1. Weak Acids

2. Question
Is it possible for a strong acid solution and a weak acid solution to have the same pH?

3. Weak Acids are in Equilibrium
HX(aq)  H+ + X-
Ka = [H+][X-]
[HX]
Ka – acid-dissociation constant

4. Example
A student prepared a .10M solution of formic acid (HCHO2) and measured its pH to be A) calculate the Ka B) What is the % of the acid dissociated?

5. Example
Calculate the pH of a .20M solution of HCN whose Ka = 4.9 x 10-10

6. Example
Calculate the % HF ionized in a .10M HF solution. Ka = 6.8 x 10-4

7. Polyprotic Acid Acids capable of furnishing more than one proton
H2SO4  H+ + HSO4- Ka1 = 1.7x10-2
HSO4-  H+ + SO Ka2 = 6.4x10-8
If difference in Ka1 and Ka2 is > 103 only need to consider Ka1

9. Example
A solution of .0037M H2CO3 dissociates in water. What is the approximate pH of the solution?