5
$\begingroup$

If an acid $\ce{AH}$ reacts with a base $\ce{B}$ in aqueous solution, in textbook they write

$$\ce{AH + B -> A- + BH+}\label{rxn:1}\tag{1}$$

But first I add acid to water and then base, so why we don't write the equations like this:

  • When I add acid to water: $$\ce{AH + H2O -> A- + H3O+}$$

  • When I add base to the acidic solution: $$ \begin{align} \ce{B + H2O &-> BH+ + OH-}\\ \ce{B + H3O+ &-> BH+ + H2O} \end{align} $$

So the equation $\eqref{rxn:1}$ isn't true because the base doesn't react directly with the acid, but with $\ce{H3O+}$ formed by the acid reaction with water. Is what I have written true?

$\endgroup$
5
$\begingroup$

With strong bases and acids, only $\ce{OH-}$ and $\ce{H3O+}$ react, right, because $\ce{AH}$ and $\ce{B}$ (practically) don't exist in aqueous solution.

For weak acids and bases, that's not true, but still there the water can "transport" protons much faster between AH and B than direct exchange after diffusion. As was noted below, that's called the Grotthuss mechanism.

So yes, you are right, but the formula (1) is a valid simplification which is, for most uses, as good.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.