Guided lesson

Tests for Water

4CH1-2.494CH1-2.50

2 guided lessons · 18 checks · 2. Inorganic Chemistry → Chemical Tests

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Chemical test for water

Anhydrous copper(II) sulfate is the chemical detective for water: the white powder turns blue the moment water is added, because it binds five water molecules into its crystal structure. The change from white to blue is the positive result, and the equation shows the water joining the salt rather than merely wetting it.

What you know already

From Tests for Cations you already know how precipitate colours and a litmus-confirmable gas identify ions in solution. This note turns to the solvent itself, with a chemical test and a physical test that together establish both the presence and the purity of water.

Key points of understanding

White anhydrous copper(II) sulfate turns blue when water is added.
The equation is CuSO4 plus 5H2O giving CuSO4.5H2O.
The white colour belongs to the anhydrous form.
The blue colour belongs to the hydrated form with five waters.
Copper sulfate crystals turn light blue in the presence of water.

copper sulfate crystals — Copper sulfate turns a light blue colour in the presence of water

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1.Chemical test for water

4CH1-2.49

Key points

White anhydrous copper(II) sulfate turns blue when water is added.
The equation is CuSO4 plus 5H2O giving CuSO4.5H2O.
The white colour belongs to the anhydrous form.

Guided content from the SME authoring corpus — note rn_YWDXCCmjfjkJcs6c, pinned at a8889009338b · promoted SyllabAI/syllabai-resources e967e75f1339

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2.Physical test for water

4CH1-2.50

The physical test asks whether a liquid sample is pure water by checking its boiling point. A little of the liquid is heated gently in a boiling tube with a thermometer, and pure water boils at exactly 100 degrees Celsius. Dissolved impurities push the boiling point higher, and they also depress the melting point, so a reading above 100 signals contamination.