Coordination complexes
To show the formation of coordination complexes of copper ions through reactions with water, ammonia and sodium chloride.
What students learn
The science behind this experiment
When a substance dissolves in water, its molecules and ions are surrounded by water molecules. In some cases the water molecules coordinate with the solute ions, becoming part of a chemical structure with the solute called a coordination complex.
The shape adopted by the complex may be associated with a characteristic colour.
Equipment used
- Test tubes — 1473.60
- Test tube rack — 1680.06
- Test tube holder — 5423.30
- Spatula — 5460.34
- Spirit burner — 5514.10
- Dropping pipette — 1441.50+5448.00
Chemicals and reagents
- Copper sulphate — R:22-35/38-50/53 S:22-60-61
- Ammonia
- Sodium chloride
- Distilled water
Safety notes
- Take care when using the burner and hot glassware.
Questions for students
- Record your observation of the colour of the solution and suggest an explanation.
- What happens on adding more ammonia?
- What happens on adding sodium chloride?
What to expect
<p>Anhydrous copper sulphate has a dirty white colour, whereas the hydrate CuSO4•5H2O has a blue colour because.</p><p>Dissolving either of these salts in water gives a blue solution because the copper ions coordinate with water molecules.</p><p>Adding a small quantity of ammonia makes the pH of the solution shift towards alkaline values and some copper.</p><p>The precipitate dissolves because a tetraammine complex of copper is formed with the ammonia and a royal blue solution is obtained.</p><p>The solution becomes bright green due to the formation of copper(II) chloride complexes.</p>
Disposal
Dispose of the solutions 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