Question

Which of the following acids give effervescence on reaction with sodium carbonate?
A.Methanoic acid
B.Propanoic acid
C.Ethanoic acid
D.All of these

Answer 1

Hint:Baking soda being the salt of a strong base and a weak acid is slightly basic in nature. It reacts with any acid liberating carbon dioxide gas which is marked by a fizzy sound and the release of effervescence.

Complete step by step answer:
In the above options, all are organic acids and the strength of the organic acids depend a lot on the number of carbon atoms present or the length of the chain. The greater the number of the carbon atoms or alkyl groups, the stronger will be the bond between oxygen and hydrogen of the carboxylic group and hence the lesser is the availability of the proton.
So, among the three organic acids, methanoic acid or formic acid will be most acidic, followed by ethanoic acid or acetic acid, and lastly propanoic acid.
All the acids will react will sodium carbonate to release carbon dioxide by the following reaction:
\[\text{RCOOH + N}{{\text{a}}_{\text{2}}}\text{C}{{\text{O}}_{\text{3}}}\to \text{RCOONa + C}{{\text{O}}_{\text{2}}}\text{ + }{{\text{H}}_{\text{2}}}\text{O}\]

Hence the correct answer is option D, all of these.

Note:
Carboxylic acid is an organic acid with the functional group $\text{RCOOH}$ which is milder than the inorganic acids like sulphuric acids. Baking soda is formed due to the reaction between sodium hydroxide and carbonic acid. As carbonic acid is unstable, it is generally prepared by heating sodium hydrogen carbonate. This is slightly basic in nature and in the presence of a proton, it dissociates to form sodium salt of the proton along with water and carbon dioxide.