Overall Verdict & Exam Experience
The May/June 2026 series for Cambridge IGCSE Chemistry (0620 Variant 3) provided a fair and comprehensive test of candidate understanding across the updated syllabus. While standard multiple-choice items in Papers 13 and 23 tested broad factual recall, the extended theory (Paper 43) and practical papers (Papers 53/63) placed significant demands on procedural clarity, rigorous calculation methods, and accurate chemical terminology.
Where the Marks Are Won and Lost
Significant mark allocations were concentrated in core physical and organic chemistry domains:
- Organic Chemistry: High weighting was given to drawing structural isomers, deducing empirical formulae from percentage composition (such as determining \(\text{C}_2\text{H}_3\) from 88.9% C and 11.1% H), identifying condensation monomer pairs (diols and dicarboxylic acids), and drawing two complete repeat units of addition polymers with correct continuation bonds.
- Rates and Energetics: Candidates frequently lost marks in rate explanations by failing to refer explicitly to collision frequency per unit time rather than just collision chance, or failing to state that a higher fraction of particles possess energy \(\ge E_a\).
- Stoichiometry & Quantitative Chemistry: Step-by-step mole calculations from thermal decomposition equations proved highly accessible when working was methodically laid out: converting mass to moles of gas (\(n = m / M_r\)), using the stoichiometric ratio, and calculating reactant mass.
- Experimental Design & Qualitative Analysis: The 6-mark experimental planning task on extracting and titrating oxalic acid with acidified potassium manganate(VII) rewarded structured, logical steps (fixed mass, crushing/extracting with solvent, known aliquot, end-point colour change from purple to colourless, and comparative conclusion).
Examiner Pitfalls & Common Mistakes
Examiner reports highlight recurring errors across components:
- Confusing intermolecular forces between molecules with covalent bonds inside molecules.
- Incomplete definitions: defining an isotope without specifying 'atoms of the same element' or 'same proton number', and defining an alkali without noting it is a soluble base.
- Omitting state symbols when specifically instructed on precipitation ionic equations (e.g. \(\text{Ag}^+(\text{aq}) + \text{Cl}^-(\text{aq}) \rightarrow \text{AgCl}(\text{s})\)).
- Drawing polymer structures with carbon atoms having incorrect valencies or missing open horizontal continuation bonds.
Preparation & Strategic Guidance
Candidates should focus revision on drawing displayed organic structures neatly without shorthand connectivity errors, drilling standard cation/anion flame and precipitation tests, and mastering formal collision theory phrases.