Skill Align HSC Chemistry - Free Online Pack 0
A complete original HSC Chemistry practice paper built around the coastal desalination and water-quality monitoring context.
- Paper
- Question and Answer Book
- Reading
- 5 minutes
- Writing
- 3 hours
- Assessment
- 100 marks
A Skill Align-authored Chemistry Formulae Sheet, Data Sheet and Periodic Table is included at the back of the candidate paper. The current official NESA reference sheet is also linked in the product resources. NESA-approved calculators may be used.
Section I: Objective-response questions
Attempt Questions 1-20. Allow about 35 minutes for this section. Select the alternative A, B, C or D that best answers each question.
Question 1
1 mark- Kc = [NO₂]²/[N₂O₄]
- Kc = [N₂O₄]/[NO₂]²
- Kc = [NO₂]/[N₂O₄]
- Kc is obtained by adding all equilibrium concentrations.
Question 2
1 mark- CH₃COOH
- H₃O⁺
- CH₃COO⁻
- OH⁻
Question 3
1 mark- ethanoic acid
- 1-bromopropane
- propanone
- poly(propene)
Question 4
1 mark- Measure the untreated sample once and assign all absorbance to nitrate.
- Remove the reagent blank because natural colour is part of the nitrate signal.
- Use a flame test as the quantitative result and omit calibration.
- Clarify every sample and standard consistently, use a sample-matrix blank, and verify nitrate recovery with a matrix spike.
Question 5
1 mark- pH = 11.40, because every dilute solution is treated as basic
- pH = 2.60, because [H₃O⁺] = 2.5 × 10⁻³ mol L⁻¹ before applying −log₁₀
- pH = 2.5 × 10⁻³, because concentration and pH have the same numerical value
- pH = 7.00, because water is the solvent
Question 6
1 mark- Use dilute aqueous NaOH and heat; aqueous OH⁻ replaces Br in a nucleophilic substitution.
- Keep ethanolic NaOH because elimination to propene is the required route to the alcohol.
- Use concentrated sulfuric acid because dehydration directly replaces Br with OH.
- Add bromine water because oxidation of the carbon-halogen bond forms the alcohol.
Question 7
1 mark- 6.5 mg L⁻¹ nitrate, because only the lower concentration is adjusted
- 8.0 mg L⁻¹ nitrate, because every sample is rounded to the nearest upper standard
- 0.35 mg L⁻¹ nitrate, because absorbance and concentration have the same numerical value
- 7.0 mg L⁻¹ nitrate, because 0.35 lies halfway between the two neighbouring standard signals
Question 8
1 mark- The net reaction proceeds in the opposite direction until the current quotient becomes zero.
- The system is already at equilibrium because both the current quotient and Kc are positive.
- The net reaction proceeds towards NO₂ until Q equals Kc.
- A catalyst must be added before the equilibrium composition can change.
Question 9
1 mark- 1-bromopropane
- propan-1-ol
- methyl propanoate
- propene
Question 10
1 mark- Adding distilled water produces no visible change, which uniquely identifies the ion.
- Adding aqueous BaCl₂ gives a white BaSO₄ precipitate.
- Heating to dryness identifies the ion solely from the mass of residue.
- Any colourless solution confirms the ion without a reagent blank.
Question 11
1 mark- The equilibrium shifts towards NO₂.
- The equilibrium shifts away from NO₂.
- Kc increases because a catalyst-like stress has been applied.
- Both forward and reverse reactions stop until the original condition is restored.
Question 12
1 mark- The acid with the smaller Ka is stronger because it ionises less.
- Both acids have identical strength because each is weak.
- Acid strength can be inferred only from the initial concentration, not Ka.
- Methanoic acid has the greater tendency to ionise and is the stronger acid.
Question 13
1 mark- 1-bromopropane
- poly(propene)
- propan-1-ol
- ethanol
Question 14
1 mark- Qsp > Ksp, so AgCl precipitates until saturation is restored.
- Qsp equals Ksp, so the ion concentrations cannot change.
- Qsp is irrelevant because precipitation reactions are irreversible.
- The salt must dissolve completely because both ions are present.
Question 15
1 mark- 0.060 mol CH₃COOH and 0.040 mol CH₃COO⁻; the base-to-acid ratio decreases
- 0.050 mol of each component because a buffer prevents reaction
- 0.040 mol CH₃COOH and 0.060 mol CH₃COO⁻; the base-to-acid ratio increases
- 0.040 mol of each component because OH⁻ consumes both components equally
Question 16
1 mark- Every covalent bond in the polymer breaks when the material softens.
- methyl side groups reduce close packing, producing a tough, flexible thermoplastic
- Polymer properties are independent of chain structure and intermolecular forces.
- The repeat unit is held together only by intermolecular forces, not covalent bonds.
Question 17
1 mark- The equilibrium percentage of NO₂ increases from 45% at 25 °C to 72% at 75 °C, consistent with endothermic N₂O₄ dissociation.
- The graph proves a catalyst changes the value of Kc.
- Higher temperature always increases equilibrium yield for every reaction.
- The points show reaction rate only and contain no equilibrium information.
Question 18
1 mark- Accept the proposal because every indicator gives the same endpoint volume in any acid-base titration.
- Accept the proposal because the initial solution is acidic, regardless of the steep region.
- Reject all indicators because a pH change cannot locate an equivalence region.
- Methyl orange can be suitable because its transition overlaps the rapid pH rise; its range need not contain pH 7.0, and bromothymol blue is also suitable for this curve.
Question 19
1 mark- The highest reactor temperature, without energy use or container performance
- Feedstock and process energy per usable container, worker and reagent hazards, failure rate, collection rate and measured recovery or disposal outcomes
- The carbon mass in one unused container, without route or end-of-life data
- A supplier statement that the feedstock is renewable, without a functional-unit comparison
Question 20
1 mark- Collect independently located duplicate samples, carry a field blank through transport, and use a matrix spike to test recovery.
- Read one cuvette repeatedly and treat display stability as proof of representative sampling.
- Remove the blank so all absorbance is attributed to nitrate.
- Select the result with the greatest number of decimal places.
Section II: Written-response questions
Attempt Questions 21-40. Allow about 2 hours and 25 minutes for this section. Show all relevant working and use the supplied chemical evidence where relevant.
Question 21
2 marksConsider Fe³⁺(aq) + SCN⁻(aq) ⇌ FeSCN²⁺(aq).
