Chapter U6, Problem 1STP

Interpretation Introduction

Interpretation:

An acid and base form of the indicator needs to be identified.

Concept introduction:

According to Bronsted acid- base theory, an acid is a substance which is a proton donor and base is a proton acceptor.

Conjugate base of an acid is formed when an acid loses a proton.

Conjugate acid of a base is formed when a base gains a proton.

Answer to Problem 1STP

Among the given options, option (C) is the correct answer.

Explanation of Solution

Reason for correct option:

Since HIn (aq) indicates the acid form of the indicator and this acid on losing a proton becomes In- (aq) which is a conjugate base of the acid HIn (aq).

Hence, HIn (aq) is an acid and In- is the base.

Conclusion

Reasons for incorrect options:

(A) H+ (aq) is the proton and it does not indicate the acid form of the indicator.

(B) In^-(aq) is not the acid form of the indicator because it does not have protons to donate.

(D) HIn (aq) is an acid but H⁺(aq) is not the base form of the indicator.