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}
