Answer:
The hydroxide ion [tex]\rm OH^{-}[/tex] is the conjugate base in this equation.
Explanation:
The acid and base in a conjugate pair differ only by a proton [tex]\rm H^{+}[/tex]. As the Bronsted-Lowry acid-base theory goes, the substance with that extra proton [tex]\rm H^{+}[/tex] is considered to be the acid. The other substance in the pair is considered to be the base.
In this reaction, there are two conjugate acid-base pairs:
[tex]\rm {NO_2}^{-} + H^{+} \to HNO_2[/tex]:
- Base: [tex]\rm {NO_2}^{-}[/tex], which accepts a proton;
- Acid: [tex]\rm HNO_2[/tex].
[tex]\rm H_2O \to OH^{-} + H^{+}[/tex]:
- Acid: [tex]\rm H_2O[/tex], which supplies a proton;
- Base: [tex]\rm OH^{-}[/tex].
By convention, an acid A reacts with a base B to produce
- a conjugate base of A, and
- a conjugate acid of B.
In other words,
[tex]\text{Acid A} + \text{Base B} \to \text{Conjugate Base of A} + \text{Conjugate Acid of B}[/tex].
For this reaction,
- Acid A is [tex]\rm H_2O[/tex], and
- Base B is [tex]\rm {NO_2}^{-}[/tex].
On the right-hand side of the equation:
- The Conjugate Base of A is [tex]\rm OH^{-}[/tex], and
- The Conjugate Acid of B is [tex]\rm HNO_2[/tex].
