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.


Example

Procedure:
  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.

Observation:

  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+

Explanation:
  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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