What is the conjugate acid in the following equation:

NO2 - + H2O / longrightarrow ⟶ HNO2 + OH-

HNO₂

Explanation:

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

Thus, NO₂⁻ is the base, because it accepts a proton from the water.

H₂O is the acid, because it donates a proton to the nitrite ion.

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.

NO₂⁻/HNO₂ make one conjugate acid/base pair, and H₂O/OH⁻ are the other conjugate acid/base pair.

NO₂⁻ + H₂O ⇌ HNO₂ + OH⁻

base acid conj. conj.

acid base