100 marks · an original Intuition practice paper realising the consensus predictions — every question links to the evidence behind it. Prefer the PDF?
This full-length practice paper was built from the consensus of a six-model AI panel (fable, opus, gpt-5.6-sol, gemini-3.1-pro, grok, deepseek), each of which independently predicted the 2026 examination from the 2019–2025 papers and NESA marking feedback. The 142 question-level predictions were clustered; every cluster with consensus probability ≥ 0.55 is realised in this paper, the remainder is drawn from the panel's watch list, and Module 8 chemical synthesis is deliberately light in line with the panel's rested call. Each Section II question is tagged with the consensus cluster it realises and the probability that a question of that kind appears in 2026. Every question is original — none is copied from a past paper.
General instructions
20 marks — Attempt Questions 1–20 — Allow about 35 minutes for this section
Use the multiple-choice answer sheet for Questions 1–20.
An aqueous solution of an unknown acid HA is represented below.
particle diagram of a droplet containing twelve intact HA molecules and only two H⁺/A⁻ ion pairs, with the particles closely spaced throughout the droplet — i.e. mostly molecular (weak) but with many solute particles per unit volume (concentrated).
Which row of the table best describes this solution?
| Strong | Concentrated | |
|---|---|---|
| A. | ✓ | ✓ |
| B. | ✓ | ✗ |
| C. | ✗ | ✓ |
| D. | ✗ | ✗ |
A 0.10 mol L⁻¹ solution of hydrochloric acid is diluted by a factor of 100.
What is the pH of the diluted solution?
Consider the following compound.
full structural formula of a six-carbon chain: CH₃–CH(CH₃)–CH₂–CHCl–CH₂–CH₃, i.e. a methyl group on the second carbon and a chlorine on the fourth carbon when numbered from the methyl end.
What is the preferred IUPAC name of this compound?
Consider the following equilibrium.
2C(s) + O₂(g) ⇌ 2CO(g)
What is the correct equilibrium expression for this reaction?
A. $K = \dfrac{[CO]^2}{[C]^2[O_2]}$
B. $K = \dfrac{[CO]^2}{[O_2]}$
C. $K = \dfrac{[O_2]}{[CO]^2}$
D. $K = \dfrac{[CO]}{[O_2]}$
How many carbon environments are present in a molecule of 2,3-dimethylbutane?
Equal volumes of 4.0 × 10⁻³ mol L⁻¹ lead(II) nitrate solution and 4.0 × 10⁻³ mol L⁻¹ sodium chloride solution are mixed. The Ksp of lead(II) chloride is 1.7 × 10⁻⁵.
Which of the following is correct?
The mass spectrum of a haloalkane shows a molecular ion peak at m/z = 136 and a peak of approximately equal intensity at m/z = 138.
Which halogen does the compound contain?
A weak monoprotic acid is titrated with a standardised sodium hydroxide solution. The pH at the equivalence point is 8.9.
Which indicator is most appropriate for this titration?
What is the conjugate acid of the hydrogen carbonate ion, HCO₃⁻?
Soap is added to water containing a droplet of grease, and the mixture is agitated so that a micelle forms around the droplet.
Which statement best describes the arrangement of the soap anions in the micelle?
The following equilibrium is established in aqueous solution.
[Co(H₂O)₆]²⁺(aq) + 4Cl⁻(aq) ⇌ [CoCl₄]²⁻(aq) + 6H₂O(l) (forward reaction endothermic)
The [Co(H₂O)₆]²⁺ ion is pink and the [CoCl₄]²⁻ ion is blue.
What is observed when a violet equilibrium mixture is heated, and why?
A reaction is non-spontaneous at low temperatures but becomes spontaneous at high temperatures.
Which row of the table shows the signs of ΔH and ΔS for this reaction?
| ΔH | ΔS | |
|---|---|---|
| A. | > 0 | < 0 |
| B. | < 0 | < 0 |
| C. | < 0 | > 0 |
| D. | > 0 | > 0 |
Methanol is refluxed with propanoic acid in the presence of concentrated sulfuric acid.
What is the name of the ester produced?
The molar solubility of silver chromate, Ag₂CrO₄, is s mol L⁻¹.
Which expression gives its solubility product, Ksp?
