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Cambridge practical and extended reasoning

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AI-assisted English content review; independent teacher approval pending.

Practice scope and review

Original, AI-authored English practice with worked guidance. Selected topics only; independent teacher review is pending. This is not a complete syllabus, official past-paper collection or predicted exam score. Check your own exam-board specification: these concepts are not certified against a particular board or exam year.

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Cambridge International AS & A Level Chemistry (9701), examination year 2027: AI-assisted conceptual alignment to official sources, not teacher or exam-board certification. Syllabus mapping and remaining coverage.

4 questions in this topic

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Original multi-stage supplied-data practice. Partial written support only, not complete syllabus coverage, official results or practical certification.

Subtopics in this topic (4)
  • Titre selection, bounds and dilution bias
  • Neutralisation heat and competing corrections
  • Initial rate, order and collection delay
  • Chromatography identity claims and uncertainty

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Question 1Fictional titres / cm^3 are rough 25.10, then 24.60, 24.65, 24.60. A stated selection rule accepts non-rough titres within 0.10 cm^3. Each neutralises 25.00 cm^3 of monoprotic acid with 0.1000 mol/dm^3 NaOH. Calculate the mean and acid concentration, retaining guard digits. Each burette reading has maximum error 0.05 cm^3; the acid pipette has maximum error 0.03 cm^3. Treat titrant concentration as exact; estimate a first-order worst-case concentration percentage bound. Explain why dividing the reading bound by sqrt(3) is unjustified, and predict the bias from water remaining in the titrant burette. Give a connected worked response with calculations, justified conclusions and limitations. All datasets are original fictional practice, not official experiment results. Written/supplied-data work only; any actual laboratory or field activity requires teacher approval, risk assessment and supervision. No human trials. Primary reading: https://www.cambridgeinternational.org/Images/664563-2025-2027-syllabus.pdf5 indicative marks
Calculate, analyse and evaluate5 indicative marksCalculator allowed

Fictional titres / cm^3 are rough 25.10, then 24.60, 24.65, 24.60. A stated selection rule accepts non-rough titres within 0.10 cm^3. Each neutralises 25.00 cm^3 of monoprotic acid with 0.1000 mol/dm^3 NaOH. Calculate the mean and acid concentration, retaining guard digits. Each burette reading has maximum error 0.05 cm^3; the acid pipette has maximum error 0.03 cm^3. Treat titrant concentration as exact; estimate a first-order worst-case concentration percentage bound. Explain why dividing the reading bound by sqrt(3) is unjustified, and predict the bias from water remaining in the titrant burette. Give a connected worked response with calculations, justified conclusions and limitations. All datasets are original fictional practice, not official experiment results. Written/supplied-data work only; any actual laboratory or field activity requires teacher approval, risk assessment and supervision. No human trials. Primary reading: https://www.cambridgeinternational.org/Images/664563-2025-2027-syllabus.pdf

Cambridge 2027: Partial conceptual match

Titre selection, bounds and dilution bias: selected written evidence only. Selected titres, unrounded mean, molar balance and additive reading/pipette bounds independently calculated; direction of dilution bias checked. Science practical-N and computing rN rows are internal identifiers, not official numbered leaf syllabus codes. Aggregate rows are only partially supported. Actual apparatus use, candidate coding execution and practical attainment are not demonstrated here. Independent teacher review remains required.

AI-assisted placement. Independent teacher approval pending.

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Worked guidance

  1. Keep the rough result in the record but exclude it under the declared rule. The other three span 0.05 cm^3, so all qualify. Their sum is 73.85 cm^3 and mean 24.6166667 cm^3. For HA + NaOH -> NaA + H2O, n(NaOH) = 0.1000 x 24.6166667/1000 mol and c(HA) = n/0.02500 = 0.0984667 mol/dm^3.
  2. Two endpoint bounds add to 0.10 cm^3. The first-order ratio bound is 100(0.10/24.6166667 + 0.03/25.00) = 0.52623%. This excludes endpoint chemistry and titrant uncertainty, so it is not a full uncertainty statement. Averaging can reduce independent random variation, not a shared burette calibration error.
  3. A wet unconditioned burette makes actual base concentration smaller than the value entered in the calculation. More volume is then required for the same acid amount; multiplying by the nominal concentration biases acid concentration high. Endpoint overshoot is another plausible high-bias mechanism, distinguishable by procedural records. Real corrosive solutions require a teacher-approved risk assessment, eye protection and supervised technique; no titration is to be performed from these data.