Question 22
2 marksThe relevant weak acid is carbonic acid, H₂CO₃.
Question 23
2 marksThe condensed formula CH₃CH₂Br is used in the first reaction.
Question 24
2 marksThe target analyte is chloride in desalinated water.
Question 25
3 marksA 3.2 × 10⁻³ mol L⁻¹ HNO₃ reference gives a meter reading of pH 2.55. The laboratory acceptance limit is ±0.10 pH unit from the theoretical value.
Question 26
3 marksA coastal-water reagent sequence begins with CH₃CH₂Br + OH⁻ → CH₃CH₂OH + Br⁻.
Question 27
3 marksStandards of 0, 5, 10 and 15 mg L⁻¹ give signals 0.00, 0.25, 0.50 and 0.75; the sample signal is 0.60.
Question 28
3 marksFe³⁺(aq) + SCN⁻(aq) ⇌ FeSCN²⁺(aq). The following equilibrium data are measured at a fixed temperature. At equilibrium, [Fe³⁺] = 0.020 mol L⁻¹, [SCN⁻] = 0.010 mol L⁻¹ and [FeSCN²⁺] = 0.040 mol L⁻¹.
Question 29
4 marksbromoethane → ethanol → ethanoic acid; ethanoic acid + ethanol ⇌ ethyl ethanoate + water
Question 30
4 marksDetermine dissolved chloride, Cl⁻, by quantitative precipitation with excess Ag⁺: Ag⁺(aq) + Cl⁻(aq) → AgCl(s). A 100.0 mL sample produces 0.287 g AgCl; M(AgCl) = 143.3 g mol⁻¹.
Question 31
4 marksThe forward reaction and plotted equilibrium percentages are supplied for Fe³⁺(aq) + SCN⁻(aq) ⇌ FeSCN²⁺(aq).
Question 32
4 marks25.00 mL of 0.1000 mol L⁻¹ HCl is neutralised by 0.1250 mol L⁻¹ NaOH. Indicator evidence: the rapid pH change spans pH 6.0–7.6.
Question 33
4 marksMolecular ion m/z 58; strong IR absorption near 1715 cm⁻¹; two ¹³C environments; one ¹H singlet integrating to six hydrogens.
Question 34
4 marksFor calcium carbonate scaling, Ksp = 3.36 × 10⁻⁹. After two streams mix, [Ca²⁺] = 2.0 × 10⁻⁴ mol L⁻¹ and [CO₃²⁻] = 3.0 × 10⁻⁵ mol L⁻¹.
Question 35
4 marksThe process buffer is H₂CO₃/HCO₃⁻ in treated water; a small amount of HCl is added.
Question 36
4 marksThe proposed polymer is poly(ethene), made from ethene. A saturated carbon backbone formed by opening the C=C bonds of ethene.
Question 37
7 marksA desalination plant balances ferric-thiocyanate process monitoring, carbonate scaling, heat demand and water throughput. Main equilibrium: Fe³⁺(aq) + SCN⁻(aq) ⇌ FeSCN²⁺(aq). At the current composition: The current concentration quotient is 80 while Kc is 200. Temperature evidence for equilibrium composition is 15 °C: 88%, 35 °C: 73%, 55 °C: 59%. The forward reaction is exothermic under the supplied model. The proposed trial makes three changes: (1) additional Fe³⁺ solution is introduced at constant temperature; (2) move from 35 °C to 55 °C with all other reactor settings held constant; and (3) add a separation-and-recycle stage after the reactor. Precipitation evidence: CaCO₃(s) ⇌ Ca²⁺(aq) + CO₃²⁻(aq); Ksp = 3.36 × 10⁻⁹. After two streams mix, [Ca²⁺] = 2.0 × 10⁻⁴ mol L⁻¹ and [CO₃²⁻] = 3.0 × 10⁻⁵ mol L⁻¹. Process constraints: the highest-temperature trial uses 35% more heating energy than the middle trial; the proposed recovery stage returns 80% of soluble iron reagent, and finished water must contain no visible carbonate solid.
Question 38
7 marksDetermine the acidity of desalinated water by standardising NaOH, titrating replicate aliquots and reporting uncertainty.
Question 39
7 marksCompare fossil ethene with ethanol-derived ethene for packaging used by the coastal plant. Functional unit: 10 000 single-use desalination-sample bottles. Route A uses fossil ethene, 86 GJ of process energy and 24 kg of solvent loss; it gives 98% specification-grade polymer and 18% collection. Route B uses ethanol-derived ethene, 112 GJ and 9 kg of solvent loss; it gives 95% specification-grade polymer and 62% collection. Both bottles have the same tested service life.
Question 40
7 marksValidate chloride results across intake, product and brine samples using matrix-matched standards, blanks, spikes and replicate measurements.
Worked Solutions And Marking Guide
General marking principles
- Award credit for chemically accurate equivalent wording and logically equivalent calculations.
- Apply discrete criteria only to independently assessable operations; apply quality bands to integrated analytical and extended responses.
- Use indicative content as examples rather than an exhaustive checklist, and require conclusions to be supported by the supplied evidence.
Section I: Objective-response questions Question 1
Answer: Kc = [NO₂]²/[N₂O₄]
Stoichiometric coefficients become powers in the reaction quotient. Include every species defined with a composition-dependent activity or concentration, and omit only a pure solid or liquid phase whose activity is constant.
Section I: Objective-response questions Question 2
Answer: CH₃COO⁻
A Brønsted–Lowry acid donates H⁺, so removal of one proton from CH₃COOH forms CH₃COO⁻. H₃O⁺ and OH⁻ describe other acid-base species, not this conjugate pair.
Section I: Objective-response questions Question 3
Answer: 1-bromopropane
The parent chain, functional group and locants identify CH₃CH₂CH₂Br as 1-bromopropane. The alternatives represent different carbon skeletons, functional groups or a polymer rather than the stated molecule.
Section I: Objective-response questions Question 4
Answer: Clarify every sample and standard consistently, use a sample-matrix blank, and verify nitrate recovery with a matrix spike.
Turbidity and natural colour can add non-analyte absorbance. Consistent clarification, a matrix blank and spike recovery test whether the selective colour response and calibration isolate nitrate in this river-water matrix.
Section I: Objective-response questions Question 5
Answer: pH = 2.60, because [H₃O⁺] = 2.5 × 10⁻³ mol L⁻¹ before applying −log₁₀
HCl is fully dissociated at this concentration, so the hydronium concentration is set stoichiometrically. Applying the base-10 logarithm gives pH 2.60; the answer is also consistent with an acidic reference solution.
