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

$H X \left(g\right) + {H}_{2} O \left(l\right) r i g h t \le f t h a r p \infty n s {H}_{3} {O}^{+} + {X}^{-}$
For $H F$ 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 $\text{hydronium ion}$, represented as ${H}_{3} {O}^{+}$, but more likely a transient cluster of 3-4 water molecules with an extra ${H}^{+}$ attached, i.e. ${H}_{9} {O}_{4}^{+}$ or ${H}_{7} {O}_{3}^{+}$.