Do strong acids completely dissociate in water?
For all practical purposes, strong acids completely dissociate in water.
That is the definition: A strong acid is an acid that completely dissociates in water.
In theory, every reaction is an equilibrium reaction. For example
HCl + H₂O ⇌ H₃O⁺ + Cl⁻
We see that the position of equilibrium lies far to the right.
We can calculate that in 1 mol/L HCl there are more than 1200 H₃O⁺ ions for every molecule of undissociated HCl.
For all practical purposes, HCl is completely dissociated in solution.
Strong acids have a large dissociation constant, so they dissociate completely in water.