A) and (B) are two unsaturated hydrocarbons, each containing 2 carbon atoms. On reaction with bromine, (A) adds one molecule of bromine per molecule and (B) adds two molecules of bromine per molecule. Write structural formula of (A) and (B). Write balanced chemical equation of reaction of (B) with bromine.

(A) and (B) are two unsaturated hydrocarbons, each containing 2 carbon atoms. On reaction with bromine, (A) adds one molecule of bromine per molecule and (B) adds two molecules of bromine per molecule. Write structural formula of (A) and (B). Write balanced chemical equation of reaction of (B) with bromine.

Ans.

The structural formula of (A) and (B): (A) and (B) are two unsaturated hydrocarbons, which means they have at least one double or triple bond between carbon atoms. Since they have 2 carbon atoms each, they can only have one double or triple bond. The general formula for a hydrocarbon with a double bond is CnH2n, and the general formula for a hydrocarbon with a triple bond is CnH2n-2. Therefore, (A) and (B) must have the following structural formulas:
- (A): CH2=CH2. This is called ethene or ethylene. It has one double bond between the two carbon atoms.
- (B): HC≡CH. This is called ethyne or acetylene. It has one triple bond between the two carbon atoms.
Balanced chemical equation of reaction of (B) with bromine: When an unsaturated hydrocarbon reacts with bromine, it undergoes an addition reaction, in which the bromine atoms are added across the double or triple bond. The number of bromine molecules that are added depends on the number of bonds that are broken. For example, ethene adds one molecule of bromine per molecule, while ethyne adds two molecules of bromine per molecule. The balanced chemical equation of reaction of (B) with bromine is:
- HC≡CH + 2Br2 → BrC≡CBr + 2HBr
- This means that one molecule of ethyne reacts with two molecules of bromine to produce one molecule of 1,2-dibromoethyne and two molecules of hydrogen bromide.

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