Question

When sodium benzoate is heated with soda lime, it gives:
A. benzene
B. benzoic acid
C. calcium benzoate
D. none of these

Answer 1

Hint:The chemical formula of sodium benzoate is ${{{C}}_6}{{{H}}_5}{{COONa}}$ and that of soda lime is ${{CaHNa}}{{{O}}_2}$. We know that the soda lime is obtained when calcium oxide is mixed with sodium hydroxide. Sodium benzoate has been used as a food preservative for long days.

Complete answer:
Sodium benzoate is a chemical which is used to preserve beverages. The maximum limit of usage of sodium benzoate is $0.1\% $ of the weight of the product. Little amount of sodium benzoate is naturally found in some fruits like apples, prunes etc. Soda lime is used in respiration. It eliminates carbon dioxide and prevents carbon dioxide poisoning. It is used as a drying agent. It absorbs carbon dioxide.
Decarboxylation reaction is a chemical reaction in which carbon dioxide is removed from any compound. While carboxylation is the addition of carbon dioxide to any compound. Decarboxylation reaction is possible only if there is a carboxyl group in the compound.
When sodium benzoate is heated with soda lime, it undergoes decarboxylation. The carboxyl group in sodium benzoate is converted to sodium carbonate. It also forms benzene. The chemical reaction is given below:
${{{C}}_6}{{{H}}_5}{{COONa}} + {{NaOH}}\xrightarrow[\Delta ]{{{{CaO}}}}{{{C}}_6}{{{H}}_6} + {{N}}{{{a}}_2}{{C}}{{{O}}_3}$
Thus the major product formed when sodium benzoate is heated with soda lime is benzene.

Hence, the correct option is A.

Note:
Benzoic acid can directly produce benzene. This process is called pyrolysis. The term pyro means heat or high temperature and lysis means break or decompose.
The decarboxylation of sodium benzoate in the presence of soda lime occurs at lower temperatures. Benzoic acid can also produce benzene by decarboxylation reaction. This reaction is called the Duma reaction.