Zinc is a metal that reacts with dilute sulfuric acid. A student is asked to plan the preparation of pure, dry crystals of zinc sulfate, starting with zinc ...
Question 1 Report
Zinc is a metal that reacts with dilute sulfuric acid. A student is asked to plan the preparation of pure, dry crystals of zinc sulfate, starting with zinc powder and dilute sulfuric acid. No apparatus diagram is provided.
(a) Plan a method the student could use to prepare dry crystals of zinc sulfate. Your plan should include how to make sure all of the acid reacts, how to remove the excess zinc, and how to obtain the dry crystals. [4]
(b) Name the apparatus the student uses to separate the excess zinc from the solution. [1]
(c) State the name of the gas that is given off during the reaction. [1]
Answer Details
This question tests planning the preparation of a pure, dry soluble salt from a metal and an acid: react in excess metal, filter, then crystallise.
(a) A suitable plan, any four steps [4]:
- Warm the dilute sulfuric acid in a beaker (this speeds up the reaction) [1].
- Add zinc powder a little at a time until no more dissolves, so the zinc is in excess and all the acid has reacted [1].
- Filter the mixture to remove the excess zinc, leaving zinc sulfate solution as the filtrate [1].
- Heat the filtrate to the point of crystallisation (until crystals just start to form) and leave it to cool so crystals grow [1].
- Dry the crystals between sheets of filter paper [1].
The reaction is \(Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2\).
(b) The excess zinc is separated from the solution using a filter funnel and filter paper [1].
(c) The gas given off during the reaction is hydrogen [1] (it burns with a squeaky pop). [Total 6]
Exam tip: use excess metal to guarantee no leftover acid, then crystallise (not evaporate to dryness) so the salt keeps its water of crystallisation and forms proper crystals.
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