1. Buffers
A buffer is a mixture of chemicals that make a solution resist a change of pH
pH remains relatively constant when adding an acid or base
One kind of buffer system is a solution of a weak acid and one of its salts
What is a weak acid?
What qualifies as “one of its salts?”

2. Weak acids vs. Strong acids
Weak acids DO NOT IONIZE completely
HCl HBr HI HNO3 H2SO4
Strong acids have “large & very large” Ka values meaning they DO IONIZE completely
It’s the free H+ (or OH-) that affects the pH

3. The classic example of a weak acid is acetic acid CH3COOH (HC2H3O2)
What about its salt?
The salt can be any of the following:
NaCH3COO
LiCH3COO
KCH3COO
Ca(CH3COO)2
The ca+ion is only a spectator
All of these salts completely ionize in water so the buffer looks like this ….

4. CH3COOH CH3COOH CH3COOH CH3COOH CH3COOH CH3COOH CH3COOH CH3COOH

5. Add in acid (H+) CH3COOH CH3COOH CH3COOH CH3COOH CH3COOH CH3COOH

6. When you add in H+ it will bond to the acetate ion.
H + + CH3COO-  CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3COOH

7. Add in base (OH-) CH3COOH CH3COOH CH3COOH CH3COOH CH3COOH CH3COOH

8. When you add in OH- it bonds with the CH3COOH
HOH
HOH
HOH
CH3COO-
HOH
CH3COO-
OH- + CH3COOH 
HOH + CH3COO-
CH3COO-
CH3COO-
CH3COO-
CH3COO-
CH3COO-
HOH
CH3COO-
HOH
CH3COO-
CH3COO-
CH3COO-
CH3COO-
CH3COO-
HOH
CH3COO-
CH3COO-
HOH
CH3COO-

9. Buffer Capacity There comes a point when the buffer is “used up”
It can no longer take H+ (or OH-) ions out of solution and the pH drastically changes

10. Practice
Write an equation to show the addition of an acid and a base to the following buffer systems
NH4+ / NH3
CH3COOH / CH3COO-
H2PO4- / HPO4-2

11. Practice Answers H+ + CH3COO-  CH3COOH OH- + CH3COOH  CH3COO-
NH4+ / NH3
H+ + NH3  NH4+
OH- + NH4+  NH3
CH3COOH / CH3COO-
H+ + CH3COO-  CH3COOH
OH- + CH3COOH  CH3COO-
H2PO4- / HPO4-2
H+ + HPO4-2  H2PO4-
OH- + H2PO4-  HPO4-2

12. THE END