Textbook Question 6C.21 Relative Acid Strength of Formic and Acetic Acid?

[Sofia Lucido 3L]

Question 6C.21 in the textbook asks for an explanation of the relative strengths of acetic acid and formic acid. I said that acetic acid was stronger because it is a larger molecule that is therefore better able to distribute the negative charge once the H proton is lost. The textbook said formic acid is slightly stronger, but did not provide reasoning. Can someone explain why?

Thanks!

[Nick Pascua 2L]

Hi,

I think it's because acetic acid has a methyl group while formic acid has a carboxyl group. With that being said, formic acid does not have an electron-donating group unlike acetic acid in which the CH3 (methyl grou) contributes electron density to the O-H bond thus making it harder to remove the H. Since formic acid is better at removing H than acetic acid, formic acid is slightly a stronger acid.