9701_s26_ci_35 — 2026 May-June Chemistry 9701 Confidential Instructions 3 Variant 5 · Cambridge CAIE AS & A Level

Using incorrect practical observation language

“'Gas released' is not credited in place of effervescence. 'No observation' is not the same as 'no visible change'. 'Clear' is not a colour.”— Paper 3, March 2025

How to fix: Memorise these rules: (1) 'White precipitate' with limewater — NOT 'milky' or 'cloudy'. (2) 'Colourless' NOT 'clear' — clear means transparent, not a colour. (3) 'Effervescence' or 'bubbling' — NOT 'gas released'. (4) 'No visible change' — NOT 'no observation'. (5) A precipitate only forms when two solutions mix — adding a solid is NOT precipitate formation. (6) Always state the INITIAL colour before describing a colour change.

Premature rounding and significant figure errors in calculations

“Harsh or early rounding of numbers should be avoided, as it leads to sizable inaccuracies later.”— Paper 2, March 2025

How to fix: Keep full calculator values until the FINAL answer. Give final answers to 3 significant figures unless told otherwise. Never give 1 sf. In multi-step calculations, show each step labelled (e.g. '[OH⁻] = 0.0158 mol dm⁻³') — examiners cannot award marks for unexplained numbers picked out of working.

Errors in q = mcΔT enthalpy calculations

“Common errors were the use of the mass of the solid instead of the solution, and use of 4.2 for c instead of 4.18.”— Paper 3, May/June 2024

How to fix: Three rules: (1) Use the mass of the SOLUTION (usually water), NOT the mass of the solid being dissolved. (2) Use c = 4.18 J g⁻¹ K⁻¹ (not 4.2). (3) Do NOT add 273 to a temperature CHANGE — a change in °C equals a change in K. Also convert J to kJ (÷1000) and divide by moles for ΔH in kJ mol⁻¹.