Question

How would you test whether the substance is alkane and or alkene?

Answer 1

Alkanes are defined as the organic compounds which have a single bond between the carbon atoms. The general formula for alkanes is ${{C}_{n}}{{H}_{2n+2}}$ . Alkanes are of different types- branched alkanes, cycloalkanes and chain alkanes whereas alkenes are compounds that have double bonds between the carbon atoms. Its general formula is ${{C}_{n}}{{H}_{2n}}$ .

Complete step-by-step answer: The test used to differentiate between alkane and alkene is Bromine test. It is used to detect the unsaturation in a compound. It is an additional reaction in which bromine water is used. It can be made in the laboratory by mixing fumes of bromine with water. Bromine has a very good oxidising property and it is of yellow colour. Bromine water can also be prepared by ionization of $NaBr$ in presence of hydrochloric acid and bleach.
Firstly we will test alkene with bromine water-
When alkene is reacted with bromine water, the bromine molecule undergoes additional reactions. The bromine water is of yellow colour but when the bromine is added to double bond it decolours its colour. The colour of bromine changes from yellow to colourless.
Now we will test alkane with bromine water-
When alkane is reacted with bromine water, the bromine molecule does not undergo addition reaction because it is a saturated molecule that means there is no presence of double bonds. Hence no reaction will take place when bromine water is reacted with alkane.

Note: We should note that the bromine water test takes place at room temperature in case of gaseous alkenes. The bromine water will take place in the presence of $CC{{l}_{4}}$ in case of liquid alkenes. This test only works by halogenations mechanism.