Question

When they dissolve in water, what do all acids cause?

Answer 1

An increase in the concentration of the characteristic cation of the solvent, which is typically water.

Explanation:

Typically hydrogen halides dissolve in water according to the reaction:

`HX(g) + H_2O(l) rightleftharpoons H_3O^(+) + X^(-)`

For `HF` the equilibrium lies to the left. For the lower hydrogen halides, the equilibrium lies STRONGLY to the right, and causes an INCREASE in the concentration of `"hydronium ion"`, represented as `H_3O^+`, but more likely a transient cluster of 3-4 water molecules with an extra `H^+` attached, i.e. `H_9O_4^+` or `H_7O_3^+`.