Precipitation and complexation of copper(II) with an ammonia solution

Chemicals needed

ammonia solution 3,5 %

distilled water

copper(II) sulfate (or pentahydrate) Xn    N    R 22-36/38-50/53    S (2)-26-36/37/39-60-61

Equipment needed

test tube

Test procedure

• Add into a test tube a small spatula-tipful copper(II) sulfate and dissolve with approx. 1 ml distilled water. A clear, slighty light blue solution develops.
• Add dropwise ammonia solution 3.5%. A voluminous, tough blue deposit is precipitated, which with further additions of ammonia is again dissolved, forming a clear, dark blue solution.

Disposal

The diluted solution can be discharged into the drainage.

Elucidation

Copper(II) precipitates like many metallic cations in an alkaline milieu as a hydroxide. With a surplus of ammonia the soluble copper(II) tetraammine complex is formed - [Cu(NH3)4]²⁺.

Photos

diluted copper(II) sulfate solution

Precipitation of copper(II) hydroxide

copper(II) tetraammine solutions

Literature

derived from a school experiment