Question

How can I identify conjugate acids and bases?

Answer 1

Explanation:

A conjugate acid contains one more $H$ atom and one more $+$ charge than the base that formed it.

A conjugate base contains one less $H$ atom and one more - charge than the acid that formed it.

Let us take the example of bicarbonate ions reacting with water to create carbonic acid and hydronium ions.

${HCO}_3^{-}+H_{2}O\to H_2{CO}_3+{OH}^{-}$

Base $+$ Acid $\to$ Conj $A+$ Conj $B$

We see that ${HCO}_3^{-}$ becomes $H_2{CO}_3$. It has one more $H$ atom and one more $+$ charge $(-1+1=0).$

So $H_2{CO}_3$ is the conjugate acid of ${HCO}_3^{-}$

The $H_{2}O$ becomes ${OH}^{-}$. It has one less $H$ atom and one more $-$ charge.

So ${OH}^{-}$ is the conjugate base of $H_{2}O$.