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70
Chemistry of the Environment
Chemical Tests for Water
Cobalt (II) Chloride:
Anhydrous Cobalt (II) Chloride is blue in colour. Cobalt (II) Chloride paper is used to test the
presence of water. In the presence of water, it changes from blue to pink.
anhydrous cobalt(II) chloride + water ⇌ hydrated cobalt(II) chloride
CoCl (s) + 6H O (l) ⇌ CoCl •6H O (s)
Copper (II) Sulfate:
Anhydrous Copper (II) Sulfate is white in colour and can be used to test the presence of water. In
the presence of water, it changes from white to blue.
anhydrous copper(II) sulfate + water ⇌ hydrated copper(II) sulfate
CuSO (s) + 5H O (l) ⇌ CuSO •5H O (s)
Tests for the Purity of Water
All pure substances have a fixed melting and boiling point. The melting point of pure water is 0℃
and the boiling point of pure water is 100℃. When water is mixed with impurities, the boiling
point tends to increase while the melting point tends to decrease.
Distilled Water
Distilled water is created by heating water until it turns into vapour and then condensing it back
into a liquid. This process removes most impurities, making distilled water highly pure. It is often
used in practical chemistry for this reason, while tap water, which contains more impurities, is
generally avoided as it can interfere with chemical reactions.