Which analytical technique is most appropriate for determining the concentration of lead ions present at very low levels in a sample of drinking water?
titration curve with volume of titrant (mL) on the x-axis (0 to 40 mL) and pH on the y-axis (0 to 14). The curve starts at pH 2.9, rises gradually through a buffer region around pH 4.9, then jumps steeply from pH about 7 to pH about 11 at 20.0 mL, and flattens near pH 12.5.
The titration curve shown was obtained by adding titrant to a 25.0 mL sample.
Which combination produced this curve?
Which pair of monomers can react to form a polyester?
Which of the following correctly describes the ¹H NMR spectrum of chloroethane, CH₃CH₂Cl?
25.0 mL of 0.10 mol L⁻¹ sodium hydroxide solution is mixed with 25.0 mL of 0.050 mol L⁻¹ hydrochloric acid.
What is the pH of the resulting solution?
A solution of ethanoic acid is diluted with distilled water at constant temperature.
Which row of the table describes the effect of the dilution?
| Ka | Degree of ionisation | |
|---|---|---|
| A. | Unchanged | Increases |
| B. | Unchanged | Decreases |
| C. | Decreases | Decreases |
| D. | Decreases | Increases |
80 marks — Attempt Questions 21–37 — Allow about 2 hours and 25 minutes for this section
Answer the questions in the spaces provided. Show all relevant working in questions involving calculations.
Consider the following organic reaction.
CH₃–CH=CH₂ + H₂O → organic product
The reaction proceeds only in the presence of substance X, and the major organic product contains a hydroxyl group on the central carbon atom.
Identify substance X and give the IUPAC name of the major organic product. (2)
| Substance X | IUPAC name of major organic product |
|---|---|
A student determined the enthalpy of combustion of propan-1-ol (molar mass 60.09 g mol⁻¹) using a spirit burner to heat water in an uninsulated aluminium can.
results table — mass of water in can 250.0 g; initial temperature of water 21.5 °C; final temperature of water 41.5 °C; mass of spirit burner before heating 185.230 g; mass of spirit burner after heating 184.380 g (mass of propan-1-ol burned 0.850 g); specific heat capacity of water 4.18 J g⁻¹ K⁻¹.
(a) Calculate the molar enthalpy of combustion of propan-1-ol obtained in this experiment. (3)
(b) The accepted value for the molar enthalpy of combustion of propan-1-ol is −2021 kJ mol⁻¹. Explain why the experimental value is significantly less exothermic than the accepted value, and justify ONE change to the procedure that would improve the accuracy of the result. (2)
Sodium ethanoate, CH₃COONa, dissolves completely in water to give a basic solution.
Calculate the pH of a 0.25 mol L⁻¹ solution of sodium ethanoate at 25 °C. Include a relevant equilibrium equation in your answer, and justify any approximation you make. The Ka of ethanoic acid is 1.8 × 10⁻⁵. (4)
The following equilibrium is established in a sealed vessel of fixed volume at constant temperature.
2NO₂(g) ⇌ N₂O₄(g)
NO₂ is brown and N₂O₄ is colourless.
At time t₁, an additional amount of NO₂ gas is injected into the vessel.
(a) On the axes provided, sketch the concentration of N₂O₄ from before t₁ until the system reaches a new equilibrium. (1)
axes with Time on the x-axis (marked t₁ partway along) and [N₂O₄] on the y-axis; a horizontal line is shown up to t₁. Expected sketch: the line remains continuous at t₁ (no instantaneous jump), then rises with decreasing slope to a new, higher plateau.
(b) Explain, in terms of collision theory, how the system responds to the addition of NO₂. In your answer, refer to the relative changes in the forward and reverse reaction rates. (3)
The following equilibrium is established in a sealed 1.00 L vessel at 700 K, at which temperature Keq = 49.0.
H₂(g) + I₂(g) ⇌ 2HI(g)
At equilibrium, the vessel contains 0.200 mol of H₂, 0.200 mol of I₂ and 1.40 mol of HI.
An additional amount of iodine gas is then injected into the vessel at constant temperature. When equilibrium is re-established, the concentration of HI is 1.60 mol L⁻¹.
Calculate the amount, in moles, of iodine gas that was added. (4)
A 25.0 mL sample of barium hydroxide solution was titrated with 0.100 mol L⁻¹ sulfuric acid while the electrical conductivity of the mixture was recorded.
graph of conductivity (arbitrary units) against volume of H₂SO₄ added (mL). The conductivity starts high (about 8 units), falls in a straight line to almost zero at 22.0 mL, then rises in a straight line to about 5 units at 35 mL, giving a sharp V shape with its minimum at 22.0 mL.
