Question

Select the best indicator from the given table for titration of $20mL$ of $0.02MC{H}_{3}COOH$ with $0.02MNaOH$. Given $p{K}_a\text{of}C{H}_{3}COOH=4.74)$

	Indicator	$pH$ range
(I)	Bromothymol blue	$6.0-7.6$
(II)	Thymolphathalein	$9.3-10.5$
(III)	Malachite green	$11.4-13$
(IV)	M-Cresol purple	$7.4-9.0$

• A. $\left(I\right)$
• B. $\left(II\right)$
• C. $\left(III\right)$
• D. $\left(IV\right)$

Answer 1

The correct option is B $\left(II\right)$

Since $pH=(SW+WA)=7+1/2(pKa+logC)$ {at equilance pointer}

$C=0.01$ after mixing

$\therefore pH=7+1/2(4.74+log0.01)$

$\therefore pH=8.37$

So, it lies in range of $\left(IV\right)$ and somenehat of $\left(II\right)$