1. Buffers and Titration

2. What is a buffer?
A solution that resists pH change due to the addition of OH- or H30+ ions.
Example: Acetic acid Acetate
HC2H302 + H H30+ + C2H302-
If a strong base is added, the H30+ resists pH change by forming water.
H30+ + OH H20 + H20
If a strong acid is added, the additional H30+ reacts with acetate to form water and resist pH change. (H30+ is used, therefore no pH change occurs)
H30+ + C2H HC2H302 + H20

3. Adding a strong base to a weak acid
-Notice that the buffer RESISTS pH change, it doesn’t cancel it completely.
- Once the buffer’s capacity is used up, the pH will drastically change. This is known as the equivalence point.
Volume of base added

4. What is titration?
The addition of a measured volume of a solution of known concentration to find the concentration of an unknown solution.
Solution of known concentration
- Add drops of the known solution
- Graph pH vs. volume
- Find the equivalence point.
- Find the concentration of the unknown solution.
Solution of unknown concentration

5. Why titrate? Common uses of titration are:
-Monitoring blood sugar levels in diabetics
-Analyzing urine samples.
-Finding the concentration of vitamins C and E in food products.
-Accurately measure the pH and concentration of ammonia and nitrates in aquarium water.
-Find the degree of contamination in acid rain.
ANYTIME there is a solution with an unknown concentration of a substance, titrations are used!

6. Titration Calculations
Ma x Va = Mb x Vb
M is molarity (mol/L), aka concentration
V is the volume in LITERS

7. Practice
If 85 mL of a 0.8 M NaOH solution are needed to neutralize 350 mL of an HCl solution. What is the concentration of the HCl solution?
HINT: Ma x Va = Mb x Vb NaOH is a base, HCl is an acid
Answer: Ma x .350 = 0.8 x .085
Ma = 0.19 M
UNITS!

8. HINT: Ma x Va = Mb x Vb NaOH is a base, HCl is an acid Mb = .0225 M
It takes mL of a 0.35 M HCl solution to neutralize 315 mL of NaOH solution. What is the concentration of the NaOH solution?
HINT: Ma x Va = Mb x Vb NaOH is a base, HCl is an acid
Mb = M
UNITS!