Question

Assign appropriate reason for the following:

Hydrogen fluoride is a much weaker acid than HCl in aqueous solution.

Answer 1

1. HF is a weaker acid than HCl because the \[\ce{H - F}\] bond is very strong, requiring more energy to break.
2. The bond dissociation energy of \[\ce{H - F}\] (574 kJ/mol) is higher than \[\ce{H - Cl}\] (432 kJ/mol), making HF less likely to ionise in water.
3. HF molecules strongly associate via hydrogen bonding, reducing free H⁺ ions in solution, thus lowering acidity.
4. HCl dissociates more easily to release H₃O⁺ ions, making it a stronger acid in aqueous solution.