Question

The $K_a$ values for $HP{O}_4^{2-}$ and $HS{O}_3^{-}$ are $4.8\times {10}^{-13}$ and $6.3\times {10}^{-8}$ respectively. Therefore, it follows that $HP{O}_4^{2-}$ is a ____________ acid than $HS{O}_3^{-}$ and $P{O}_4^{3-}$ is a ____________ base than $S{O}_3^{2-}$.

• A. weaker, stronger respectively
• B. stronger, weaker respectively
• C. weaker, weaker respectively
• D. stronger, stronger respectively

Answer 1

The correct option is A weaker, stronger respectively

As we know, greater the value of dissociation constant of the acid ($K_a$), greater is the strength of the acid.

So, $HP{O}_4^{2-}$ is a weaker acid than $HS{O}_3^{-}$ and $P{O}_4^{3-}$ is a stronger base than $S{O}_3^{2-}$, because conjugate base of a weak acid is strong.

Option A is correct.