Water of crystallization
To show the presence of water in a coordination complex, not as an impurity but as part of the structure of the crystals.
What students learn
The science behind this experiment
Copper ions coordinate easily with water molecules to form coloured crystals or solutions. There is a marked difference in colour between anhydrous copper sulphate and the hydrate. This experiment shows the presence of water in the coordination complex.
Heating hydrated copper sulphate, CuSO4•5H2O, drives off the water coordinated with the copper ions.
Equipment used
- Test tubes — 1473.60
- Test tube rack — 1680.06
- Test tube holder — 5423.30
- Spatula — 5460.34
- Spirit burner — 5514.10
Chemicals and reagents
- Copper sulphate — R:22-35/38-50/53 S:22-60-61
Safety notes
- Take care when working with the burner and hot glassware.
Questions for students
- Record your observations.
What to expect
<p>Some water vapour condenses on the upper part of the test tube, confirming the presence of water in the compound. The blue copper sulphate becomes dirty white in colour, showing that the water is not an impurity in the crystals but that a change in the chemical composition of the substance has occurred.</p><p>On adding a few drops of distilled water, the anhydrous copper sulphate becomes blue again showing that the hydrate has reformed.</p>
Disposal
Dissolve the copper sulphate in water and dispose into the liquid wastes container.
Run this experiment in your classroom
This experiment is part of the ATP Mobile Lab — a self-contained laboratory that turns an ordinary classroom into a working science lab, with over 200 experiments in physics, chemistry, biology, robotics and engineering. Gali, the AI tutor built into ATP Connect, guides students through each step and answers their questions at the bench.
See the Mobile LabTalk to our team