Identify the conjugate acid base pair

H3PO4 (ag) + CO32=HCO3 - (ag) + HPO42 - (ag)

H₃PO₄/H₂PO₄⁻ and HCO₃⁻/CO₃²⁻

Explanation:

An acid is a proton donor; a base is a proton acceptor.

Thus, H₃PO₄ is the acid, because it donates a proton to the carbonate ion.

CO₃²⁻ is the base, because it accepts a proton from the phosphoric acid.

The conjugate base is what's left after the acid has given up its proton.

The conjugate acid is what's formed when the base has accepted a proton.

H₃PO₄/H₂PO₄⁻ make one conjugate acid/base pair, and HCO₃⁻/CO₃²⁻ are the other conjugate acid/base pair.

H₃PO₄ + CO₃²⁻ ⇌ H₂PO₄⁻ + HCO₃⁻

acid base conj. conj.

base acid