C3: Chemical Formulae, Stoichiometry and Hydrated Salts
Official Cambridge & Imperial ESAT specification requirements for Chemical Formulae, Stoichiometry and Hydrated Salts on the Chemistry paper. Understand the syllabus boundaries, spot distractor traps engineered by examiners, and master the 2-step Sub-90 shortcuts that compress solve time well below the 88.8-second cutoff.
Official Syllabus Subtopics
Requirements specified in the UAT-UK framework
- 1Writing and balancing chemical equations with state symbols (s, l, g, aq)
- 2Empirical formula determination from reacting masses or mass percentage composition
- 3Molecular formula from empirical formula and molar mass Mᵣ
- 4Water of crystallisation in hydrated salts: M · xH₂O calculation
Sub-90 Exam Speed Tips
How top candidates solve this spec under the 88.8s clock
To find an empirical formula, divide each element’s mass by its Aᵣ, then divide through by the smallest value.
In hydrated salt heating, ensure mass loss represents purely water vapour loss.
Examiners engineer distractor options using common algebraic expansions and sign slips. Always test structural ratios or invariants before calculating arithmetic values.
Tested Topics in Specification C3
Master the individual question patterns and Sub-90 shortcuts for this specification.
Empirical/Molecular Formula from Reacting Mass Fractions & Hydrated Salt Water of Crystallisation (M·xH2O)
For hydrated salts M·xH2O heated from m(hydrated) to m(anhydrous): m(water) = m(hydrated) - m(anhydrous), and x = (m(water) / 18) ÷ (m(anhydrous) / Mᵣ(anhydrous)). Watch for 1 : 1.33 -> 3 : 4 (Fe3O4) and 1 : 1.5 -> 2 : 3 (Fe2O3).
Ready to Master Specification C3 Under Exam Conditions?
Practice timed questions under the authentic Pearson VUE interface with live split stopwatch pacing, dry-wipe scratchpad, and distractor forensics.