What is the Ka of a strong acid like HCl?

1 Answer
Aug 23, 2016

The approximate value of pKa is 7 for HCl.

Explanation:

Hydrochloric acid is a strong acid and it is considered to completely dissociate in water under the following equation:

HCl(aq)+H2O(l)H3O+(aq)+Cl(aq)

The equilibrium constant Ka is written as:

Ka=[H3O+][Cl]HCl

Since the acid dissociates completely, the concentration of products ([H3O+]and[Cl]) is very large and the concentration of the reactant ([HCl]) is very small. Therefore, the value of Ka is going to be very large (~107).

Since pKa=logKa, therefore, the value of the pKa is going to be a negative number.

The approximate value of pKa is 7 for HCl.