Question

When dissolved in water, what do acids produce?

Answer 1

Dissolution of a gas in water causes an increase in the concentration of the characteristic cation of the solvent, i.e. `H_3O^+`, the `"hydronium ion"`.

Explanation:

We (well) know that water undergoes autoprotolysis......which we represent as:

`2H_2O(l) rightleftharpoonsH_3O^+ + HO^-`

And such protolysis may be quantitatively measured...

`K_w=[H_3O^+][HO^-]=10^-14`

Taking `log_10` of both sides we get...........on rearrangement.

`-log_10(10^-14)=-log_10[H_3O^+]-log_10[HO^-]`

But `-log_10(10^-14)=-(-14)=14` by definition, and also `pH=-log_10[H_3O^+]` and `pOH=-log_10[HO^-]`, i.e. `pH+pOH=14`.

And so the moral, dissolution of an acid in water causes AN INCREASE in the concentration of the characteristic cation, `H_3O^+`, and a DECREASE in `pH`.