Question

Describe two chemical tests that can be used to distinguish between the following pair of compounds?

PLEASE, WRITE OUT THE EQUATIONS, INCLUDING THE REAGENTS AND THE PRODUCTS.
i) butane and 2-butene

Answer 1

Try the bromine decolourization test and the Baeyer unsaturation tests.

Explanation:

Test 1. Bromine decolourization test

Add a few drops of a solution of `"Br"_2` in `"CCl"_4` to a solution of each hydrocarbon in `"CCl"_4`.

The butane will not react (left-hand test tube). The but-2-ene will decolourize the bromine solution (right-hand test tube).

`"CH"_3"CH=CHCH"_3 + underbrace("Br"_2)_color(red)("brown") → underbrace("CH"_3"CHBrCHBrCH"_3)_color(red)("colourless")`

Test 2. The Baeyer test

Bubble each gas through a cold, dilute, aqueous solution of `"KMnO"_4`.

With butane, there will be no colour change (top test tube).

With but-2-ene, the purple colour will disappear and a dark brown precipitate will form (bottom test tube).

`"3CH"_3"CH=CHCH"_3 + underbrace("2MnO"_4^"-")_color(red)("purple") + 4"H"_2"O"`

`→ "3CH"_3"CH(OH)CH(OH)CH"_3 + underbrace("2MnO"_2)_color(red)("dark brown precipitate") + 2"OH"^"-"`