Determine the pH of a 0.048 M hypochlorous acid (HClO) solution. Hypochlorous acid is a weak acid (Ka = 4.0 ✕ 10−8 M).

pH of 0.048 M HClO is 4.35.

Explanation:

HClO is a weak acid and it is dissociated as,

HClO ⇄ H⁺ + ClO⁻

We can write the equilibrium expression as,

Ka =

Ka = 4.0 × 10⁻⁸ M

4.0 × 10⁻⁸ M =

Now we can find x by rewriting the equation as,

x² =  4.0 × 10⁻⁸ × 0.048

   = 1.92 × 10⁻⁹

Taking sqrt on both sides, we will get,

x = [H⁺] = 4.38 × 10⁻⁵

pH = -log₁₀[H⁺]

     = - log₁₀[ 4.38 × 10⁻⁵]

   = 4.35

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