Question

The indicator used for the filtration of weak base and strong acid is

• A. thymol blue
• B. methyl orange
• C. phenolphthalein
• D. fluorescein

Answer 1

Answer: (B)

Key Idea: The indicators show change in colour with change in $pH$ . The indicator used should be such that it shows colour change in the same pH range as required around equivalence point. In titration of weak base and strong acid, the pH change lies between 6 to 4.
Indicator
pH range
Thymol blue
$9.3-10.5$
Methyl orange
$4.2-6.2$
Phenolphthalein
$8.3-10.0$
$\therefore$ Methyl orange should be used as indicator.