Question

Choose the correct option for the given statements.

Statement-I: Titration of a strong acid with a weak base uses methyl orange as an indicator.

Statement-II: Titration of a weak acid with a strong base doesn't uses phenolphthalein as an indicator.

• A. Statement I is correct and Statement II is correct
• B. Statement I is correct and Statement II is incorrect
• C. Statement I is incorrect and Statement II is incorrect
• D. Statement I is incorrect and Statement II is correct

Answer 1

The correct option is B

Statement I is correct and Statement II is incorrect

(A) For statement 1:

1. For titration of strong acid and weak base, methyl orange is a suitable indicator.
2. Initially with the addition of strong acid, the $\mathrm{pH}$ of weak base falls slowly.
3. However after reaching equivalence point, the $\mathrm{pH}$ falls sharply in the $\mathrm{pH}$ range of $3.2$to $4.4$ .
4. Hence methyl orange will work as an indicator for the titration of strong acid and weak base.
5. Hence statement $1$ is true.

(B) For statement 2:

1. For titration of strong acid and weak base, phenolphthalein is a suitable indicator.
2. With the addition of alkali, weak acid will form a buffer solution with slowly increasing $\mathrm{pH}$
3. However after reaching equivalence point, the $\mathrm{pH}$ rises sharply in the $\mathrm{pH}$ range of $8.2$ to $10.0$.
4. Hence, Phenolphthalein will work as a suitable indicator for titration of weak acid and strong base.
5. Hence, statement $2$ is false

Therefore, the option B is correct.