Section I: Objective-response questions Question 6
Answer: Use dilute aqueous NaOH and heat; aqueous OH⁻ replaces Br in a nucleophilic substitution.
Ethanolic hydroxide favours elimination, so it is not the intended preparation of propan-1-ol. Heating with dilute aqueous NaOH provides OH⁻ for nucleophilic substitution at the carbon bonded to Br.
Section I: Objective-response questions Question 7
Answer: 7.0 mg L⁻¹ nitrate, because 0.35 lies halfway between the two neighbouring standard signals
The sample response is bracketed by the two standards and is exactly halfway between their signals. Linear interpolation therefore places the concentration halfway between 6.0 and 8.0 mg L⁻¹, at 7.0 mg L⁻¹ nitrate.
Section I: Objective-response questions Question 8
Answer: The net reaction proceeds towards NO₂ until Q equals Kc.
Comparing the quotient calculated from current concentrations with Kc predicts direction: a smaller quotient drives products and a larger quotient drives reactants. A catalyst changes the rate of approach, not Kc or the final composition.
Section I: Objective-response questions Question 9
Answer: methyl propanoate
Following each stated functional-group conversion leads to methyl propanoate. The other substances are a starting material, an intermediate or a separate monomer or polymer.
Section I: Objective-response questions Question 10
Answer: Adding aqueous BaCl₂ gives a white BaSO₄ precipitate.
The selected reagent gives a characteristic chemical response: Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s). Controls are still needed because an observation alone may not exclude every interference.
Section I: Objective-response questions Question 11
Answer: The equilibrium shifts towards NO₂.
Because temperature is fixed, Kc is unchanged. The added N₂O₄ is consumed as the system establishes a new equilibrium. The system then establishes a new equilibrium; this predicts composition rather than reaction rate.
Section I: Objective-response questions Question 12
Answer: Methanoic acid has the greater tendency to ionise and is the stronger acid.
For comparable conditions, the larger Ka indicates greater ionisation and the stronger weak acid. Therefore Methanoic acid has the greater tendency to ionise and is the stronger acid.
Section I: Objective-response questions Question 13
Answer: ethanol
All independent signals must be satisfied together. The O–H absorption, ethyl splitting pattern, two carbon environments and M = 46 support ethanol. Alternatives that match only molecular mass or one absorption are insufficient.
Section I: Objective-response questions Question 14
Answer: Qsp > Ksp, so AgCl precipitates until saturation is restored.
The ion product must be compared with Ksp. Qsp = (2.0 × 10⁻⁵)(3.0 × 10⁻⁵) = 6.0 × 10⁻¹⁰; therefore Qsp > Ksp, so AgCl precipitates until saturation is restored.
Section I: Objective-response questions Question 15
Answer: 0.040 mol CH₃COOH and 0.060 mol CH₃COO⁻; the base-to-acid ratio increases
Added OH⁻ reacts stoichiometrically with CH₃COOH to form CH₃COO⁻ and water. Subtracting and adding 0.010 mol gives 0.040 mol acid and 0.060 mol conjugate base, so the base-to-acid ratio increases.
Section I: Objective-response questions Question 16
Answer: methyl side groups reduce close packing, producing a tough, flexible thermoplastic
Polymer chains contain covalent backbones, while forces and packing between chains affect bulk properties. For this material, methyl side groups reduce close packing, producing a tough, flexible thermoplastic
Section I: Objective-response questions Question 17
Answer: The equilibrium percentage of NO₂ increases from 45% at 25 °C to 72% at 75 °C, consistent with endothermic N₂O₄ dissociation.
The plotted values are stated equilibrium percentages for N₂O₄(g) ⇌ 2NO₂(g). The forward dissociation of N₂O₄ is endothermic. The equilibrium percentage of NO₂ increases from 45% at 25 °C to 72% at 75 °C, consistent with endothermic N₂O₄ dissociation. The graph describes equilibrium composition rather than reaction time.
Section I: Objective-response questions Question 18
Answer: Methyl orange can be suitable because its transition overlaps the rapid pH rise; its range need not contain pH 7.0, and bromothymol blue is also suitable for this curve.
Suitability depends on a transition occurring within the steep part of the curve. The pH rises from 3.3 to 10.7 over 0.40 mL, overlapping methyl orange's pH 3.1–4.4 interval and containing bromothymol blue's pH 6.0–7.6 interval. Methyl orange cannot be rejected solely because its range does not contain pH 7.0; the sparse readings do not prove identical endpoint errors.
Section I: Objective-response questions Question 19
Answer: Feedstock and process energy per usable container, worker and reagent hazards, failure rate, collection rate and measured recovery or disposal outcomes
The claim concerns delivered service, so the functional unit must include production efficiency, hazards, use failures and actual recovery or disposal. Reactor temperature, carbon content or a renewable label alone cannot compare 1,000 successful uses.
Section I: Objective-response questions Question 20
Answer: Collect independently located duplicate samples, carry a field blank through transport, and use a matrix spike to test recovery.
Independent locations test sampling variation, the field blank detects contamination introduced during handling, and the matrix spike tests recovery in the river-water matrix. Repeat readings from one cuvette address only short-term instrument precision.
Section II: Written-response questions Question 21
Indicative answer: - The correct expression is Kc = [FeSCN²⁺]/([Fe³⁺][SCN⁻]). - Stoichiometric coefficients become powers; every species whose activity varies in the defined mixture is included, while a pure solid or liquid phase is omitted because its activity is constant.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: The correct expression is Kc = [FeSCN²⁺]/([Fe³⁺][SCN⁻]).
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 5 - Equilibrium and Acid Reactions task.
Do not credit by itself: Uses a general equilibrium statement without applying the stated equation, quotient, phase model or data.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Stoichiometric coefficients become powers; every species whose activity varies in the defined mixture is included, while a pure solid or liquid phase is omitted because its activity is constant.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 5 - Equilibrium and Acid Reactions task.
Do not credit by itself: Uses a general equilibrium statement without applying the stated equation, quotient, phase model or data.
Section II: Written-response questions Question 22
Indicative answer: - H₂CO₃(aq) + H₂O(l) ⇌ H₃O⁺(aq) + HCO₃⁻(aq). - H₂CO₃/HCO₃⁻ is the acid/conjugate-base pair; H₂O/H₃O⁺ is the base/conjugate-acid pair.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: H₂CO₃(aq) + H₂O(l) ⇌ H₃O⁺(aq) + HCO₃⁻(aq).
