How many chemical reactions can you identify by using the solution of copper(II) sulfate and solution A

Identify solution A, and see how many reactions you can make.

This session should take one hour.


Materials per group

  • Aqueous copper(II) sulfate, 0.25 mol dm–3
  • Aqueous ammonium carbonate, 0.25 mol dm–3, labelled A.

Equipment per group

  • Test tubes
  • Test tube racks
  • Glass rods
  • pH paper
  • Lime water
  • Safety glasses

Health, safety and technical notes

  • Read our standard health and safety guidance here.
  • Wear eye protection.
  • This is an open problem and requires the students to exercise care and make careful observations.


One approach is to look at solution A first. On warming, this solution evolves ammonia, which gives the characteristic smell and carbon dioxide.

On mixing solution A with aqueous copper sulfate a blue/green precipitate (Cu(OH)2. CuCO3) is formed initially.

On adding excess A, this dissolves to form a deep blue solution of Cu(NH3)42+(aq).

Evaluation of solution 

The best answers are those that identify A, and identify the correct reactions. Some of these can be written as:

  1. (NH4)2 CO3 (aq) ⇌ 2NH3 (aq) + “H2 CO3 ”(aq)
  2. (NH4)2 CO3 (aq) ⇌ 2NH4+(aq) + CO32–(aq)
  3. NH4 +(aq) + H2O(l) ⇌ NH3 (g) + H3O+(aq)
  4. CO32–(aq) + H2O(l) ⇌ HCO3–(aq) + OH–(aq)
  5. “H2CO3 ”(aq) ⇌ H2O(l) + CO2 (g)
  6. Cu2+(aq) + 2OH(aq) ⇌ Cu(OH)2(s)
  7. Cu2+(aq) + CO32–(aq) ⇌ CuCO3(s)
  8. Cu2+(aq) + 4NH3 (aq) ⇌ Cu(NH3)4 2+(aq)
  9. Ca(OH)2 (s) + CO2 (g) → CaCO3 (s) + H2O(l)
  10. CaCO3(s) + H2O(l) + CO2 (g) →  Ca(HCO3)2 (aq)


This resource is part of a collection of problem-solving activities, designed to engage learners in small group work. Find out how to use these resources, and obtain a list of suggested ‘junk items’ here.