Qualitative reaction on iron II

Presence of Fe(II) ions causes the formation of precipitates.

Scientific name: Qualitative reaction on Fe(II) ions with potassium hexacyanoferrate and potassium hydroxide is demonstrated.


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Reaction formula

3Fe2+ + 2[Fe(CN)6]3- → Fe3[Fe(CN)6]2-

Fe2+ + 2OH- → Fe(OH)2

Step-by-step instruction

  1. Prepare a solution which you want to test on presence of Fe2+ ions. For demonstration take iron (II) sulfate solution.
  2. Add a few drops of potassium hexacyanoferrate solution. If the solution under study contains Fe2+ ions the formation of a dark blue precipitate is observed.
  3. Another way to determine the presence of Fe2+ ions is the reaction with sodium hydroxide. Add a few drops of sodium hydroxide solution to the solution under study. If it contains Fe2+ ions the formation of a greenish-white precipitate will be observed.

Scientific background

Qualitative analysis is the determination of the presence of an element in the compounds and mixtures without estimation of its amount. Qualitative reactions are one of the most common tools of qualitative analysis. If the sample under study contains ions specific to the qualitative reaction the release of gas bubbles or precipitate formation or color change is expected. This experiment demonstrates the way to detect 2+ ions. Iron (II) sulfate is used for testing qualitative reactions on Fe2+ ions. When iron (II) sulfate solution is mixed with potassium hexacyanoferrate (III) solution it forms a dark blue precipitate of iron (II) hexacyanoferrate (III)

3Fe2+ + 2[Fe(CN)6]3- → Fe3[Fe(CN)6]2-

Potassium hydroxide could also be used for detecting Fe2+ ions. It reacts with Fe2+ ions producing a greenish-white iron (II) hydroxide.

Fe2+ + 2OH- → Fe(OH)2


Published on 16 April 2015

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