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Experiment 23: Prepare Sulphur dioxide gas

Experiment 23: Prepare Sulphur dioxide gas


Prepare and study Sulphur dioxide gas

Materials required:

  • Iron fillings/ nails
  • conc. sulphuric acid
  • dil. sulphuric acid
  • potassium permanganate solution
  • potassium dichromate solution
  • red and blue litmus papers
  • test tube
  • delivery tube


  • Place few pieces of iron filings (about 5 g) in a test tube and arrange the apparatus as shown in Fig
  • Add 5 - 10 mL of conc. sulphuric acid carefully
  • Place the cork in its position on the test tube (along with delivery tube) and heat the contents gently. The gas formation starts after some time.
  • Collect the gas in the gas jar and study its properties as per the steps given in the observation table
  • Dispose the remaining sulphuric acid in the test tube only after diluting with ~250mL of water






    Look at the colour of the gas liberated

    White fumes


    Fan the gas gently towards your nose

    Strong pungent

    Litmus test

    Bring moist blue and red litmus papers

    near to the mouth of the test tube

    Turn wet blue litmus to red

    Reaction with potassium permanganate

    Take about 2 mL of potassium

    permanganate solution in a test

    tube, add about 1 mL of dilute

    HSO4 and pass sulphur dioxide

    gas in this solution.

    Potassium permanganate solution is decolorized

    Reaction with potassium dichromate

    Pass sulphur dioxide through

    another test tube containing

    acidified potassium dichromate


    Orange solution turns green


  • Sulphur dioxide is acidic in nature.
  • It is a strong reducing agent. It decolourises acidified potassium permanganate (KMnO4) solution.
  • Acidified potassium dichromate solution (K2Cr2O2) is also turned green by SO2.
  • The reactions with KMnO2 and K2Cr2O7 are due to the reducing property of SO2 and oxidising nature of acidified KMnO4 and K2Cr2O7.


  • Sulphur dioxide is prepared by the action of hot concentrated sulphuric acid on iron fillings

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