(a) Explain the shape of the graph, naming the ions responsible for the conductivity in each region. Include a balanced chemical equation in your answer. (4)
(b) Calculate the concentration of the barium hydroxide solution. (1)
The concentration of copper ions in wastewater discharged from an electroplating factory was determined by atomic absorption spectroscopy.
A 25.00 mL sample of the wastewater was diluted to 250.0 mL with distilled water. The absorbance of the diluted sample was 0.264.
calibration table and graph — standards of 0.0, 1.0, 2.0, 3.0 and 4.0 mg L⁻¹ Cu²⁺ giving absorbances 0.000, 0.110, 0.220, 0.330 and 0.440 respectively; the calibration graph is a straight line through the origin with gradient 0.110 L mg⁻¹.
(a) Determine the concentration of copper ions, in mg L⁻¹, in the undiluted wastewater. (3)
(b) The local discharge limit for copper is 8.0 × 10⁻⁵ mol L⁻¹. Determine, with calculations, whether the factory complies with the discharge limit. The molar mass of copper is 63.55 g mol⁻¹. (2)
A 25.0 mL sample of 0.100 mol L⁻¹ propanoic acid was titrated with 0.100 mol L⁻¹ sodium hydroxide solution, and the pH was recorded throughout.
titration curve with volume of NaOH (mL) on the x-axis (0–40 mL) and pH on the y-axis (0–14). The curve starts at pH 2.9, passes through pH 4.87 at 12.5 mL (half-equivalence, buffer plateau), rises steeply through the equivalence point at 25.0 mL where the pH is 8.8, and levels off near pH 12.3. The points (12.5 mL, pH 4.87) and (25.0 mL, pH 8.8) are readable from the graph.
(a) Use the titration curve to determine the Ka of propanoic acid. Show your reasoning on or beside the curve. (2)
(b) Explain why the pH at the equivalence point is greater than 7. Include a relevant equation in your answer. (2)
A solution is known to contain ONE of the cations Ba²⁺, Ca²⁺ or Pb²⁺.
A student added a few drops of dilute sulfuric acid to a sample of the solution. A white precipitate formed, and the student concluded that the solution contained Ba²⁺.
(a) Explain why the student's conclusion is not valid. Support your answer with at least one balanced net ionic equation. (2)
(b) Design a valid sequence of tests that would identify which of the three cations is present. For each test, state the expected observation for each possible cation and include balanced net ionic equations, with states, for any precipitation reactions. (4)
Ammonia is synthesised industrially from nitrogen and hydrogen.
N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ΔH = −92 kJ mol⁻¹
Explain why a moderate temperature of about 450 °C is used in this process, rather than a low temperature that would maximise the equilibrium yield of ammonia. (3)
The label of an antacid product states that each tablet contains 300 mg of calcium carbonate.
A student analysed one tablet of mass 1.200 g by back titration:
titration results table — Titre 1: 20.10 mL; Titre 2: 19.20 mL; Titre 3: 19.15 mL; Titre 4: 19.25 mL.
(a) Write balanced chemical equations for the two neutralisation reactions that occur in this analysis. (1)
(b) Calculate the mass of calcium carbonate in the tablet. The molar mass of CaCO₃ is 100.09 g mol⁻¹. (5)
(c) Assess whether the analysis supports the claim on the label. (1)
A buffer is prepared by dissolving equal amounts of ethanoic acid and sodium ethanoate in water.
Explain, with reference to an equilibrium equation, how this buffer resists changes in pH when a small amount of hydrochloric acid is added AND when a small amount of sodium hydroxide is added. (4)
A solution contains barium ions and calcium ions, each at a concentration of 0.010 mol L⁻¹. Solid sodium sulfate is added gradually with stirring. Assume the volume of the solution does not change.
Ksp(BaSO₄) = 1.08 × 10⁻¹⁰ Ksp(CaSO₄) = 4.93 × 10⁻⁵
(a) Show by calculation that barium sulfate precipitates first. (2)
(b) Calculate the concentration of barium ions remaining in solution at the point where calcium sulfate just begins to precipitate, and hence explain why this procedure could be used to separate the two ions. (3)
Calcium carbonate decomposes on strong heating.