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 6 - Acid/base Reactions task.
Do not credit by itself: Omits the reversible reaction with water or misidentifies one of the conjugate acid-base pairs in that reaction.
Integrated response (1 mark)
Award one mark when the response accurately establishes: H₂CO₃/HCO₃⁻ is the acid/conjugate-base pair; H₂O/H₃O⁺ is the base/conjugate-acid pair.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 6 - Acid/base Reactions task.
Do not credit by itself: Omits the reversible reaction with water or misidentifies one of the conjugate acid-base pairs in that reaction.
Section II: Written-response questions Question 23
Indicative answer: - The IUPAC name is bromoethane. - The carbon-halogen bond places the molecule in the haloalkane class and supplies the reactive site used to form ethanol.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: The IUPAC name is bromoethane.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 7 - Organic Chemistry task.
Do not credit by itself: Names a reaction or property without applying the supplied organic structure, condition or chemical evidence.
Integrated response (1 mark)
Award one mark when the response accurately establishes: The carbon-halogen bond places the molecule in the haloalkane class and supplies the reactive site used to form ethanol.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 7 - Organic Chemistry task.
Do not credit by itself: Names a reaction or property without applying the supplied organic structure, condition or chemical evidence.
Section II: Written-response questions Question 24
Indicative answer: - Qualitative analysis establishes identity or presence, whereas quantitative analysis determines amount or concentration. - Select argentometric titration: a standard AgNO₃ solution gives a stoichiometric endpoint for Cl⁻ over the expected concentration range.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: Qualitative analysis establishes identity or presence, whereas quantitative analysis determines amount or concentration.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 8 - Applying Chemical Ideas task.
Do not credit by itself: Confuses evidence of chloride presence with a concentration measurement, or selects a quantitative method without explaining its stoichiometric response.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Select argentometric titration: a standard AgNO₃ solution gives a stoichiometric endpoint for Cl⁻ over the expected concentration range.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 8 - Applying Chemical Ideas task.
Do not credit by itself: Confuses evidence of chloride presence with a concentration measurement, or selects a quantitative method without explaining its stoichiometric response.
Section II: Written-response questions Question 25
Indicative answer: - Complete dissociation gives [H₃O⁺] = 3.2 × 10⁻³ mol L⁻¹ and pH = −log₁₀(3.2 × 10⁻³) = 2.49. - The absolute difference is |2.55 − 2.49| = 0.06 pH unit. - The meter passes the stated ±0.10 check because 0.06 is within the acceptance limit.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: Complete dissociation gives [H₃O⁺] = 3.2 × 10⁻³ mol L⁻¹ and pH = −log₁₀(3.2 × 10⁻³) = 2.49.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 6 - Acid/base Reactions task.
Do not credit by itself: Accepts or rejects the probe without calculating the theoretical reference pH and comparing the absolute reading difference with the stated ±0.10 pH-unit limit.
Integrated response (1 mark)
Award one mark when the response accurately establishes: The absolute difference is |2.55 − 2.49| = 0.06 pH unit.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 6 - Acid/base Reactions task.
Do not credit by itself: Accepts or rejects the probe without calculating the theoretical reference pH and comparing the absolute reading difference with the stated ±0.10 pH-unit limit.
Integrated response (1 mark)
Award one mark when the response accurately establishes: The meter passes the stated ±0.10 check because 0.06 is within the acceptance limit.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 6 - Acid/base Reactions task.
Do not credit by itself: Accepts or rejects the probe without calculating the theoretical reference pH and comparing the absolute reading difference with the stated ±0.10 pH-unit limit.
Section II: Written-response questions Question 26
Indicative answer: - The reaction is nucleophilic substitution: hydroxide replaces bromide at the carbon bearing Br. - A suitable condition is dilute aqueous NaOH and heat. - The two-carbon skeleton is retained as ethanol forms; the balanced equation has a one-to-one haloalkane-to-alcohol ratio and accounts for bromine as Br⁻.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: The reaction is nucleophilic substitution: hydroxide replaces bromide at the carbon bearing Br.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 7 - Organic Chemistry task.
Do not credit by itself: Identifies the reaction without linking the supplied equation to the specific bond or functional-group change, condition and atom accounting.
Integrated response (1 mark)
Award one mark when the response accurately establishes: A suitable condition is dilute aqueous NaOH and heat.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 7 - Organic Chemistry task.
Do not credit by itself: Identifies the reaction without linking the supplied equation to the specific bond or functional-group change, condition and atom accounting.
Integrated response (1 mark)
Award one mark when the response accurately establishes: The two-carbon skeleton is retained as ethanol forms; the balanced equation has a one-to-one haloalkane-to-alcohol ratio and accounts for bromine as Br⁻.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 7 - Organic Chemistry task.
Do not credit by itself: Identifies the reaction without linking the supplied equation to the specific bond or functional-group change, condition and atom accounting.
Section II: Written-response questions Question 27
Indicative answer: - The linear slope is 0.050 signal units per mg L⁻¹; c = 0.60/0.050. - The sample concentration is 12.0 mg L⁻¹ before any stated dilution correction. - The sample signal lies between the lowest and highest standards, so interpolation rather than extrapolation is supported.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: The linear slope is 0.050 signal units per mg L⁻¹; c = 0.60/0.050.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 8 - Applying Chemical Ideas task.
Do not credit by itself: Misreads the supplied calibration or reports a concentration inconsistent with its in-range signal.
Integrated response (1 mark)
Award one mark when the response accurately establishes: The sample concentration is 12.0 mg L⁻¹ before any stated dilution correction.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 8 - Applying Chemical Ideas task.
Do not credit by itself: Misreads the supplied calibration or reports a concentration inconsistent with its in-range signal.
Integrated response (1 mark)
Award one mark when the response accurately establishes: The sample signal lies between the lowest and highest standards, so interpolation rather than extrapolation is supported.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 8 - Applying Chemical Ideas task.
Do not credit by itself: Misreads the supplied calibration or reports a concentration inconsistent with its in-range signal.
Section II: Written-response questions Question 28
Indicative answer: - Substitute the equilibrium concentrations into Kc = [FeSCN²⁺]/([Fe³⁺][SCN⁻]). - Kc = 0.040/(0.020 × 0.010) = 200. - The calculated Kc of 200 describes the product-to-reactant equilibrium ratio for the stated equation and temperature; it does not by itself describe reaction rate.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: Substitute the equilibrium concentrations into Kc = [FeSCN²⁺]/([Fe³⁺][SCN⁻]).
