Testing for Gases

The Test for Sulfur Dioxide Gas,  SO2(g).

1)  Sulfur dioxide gas has no colour.

2)  Sulfur dioxide gas smells like burnt matches.

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

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


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        arrow      sulfate      +    sulfate   +  water.    

 K2Cr2O7(aq) + 3SO2(g) + H2SO4(aq) arrow Cr2(SO4)3(aq) + K2SO4(aq) + H2O(l)

Collecting Sulfur Dioxide Gas.

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

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