CaCO₃(s) → CaO(s) + CO₂(g) ΔH = +178 kJ mol⁻¹, ΔS = +161 J K⁻¹ mol⁻¹
(a) Calculate ΔG for this reaction at 25 °C and state whether the reaction is spontaneous at this temperature. (2)
(b) Calculate the minimum temperature at which the decomposition becomes spontaneous. Assume ΔH and ΔS do not change with temperature. (2)
The flow chart shows a series of reactions beginning with 2-methylpropene.
flow chart — Compound A (2-methylpropene, (CH₃)₂C=CH₂) reacts with H₂O in the presence of dilute H₂SO₄ to give two isomeric alcohols, Compound B (the major product) and Compound C (the minor product). Compound C is heated under reflux with excess acidified potassium dichromate to give Compound D. Compound D is heated under reflux with ethanol and concentrated sulfuric acid to give Compound E. An arrow from Compound B to acidified potassium dichromate is labelled "no reaction".
(a) Draw the full structural formulae of compounds B, C and D, and give the IUPAC name of each. (3)
(b) Draw the structural formula of compound E and give its IUPAC name. (2)
(c) Explain why compound B does not react with acidified potassium dichromate. (1)
A student used a simple calorimeter to measure the molar enthalpy of neutralisation of sodium hydroxide with hydrochloric acid, and then with ethanoic acid of the same concentration. The reaction with ethanoic acid was found to be significantly less exothermic per mole of water formed.
Explain this observation. (3)
An ester, compound X, was produced by refluxing an alcohol with ethanoic acid in the presence of concentrated sulfuric acid. Elemental analysis shows that X has the molecular formula C₅H₁₀O₂.
The following spectra of purified X were obtained.
mass spectrum — molecular ion peak at m/z = 102 (low intensity, labelled M⁺); base peak at m/z = 43 (100%, labelled); other significant peaks at m/z = 87 (weak) and m/z = 59 (moderate).
infrared spectrum — strong sharp absorption at 1743 cm⁻¹; absorptions at 2870–2990 cm⁻¹; strong absorptions at 1240 cm⁻¹ and 1050 cm⁻¹; NO broad absorption in the 2500–3300 cm⁻¹ region.
¹³C NMR spectrum — four signals: δ 170.7, δ 67.3, δ 21.8 and δ 21.3 ppm.
¹H NMR data table with separate columns for chemical shift, splitting and relative integration — δ 4.99 ppm, septet, 1H; δ 2.01 ppm, singlet, 3H; δ 1.22 ppm, doublet, 6H.
Determine the structure of compound X, and identify the alcohol from which it was made.
In your answer:
| Q | Answer | Note |
|---|---|---|
| 1 | C | Mostly molecular ⇒ weak; many particles per volume ⇒ concentrated |
| 2 | C | [H⁺] = 1.0 × 10⁻³ mol L⁻¹ ⇒ pH 3.0 |
| 3 | A | Lowest locant set {2,4}; substituents cited alphabetically (chloro before methyl) |
| 4 | B | Solids excluded; CO squared; products over reactants |
| 5 | D | Symmetry: four equivalent CH₃ carbons + two equivalent CH carbons = 2 environments |
| 6 | C | Q = (2.0 × 10⁻³)(2.0 × 10⁻³)² = 8.0 × 10⁻⁹ < 1.7 × 10⁻⁵ |
| 7 | B | ⁷⁹Br/⁸¹Br ≈ 1:1 gives equal M and M+2 peaks (Cl would give 3:1) |
| 8 | D | Indicator range must span the equivalence pH of 8.9 |
| 9 | B | Conjugate acid = HCO₃⁻ + H⁺ = H₂CO₃ |
| 10 | A | Hydrophobic tails into grease, hydrophilic heads to water |
| 11 | B | Heating favours the endothermic (forward) direction ⇒ blue [CoCl₄]²⁻ |
| 12 | D | ΔG = ΔH − TΔS < 0 only at high T requires ΔH > 0 and ΔS > 0 |
| 13 | B | Alcohol gives the alkyl part (methyl), acid the -oate part (propanoate) |
| 14 | C | Ksp = [Ag⁺]²[CrO₄²⁻] = (2s)²(s) = 4s³ |
| 15 | C | AAS is the standard trace-metal technique |
| 16 | A | Acidic start (pH 2.9), buffer region, basic equivalence point |
| 17 | D | Polyester = diol + dicarboxylic acid condensation |
| 18 | A | CH₃ (3H) split by 2H into a triplet; CH₂ (2H) split by 3H into a quartet |
| 19 | C | Excess OH⁻ = 1.25 mmol / 50.0 mL = 0.025 mol L⁻¹; pOH 1.60; pH 12.40 |
| 20 | A | Ka is temperature-dependent only; equilibrium shifts to ions on dilution |
Q21. X = dilute sulfuric acid (or H₃PO₄) catalyst; major product propan-2-ol (OH on the central carbon per Markovnikov).
