Five ion exchange reactions

Getting multicolored precipitations

Scientific name: Getting multicolored precipitates by ion exchange reactions


Copper (II) Hydroxide Precipitate

by LNHSChemistry

Iron complexes

by Adam Bridgeman

Copper(II) complexes and precipitates

by Hegelrast

Barium chromate precipitate

by ChemToddler

Nickel complexes

by ChemToddler


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Reaction formula

FeCl3 + 6KSCN → K3[Fe(SCN)6] + 3KCl

K2CrO4 + BaCl2 → BaCrO4 + 2KCl

NiSO4 + 2NaOH → Ni(OH)2 + Na2SO4

CuSO4 + 2NaOH → Cu(OH)2 + Na2SO4

CuSO4 + 4NH4OH → [Cu(NH3)4]SO4 + 4H2O

Step-by-step instruction

  1. Take a test-tube, pour 3 ml of iron (III) chloride solution into it. Add dropwise 1-3 ml of potassium thiocyanate and shake the mixture. You now have a red or dark-red solution of K3[Fe(SCN)6].
  2. Take 1 g of potassium chromate and dissolve it in 5 ml of water in the first test-tube. Dissolve 1 g of barium chloride in 5 ml of water in the second test-tube. Add dropwise 1-3 ml of barium chloride solution to the first test-tube. You now have a bright-yellow precipitate of BaCrO4.
  3. Dissolve 1 g of nickel (II) sulphate-hexahydrate in 5 ml of water in a test-tube. Add dropwise 1 ml of sodium hydroxide solution. You now have a light-green precipitate of Ni(OH)2.
  4. Take a test-tube, pour 3 ml of copper sulphate solution and add dropwise 1 ml of sodium hydroxide. You now have a light-blue precipitate of Cu(OH)2.
  5. Take a test-tube, pour 3 ml of copper sulphate solution and add dropwise 1 ml of ammonium hydroxide. You now have a bright-blue solution of [Cu(NH3)4]SO4.

Scientific background

Some salts, hydroxides and complexes have a bright color. This is due to the characteristics of their chemical structure. Generally, the production of brightly colored compounds is used as a qualitative reaction for one of the reagents. A Qualitative reaction is a reaction that allows us to say whether there is a substance in a solution or not, but does not allow you to say how much of it there is. When we added potassium thiocyanate to iron (III) chloride solution, a red compound was formed:

FeCl3 + 6KSCN → K3[Fe(SCN)6] + 3KCl.

This compound can be used as "chemical blood".

For the detection of chromate CrO42- ions in the solution, barium Ba2+ ions can be used:

K2CrO4 + BaCl2 → BaCrO4 + 2KCl

In this reaction a yellow precipitate was formed. Also this reaction can be used for the detection of barium ions in the solution.

Some hydroxides have different colors. In this experiment green nickel hydroxide Ni(OH)2 and blue copper hydroxide Cu(OH)2 were formed. These colors are typical for many of the compounds of copper and nickel, respectively.

But if we add ammonia instead of sodium hydroxide to the solution of copper sulphate, we get a bright blue complex [Cu(NH3)4]SO4. Its color is due to the special unit of the coordination sphere of copper (the coordination sphere in the formula is written in square brackets).


Published on 08 October 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst