Question

Is the conjugate base of a weak acid a strong base? Explain. Explain why Cl^- does not affect the pH of an aqueous solution.

Short answer

Yes, the conjugate base of a weak acid is a strong base, and the pH depends only on H⁺ ion concentration, not on the concentration of anion, i.e., Cl^-.

Step-by-step solution

Conjugate base of weak acid

Weak acids are weak because they give fewer H⁺ ions. The reason for this is that they have strong bonds with their H⁺. On releasing H^+, they will give a conjugate base

$HA\rightleftharpoons H^{+}+A^{-}$

Now the base formed will have a high tendency to accept the proton; hence it is a strong conjugate base.

Cl- does not affect the pH of an aqueous solution 

The conjugate base of a strong acid has no affinity for protons compared with that of the water molecule. Thus, strong acids completely dissociate in an aqueous solution.

Thus, when anion Cl^- (Conjugate base of strong acid HCl)is placed in water, they do not combine with H⁺and therefore do not affect the pH.