Part a (1 mark)

Awards one mark for establishing this question-specific chemical point: From the supplied HO-R-OH, a suitable repeat unit is [-O-R-O-C(=O)-CH₂-CH₂-C(=O)-]ₙ, where R is the defined algal-derived carbon skeleton and ester links occur in the backbone.

Part a (1 mark)

Awards one mark for establishing this question-specific chemical point: The single-bond ester oxygen comes from a hydroxyl group of the algal-derived diol.

Part a (1 mark)

Awards one mark for establishing this question-specific chemical point: The carbonyl oxygen remains with the carboxylic-acid-derived acyl group.

Part a (1 mark)

Awards one mark for establishing this question-specific chemical point: For each condensation linkage, the acid's hydroxyl oxygen and an alcohol hydroxyl hydrogen leave together as H₂O.

Part (b)(i) (1 mark)

Awards one mark for establishing this question-specific chemical point: A diol has two hydroxyl functional groups.

Part (b)(i) (1 mark)

Awards one mark for establishing this question-specific chemical point: Butanedioic acid has two carboxyl functional groups.

Part (b)(ii) (1 mark)

Awards one mark for establishing this question-specific chemical point: Condensation between -OH and -COOH forms an ester link.

Part (b)(ii) (1 mark)

Awards one mark for establishing this question-specific chemical point: Water is eliminated for each ester linkage formed.

Part c (1 mark)

Awards one mark for establishing this question-specific chemical point: Yield ratio = 8.64/10.8 = 0.800.

Part c (1 mark)

Awards one mark for establishing this question-specific chemical point: Percentage yield = 0.800 × 100 = 80.0%.

Part (d)(i) (1 mark)

Awards one mark for establishing this question-specific chemical point: The 80.0% result establishes the purified polymer mass relative to the stated theoretical mass.

Part (d)(i) (1 mark)

Awards one mark for establishing this question-specific chemical point: The isolated yield alone does not establish environmental superiority or complete reaction.

Part (d)(ii) (1 mark)

Awards one mark for establishing this question-specific chemical point: Compare equal-thickness algal and conventional polyester samples under the same temperature, light and exposure time.

Part (d)(ii) (1 mark)

Awards one mark for establishing this question-specific chemical point: Measure strength retention, mass change or degradation products after the controlled exposure.

Part (a)(i) (1 mark)

Awards one mark for establishing this question-specific chemical point: Glucose is a monosaccharide containing multiple hydroxyl groups.

Part (a)(i) (1 mark)

Awards one mark for establishing this question-specific chemical point: The supplied equation gives a one-to-two glucose-to-ethanol mole ratio.

Part (a)(ii) (1 mark)

Awards one mark for establishing this question-specific chemical point: Fermentation is enzyme-catalysed under anaerobic conditions.

Part (a)(ii) (1 mark)

Awards one mark for establishing this question-specific chemical point: C₆H₁₂O₆(aq) → 2C₂H₅OH(aq) + 2CO₂(g) is balanced for carbon, hydrogen and oxygen atoms.

Part b (1 mark)

Awards one mark for establishing this question-specific chemical point: Initial glucose mass = 180 × 0.500 = 90.0 g.

Part b (1 mark)

Awards one mark for establishing this question-specific chemical point: Consumed glucose mass = 0.750 × 90.0 = 67.5 g.

Part b (1 mark)

Awards one mark for establishing this question-specific chemical point: n(glucose) = 67.5/180.16 = 0.3747 mol.

Part b (1 mark)

Awards one mark for establishing this question-specific chemical point: n(ethanol) = 2 × 0.3747 = 0.749 mol.

Part b (1 mark)

Awards one mark for establishing this question-specific chemical point: Using M(ethanol) = 46.07 gives 34.5 g ethanol.

Part c (1 mark)

Awards one mark for establishing this question-specific chemical point: The required reaction representation is C₆H₁₂O₆(aq) → 2C₂H₅OH(aq) + 2CO₂(g).

Part c (1 mark)

Awards one mark for establishing this question-specific chemical point: The carbohydrate glucose is converted into the alcohol ethanol and carbon dioxide while conserving six carbon atoms.

Part c (1 mark)

Awards one mark for establishing this question-specific chemical point: Fermentation includes coupled oxidation and reduction steps mediated by yeast enzymes.

Part (d)(i) (1 mark)

Awards one mark for establishing this question-specific chemical point: Residual glucose would support incomplete conversion of the supplied glucose rather than complete fermentation.

Part (d)(i) (1 mark)

Awards one mark for establishing this question-specific chemical point: Ethanol lost during collection or carbon diverted to other products could lower recovered ethanol even if glucose was consumed, so recovery alone cannot select a cause.

Part (d)(ii) (1 mark)

Awards one mark for establishing this question-specific chemical point: Run replicate batches at fixed temperature, pH and yeast loading, measure ethanol concentration by gas chromatography or a validated density method, and compare measured yield with residual glucose and carbon-dioxide data.