Self-marking points

View marking points
  1. Use the three non-rough titres: mean 24.6167 cm^3, recorded as 24.62 cm^3.
  2. The 1:1 acid concentration is 0.09847 mol/dm^3 at four significant figures.
  3. Titre bound is 0.10 cm^3 from two readings; concentration bound is about 0.526%.
  4. A common calibration bound is not reduced simply because three titres were averaged.
  5. Water dilution of titrant tends to require a larger titre and overestimate acid concentration if nominal NaOH concentration is used.

Examiner tip

Indicative original worked practice, independent teacher approval pending. Explain assumptions and alternatives; do not equate a correct written answer with observed practical performance.

Question 2Written fictional calorimetry: 25.0 cm^3 of 1.00 mol/dm^3 monoprotic acid and 25.0 cm^3 of 1.00 mol/dm^3 NaOH start at the same temperature. Mixed solution mass is 50.0 g, specific heat capacity 4.18 J/(g K), cup heat capacity 20.0 J/K, observed rise 5.00 K. Calculate the reaction enthalpy per mole neutralised. A cooling-line extrapolation instead gives 5.40 K at mixing time. Recalculate, explain the sign and bias direction, and evaluate why the extrapolation is not automatically the true value. No experiment is requested. Give a connected worked response with calculations, justified conclusions and limitations. All datasets are original fictional practice, not official experiment results. Written/supplied-data work only; any actual laboratory or field activity requires teacher approval, risk assessment and supervision. No human trials. Primary reading: https://www.cambridgeinternational.org/Images/664563-2025-2027-syllabus.pdf5 indicative marks
Calculate, analyse and evaluate5 indicative marksCalculator allowed

Written fictional calorimetry: 25.0 cm^3 of 1.00 mol/dm^3 monoprotic acid and 25.0 cm^3 of 1.00 mol/dm^3 NaOH start at the same temperature. Mixed solution mass is 50.0 g, specific heat capacity 4.18 J/(g K), cup heat capacity 20.0 J/K, observed rise 5.00 K. Calculate the reaction enthalpy per mole neutralised. A cooling-line extrapolation instead gives 5.40 K at mixing time. Recalculate, explain the sign and bias direction, and evaluate why the extrapolation is not automatically the true value. No experiment is requested. Give a connected worked response with calculations, justified conclusions and limitations. All datasets are original fictional practice, not official experiment results. Written/supplied-data work only; any actual laboratory or field activity requires teacher approval, risk assessment and supervision. No human trials. Primary reading: https://www.cambridgeinternational.org/Images/664563-2025-2027-syllabus.pdf

Cambridge 2027: Partial conceptual match

Neutralisation heat and competing corrections: selected written evidence only. Both heat-capacity terms, stoichiometric amount, signs and two enthalpy estimates independently checked; RSC context not attributed invented results. Science practical-N and computing rN rows are internal identifiers, not official numbered leaf syllabus codes. Aggregate rows are only partially supported. Actual apparatus use, candidate coding execution and practical attainment are not demonstrated here. Independent teacher review remains required.

AI-assisted placement. Independent teacher approval pending.

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Worked guidance

  1. The equal 1:1 amounts are 1.00 x 0.0250 = 0.0250 mol. Include both heat capacities: q = (50.0 x 4.18 + 20.0) x 5.00 = 1145 J. Thus delta H = -1145/0.0250/1000 = -45.8 kJ/mol. The minus sign belongs to the chemical reaction, not to the warming cup.
  2. At 5.40 K, q = 229 x 5.40 = 1236.6 J and delta H = -49.464 kJ/mol, rounded to -49.5. The correction increases the release magnitude by 3.66 kJ/mol before rounding. Neither number is presented as an official Cambridge result or a measured standard enthalpy.
  3. Loss to surroundings before the maximum and omission of the cup both bias the magnitude downward in this model. Extrapolation can fail if mixing is slow, the sensor lags or the cooling trend is not locally suitable. Inspect a temperature-time record and independent repeats, keep starting temperatures matched and state the water-like heat-capacity approximation. RSC's class-practical safety notes motivate teacher approval and suitable eye protection; this is supplied-data analysis, not its protocol or permission for home chemistry.

