Weak base B has a pK_b of 6.78 and weak acid HA has a pK_a of 5.12.

a. Which is the stronger base, B or A⁻ ?

b. Which is the stronger acid, HA or BH⁺?

c. Consider the following reaction:

B(aq) + HA(aq) ⇌ BH⁺(aq) + A⁻(aq)

Based on the information about the acid/base strengths for the species in this reaction, is this reaction favored to proceed more to the right or more to the left? Why?

d. An aqueous solution is made in which the concentration of weak base B is one half the concentration of its acidic salt, BHCl, where BH+ is the conjugate weak acid of B. Calculate the pH of the solution.

e. An aqueous solution is made in which the concentration of weak acid HA is twice the concentration of the sodium salt of the weak acid, NaA. Calculate the pH of the solution.

f. Assume the conjugate pairs B/BH⁺ and HA/A⁻ are capable of being used as color-based end point indicators in acid–base titrations, where B is the base form indicator and BH⁺ is the acid form indicator, and HA is the acid form indicator and A⁻ is the base form indicator. Select the indicator pair that would be best to use in each of the following titrations:

(1) Titration of a strong acid with a strong base.

(i) B/BH⁺ 

(ii) HA/A⁻

(2) Titration of a weak base with a strong acid.

(i) B/BH⁺ 

(ii) HA/A⁻