How would you compare a strong acid and a weak acid in terms of the acid dissociation constant?

1 Answer
anor277
Apr 4, 2017

For a strong acid, by definition, #K_a#, the acid dissociation constant is LARGE.........

Explanation:

A strong acid is an acid for which the following equilibrium lies strongly to the RIGHT as we face the page:

#HX + H_2O rightleftharpoons X^(-) + H_3O^+#

And as with any equilibrium, we can quantify the expression by using the relationship:

#K_"eq"=([H_3O^+][X^-])/([HX])#

Now, by definition, for a strong acid, the given equilibrium lies to the right, and thus the NUMERATOR in the expression is LARGE because the product #[H_3O^+]xx[X^-]# is LARGE, and necessarily, the DENOMINATOR is SMALL.

Strong acids in water include the mineral acids #H_2SO_4#, #HX (X!=F)#, #HClO_4# and dissociation is quantitative.

For more of the same, see here.

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