Question

give a chemical test to distinguish between saturated and unsaturated hydrocarbons

Answer 1

A chemical test to distinguish between saturated and unsaturated hydrocarbon.

Bromine water test - Unsaturated hydrocarbon gives addition reaction with Br2. So the colour of Br2-water gets decolourized.

R-C=C=R + Br2 --> R-BrC-CBr-R

whereas,

Saturated hydrocarbons do not react with Br2-water so the colour of Br2 -water does not get decolourised.

Answer 2

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By adding  cold dilute Baeyer's reagnant

More about Baeyer's Reagnant.

• Baeyer's reagnant is cold dilute

• It is an oxidising agent.

If this mixture is added to an unsaturated compounds such as alkenes or alkanes then :

• Purple colour of  changes .

• It is first converted to a green compound   which is unstable in alkaline medium.

• This again changes to brown  

• The supernatant liquid gets decolourised.

However saturated compounds do not respond to the above test.

In simple words........... your answer is :

In order to test unsaturation first add cold dilute Baeyer's reagnant.

If the reagnant decolorises from purple to colourless then the compound is unsaturated

Otherwise if the reaction does not occur , then it is a saturated compound.

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