Self-marking points

View marking points
  1. Amount neutralised is 0.0250 mol and observed heat absorbed is 1145 J.
  2. Observed enthalpy is -45.8 kJ/mol; corrected estimate is -49.5 kJ/mol.
  3. The reaction releases energy while the solution and cup absorb it; signs are opposite.
  4. Uncorrected heat loss tends to reduce the magnitude of the exothermic estimate; neglecting cup capacity also reduces it.
  5. Cooling extrapolation depends on timing, mixing and an appropriate heat-loss model, not merely a more negative answer.

Examiner tip

Indicative original worked practice, independent teacher approval pending. Explain assumptions and alternatives; do not equate a correct written answer with observed practical performance.

Question 3Fictional gas-volume records at t = 0, 10, 20 s are A: 0.0, 8.0, 14.0 cm^3 and B: 0.0, 15.5, 25.0 cm^3. Reactant X concentrations are 0.100 and 0.200 mol/dm^3 respectively, at equal total volume, other reactant excess and matched temperature. Estimate early rates over 0-10 s and the apparent order in X using n=ln(rateB/rateA)/ln(2). Compare with 10-20 s rates and evaluate the claim that these data prove first order. Outline controls, replicates and a collection check for a teacher-approved system, not a reagent recipe. Give a connected worked response with calculations, justified conclusions and limitations. All datasets are original fictional practice, not official experiment results. Written/supplied-data work only; any actual laboratory or field activity requires teacher approval, risk assessment and supervision. No human trials. Primary reading: https://www.cambridgeinternational.org/Images/664563-2025-2027-syllabus.pdf5 indicative marks
Calculate, analyse and evaluate5 indicative marksCalculator allowed

Fictional gas-volume records at t = 0, 10, 20 s are A: 0.0, 8.0, 14.0 cm^3 and B: 0.0, 15.5, 25.0 cm^3. Reactant X concentrations are 0.100 and 0.200 mol/dm^3 respectively, at equal total volume, other reactant excess and matched temperature. Estimate early rates over 0-10 s and the apparent order in X using n=ln(rateB/rateA)/ln(2). Compare with 10-20 s rates and evaluate the claim that these data prove first order. Outline controls, replicates and a collection check for a teacher-approved system, not a reagent recipe. Give a connected worked response with calculations, justified conclusions and limitations. All datasets are original fictional practice, not official experiment results. Written/supplied-data work only; any actual laboratory or field activity requires teacher approval, risk assessment and supervision. No human trials. Primary reading: https://www.cambridgeinternational.org/Images/664563-2025-2027-syllabus.pdf

Cambridge 2027: Partial conceptual match

Initial rate, order and collection delay: selected written evidence only. Both finite slopes, log rate order and late slopes independently checked; finite-interval and recovery limitations explicit. Science practical-N and computing rN rows are internal identifiers, not official numbered leaf syllabus codes. Aggregate rows are only partially supported. Actual apparatus use, candidate coding execution and practical attainment are not demonstrated here. Independent teacher review remains required.

AI-assisted placement. Independent teacher approval pending.

Show indicative guidance

Worked guidance

  1. Divide each first volume increment by 10 s: 8.0/10 = 0.800 and 15.5/10 = 1.55 cm^3/s. Their ratio is 1.9375, giving ln(1.9375)/ln(2) = 0.95420. This is near one but no error bars are supplied, so numerical closeness alone cannot establish an order.
  2. The next interval gives (14.0 - 8.0)/10 = 0.600 and (25.0 - 15.5)/10 = 0.950 cm^3/s. Faster depletion in B, gas dissolution or delayed collection could all distort the initial ratio. An initial tangent from denser early-time records is a plausible alternative estimator if the start is captured reliably.
  3. A written plan should vary X across several settings with constant final volume, repeat independently in randomised order, and record temperature and time-zero conventions. A collection-efficiency or leak check addresses gas recovery; it does not establish reaction mechanism. A teacher must select and risk-assess any actual reaction and venting arrangement. These invented records are not an instruction to make gas or seal a reaction vessel.

