9701_s26_qp_24 — 2026 May-June Chemistry 9701 Question Paper 2 Variant 4 · Cambridge CAIE AS & A Level

Imprecise curly arrows in organic mechanisms

“A curly arrow should start clearly on a bond or on a lone pair and the arrowhead should point clearly in the direction of the destination of the electron pair.”— Paper 4, May/June 2024

How to fix: Practice drawing mechanisms with a ruler. For EVERY curly arrow: (1) tail starts on a lone pair or the CENTRE of a bond, never on an atom; (2) head points to the exact atom or bond where the electron pair is going. In electrophilic substitution, the first arrow starts INSIDE the benzene ring circle. The intermediate's positive charge goes inside the partially delocalised ring, NOT on the sp³ carbon. The second arrow starts on the C–H BOND, not on the H atom.

Stating facts without explaining HOW or WHY

“Candidates are reminded to address 'explain' questions fully — not merely to state facts or rules of thumb, but then to show how these combine to give reasons for chemical phenomena.”— Paper 2, March 2025

How to fix: When a question says 'explain': State the fact THEN link it to the consequence. For example, don't just say 'nuclear charge increases' — say 'nuclear charge increases, so the attraction between the nucleus and the bonding electrons is stronger, which means more energy is needed to break the bond'. Build chains: Cause → Mechanism → Effect.

Imprecise or incomplete definitions

“Most answers omitted that the elements were required to be in their 'standard states'.”— Paper 2, May/June 2024

How to fix: Learn these definitions WORD-PERFECT: lattice energy, enthalpy of formation, enthalpy of neutralisation, ionisation energy, electronegativity, buffer solution, coordination number, standard cell potential. Write them out from memory and check against the syllabus. Every missing keyword (e.g. 'gaseous', 'standard states', '1 mole') costs a mark.