What is the role of phosphoric acid in the ethene hydration reaction?

• A. Catalyst
• B. Solvent
• C. Inhibitor
• D. Reactant

Answer: (A)

Acid-catalyzed hydration of an alkene is being tested here. Phosphoric acid acts as a catalyst by providing protons that start the electrophilic addition to the carbon–carbon double bond of ethene. This creates a more reactive intermediate, water then adds to form ethanol, and the acid is regenerated in the process. Because it is not consumed and does not become part of the final product, its role is to speed up the reaction rather than to supply reactants or become a product. It’s not the solvent, since the reaction occurs with water as a reactant and the acid simply accelerates the process on the catalyst.