6-2.Equilibrium-II (Ionic Equilibrium)Medium

It has been found that the $pH$ of a $0.01$ $M$ solution of an organic acid is $4.15 .$ Calculate the concentration of the anion, the ionization constant of the acid and its $p{K_a}$

Solution

Let the organic acid be $HA$.

$\Rightarrow HA \longleftrightarrow H ^{+}+ A$

Concentration of $HA =0.01 \,M \,pH$

$=4.15$

$-\log \left[ H ^{+}\right]=4.15$

$\left[ H ^{+}\right]=7.08 \times 10^{-5}$

Now, $K_{a}=\frac{\left[ H ^{+}\right]\left[ A ^{-}\right]}{[ HA ]}$

$\left[ H ^{+}\right]=\left[ A ^{-}\right]=7.08 \times 10^{-5}$

$[ HA ]=0.01$

Then, $K_{a}=\frac{\left(7.08 \times 10^{-5}\right)\left(7.08 \times 10^{-5}\right)}{0.01}$

$K_{a}=5.01 \times 10^{-7}$

$p K_{a}=-\log K_{a}$

$=-\log \left(5.01 \times 10^{-7}\right)$

$p K_{a}=6.3001$

Derive the equation of ionization constants ${K_a}$ of weak acids $HX$.

Advanced

Medium

Difficult

Medium

Medium