Q22 (a). q = 250.0 × 4.18 × 20.0 = 20 900 J = 20.9 kJ; n = 0.850/60.09 = 1.41 × 10⁻² mol; ΔcH = −20.9/0.01415 = −1.48 × 10³ kJ mol⁻¹. (b). Major heat losses to the surroundings, the can and by incomplete combustion mean not all released energy heats the water. Improvement: insulate/shield the apparatus or reduce the flame-to-can distance (any justified change that channels more heat into the water; "repeat trials" alone is reliability, not accuracy — no mark).
Q23. CH₃COO⁻ + H₂O ⇌ CH₃COOH + OH⁻; Kb = Kw/Ka = 5.6 × 10⁻¹⁰; x = √(5.6 × 10⁻¹⁰ × 0.25) = 1.18 × 10⁻⁵ (approximation valid: x/c ≈ 0.005% ≪ 5%); pOH = 4.93; pH = 9.07.
Q24 (a). [N₂O₄] continuous at t₁ (no step), rising with decreasing gradient to a higher plateau. (b). Added NO₂ raises [NO₂], so NO₂–NO₂ collision frequency and hence forward rate rise immediately; the reverse rate is initially unchanged. Because forward rate > reverse rate, net conversion to N₂O₄ occurs; as [NO₂] falls and [N₂O₄] rises the forward rate falls and reverse rate rises until the rates are equal again. Le Chatelier alone (without rates) caps at 1 mark.
Q25. Check: K = 1.40²/(0.200 × 0.200) = 49.0 ✓. Let a = mol I₂ added; shift forward by x: 1.40 + 2x = 1.60 ⇒ x = 0.100. New [H₂] = 0.100; K = 1.60²/(0.100 × (0.100 + a)) = 49.0 ⇒ 0.100 + a = 2.56/4.90 = 0.522 ⇒ a = 0.42 mol (concentrations, not moles, in K; here V = 1.00 L so they coincide numerically — working must show the expression).
Q26 (a). Ba²⁺(aq) + 2OH⁻(aq) + 2H⁺(aq) + SO₄²⁻(aq) → BaSO₄(s) + 2H₂O(l). Conductivity falls because the highly mobile OH⁻ ions are converted to water and Ba²⁺ is removed as insoluble BaSO₄ — the ions are removed without replacement; near zero at equivalence because almost no ions remain; rises after equivalence as excess H⁺ (very high mobility) and SO₄²⁻ accumulate. (b). n(H₂SO₄) = 0.100 × 0.0220 = 2.20 × 10⁻³ mol = n(Ba(OH)₂); c = 2.20 × 10⁻³/0.0250 = 0.0880 mol L⁻¹.
Q27 (a). From the calibration line: 0.264/0.110 = 2.4 mg L⁻¹ in the diluted sample; dilution factor 250.0/25.00 = 10; undiluted = 24 mg L⁻¹. (b). 24 mg L⁻¹ ÷ 63.55 g mol⁻¹ = 3.8 × 10⁻⁴ mol L⁻¹ > 8.0 × 10⁻⁵ mol L⁻¹ (≈ 4.7 × the limit) ⇒ not compliant.
Q28 (a). At half-equivalence (12.5 mL) pH = pKa = 4.87 ⇒ Ka = 10⁻⁴·⁸⁷ = 1.3 × 10⁻⁵. Annotation of the half-equivalence volume required. (b). At equivalence only the propanoate ion is present; CH₃CH₂COO⁻ + H₂O ⇌ CH₃CH₂COOH + OH⁻ generates excess OH⁻, so pH > 7.
Q29 (a). All three sulfates are insoluble or slightly soluble: Ba²⁺ + SO₄²⁻ → BaSO₄(s), Pb²⁺ + SO₄²⁻ → PbSO₄(s) (and CaSO₄ may also form), so a white precipitate does not distinguish the cations. (b). Valid sequence, e.g.: (1) add NaCl(aq) or dilute HCl — white precipitate PbCl₂(s) only if Pb²⁺: Pb²⁺(aq) + 2Cl⁻(aq) → PbCl₂(s); Ba²⁺/Ca²⁺ give no precipitate. (2) If no precipitate, flame test: apple-green ⇒ Ba²⁺, brick-red ⇒ Ca²⁺ (or add F⁻/SO₄²⁻ with correct solubility logic). Marks for correct order, observations for every cation, and net ionic equations with states.
