Question

The range of most suitable indicator which should be used for titration of $X^{-}N{a}^{+}$ $(0.1M,10mL)$ with $0.1M$ $HCl$ should be:
(Given that $K_{b\left(X^{-}\right)}={10}^{-6}$)

• A. $2-3$
• B. $3-5$
• C. $6-8$
• D. $8-10$

Answer 1

Answer: (B)

$3-5$

In the titration of a monoacidic weak base with a strong acid, the $pH$ at the equivalent point is always calculated by the formula given below:
$pH=\frac{1}{2}[p{K}_w-p{K}_b-logC]$

Substituting values in the above expression, we get
$pH=\frac{1}{2}[14-6-log(0.1\left)\right]=4.5$

Hence, the range of most suitable indicator is $3-5$.

Option B is correct.