MHT CET · Chemistry · Ionic Equilibrium

Identify the conjugate acid-base pair respectively from following equilibrium reaction.
\(\mathrm{HPO}_{4(\mathrm{aq})}^{2-}+\mathrm{H}_2 \mathrm{O}_{(\ell)} \rightleftharpoons \mathrm{PO}_{4(\mathrm{aq})}^{3-}+\mathrm{H}_3 \mathrm{O}_{(\mathrm{aq})}^{+}\)

A \(\mathrm{H}_3 \mathrm{O}^{+}\)and \(\mathrm{H}_2 \mathrm{O}\)
B \(\mathrm{H}_2 \mathrm{O}\) and \(\mathrm{HPO}_4^{2-}\)
C \(\mathrm{PO}_4^{3-}\) and \(\mathrm{H}_3 \mathrm{O}^{+}\)
D \(\mathrm{H}_3 \mathrm{O}^{+}\)and \(\mathrm{HPO}_4{ }^{2-}\)

Verified Solution

Answer & Solution

Correct Answer

(A) \(\mathrm{H}_3 \mathrm{O}^{+}\)and \(\mathrm{H}_2 \mathrm{O}\)

Step-by-step Solution

Detailed explanation

\(\mathrm{HPO}_{4}^{2-}\) acts as an acid (proton donor) and \(\mathrm{PO}_{4}^{3-}\) is its conjugate base. \(\mathrm{H}_2 \mathrm{O}\) acts as a base (proton acceptor) and \(\mathrm{H}_3 \mathrm{O}^{+}\) is its conjugate acid.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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Identify the conjugate acid-base pair respectively from following equilibrium reaction.\(\mathrm{HPO}_{4(\mathrm{aq})}^{2-}+\mathrm{H}_2 \mathrm{O}_{(\ell)} \rightleftharpoons \mathrm{PO}_{4(\mathrm{aq})}^{3-}+\mathrm{H}_3 \mathrm{O}_{(\mathrm{aq})}^{+}\)

Step-by-step Solution

Identify the conjugate acid-base pair respectively from following equilibrium reaction.
\(\mathrm{HPO}_{4(\mathrm{aq})}^{2-}+\mathrm{H}_2 \mathrm{O}_{(\ell)} \rightleftharpoons \mathrm{PO}_{4(\mathrm{aq})}^{3-}+\mathrm{H}_3 \mathrm{O}_{(\mathrm{aq})}^{+}\)