How would you explain conjugate acids and bases?

1 Answer
Jan 20, 2018

Correctly, or at least I would try to do so....

Explanation:

You know or should know that an acid, $H X$, is a proton donor in some solvent, typically water.....and we could represent its characteristic reaction in the following way....

${\underbrace{H X \left(a q\right)}}_{\text{parent acid" + H_2O(aq) rarr underbrace(X^(-))_"conjugate base" + underbrace(H_3O^+)_"hydronium ion}}$

The hydronium ion is a conceptual species; it is a cluster of water molecules, 3 or 4 or more to give say ${H}_{7} {O}_{3}^{+}$, with an EXTRA ${H}^{+}$..we write ${H}^{+}$ or ${H}_{3} {O}^{+}$ as a shorthand....

${H}_{3} {O}^{+}$ is the so-called $\text{CONJUGATE ACID}$ of water, i.e. the original acid PLUS a proton...of course we conserve mass and charge. And $H {O}^{-}$ is the so-called $\text{CONJUGATE BASE}$ of water, i.e. the original acid MINUS a proton.

And using this formalism, all strong acids react in solution to give their $\text{CONJUGATE BASES}$. What are the conjugate bases of $H C l {O}_{4}$, ${H}_{2} S {O}_{4}$, $H N {O}_{3}$?

To go to another example...what is the conjugate acid of $N {H}_{3}$. I make it $N {H}_{4}^{+}$ (and I hope you do too). But what is the conjugate base of ammonia? This is so strong a base that it does not occur in water, but DOES occur in liquid ammonia.

Confused yet? But all I have done is to add or subtract protons, ${H}^{+}$, and CONSERVED CHARGE and MASS.....

See here and links for further examples.