Question

Why maleic acid is more acidic than fumaric acid?

Answer 1

When maleic acid loses hydrogen ion, then it forms a very strong intra-hydrogen bond so the acid is more stable and strong also. Also it contains two carboxyl groups on both sides so it is more stable while in fumaric acid, the carboxyl groups are at opposite ends.

Answer 2

Explanation:

Maleic acid is cis-butenedioic acid whereas fumaric acid is trans-butenedioic acid.

Maleic acid is able to lose $H^{+}$ ion and it results in the formation of intra-hydrogen bond. Whereas fumaric acid being a trans isomer has strong interaction with both the oxygen atoms of each carboxylic group.

Hence, fumaric acid is unable to give hydrogen ions as compared to maleic acid.

That is why, maleic acid is a stronger acid than fumaric acid.