Part (a)(i) (1 mark)

Awards one mark for establishing this question-specific chemical point: The oxidation half-equation is V²⁺ → V³⁺ + e⁻.

Part (a)(ii) (1 mark)

Awards one mark for establishing this question-specific chemical point: The reduction half-equation consumes two H⁺ per electron.

Part (a)(ii) (1 mark)

Awards one mark for establishing this question-specific chemical point: Adding the half-equations conserves charge and electrons.

Part (a)(ii) (1 mark)

Awards one mark for establishing this question-specific chemical point: Electron flow is from the V²⁺ half-cell to the VO₂⁺ half-cell.

Part b (1 mark)

Awards one mark for establishing this question-specific chemical point: V²⁺ is oxidised to V³⁺ at the negative electrode during discharge.

Part b (1 mark)

Awards one mark for establishing this question-specific chemical point: VO₂⁺ is reduced to VO²⁺ at the positive electrode during discharge.

Part b (1 mark)

Awards one mark for establishing this question-specific chemical point: One mole of electrons is released per mole of V²⁺ oxidised and one mole of electrons is consumed per mole of VO₂⁺ reduced.

Part b (1 mark)

Awards one mark for establishing this question-specific chemical point: Electrons flow from the negative electrode through the external circuit to the positive electrode.

Part c (1 mark)

Awards one mark for establishing this question-specific chemical point: Charge Q = It = 2.50 × (38.6 × 60) = 5790 C.

Part c (1 mark)

Awards one mark for establishing this question-specific chemical point: n(e⁻) = 5790/96485 = 0.0600 mol.

Part c (1 mark)

Awards one mark for establishing this question-specific chemical point: The one-electron half-reaction gives 0.0600 mol VO₂⁺ reduced.

Part c (1 mark)

Awards one mark for establishing this question-specific chemical point: Time must be converted from minutes to seconds.

Part d (1 mark)

Awards one mark for establishing this question-specific chemical point: Before and after the same discharge, measure each tank's volume, total vanadium concentration and oxidation-state distribution separately to establish compartment-specific species inventories.

Part d (1 mark)

Awards one mark for establishing this question-specific chemical point: A loss of active vanadium from one compartment accompanied by a gain or misplaced vanadium species in the other supports membrane crossover.

Part d (1 mark)

Awards one mark for establishing this question-specific chemical point: Usable V²⁺ and VO₂⁺ remaining in their correct compartments at the discharge cutoff, without a corresponding transfer between tanks, support incomplete utilisation.

Part d (1 mark)

Awards one mark for establishing this question-specific chemical point: Membrane repair or replacement follows a crossover diagnosis; residual usable reactants instead support testing flow, mixing or discharge-cutoff settings.

Part a (1 mark)

Awards one mark for establishing this question-specific chemical point: Struvite precipitation transfers dissolved phosphate into a solid product.

Part a (1 mark)

Awards one mark for establishing this question-specific chemical point: The one-to-one formula links phosphate moles to struvite moles.

Part a (1 mark)

Awards one mark for establishing this question-specific chemical point: Magnesium availability, pH, phosphate speciation, mixing and competing ions affect struvite recovery.

Part b (1 mark)

Awards one mark for establishing this question-specific chemical point: Precipitation occurs when the ionic product exceeds the solubility threshold.

Part b (1 mark)

Awards one mark for establishing this question-specific chemical point: Increasing suitable magnesium ion concentration can promote nucleation.

Part b (1 mark)

Awards one mark for establishing this question-specific chemical point: Controlled pH changes phosphate speciation and struvite formation.

Part b (1 mark)

Awards one mark for establishing this question-specific chemical point: Filtration separates the solid from treated water.

Part b (1 mark)

Awards one mark for establishing this question-specific chemical point: Wash the recovered solid and assay its phosphorus, magnesium and contaminant content before claiming struvite purity.

Part c (1 mark)

Awards one mark for establishing this question-specific chemical point: Recovered phosphate = 0.850 × 0.0200 = 0.0170 mol.

Part c (1 mark)

Awards one mark for establishing this question-specific chemical point: The stoichiometric struvite amount is also 0.0170 mol.

Part c (1 mark)

Awards one mark for establishing this question-specific chemical point: m(struvite) = 0.0170 × 245.4 = 4.17 g.

Part c (1 mark)

Awards one mark for establishing this question-specific chemical point: Unrecovered phosphate = 0.0200-0.0170 = 0.00300 mol.

Part d (1 mark)

Awards one mark for establishing this question-specific chemical point: Adopt struvite recovery only when the separated solid meets phosphorus-availability, contaminant and purity requirements for land application.

Part d (1 mark)

Awards one mark for establishing this question-specific chemical point: Use plant-available phosphorus delivered to soil as the functional unit.

Part d (1 mark)

Awards one mark for establishing this question-specific chemical point: Measure heavy metals, pathogens, crop uptake and runoff in a field trial.

Part d (1 mark)

Awards one mark for establishing this question-specific chemical point: Include magnesium reagent, aeration, pumping and dewatering in the lifecycle comparison.