Q30. At low temperature the equilibrium yield is high but the rate is far too slow to be economic (few molecules exceed the activation energy); raising the temperature increases the fraction of successful collisions and the rate, though it shifts the exothermic equilibrium backwards. 450 °C is a compromise between acceptable rate and acceptable yield.
Q31 (a). CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ and HCl + NaOH → NaCl + H₂O. (b). Titre 1 (20.10 mL) is an outlier — exclude; mean concordant titre = (19.20 + 19.15 + 19.25)/3 = 19.20 mL. n(NaOH) = 1.920 × 10⁻³ mol = n(excess HCl) per 25.00 mL aliquot; × 10 = 1.920 × 10⁻² mol excess HCl total. Initial HCl = 0.02500 mol; reacted with tablet = 5.80 × 10⁻³ mol; n(CaCO₃) = 2.90 × 10⁻³ mol; mass = 0.290 g (290 mg). (c). 290 mg is 3% below the 300 mg claim — a justified verdict either way scores (e.g. does not fully support the claim, or is within reasonable experimental uncertainty of it).
Q32. CH₃COOH ⇌ CH₃COO⁻ + H⁺. Added H⁺ reacts with the large reservoir of CH₃COO⁻ (equilibrium shifts left), so [H⁺] rises only slightly; added OH⁻ removes H⁺ and the equilibrium shifts right, ethanoic acid ionising to replace it. Both components must be present in comparable, substantial amounts; both directions required for full marks.
Q33 (a). BaSO₄ begins at [SO₄²⁻] = 1.08 × 10⁻¹⁰/0.010 = 1.1 × 10⁻⁸ mol L⁻¹; CaSO₄ at 4.93 × 10⁻⁵/0.010 = 4.9 × 10⁻³ mol L⁻¹ ⇒ BaSO₄ first (by ~10⁵ times). (b). When CaSO₄ just starts, [SO₄²⁻] = 4.93 × 10⁻³ ⇒ [Ba²⁺] = 1.08 × 10⁻¹⁰/4.93 × 10⁻³ = 2.2 × 10⁻⁸ mol L⁻¹ — essentially all Ba²⁺ (99.9998%) is removed before any CaSO₄ forms, so filtering at this point separates the ions.
Q34 (a). ΔG = 178 − 298 × 0.161 = +130 kJ mol⁻¹ ⇒ not spontaneous at 25 °C. (b). ΔG = 0 at T = 178/0.161 = 1.11 × 10³ K (≈ 833 °C); spontaneous above this temperature.
Q35 (a). B = 2-methylpropan-2-ol (tertiary, major by Markovnikov); C = 2-methylpropan-1-ol (primary); D = 2-methylpropanoic acid (primary alcohol fully oxidised by excess oxidant under reflux). Full structural formulae required. (b). E = ethyl 2-methylpropanoate, (CH₃)₂CHCOOCH₂CH₃. (c). B is a tertiary alcohol: the carbon bearing the OH has no hydrogen atom to be removed, so it cannot be oxidised by dichromate.
Q36. Neutralisation itself (H⁺ + OH⁻ → H₂O) releases the same energy per mole, but ethanoic acid is only partially ionised; part of the released energy is consumed breaking the O–H bonds ionising the remaining molecular acid as the equilibrium shifts, so the net measured enthalpy is less exothermic.
Q37. X = propan-2-yl ethanoate (isopropyl ethanoate), CH₃COOCH(CH₃)₂, made from propan-2-ol. Justification: M⁺ = 102 matches C₅H₁₀O₂; base peak m/z 43 = CH₃CO⁺ (acylium; C₃H₇⁺ also accepted with reasoning), m/z 87 = M − CH₃, m/z 59 = CH₃COO⁺; IR 1743 cm⁻¹ ester C=O with C–O at 1240/1050 and no O–H rules out acid/alcohol; ¹³C: 4 environments for 5 carbons ⇒ two equivalent CH₃ (δ 170.7 C=O, δ 67.3 O–CH); ¹H: septet 1H at δ 4.99 (CH adjacent to 6H, deshielded by O), doublet 6H (two CH₃ adjacent to 1H), singlet 3H at δ 2.01 (CH₃C=O, no neighbours). Marks: correct structure + name (2), each spectrum explicitly linked (4), base-peak fragment identified (1), integration vs splitting used correctly (1), alcohol named (1).
