synthesis and design | Q5, Q6, Q9 | 21 | ___ | Review Haber and contact processes, ethanol production, fuel cells, yields, polymers, peptides and carbohydrates. |