Question

For the reaction H2PO4- HAsO4 2-HPO4 2-+H2AsO4- what species are a conjugate acid-base pair?

Answer 1

Ionic equation:

$\text{H}_2\text{PO}_4^{-} + \text{HAsO}_4^{2-} \to \text{HPO}_4^{2-} + \text{H}_2\text{AsO}_4^{-}$

The acid and base in a conjugate pair differ by only one proton $\text{H}^{+}$. The acid loses one proton to produce a conjugate base, whereas the base gains a proton to produce its conjugate acid.

$\text{H}_2\text{PO}_4^{-}$ loses one proton to produce $\text{HPO}_4^{2-}$ in this reaction.

$\text{H}_2\text{PO}_4^{-} \to \text{H}^{+} + \text{HPO}_4^{2-}$

Meanwhile, $\text{HAsO}_4^{2-}$ gains one proton to form $\text{H}_2\text{AsO}_4^{-}$.

$\text{HAsO}_4^{2-} + \text{H}^{+} \to \text{H}_2\text{AsO}_4^{-}$

Therefore

• $\text{H}_2\text{PO}_4^{-}$ is the conjugate acid  $\text{HPO}_4^{2-}$, its conjugate base.
• $\text{HAsO}_4^{2-}$ is the conjugate base of $\text{H}_2\text{AsO}_4^{-}$, its conjugate acid.

Answer 2

Ionic equation:

The acid and base in a conjugate pair differ by only one proton . The acid loses one proton to produce a conjugate base, whereas the base gains a proton to produce its conjugate acid.

loses one proton to produce  in this reaction.

Meanwhile,  gains one proton to form .

Therefore

• is the conjugate acid  , its conjugate base.

• is the conjugate base of , its conjugate acid.