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 5 - Equilibrium and Acid Reactions task.
Do not credit by itself: Uses a concentration power inconsistent with the supplied balanced equation or treats Kc as a measure of reaction speed.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Kc = 0.040/(0.020 × 0.010) = 200.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 5 - Equilibrium and Acid Reactions task.
Do not credit by itself: Uses a concentration power inconsistent with the supplied balanced equation or treats Kc as a measure of reaction speed.
Integrated response (1 mark)
Award one mark when the response accurately establishes: The calculated Kc of 200 describes the product-to-reactant equilibrium ratio for the stated equation and temperature; it does not by itself describe reaction rate.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 5 - Equilibrium and Acid Reactions task.
Do not credit by itself: Uses a concentration power inconsistent with the supplied balanced equation or treats Kc as a measure of reaction speed.
Section II: Written-response questions Question 29
Indicative answer: - Identify bromoethane and account for the first conversion to ethanol using the displayed reagent and condition. - Trace the oxidation and esterification arrows from the displayed condensed structures and identify each functional-group change. - Account for ethyl ethanoate and the displayed water product using the reaction stoichiometry. - Transfer the ester-containing mixture to a separating funnel, neutralise residual acid, dry the organic layer and collect the intended ester by an appropriate distillation step.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: Identify bromoethane and account for the first conversion to ethanol using the displayed reagent and condition.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 7 - Organic Chemistry task.
Do not credit by itself: Names a reaction without tracing the supplied structures, conditions, atom accounting and product-specific work-up through the pathway.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Trace the oxidation and esterification arrows from the displayed condensed structures and identify each functional-group change.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 7 - Organic Chemistry task.
Do not credit by itself: Names a reaction without tracing the supplied structures, conditions, atom accounting and product-specific work-up through the pathway.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Account for ethyl ethanoate and the displayed water product using the reaction stoichiometry.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 7 - Organic Chemistry task.
Do not credit by itself: Names a reaction without tracing the supplied structures, conditions, atom accounting and product-specific work-up through the pathway.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Transfer the ester-containing mixture to a separating funnel, neutralise residual acid, dry the organic layer and collect the intended ester by an appropriate distillation step.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 7 - Organic Chemistry task.
Do not credit by itself: Names a reaction without tracing the supplied structures, conditions, atom accounting and product-specific work-up through the pathway.
Section II: Written-response questions Question 30
Indicative answer: - Use n(precipitate) = mass/molar mass and the supplied one-to-one precipitate-to-target relationship; convert sample volume to litres. - n(AgCl) = 0.287/143.3 = 2.00 × 10⁻³ mol, so c(Cl⁻) = 0.00200/0.1000. - The calculated concentration is 2.00 × 10⁻² mol L⁻¹ Cl⁻. - Identify and justify any ONE relevant operation: allow complete precipitation to avoid low recovery; transfer and filter quantitatively to avoid solid loss; wash to remove soluble contamination; or dry and cool before weighing to constant mass to exclude water or unstable weighing. One justified operation earns this mark; the full workflow is not required.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: Use n(precipitate) = mass/molar mass and the supplied one-to-one precipitate-to-target relationship; convert sample volume to litres.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 8 - Applying Chemical Ideas task.
Do not credit by itself: Uses the precipitate's concentration as a different analyte without the stated mole ratio, or names an operation without explaining its effect on accuracy.
Integrated response (1 mark)
Award one mark when the response accurately establishes: n(AgCl) = 0.287/143.3 = 2.00 × 10⁻³ mol, so c(Cl⁻) = 0.00200/0.1000.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 8 - Applying Chemical Ideas task.
Do not credit by itself: Uses the precipitate's concentration as a different analyte without the stated mole ratio, or names an operation without explaining its effect on accuracy.
Integrated response (1 mark)
Award one mark when the response accurately establishes: The calculated concentration is 2.00 × 10⁻² mol L⁻¹ Cl⁻.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 8 - Applying Chemical Ideas task.
Do not credit by itself: Uses the precipitate's concentration as a different analyte without the stated mole ratio, or names an operation without explaining its effect on accuracy.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Identify and justify any ONE relevant operation: allow complete precipitation to avoid low recovery; transfer and filter quantitatively to avoid solid loss; wash to remove soluble contamination; or dry and cool before weighing to constant mass to exclude water or unstable weighing. One justified operation earns this mark; the full workflow is not required.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 8 - Applying Chemical Ideas task.
Do not credit by itself: Uses the precipitate's concentration as a different analyte without the stated mole ratio, or names an operation without explaining its effect on accuracy.
Section II: Written-response questions Question 31
Indicative answer: - The graph shows the direction and size of the equilibrium-yield trend across the supplied temperatures. - Equilibrium FeSCN²⁺ decreases from 88% at 15 °C to 59% at 55 °C, so increasing temperature favours the reverse direction and the forward complex-formation reaction is inferred to be exothermic. - Infer the temperature response from the plotted equilibrium values; no separate enthalpy statement is supplied. - Higher temperature generally increases the rate of both forward and reverse reactions by increasing the fraction of collisions above activation energy, but rate evidence is still required to select a practical operating temperature.
Question-specific marking approach
Read the response as a whole. Match its demonstrated quality to the best-fitting band; indicative content is non-exhaustive and no single listed point guarantees a mark.
Overall response quality
Award marks holistically using the quality bands below. The indicative content identifies possible evidence and is not a point tally.
Acceptable alternatives: Accept other chemically accurate, relevant and well-supported approaches that address the complete task.
Do not credit by itself: Do not award the top band to an unordered list that does not integrate the stimulus, chemical reasoning and any required judgement.
Holistic marking bands
| Marks | Descriptor |
|---|---|
| 4 | Provides a clear, scientifically accurate and integrated response to 'Analyse the temperature data and distinguish equilibrium yield from rate.' that applies the stimulus and combines the plotted equilibrium-composition trend, a temperature-response or thermochemical inference drawn from that graph, the separate kinetic effect of temperature, the distinction between equilibrium yield and rate, and a conclusion limited to the supplied evidence. |
| 3 | Addresses most task components with relevant chemistry and stimulus evidence, but integration or precision is uneven. |
| 2 | Provides some relevant chemical information, but the response or its application to the stimulus is incomplete or mainly descriptive. |
| 1 | States one relevant chemical fact or identifies one relevant feature of the stimulus. |
Section II: Written-response questions Question 32
Indicative answer: - Write or apply the balanced neutralisation stoichiometry. - n(HCl) = 0.02500 × 0.1000 = 2.500 × 10⁻³ mol; V(NaOH) = n/c = 0.02000 L. - The equivalence-point volume is 20.00 mL NaOH. - bromothymol blue (transition range pH 6.0–7.6) is suitable because its transition lies within the supplied steep region, pH 6.0–7.6.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: Write or apply the balanced neutralisation stoichiometry.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 6 - Acid/base Reactions task.
