### 12.63

Posted:

**Tue Dec 05, 2017 7:34 pm**The question states: The percentage deprotonation of benzoic acid in a 0.110 m solution is 2.4%. What is the pH of the solution and the Ka of benzoic acid?

In class we learned that if Ka is less than 10^-2 or if deprotonation is less than 5%, then we can assume the change in molarity is negligible and we can use the approximation. However, the solutions manual seems to not use the approximation for this problem. Is there something about this problem that does not allow us to use the approximation method?

In class we learned that if Ka is less than 10^-2 or if deprotonation is less than 5%, then we can assume the change in molarity is negligible and we can use the approximation. However, the solutions manual seems to not use the approximation for this problem. Is there something about this problem that does not allow us to use the approximation method?