Examples of Redox Reaction - Change of Iron(III) Ion to Iron(II) Ion

  1. The change of iron(III) ion for iron(II) ion is a reduction process. This can be done by mixing a reducing agent.


  1. 2 cm³ of iron(III) sulphate solution is poured into a test tube.
  2. Half spatula of zinc powder is added into the solution.
  3. The mixture is then shaken and warmed gently.
  4. The observation is recorded.


  1. Zinc powder dissolves. 
  2. The brown coloured of iron(III) sulphate solution turn light green.

Half Equations:

Fe3+ → Fe2+ + e

Zn  → Zn2+ + 2e

Ionic Equation

2Fe3+ + Zn → 2Fe2+ + Zn2+

  1. The brown colour of iron(III) sulphate solution turns light green shows that iron(III) ions, Fe3+ are
  2. reduced to iron(II) ion, Fe2+.
  3. Iron(III) ion, Fe3+ undergoes reduction by receiving electron to form iron(II) ion,Fe2+
  4. Zinc powder added is oxidised to form zinc ion, Zn2+

Oxidising agent: Iron(III) ions Fe3+
Reducing agent:  Zinc powder

Confirmation Test

2 cm³ of solution of the product is filled into a test tube.

Test 1 : Dilute sodium hydroxide solution (NaOH) is then added into the test tube until excess.
Result : Dirty green precipitate formed. The precipitate does not dissolve in excess sodium hydroxide solution.

Test 2 : Dilute ammonium hydroxide solution (NH4OH)/ammonia aqueous (NH3) is then added into the test tube until excess
Result : Green precipitate formed. The precipitate does not dissolve in excess ammonium hydroxide solution /ammonia aqueous.

Test 3 : 2cm³ of potassium thiocyanate is added into the test tube.
Result : No change observed

Other oxidation agents that get to replace bromine water
  1. Magnesium
    Half Equations
    Mg  → Mg2+ + 2e
  2. Sulphur dioxide gas
    Half Equations
    SO2 +     2H2O →      SO42- +   4H+ +  2e
  3. Hydrogen sulphide gas
    Half Equations
    H2S →     2H+ +  S +  2e
  4. Solution of sodium sulphide, Na2SO3
    Half Equations
    SO32- +  H2O →     SO42- + 2H+ +  2e
  5. Solution of tin(II) Chloride
    Half Equations
    Sn2+ →     Sn4+ +  2e


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