Question

Q.25 Which one show more acidic character in the following * O Benzoic acid O Methanoic acid O Propanoic acid O Ethanoic acid​

Answer 1

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Answer 2

Methanoic acid shows more acidic character

Explanation:

• For determining the acidity of a carboxylic acid , we need to look at the deprotonated form of the acid $RCOO^{-}$.
• The major difference in these acids lies in their $-R$ group. Incase of methanoic acid , it is $-H$  , $-CH_3$ , for ethanoic acid and it is $-C_2H_5$ incase of propanoic acid .
• The higher carbon R groups exert a greater electron withdrawing inductive effect on the carboxyl group. Therefore the negative charge on oxygen intensifies .
• This in turn  destabilizes the$-CH_3COO^-$ ion, leading to a lesser extent of dissociation of ethanoic acid and propanoic acid in comparison to methanoic acid.
• Incase of benzoic acid , the benzoate ion becomes more destabilized due to the more pronounced $+R$ effect even though little -I (inductive effect ) is there. This causes more stability and hence more acidity of formate ion in methanoic acid.
• Therefore, methanoic acid shows the maximum acidic character.