Question

Do cycloalkanes decolourise bromine water?

Answer 1

Cycloalkanes are defined as a saturated ring structure which is a cyclic hydrocarbon. The carbon atoms are singly bonded with other carbon atoms and form rings. The smallest cycloalkane present is cyclopropane. Cycloalkanes consist of hydrogen and carbon.

Complete step-by-step answer: Bromine water is also known as bromine solution. It is a yellow coloured solution which acts as a high oxidising agent. In the laboratory, we can prepare bromine water by mixing fumes of bromine and water. But this method is not safe; therefore we use a more convenient method for the preparation of bromine water. We break down sodium bromide in the presence of hydrochloric acid and bleach. Firstly, sodium bromide is dissolved in hydrochloric acid and mixes the compounds in the beaker. After that, pour the mixture in the glass bottle and cap the bottle, swirl it gently and add some distilled water. Again swirl it gently.
Bromine water can decolourise alkene and therefore we can identify the presence of alkene in the molecule. It converts a yellow solution into a colourless solution. However, cycloalkanes do not decolourise bromine water because it consists of single carbon- carbon bonds which means that the molecule is saturated and it will show no reaction when cycloalkanes reacts with bromine water. The yellow colour of bromine remains as such.

Note: The unsaturated hydrocarbons are very much volatile than the saturated hydrocarbons. Hence, unsaturated hydrocarbons react easily with bromine solution and disappear the colour of bromine into colourless. Bromine water is used to test the presence of alkene in the solution.