Question

How do we identify a strong acid in aqueous solution?

Answer 1

As you are no doubt aware, this distinction is usually used in the context of `"acid/base chemistry"`.

Explanation:

A strong acid is completely ionized in aqueous solution; viz. for the hydrohalic acids, `HX(X!=F):`

`HX+H_2O(l) rightleftharpoonsH_3O^+ + X^-`

The strength of an acid depends upon the completion of this equilibrium; i.e. how far the equilibrium to the right. `HI`, `HBr`, and `HCl` ARE STRONG ACIDS by this criterion, because dissociation/ionization are almost complete.

On the other hand, weaker acids, incompletely ionize:

`HF(aq) + H_2O rightleftharpoons H_3O^+ +F^-`

This equilibrium lies to the left as we face it due to (i) the intrinsic strength of the `H-F`; and (ii) to the unfavourable entropy effect of the solvated `F^-` conjugate base.

For `H_2SO_4` BOTH conjugate bases are stabilized, and this acts as a diacid in water:

`H_2SO_4(aq) +H_2O(l) rarr HSO_4^(-) + H_3O^+`

`HSO_4^(-) + H_2O(l)rightleftharpoonsSO_4^(2-) +H_3O^+`