Copper complexes

Discover the bright colors of copper complexes!

10 minutes
Copper complexes



  • Put on protective gloves and eyewear.
  • Conduct the experiment on the plastic tray.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

I think I used too much of the reagent. What should I do?

Don't worry! Keep doing the experiment and see what happens. When you’re done, you can try repeating the experiment with the correct measurements and comparing your results.

Step-by-step instructions

Prepare three vials of different solutions. As you can see, all of the solutions are colorless.


Add some copper sulfate CuSO4 to each vial. Copper sulfate has a distinctive blue tint.


Shake each vial to mix the contents.


Every vial now has a distinct color, and none of these colors look like the result of mixing the initially-colorless solutions with the blue copper sulfate solution. That’s a sure sign of a chemical reaction!



Dispose of solid waste together with household garbage. Pour solutions down the sink. Wash with an excess of water.

Scientific description

Have all the solutions changed their colors? Well done – you did it! Now let's talk about what happened in each of them!

When we started, we had three colorless solutions in three vials, and a blue solution of copper sulfate CuSO4 to add to each of them.

Why is copper sulfate CuSO4 blue? In water, copper sulfate gives copper ions Cu2+ closely surrounded by 6 water molecules – [Cu(H2O)6]2+ – and this particle is what tints the solution blue!

In the first vial, adding this copper sulfate CuSO4 to calcium chloride CaCl2 turns the solution green! This color comes from a new particle – [CuCl4]2- – which is made of one copper ion Cu2+ from CuSO4 and 4 chloride ions Cl- provided by CaCl2:

Cu2+ + 4Cl- ⇄ [CuCl4]2-

You can also notice a precipitate forming: this is slightly-soluble calcium sulfate CaSO4, formed by two more ions in the solution – calcium ions Ca2+ and sulfate ions SO42-:

Ca2++ SO42- → CaSO4

Now let’s move on to the second vial! There’s a precipitate here too – from a reaction between carbonate CO32- and hydroxide OH- ions (provided by sodium carbonate Na2CO3 in solution) and the copper ions Cu2+ from CuSO4. The resulting compound is called basic copper carbonate (CuOH)2CO3, and its composition is just like that of a beautiful mineral known as malachite:

2Cu2+ + 2OH- + CO32- → (CuOH)2CO3

What a charming deep-blue solution in the third vial! It also owes its color to a particle – [Cu(NH3)4]2+ – which forms when 4 ammonia molecules NH3 provided by ammonium carbonate (NH4)2CO3 meet a copper ion Cu2+ from CuSO4.

Cu2+ + 4NH3 ⇄ [Cu(NH3)4]2+

You can also notice some bubbles forming as carbon dioxide CO2 is released from (NH4)2CO3:

(NH4)2CO3 → 2NH3 + CO2↑ + H2O