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WAEC Chemistry 2017 Paper

Question : 32

Total: 50

Solution:

Concept:

Anhydrous copper sulphate is white and turns blue when hydrated.

Explanation:

White anhydrous copper sulphate,

\mathrm{CuSO}_4

, absorbs water to form blue copper sulphate pentahydrate,

\mathrm{CuSO}_4 \cdot 5\mathrm{H}_2\mathrm{O}

The reaction is:

\mathrm{CuSO}_4(s) + 5\mathrm{H}_2\mathrm{O}(l) \rightarrow \mathrm{CuSO}_4 \cdot 5\mathrm{H}_2\mathrm{O}(s)

White

\rightarrow

Blue.

Other options like

\mathrm{FeSO}_4

\mathrm{Na}_2\mathrm{SO}_4

, and

\mathrm{PbSO}_4

do not show this colour change.

Answer:

\mathrm{CuSO}_4

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