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Testing for Gases

What are the General Tests for Sulfur Dioxide Gas?

1)  Sulfur dioxide gas, SO_2(g) has no colour.

2)  Sulfur dioxide gas smells like burnt matches.

3)  Sulfur dioxide gas turns moist litmus paper from blue to red
and moist universal indicator paper to red - it is acidic.

4)  Sulfur dioxide gas will put out a lit splint.

What is the Specific Test for Sulfur Dioxide Gas?

Sulfur dioxide gas turns acidified
potassium dichromate(VI) solution from orange to green.
Chromium is reduced from (VI) to (III).

       potassium        sulfur      sulfuric       chromium(III)    potassium                 
  dichromate(VI) + dioxide   +  acid          sulfate      +    sulfate   +  water.    

 K₂Cr₂O_7(aq) + 3SO_2(g) + H₂SO_4(aq)  Cr₂(SO₄)_3(aq) + K₂SO_4(aq) + H₂O_(l)

How is Sulfur Dioxide Gas Collected?

Sulfur dioxide gas is more dense than air and can be
collected by downward delivery or by using a gas syringe.

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