1. Tardigrade
  2. Question
  3. Chemistry
  4. The dissociation constant of a weak acid HA is 4.9 × 10 - 8 After making the necessary approximations, calculate (i) pH (ii) OH - concentration in a decimolar solution of the acid. (Water has a pH of 7).

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Q. The dissociation constant of a weak acid $HA$ is $ 4.9 \times 10^{ - 8 } $ After making the necessary approximations, calculate
(i) pH
(ii) $OH^ - $ concentration in a decimolar solution of the acid. (Water has a pH of $7$).

IIT JEEIIT JEE 1983Equilibrium

Solution:

Molarity $(C) = 0.10$,
$ [ H^+ ] = \sqrt{ K_a \cdot C } = 7 \times 10^{ - 5 } \, M$ ($\alpha$ is negligible)
$p H = 4.15$
$ [ OH^- ] = \frac{ K_w }{ [ H^+ ] } = \frac{ 10^{ - 14 }}{ 7 \times 10^{ - 5 }} = 1.43 \times 10^{ - 10} \, M$