Question

Question #bc43f

Answer 1

When an acid reacts with water, it forms a hydronium ion plus the conjugate base of the original acid. Likewise, when a base reacts with water, it forms hydroxide ion plus the conjugate acid of the original base.

Using generic symbol HA for a weak acid, we can write the following balanced proton transfer reaction with water:

`HA + H_2O harr A^(-) + H_3O^+`

Because `A^(-)` differs from `HA` only by the proton that was lost to water, we say that `A^(_)` is the conjugate base of the acid `HA`. Likewise, HA is the conjugate acid of the base `A^(-)`. In other words, `HA` and `A^(-)` form a conjugate acid-base pair.

In the same way, we can write a balanced proton transfer reaction of a base, `B`, with water:

`B + H_2O harr BH^+ + OH^(-)`

For the same reasons as above, we say that `BH^+` and `B` form a conjugate acid-base pair.