### Ionic Equilibrium Question 2

#### Question 2 - 24 January - Shift 2

If the $pKa$ of lactic acid is 5 , then the $pH$ of 0.005 $M$ calcium lactate solution at $25^{\circ} C$ is____________

$\times 10^{-1}$ (Nearest integer)

## Show Answer

#### Answer: (85)

#### Solution:

#### Formula: Salt hydrolysis of weak acid and strong base

Concentration of calcium lactate $=0.005 M$,:

concentration of lactate ion $=(2 \times 0.005) M$.

Calcium lactate is a salt of weak acid + strong base

$\therefore$ Salt hydrolysis will take place.

$ \begin{aligned} & pH=7+\frac{1}{2}(pKa+\log C) \\ & =7+\frac{1}{2}(5+\log (2 \times 0.005)) \\ & =7+\frac{1}{2}[5-2 \log 10]=7+\frac{1}{2} \times 3=8.5=85 \times 10^{-1} \end{aligned}