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GCSE Chemistry · key term
More reagent than is needed to complete the initial reaction.
Used by AQA, Edexcel and OCR
Specification 4.4.2.3, 4.8.3.2 · Paper 1, Paper 2
More of a reactant than is needed to react completely with the other reactant.
Revise: Preparation of Soluble SaltsEventually, a newly added portion remains even after stirring. This shows that the acid has been used up and the solid is now in excess.
A solution containing more of a reagent than is needed to complete the initial reaction.
Specification 3.15, 9.6C · Paper 1, Paper 2
An amount of reactant greater than the amount needed to react completely with the other reactant.
Revise: Salt Preparation from Insoluble ReactantsContinue adding it until some solid remains even after stirring. This remaining solid shows that more reactant has been added than the acid can use: the solid is in excess.
A quantity of reagent greater than that needed to complete the initial reaction.
Specification C4.2b · Paper 2 (Foundation), Paper 4 (Higher)
Revise: Ion IdentificationContinue adding sodium hydroxide until it is in excess. Zinc hydroxide dissolves to give a colourless solution, whereas the calcium hydroxide precipitate does not dissolve. The copper and iron precipitates also remain in excess sodium hydroxide.
Link each operation to its purpose: excess solid removes all the acid; filtration removes unreacted solid; evaporation concentrates the filtrate; cooling forms crystals; drying removes surface water.
Distinguish the residue from the filtrate: the excess insoluble reactant is the residue, while the salt solution is the filtrate.
When identifying an ion, give both the precipitate colour and what happens in excess sodium hydroxide where relevant.
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