Overall Verdict & Performance Profile
The May/June 2026 series for Cambridge IGCSE Chemistry (0620) maintains the rigorous standards established by recent syllabus updates. The extended theory (Paper 41) paired with the multiple-choice (Paper 21) and practical components (Papers 51/61) tests a comprehensive spectrum of foundational recall, chemical numeracy, and experimental evaluation. The overall difficulty sits solidly at a moderate level (3.4 / 5.0), rewarding candidates with sharp conceptual definitions and disciplined mathematical working.
Where the Marks Were Won and Lost
High scoring was prominent in routine atomic structure, isotope abundance calculations, and standard dot-and-cross diagrams. However, significant mark loss was observed in higher-demand physical chemistry areas:
- Electrolysis Mechanics: Explaining why oxygen is liberated at the anode during the electrolysis of dilute aqueous sodium chloride required explicit reference to the discharge of hydroxide ions (\(\text{OH}^-\)) rather than vague mentions of water reactivity.
- Equilibrium Predictions: Application of Le Chatelier’s principle to gaseous systems (e.g., \(\text{N}_2\text{O}_4 \rightleftharpoons 2\text{NO}_2\)) saw common errors where candidates failed to link pressure changes to moles of gas.
- Organic Nomenclature & Polymers: Drawing repeat units of addition polymers (such as poly(propene)) frequently suffered from missing continuation bonds or incorrect carbon backbone alignment.
Key Examiner Pitfalls
Examiner guidance highlighted several repetitive slip-ups: writing element names when ions were required (e.g., writing chlorine instead of chloride), omitting state symbols in precipitation ionic equations (\(\text{Ba}^{2+}\text{(aq)} + \text{SO}_4^{2-}\text{(aq)} \rightarrow \text{BaSO}_4\text{(s)}\)), and failing to record thermometer readings to the nearest 0.5 °C or table entries to consistent decimal places.
Strategic Revision & Future Prediction
For upcoming series, candidates must prioritize thorough practice of mole calculations involving multi-step stoichiometry, acid-base salt preparation sequences, and rates of reaction collision theory explanations with precise terminology (specifically emphasizing the frequency of successful collisions and activation energy).