O-LevelChemistryStoichiometry5070/22 · May/June 2022 · Q67 Marks
A sample of an alloy containing aluminium and copper is added to hot dilute sulfuric acid. Only the aluminium reacts with the dilute sulfuric acid. The products of the reaction are hydrogen and aqueous aluminium sulfate.
- (a)Construct the ionic equation, with state symbols, for the reaction of aluminium with dilute sulfuric acid.[2]
- (b)Describe a chemical test for aluminium ions.[2]
- (c)The aqueous aluminium sulfate formed is crystallised to make hydrated aluminium sulfate, Al2(SO4)3•xH2O. The relative formula mass of hydrated aluminium sulfate is 666. Calculate the value of x in the formula Al2(SO4)3•xH2O.[2]
- (d)State what is meant by the term alloy.[1]
Mark scheme
Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.
- [1] 2Al(s) + 6H+(aq) → 2Al³+(aq) + 3H2(g)
- [1] balancing; correct state symbol dependent on formulae
- [1] add (aqueous) sodium hydroxide
- [1] white ppt that redissolves / white ppt. soluble in excess
- [1] OR; add (aqueous) ammonia
- [1] white precipitate
- [1] Mr for aluminium sulfate is 342
- [1] x = 18
- [1] mixture of a metal with another element
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