5070_s26_gt — 2026 May-June Chemistry 5070 Grade Threshold · Cambridge CAIE O Level

Confusing equilibrium with rate of reaction — using collision theory for equilibrium

“Candidates confused equilibrium concepts with rate of reaction, often explaining shifts in equilibrium using collision theory rather than Le Chatelier's principle.”— 5070 Paper 2, May/June 2023

How to fix: Rate of reaction = how fast reactants become products (use collision theory). Equilibrium = which direction a reversible reaction shifts (use Le Chatelier's principle). If a question asks about equilibrium position, never mention collision frequency — explain that the system shifts to counteract the change.

'Produces a gas' is not an observation — must say effervescence/bubbling

“Candidates stated that a gas was produced rather than describing the observable evidence such as effervescence or bubbling.”— 5070 Paper 2, May/June 2023

How to fix: An observation is what you SEE, HEAR, or SMELL. 'A gas is produced' is a conclusion, not an observation. Write 'effervescence/bubbling' instead. Similarly: 'heat is released' should be 'temperature increases' or 'test tube becomes warm to touch'.

Drawing organic structures with wrong valencies — missing hydrogens, pentavalent carbon

“Many candidates drew organic structures with incorrect valencies, commonly showing carbon with five bonds or omitting hydrogen atoms, resulting in invalid structural formulae.”— 5070 Paper 2, May/June 2023

How to fix: Carbon ALWAYS makes exactly 4 bonds. After drawing a structure, count the bonds on every carbon atom — if any has more or fewer than 4, it is wrong. Add hydrogen atoms to fill any empty bonds. Oxygen = 2 bonds, nitrogen = 3 bonds, hydrogen = 1 bond.