Question

Calculate the pKa of hypochlorous acid (HClO, a weak acid). A 0.015 M solution of hypochlorous acid has a pH of 4.64.

Answer 1

Answer:

"7.46" is the correct answer.

Explanation:

Given that:

$pH=4.64$

$C=0.015 \ M$

The equation:

⇒ $HA \rightleftharpoons H^++A^-$

HA = C - Cα

H⁺ = Cα

A⁻ = Cα

now,

⇒ $pH=-log(H^+)$

          $=-log(C \alpha)$

          $=4.64$

    $C \alpha = 2.3\times 10^-5 \ M$

As we know,

⇒ $K_a=C \alpha^2$

         $=(\frac{C \alpha}{C} )^2\times C$

         $=\frac{(2.3\times 10^{-5})^2}{0.015}$

         $=3.5\times 10^{-8}$

hence,

⇒ $pK_a=-log(K_a)$

           $=7.46$