How do we identify a strong acid in aqueous solution?

1 Answer
May 18, 2017

Answer:

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^+#