Why is HCl a stronger acid than HF?

1 Answer
Jun 26, 2018

HCl is a strong acid, while HF is a weak acid.

Explanation:

Acid strength refers to how much an acid ionizes when dissolved in water.

In Arrhenius acid-base theory, an acid is a substance which dissolves in water to release one or more H^+ ions.

A strong acid ionizes completely when dissolved in water. For example, when dissolved in water, every single HCl molecule separates into H^+ and Cl^-.

A weak acid only partially ionizes when dissolved in water. For example, when dissolved in water, some HF molecules will separate into H^+ and F^-, but some will remain as HF molecules.

In the case of HF, this behaviour can be attributed to the electronegativity of F. The HF bond is extremely strong, preventing ionization.

The bond in HCl is comparatively weaker, allowing complete ionization.