Question

The first ionisation constant of maleic acid is higher than fumaric acid because

• A. Fumaric acid shows intermolecular H-bonding
• B. Fumaric acids shows intramolecular ionic bonding
• C. Maleic acid is tribasic acid
• D. Maleic acid shows intramolecular H-bonding

Answer 1

Answer: (A), (D)

Maleic acid shows intramolecular H-bonding

Maleic and Fumaric are dibasic acids. Maleic acid is stronger than fumaric acid in its first ionisation, because maleate ion is stabilised by intramolecular hydrogen bonding sinch both COOH group is in cis position. In fumaric acid there is no intramolecular hydrogen bonding because both the COOH group present in trans position so intramolecular hydrogen bonding is not possible for fumaric acid. But fumaric acid will form the intermolecular hydrogen bonding which is weaker than intramolecular hydrogen bonding. Hence Maleic acid is stronger than fumaric acid.
Strong acid will have high ionisation constant, so first ionisation constant for maleic acid is higher than fumaric acid.