Question

Which of the following substance can distinguish butane from butene:

• A. Bromine water
• B. Potassium dichromate
• C. Potassium iodide
• D. sodium hydroxide solution

Answer 1

The correct option is A Bromine water

Unsaturated compounds gives addition reaction with $B{r}_2$ water and decolorize it but saturated cmpounds does not give addition reactions. Hence they can distinguish by flame test as well as by bromine water test.

$B{r}_2$water is a brown coloured liquid.
(a) Unsaturated hydrocarbons give addition reaction with $B{r}_2$. So the colour of $B{r}_2$-water gets decolourized.
$R-C=C-R+B{r}_2\to R-BrC-CBr-R$
(b) Saturated hydrocarbons do not react with $B{r}_2$-water, so the colour of $B{r}_2$.-water does not get decolourised .