Do not credit by itself: Uses an unbalanced neutralisation ratio or an endpoint unsupported by the supplied titration evidence.
Integrated response (1 mark)
Award one mark when the response accurately establishes: n(HCl) = 0.02500 × 0.1000 = 2.500 × 10⁻³ mol; V(NaOH) = n/c = 0.02000 L.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 6 - Acid/base Reactions task.
Do not credit by itself: Uses an unbalanced neutralisation ratio or an endpoint unsupported by the supplied titration evidence.
Integrated response (1 mark)
Award one mark when the response accurately establishes: The equivalence-point volume is 20.00 mL NaOH.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 6 - Acid/base Reactions task.
Do not credit by itself: Uses an unbalanced neutralisation ratio or an endpoint unsupported by the supplied titration evidence.
Integrated response (1 mark)
Award one mark when the response accurately establishes: bromothymol blue (transition range pH 6.0–7.6) is suitable because its transition lies within the supplied steep region, pH 6.0–7.6.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 6 - Acid/base Reactions task.
Do not credit by itself: Uses an unbalanced neutralisation ratio or an endpoint unsupported by the supplied titration evidence.
Section II: Written-response questions Question 33
Indicative answer: - The most likely compound is propanone, CH₃COCH₃. - Its molecular mass is 58 g mol⁻¹, matching the supplied molecular ion m/z 58. - The strong absorption near 1715 cm⁻¹ supports its ketone carbonyl. - Two ¹³C environments and one ¹H singlet integrating to six hydrogens match a carbonyl carbon and two equivalent methyl groups.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: The most likely compound is propanone, CH₃COCH₃.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 8 - Applying Chemical Ideas task.
Do not credit by itself: Proposes a structure incompatible with the supplied molecular ion, functional-group absorptions or NMR environment and proton patterns.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Its molecular mass is 58 g mol⁻¹, matching the supplied molecular ion m/z 58.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 8 - Applying Chemical Ideas task.
Do not credit by itself: Proposes a structure incompatible with the supplied molecular ion, functional-group absorptions or NMR environment and proton patterns.
Integrated response (1 mark)
Award one mark when the response accurately establishes: The strong absorption near 1715 cm⁻¹ supports its ketone carbonyl.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 8 - Applying Chemical Ideas task.
Do not credit by itself: Proposes a structure incompatible with the supplied molecular ion, functional-group absorptions or NMR environment and proton patterns.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Two ¹³C environments and one ¹H singlet integrating to six hydrogens match a carbonyl carbon and two equivalent methyl groups.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 8 - Applying Chemical Ideas task.
Do not credit by itself: Proposes a structure incompatible with the supplied molecular ion, functional-group absorptions or NMR environment and proton patterns.
Section II: Written-response questions Question 34
Indicative answer: - Write the dissolution equation: CaCO₃(s) ⇌ Ca²⁺(aq) + CO₃²⁻(aq). - Form Qsp using the ion concentrations raised to their stoichiometric powers. - Qsp = (2.0 × 10⁻⁴)(3.0 × 10⁻⁵) = 6.0 × 10⁻⁹. - Qsp > Ksp, so CaCO₃ precipitates until saturation is restored.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: Write the dissolution equation: CaCO₃(s) ⇌ Ca²⁺(aq) + CO₃²⁻(aq).
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 5 - Equilibrium and Acid Reactions task.
Do not credit by itself: Uses a general equilibrium statement without applying the stated equation, quotient, phase model or data.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Form Qsp using the ion concentrations raised to their stoichiometric powers.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 5 - Equilibrium and Acid Reactions task.
Do not credit by itself: Uses a general equilibrium statement without applying the stated equation, quotient, phase model or data.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Qsp = (2.0 × 10⁻⁴)(3.0 × 10⁻⁵) = 6.0 × 10⁻⁹.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 5 - Equilibrium and Acid Reactions task.
Do not credit by itself: Uses a general equilibrium statement without applying the stated equation, quotient, phase model or data.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Qsp > Ksp, so CaCO₃ precipitates until saturation is restored.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 5 - Equilibrium and Acid Reactions task.
Do not credit by itself: Uses a general equilibrium statement without applying the stated equation, quotient, phase model or data.
Section II: Written-response questions Question 35
Indicative answer: - HCO₃⁻ consumes added H₃O⁺ to form H₂CO₃, so the pH decreases less than it would in unbuffered water. - The conjugate pair converts added strong acid or base into a weaker species, so the concentration ratio and pH change only moderately. - Buffer capacity is finite and depends on the amounts of both components; sufficient added acid or base overwhelms it. - Dilution, temperature, ionic strength and gas exchange can also affect measured pH, so constancy must be supported by data rather than assumed.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: HCO₃⁻ consumes added H₃O⁺ to form H₂CO₃, so the pH decreases less than it would in unbuffered water.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 6 - Acid/base Reactions task.
Do not credit by itself: Claims exactly constant pH or unlimited capacity without explaining the added reagent's reaction with a conjugate component and the resulting change in component ratio.
Integrated response (1 mark)
Award one mark when the response accurately establishes: The conjugate pair converts added strong acid or base into a weaker species, so the concentration ratio and pH change only moderately.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 6 - Acid/base Reactions task.
Do not credit by itself: Claims exactly constant pH or unlimited capacity without explaining the added reagent's reaction with a conjugate component and the resulting change in component ratio.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Buffer capacity is finite and depends on the amounts of both components; sufficient added acid or base overwhelms it.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 6 - Acid/base Reactions task.
Do not credit by itself: Claims exactly constant pH or unlimited capacity without explaining the added reagent's reaction with a conjugate component and the resulting change in component ratio.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Dilution, temperature, ionic strength and gas exchange can also affect measured pH, so constancy must be supported by data rather than assumed.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 6 - Acid/base Reactions task.