| Paper item | Prediction | Agreement |
|---|---|---|
|
Section I Q3 ↑ Q3 |
chem-q12-iupac-naming-mc | 0.63 · 5 (fable, opus, gpt-5.6-sol, grok, deepseek) |
|
Section I Q4 ↑ Q4 |
topic-level consensus | 0.65 (fable) · 3 (fable, gpt-5.6-sol, opus-adjacent) |
|
Section I Q5 ↑ Q5 |
topic-level consensus | 0.6–0.7 · 3 (fable, opus, gpt-5.6-sol) |
|
Section I Q6 ↑ Q6 |
topic-level consensus | 0.55 (grok) · 2 (grok, opus) |
|
Section I Q7 ↑ Q7 |
topic-level consensus | 0.45 (fable) · 2 (fable, gpt-5.6-sol) |
|
Section I Q8 ↑ Q8 |
topic-level consensus | 0.85 (gemini-3.1-pro) · 3 (gemini-3.1-pro, grok, gpt-5.6-sol) |
|
Section I Q10 ↑ Q10 |
watch list | 0.35 (fable) · 1 (fable) |
|
Section I Q18 ↑ Q18 |
topic-level consensus | 0.62 (grok) · 3 (grok, fable, opus) |
|
Section I Q19 ↑ Q19 |
topic-level consensus | 0.42 (grok) · 2 (grok, gemini-3.1-pro) |
|
Section I Q20 ↑ Q20 |
topic-level consensus | 0.60 (fable) · 1 (fable) |
|
Q21 ↑ Q21 |
topic-level consensus | — · — |
|
Q22 ↑ Q22 |
chem-q10-calorimetry-returns | 0.58 · 3 (fable, grok, opus) |
|
Q23 ↑ Q23 |
chem-q7-salt-hydrolysis-ph | 0.53 · 4 (fable, opus, grok, deepseek) |
|
Q24 ↑ Q24 |
chem-q6-collision-theory-disturbance | 0.56 · 6 (all) |
|
Q25 ↑ Q25 |
chem-q2-keq-ice-added-species | 0.56 · 5 (fable, opus, gpt-5.6-sol, grok, gemini-3.1-pro) |
|
Q26 ↑ Q26 |
chem-q11-conductometric-titration | 0.51 · 4 (fable, gpt-5.6-sol, gemini-3.1-pro, deepseek) |
|
Q27 ↑ Q27 |
chem-q8-calibration-curve-dilution | 0.55 · 5 (fable, opus, gpt-5.6-sol, grok, deepseek) |
|
Q28 ↑ Q28 |
watch list | 0.58 (gpt-5.6-sol), 0.45 (opus) · 2 |
|
Q29 ↑ Q29 |
chem-q9-ion-testing-sequence | 0.55 · 6 (all) |
|
Q30 ↑ Q30 |
topic-level consensus | P(examined) 0.65, 3/6 models rest it · — |
|
Q31 ↑ Q31 |
chem-q4-back-titration-consumer-claim | 0.61 · 5 (fable, opus, gpt-5.6-sol, grok, deepseek) |
|
Q32 ↑ Q32 |
watch list | 0.55 (fable), 0.65 (gemini-3.1-pro), 0.48 (grok) · 3 |
|
Q33 ↑ Q33 |
chem-q3-competing-precipitation | 0.53 · 5 (fable, opus, gpt-5.6-sol, grok, deepseek) |
|
Q34 ↑ Q34 |
watch list | 0.60 (fable), 0.42 (opus) · 2 |
|
Q35 ↑ Q35 |
chem-q5-reaction-pathway-flowchart | 0.57 · 6 (all) |
|
Q36 ↑ Q36 |
watch list | 0.35–0.42 · 3 (fable, gpt-5.6-sol, opus) |
|
Q37 ↑ Q37 |
chem-q1-spectroscopy-capstone | 0.72 · 6 (all) |
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Published Aug 2026, before the exams. In November 2026 we score these predictions publicly against the real paper — per-model calibration and question-level hit rates, the same harness as the 2025 backtest. How we did it.