Question

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

Answer 1

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.