Do not credit by itself: Claims exactly constant pH or unlimited capacity without explaining the added reagent's reaction with a conjugate component and the resulting change in component ratio.
Section II: Written-response questions Question 36
Indicative answer: - Opening ethene C=C bonds produces the displayed saturated covalent C–C backbone without a small-molecule by-product. - C–C and C–H bonds hold each chain together, while the non-polar chains attract one another mainly through dispersion forces. - Weak interchain attractions allow chain segments to move, supporting flexibility and thermoplastic softening without breaking the covalent backbone. - The non-polar hydrocarbon chains interact poorly with water, supporting a prediction of water resistance. The saturated backbone is relatively unreactive toward dilute aqueous acids and bases; this does not establish resistance to every chemical or a particular packaging specification.
Detailed marking criteria
Integrated response (1 mark)
Award one mark when the response accurately establishes: Opening ethene C=C bonds produces the displayed saturated covalent C–C backbone without a small-molecule by-product.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 7 - Organic Chemistry task.
Do not credit by itself: Names a polymerisation class or property without matching the supplied monomers, linkage, repeat unit or structure-property evidence.
Integrated response (1 mark)
Award one mark when the response accurately establishes: C–C and C–H bonds hold each chain together, while the non-polar chains attract one another mainly through dispersion forces.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 7 - Organic Chemistry task.
Do not credit by itself: Names a polymerisation class or property without matching the supplied monomers, linkage, repeat unit or structure-property evidence.
Integrated response (1 mark)
Award one mark when the response accurately establishes: Weak interchain attractions allow chain segments to move, supporting flexibility and thermoplastic softening without breaking the covalent backbone.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 7 - Organic Chemistry task.
Do not credit by itself: Names a polymerisation class or property without matching the supplied monomers, linkage, repeat unit or structure-property evidence.
Integrated response (1 mark)
Award one mark when the response accurately establishes: The non-polar hydrocarbon chains interact poorly with water, supporting a prediction of water resistance. The saturated backbone is relatively unreactive toward dilute aqueous acids and bases; this does not establish resistance to every chemical or a particular packaging specification.
Acceptable alternatives: Accept an equivalent equation, calculation or explanation that preserves the chemistry required by this Module 7 - Organic Chemistry task.
Do not credit by itself: Names a polymerisation class or property without matching the supplied monomers, linkage, repeat unit or structure-property evidence.
Section II: Written-response questions Question 37
Indicative answer: - Apply Kc = [FeSCN²⁺]/([Fe³⁺][SCN⁻]) and the supplied Q-versus-Kc comparison to conclude: The net reaction proceeds towards FeSCN²⁺ until Q equals Kc. - Use the listed equilibrium percentages and thermochemical direction rather than a generic temperature rule: Because the supplied forward reaction is exothermic, the equilibrium percentage of FeSCN²⁺ decreases as temperature increases. - Separate kinetic and equilibrium claims: a temperature change can affect reaction rate, but the supplied equilibrium percentages—not an assumed collision-rate trend—determine the composition conclusion. - Use CaCO₃(s) ⇌ Ca²⁺(aq) + CO₃²⁻(aq) to form the ion product, then calculate Qsp = (2.0 × 10⁻⁴)(3.0 × 10⁻⁵) = 6.0 × 10⁻⁹ and compare it with Ksp = 3.36 × 10⁻⁹; Qsp > Ksp, so CaCO₃ precipitates until saturation is restored. - Use the quantified energy, recovery, safety or throughput constraint in the stimulus to reject any operating change justified by reactor yield alone. - Recommend a specific separation, precipitation-control or recycle operation and name a measurable residual-ion, recovery, emission or product-quality check. - Use moderate temperature, controlled Fe³⁺ dosing and antiscalant or pretreatment, then verify performance with equilibrium and scaling data.
Question-specific marking approach
Read the response as a whole. Match its demonstrated quality to the best-fitting band; indicative content is non-exhaustive and no single listed point guarantees a mark.
Overall response quality
Award marks holistically using the quality bands below. The indicative content identifies possible evidence and is not a point tally.
Acceptable alternatives: Accept other chemically accurate, relevant and well-supported approaches that address the complete task.
Do not credit by itself: Do not award the top band to an unordered list that does not integrate the stimulus, chemical reasoning and any required judgement.
Holistic marking bands
| Marks | Descriptor |
|---|---|
| 7 | Provides a coherent, scientifically accurate and fully integrated response to 'Evaluate the proposed operating strategy using the supplied equilibrium, precipitation, rate, energy and separation evidence.' that uses the stimulus and combines equilibrium calculations, molecular reasoning, supplied conditions and a supported conclusion; explicitly addresses every requested component and communicates the chemical reasoning precisely. |
| 5-6 | Provides a sound response using relevant stimulus evidence and most required elements of equilibrium calculations, molecular reasoning, supplied conditions and a supported conclusion, with only minor omissions or imprecision. |
| 3-4 | Explains some relevant chemistry and uses part of the stimulus, but the reasoning, calculation, evaluation or linkage between ideas is incomplete. |
| 2 | Provides limited relevant chemical information or a partly correct calculation with little application to the supplied context. |
| 1 | States one relevant chemical fact, equation, observation or data feature. |
Section II: Written-response questions Question 38
Indicative answer: - State a testable aim and define the acid-base quantity to be measured. - Prepare or standardise the titrant against an appropriate primary standard and record concentrations with uncertainty. - Use conditioned volumetric glassware, quantitative transfer and a suitable indicator or calibrated pH probe. - Control sample volume, temperature, mixing, dissolved-gas exposure and any matrix treatment relevant to the stimulus. - Collect independent replicate titres or curves and use concordant results rather than repeated display readings from one aliquot. - Apply balanced stoichiometry, dilution factors, significant figures and an uncertainty or spread measure. - Use blanks, spikes or reference material where relevant, identify remaining systematic limitations and draw a conclusion restricted to the evidence.
Question-specific marking approach
Read the response as a whole. Match its demonstrated quality to the best-fitting band; indicative content is non-exhaustive and no single listed point guarantees a mark.
Overall response quality
Award marks holistically using the quality bands below. The indicative content identifies possible evidence and is not a point tally.
Acceptable alternatives: Accept other chemically accurate, relevant and well-supported approaches that address the complete task.
Do not credit by itself: Do not award the top band to an unordered list that does not integrate the stimulus, chemical reasoning and any required judgement.