Self-marking points

View marking points
  1. Early interval rates are 0.800 and 1.55 cm^3/s.
  2. Apparent order is 0.954, approximately 0.95, using these interval estimates.
  3. Later rates are 0.600 and 0.950 cm^3/s, showing substantial change within each run.
  4. A finite early average is not an exact initial tangent; uncertainty and more concentrations are needed before claiming first order.
  5. Keep geometry, temperature, mixing and other concentrations fixed; check leaks and start delay without pressure build-up.

Examiner tip

Indicative original worked practice, independent teacher approval pending. Explain assumptions and alternatives; do not equate a correct written answer with observed practical performance.

Question 4A fictional TLC record has origin-to-solvent-front distance 8.0 +/- 0.1 cm. Unknown U has spots at 2.4 +/- 0.1 and 5.6 +/- 0.1 cm; standard S has one at 5.6 cm on the same plate. Quoted errors are maximum bounds and may vary independently for a ratio bound. Calculate both Rf values and exact endpoint bounds for the upper spot. Evaluate 'U is pure S'. Propose a stronger comparison and explain why measurements begin at the origin, not the plate edge; provide a safety boundary without prescribing a solvent. Give a connected worked response with calculations, justified conclusions and limitations. All datasets are original fictional practice, not official experiment results. Written/supplied-data work only; any actual laboratory or field activity requires teacher approval, risk assessment and supervision. No human trials. Primary reading: https://www.cambridgeinternational.org/Images/664563-2025-2027-syllabus.pdf5 indicative marks
Calculate, analyse and evaluate5 indicative marksCalculator allowed

A fictional TLC record has origin-to-solvent-front distance 8.0 +/- 0.1 cm. Unknown U has spots at 2.4 +/- 0.1 and 5.6 +/- 0.1 cm; standard S has one at 5.6 cm on the same plate. Quoted errors are maximum bounds and may vary independently for a ratio bound. Calculate both Rf values and exact endpoint bounds for the upper spot. Evaluate 'U is pure S'. Propose a stronger comparison and explain why measurements begin at the origin, not the plate edge; provide a safety boundary without prescribing a solvent. Give a connected worked response with calculations, justified conclusions and limitations. All datasets are original fictional practice, not official experiment results. Written/supplied-data work only; any actual laboratory or field activity requires teacher approval, risk assessment and supervision. No human trials. Primary reading: https://www.cambridgeinternational.org/Images/664563-2025-2027-syllabus.pdf

Cambridge 2027: Partial conceptual match

Chromatography identity claims and uncertainty: selected written evidence only. Dimensionless ratios and independent endpoint bounds checked; purity and identity separated from shared-front correlation. Science practical-N and computing rN rows are internal identifiers, not official numbered leaf syllabus codes. Aggregate rows are only partially supported. Actual apparatus use, candidate coding execution and practical attainment are not demonstrated here. Independent teacher review remains required.

AI-assisted placement. Independent teacher approval pending.

Show indicative guidance

Worked guidance

  1. Use migration from the baseline: 2.4/8.0 = 0.30 and 5.6/8.0 = 0.70. Both numerator and denominator are lengths so Rf has no unit. Measuring from the plate edge adds an arbitrary offset and changes the ratios.
  2. To minimise the upper ratio combine the smallest numerator with largest denominator: 5.5/8.1 = 0.67901; the largest ratio is 5.7/7.9 = 0.72152. Rounded bounds are 0.679 to 0.722, not a claimed confidence interval. Shared front uncertainty also correlates Rf values on the same plate.
  3. The extra spot contradicts 'pure S' as a simple one-component interpretation, but degradation or contamination are alternatives needing investigation. The upper spot is consistent with S in this system, not uniquely identified. Co-spotting and a second teacher-selected separation can help distinguish co-migrants; a single spot might still hide multiple compounds or undetected material. This written evaluation authorises no solvent use or home chromatography.

Self-marking points

View marking points
  1. Rf values are 0.30 and 0.70, dimensionless.
  2. Upper-spot ratio bounds are 5.5/8.1 = 0.679 and 5.7/7.9 = 0.722.
  3. Two resolved spots argue against a single pure component under these conditions; co-migration with S does not prove identity.
  4. Compare U, S and a co-spot under another suitable separation system; non-detection still does not establish absolute purity.
  5. Distances share the same origin; teacher-approved solvent handling, ventilation and disposal are required for actual TLC.

Examiner tip

Indicative original worked practice, independent teacher approval pending. Explain assumptions and alternatives; do not equate a correct written answer with observed practical performance.

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