[polexia]

Alkyl groups are electron donating groups and therefore destabilise the carboxylate group, wouldn't the latter molecule with only one alkyl group be a stronger acid?

[magician4]

in fact, CH₃CH₂COOH is the slightly weaker acid ( pKs 4.87) than acetic acid (pKs 4.75), so the whole point of your question is...
... kinda pointless, i would like to say

regards

Ingo

[Babcock_Hall]

The dissociation of a proton from acetic acid to form acetate and a hydronium ion is unfavorable entropically.  IMO explanations about relative acidity of the carboxylic acids should take this effect into account.

[antimatter101]

Search up something called hyperconjugation. If you are interested, continue to search up 'alkyl shift' and 'hydride shift'. Lastly, search up carbocation. You will find that tertiary carbocations are much less than secondary, primary and methyl cations. Then you should understand why ethanoic acid is weaker than methanoic acid.

[MrTeo]

You will find that tertiary carbocations are much less than secondary, primary and methyl cations.

Er, no. It's just the opposite.

[antimatter101]

Er, sorry. Tertiary carbocation are much more stable than secondary, primary or methyl carbocations. I was sleeping when typing.

[trinitrotoluene]

in fact, CH₃CH₂COOH is the slightly weaker acid ( pKs 4.87) than acetic acid (pKs 4.75), so the whole point of your question is...
... kinda pointless, i would like to say

regards

Ingo

If these pKa's are correct, then the question is invalid.

[Borek]

They are correct. pKa for propanoic acid is sometimes given as even slightly higher (but below 5).