Holistic marking bands
| Marks | Descriptor |
|---|---|
| 7 | Provides a coherent, scientifically accurate and fully integrated response to 'Design a valid quantitative acid-base investigation and explain how its data would support a conclusion.' that uses the stimulus and combines the acid-base reactions and calculations requested in the task, the supplied measurement evidence and a supported conclusion; explicitly addresses every requested component and communicates the chemical reasoning precisely. |
| 5-6 | Provides a sound response using relevant stimulus evidence and most required elements of the acid-base reactions and calculations requested in the task, the supplied measurement evidence and a supported conclusion, with only minor omissions or imprecision. |
| 3-4 | Explains some relevant chemistry and uses part of the stimulus, but the reasoning, calculation, evaluation or linkage between ideas is incomplete. |
| 2 | Provides limited relevant chemical information or a partly correct calculation with little application to the supplied context. |
| 1 | States one relevant chemical fact, equation, observation or data feature. |
Section II: Written-response questions Question 39
Indicative answer: - Use 10 000 bottles with equal tested service life as the common functional unit. - Compare 98% and 95% specification-grade output rather than treating both manufacturing routes as equally efficient. - Account for the 86 GJ versus 112 GJ process-energy demand. - Compare the 24 kg versus 9 kg solvent loss as a material-emission burden. - Use the actual 18% versus 62% collection rates instead of assuming ideal recovery. - Treat fossil versus ethanol-derived ethene as one feedstock consideration, not a complete life-cycle conclusion. - Renewable feedstock can reduce fossil demand, but fermentation, dehydration energy, product lifetime, collection and end-of-life outcomes must all be included.
Question-specific marking approach
Read the response as a whole. Match its demonstrated quality to the best-fitting band; indicative content is non-exhaustive and no single listed point guarantees a mark.
Overall response quality
Award marks holistically using the quality bands below. The indicative content identifies possible evidence and is not a point tally.
Acceptable alternatives: Accept other chemically accurate, relevant and well-supported approaches that address the complete task.
Do not credit by itself: Do not award the top band to an unordered list that does not integrate the stimulus, chemical reasoning and any required judgement.
Holistic marking bands
| Marks | Descriptor |
|---|---|
| 7 | Provides a coherent, scientifically accurate and fully integrated response to 'Evaluate the two bottle routes using the supplied output, feedstock, energy, solvent-loss and collection evidence.' that uses the stimulus and combines the defined bottle functional unit, specification-grade output, process energy, solvent-loss evidence, feedstock source, collection rates, and a supported route comparison; explicitly addresses every requested component and communicates the chemical reasoning precisely. |
| 5-6 | Provides a sound response using relevant stimulus evidence and most required elements of the defined bottle functional unit, specification-grade output, process energy, solvent-loss evidence, feedstock source, collection rates, and a supported route comparison, with only minor omissions or imprecision. |
| 3-4 | Explains some relevant chemistry and uses part of the stimulus, but the reasoning, calculation, evaluation or linkage between ideas is incomplete. |
| 2 | Provides limited relevant chemical information or a partly correct calculation with little application to the supplied context. |
| 1 | States one relevant chemical fact, equation, observation or data feature. |
Section II: Written-response questions Question 40
Indicative answer: - Define chloride concentration as the measurand and collect representative, independently prepared intake, product and brine aliquots. - Standardise the AgNO₃ titrant against a traceable chloride standard and carry its concentration uncertainty into every result. - Validate the selected visual or instrumental endpoint with known chloride solutions and the 1:1 Ag⁺:Cl⁻ stoichiometry. - Apply reagent and matrix-appropriate blank corrections so chloride contamination is not assigned to the samples. - Use chloride spikes in each stream type to quantify recovery and reveal matrix or competing-ion endpoint bias. - Perform independent replicate titrations and apply a stated concordance or precision criterion. - Propagate titrant, aliquot and endpoint uncertainties, report appropriate significant figures and restrict the comparison to the validated matrices.
Question-specific marking approach
Read the response as a whole. Match its demonstrated quality to the best-fitting band; indicative content is non-exhaustive and no single listed point guarantees a mark.
Overall response quality
Award marks holistically using the quality bands below. The indicative content identifies possible evidence and is not a point tally.
Acceptable alternatives: Accept other chemically accurate, relevant and well-supported approaches that address the complete task.
Do not credit by itself: Do not award the top band to an unordered list that does not integrate the stimulus, chemical reasoning and any required judgement.
Holistic marking bands
| Marks | Descriptor |
|---|---|
| 7 | Provides a coherent, scientifically accurate and fully integrated response to 'Develop a titration-specific validation and reporting strategy for comparing chloride across the three water streams.' that uses the stimulus and combines balanced titration stoichiometry, titrant standardisation, endpoint detection, matrix or blank controls, independent concordant titres, uncertainty and a supported conclusion; explicitly addresses every requested component and communicates the chemical reasoning precisely. |
| 5-6 | Provides a sound response using relevant stimulus evidence and most required elements of balanced titration stoichiometry, titrant standardisation, endpoint detection, matrix or blank controls, independent concordant titres, uncertainty and a supported conclusion, with only minor omissions or imprecision. |
| 3-4 | Explains some relevant chemistry and uses part of the stimulus, but the reasoning, calculation, evaluation or linkage between ideas is incomplete. |
| 2 | Provides limited relevant chemical information or a partly correct calculation with little application to the supplied context. |
| 1 | States one relevant chemical fact, equation, observation or data feature. |
Diagnostic Checklist
| Review focus | Section | Reflection and next action |
|---|---|---|
| Module 6 - Acid/base Reactions | 2, 5, 12, 15, 18, 22, 25, 32, 35, 38 | Practise acid-base theories, pH and equilibrium calculations, buffers, indicators, titration analysis and method evaluation. |
| Module 8 - Applying Chemical Ideas | 4, 7, 10, 13, 20, 24, 27, 30, 33, 40 | Integrate qualitative and quantitative analysis, spectroscopy, chromatography, calibration, uncertainty and evidence-based identification. |
| Module 5 - Equilibrium and Acid Reactions | 1, 8, 11, 14, 17, 21, 28, 31, 34, 37 | Revise static and dynamic equilibrium, equilibrium constants, Le Chatelier's principle, solubility equilibria and quantitative equilibrium reasoning. |
| Module 7 - Organic Chemistry | 3, 6, 9, 16, 19, 23, 26, 29, 36, 39 | Review organic nomenclature, structure, reactions, synthesis pathways, polymers, fuels and structure-property relationships. |