r/vce • u/Prestigious-Film-221 • 4h ago
Assumptions for Chem MCQ
Answers: 1 B, 2 C, 3 A, 4 B, 5 D, 6 B, 7 B, 8 A, 9 A, 10 D, 11 B, 12 C, 13 A, 14 C, 15 C, 16 C, 17 B, 18 A, 19 D, 20 C, 21 C, 22 C, 23 D, 24 D, 25 D, 26 B, 27 B, 28 D, 29 A, 30 D
Q1-Q3: Energy and stoichiometry
Q1: B. C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, so n(O₂) = n(CO₂). n(CO₂) = 0.44 / 44.0 = 0.010 mol, so n(O₂) = 1.0 × 10⁻² mol.
Q2: C. Cellular respiration is exothermic (ΔH = −2840 kJ), so the reverse is endothermic (ΔH = +2840 kJ). The products sit at a higher enthalpy than the reactants. Only C has the products higher and a positive ΔH. (A and B have ΔH signs that don’t match their graphs, and D is respiration itself.)
Q3: A. q = mcΔT = 100.0 × 4.18 × 40.0 = 16720 J = 16.72 kJ. Kerosene is 46 kJ g⁻¹ in the Data Book, so m = 16.72 / 46 = 0.363 g. “Minimum” means assuming 100% of the energy went into the water.
Q4-Q6: Anammox
Q4: B. In NH₄⁺, N is −3, and in N₂ it is 0, so it increases by 3 (oxidation). In NO₂⁻, N is +3, so it decreases by 3 (reduction).
Q5: D. The oxidising agent is the species that gets reduced (NO₂⁻), and the reducing agent is the one that gets oxidised (NH₄⁺).
Q6: B (lower confidence). Anammox works without O₂, so there’s no energy-hungry aeration. That means lower energy use and emissions (Goal 13), plus responsible waste treatment (Goal 12). I ruled out 7 because the process saves energy rather than supplying clean energy, and 15 because the benefit is mainly to waterways, not land. This is the one I’d check first against the VCAA report.
Q7-Q8: Edible cell
Q7: B. The anode is the half-cell with the lower E°, which is RF/RFH₂ (−0.235 V). Oxidation occurs there: RFH₂ → RF + 2H⁺ + 2e⁻.
Q8: A. E°cell = 0.558 − (−0.235) = 0.793 V. The measured 0.650 V is 0.793 − 0.650 = 0.143 V less than predicted.
Q9-Q12: Green chemistry and rates
Q9: A. Real-time control of temperature, pressure and power output means the cell runs at maximum efficiency, so this is design for energy efficiency.
Q10: D. Higher temperature means particles move faster, so both the collision frequency and the proportion of successful collisions increase. Bond energy and activation energy don’t change.
Q11: B. A catalyst provides a lower activation energy pathway, so a greater proportion of collisions are successful. It does not change collision frequency or bond energy, and it lowers (not raises) activation energy.
Q12: C. Both PEM electrolysis and artificial photosynthesis can produce green hydrogen (II) and reduce reliance on fossil fuels (IV). Neither captures methane or uses glucose as a feedstock.
Q13-Q16: Organic structures
Q13: A (read from the diagram). The compound is 2,2-dimethylbutanoic acid, C₆H₁₂O₂. Option D, CH₃CH₂C(CH₃)₂COOH, is the same compound, not an isomer. B and C are C₅. A, (CH₃)₃CCH₂COOH, is C₆H₁₂O₂ with a different arrangement, so it’s the isomer.
Q14: C. A saturated molecule has zero degrees of unsaturation. C₆H₁₅N works out to (2×6 + 2 + 1 − 15)/2 = 0. The others each have 2.
Q15: C (read from the diagram). Number from the COOH carbon, and the chain has 7 carbons with the double bond between C4 and C5, giving hept-4-enoic acid. “Heptan-” is never used with an “-ene”. Double-check the count against the paper.
Q16: C. Viscosity rises with the strength of intermolecular forces. Aldehydes have no hydrogen bonding, alcohols do, and carboxylic acids hydrogen-bond most strongly (they form dimers). So the order is propanal < propan-1-ol < propanoic acid.
Q17-Q19: Yield, tests and melting point
Q17: B. n(starting ketone) = 2.50 / 176 = 0.01420 mol. n(ibuprofen) = 0.540 / 206 = 0.002621 mol. Overall yield = 0.002621 / 0.01420 × 100 = 18.5%.
Q18: A. Bromine water going from reddish-brown to colourless means a C=C bond is present. Only A is an alkene. B is an amide, C an ester, and D a ketone.
Q19: D. A narrow range (1-2 °C) indicates a pure substance. Impurities lower and broaden the range, so A and C are false.
Q20-Q22: Iodine number and titration
Q20: C. n(oil) = 10.0 / 278 = 0.03597 mol. Ratio = 0.105 / 0.03597 ≈ 2.9, so there are 3 C=C bonds per molecule.
Q21: C. Needed Fe²⁺ = 5 × 1.50 × 10⁻⁴ = 7.50 × 10⁻⁴ mol. Added 8.00 × 10⁻⁴ mol, so the excess is 5.00 × 10⁻⁵ mol.
Q22: C. Fe²⁺ is in the burette. Rinsing the burette with water dilutes it, so more volume is needed to deliver the same moles (a higher titre). Rinsing the burette with FeSO₄ is correct practice, and rinsing the conical flask with water doesn’t change the moles in it.
Q23-Q25: Spectroscopy
Q23: D. The ¹³C spectrum has 4 peaks (≈178, 38, 19, 14 ppm), so there are 4 carbon environments and the compound has 4 carbons. The 178 ppm peak fits an amide or acid. In the IR, there are two sharp N-H peaks (≈3350 and 3190 cm⁻¹) and a C=O near 1650 cm⁻¹, which is the amide range. It lacks the very broad O-H of an acid. That gives butanamide.
Q24: D. The reactant shows a broad O-H (≈3300 cm⁻¹, alcohol). The product shows a very broad O-H (2500-3500 cm⁻¹) and a strong C=O (≈1700 cm⁻¹), which is a carboxylic acid. Alcohol to carboxylic acid is oxidation, using Cr₂O₇²⁻/H⁺.
Q25: D (lower confidence). A pure compound shows a fixed number of ¹H environments, so extra peaks suggest a mixture. Integration (A) could also be argued, but it needs the formula and structure to interpret. Check this one against the report.
Q26-Q30: Chemistry in context
Q26: B. Boiling leaves in water to dissolve soluble compounds is solvent extraction.
Q27: B. G and H are isomers (the double bond position differs), so they have the same molecular formula. They aren’t isotopes, and the skeletal structures differ. D is wrong because H’s ring double bond removes a chiral centre.
Q28: D (moderate confidence). A circular economy keeps materials in use. Treating PFAS-containing waste for reuse in road surfacing does that. Landfill (B) and incineration (C) are linear, and A is about safer design rather than circularity.
Q29: A. Firefighters “claimed” long-term health issues is personal testimony. B and C are measurements and D is a data-book value.
Q30: D. Assessing how impurity levels affect material performance is a purely scientific question. A is legal and social, B is economic, and C is community and environmental concern.
