Answer:
pH is 7.60
Explanation:
Let's think the equations:
HClO + H₂O ⇄ ClO⁻ + H₃O⁺
As every weak acid, we make an equilbrium
The salt is dissociated in solution
NaClO → Na⁺ + ClO⁻
HClO + H₂O ⇄ ClO⁻ + H₃O⁺
Initially 0.3m 0.35m
We have the moles of acid, and the moles of conjugate base.
Reacts x X X
Some amount has reacted, so I obtained (in equilibrium) the moles of base + that amount, and the same amount for H₃O⁺ (ratio is 1:1)
HClO + H₂O ⇄ ClO⁻ + H₃O⁺
0.3 - x 0.35 + x x
Let's make the expression for Ka
Ka = [ClO⁻] . [H₃O⁺] / [HClO]
(we don't add water, because it is included in Ka)
2.9x10⁻⁸ = (0.35+x).x / (0.3-x)
Ka is in order of 10⁻⁸, I can assume that 0.3-x is 0.3 and 0.35 +x =0.3
2.9x10⁻⁸ = (0.35)x / (0.3)
(2.9x10⁻⁸ . 0.3) /0.35 = x
2.48x10⁻⁸ = x
This is [H₃O⁺]
For pH = - log [H₃O⁺]
pH = 7.60
