1. Unit 6: Acid-Base Applications Lesson 6: Buffers

2. What Is a Buffer?
A buffer is a solution containing appreciable amounts of a weak acid and its conjugate base.
It is typically made by adding equal concentrations of a weak acid and its conjugate base into water, so that pKa = pH.
It cannot be made by adding just the weak acid or base, despite the formation of an equilibrium.

3. Purpose of a Buffer
Prediction: If we add 10 mL of 0.1 M HCl, what do you think will happen to the pH of 100 mL of
a) a pH 7 buffer solution?
b) water?
Observation: What actually happens?
Use universal indicator - 10 min

4. Purpose of a Buffer
Explanation: A buffer prevents the addition of an acid or base from changing the pH of a solution to any great extent.
Because of Le Chatelier’s Principle, the equilibrium will shift, but since there are large concentrations of weak acid and base present, this has little effect on the pH.
Show example of equilibrium shift (add .1 mol acid to 1 mol buffer) on the board. – 10 min

5. Brain Break. Three circles, three related words
Brain Break! Three circles, three related words. Find the missing letter and unscramble the words.
S – stable, stallion, saddle

6. Acidic and Basic Buffers
An acidic buffer is a solution that buffers the pH in an acidic region.
A basic buffer buffers the pH in a basic region.
Using your notes from today’s lesson, suggest a procedure for preparing:
a) an acidic buffer that buffers around pH = 3
b) a basic buffer that buffers around pH = 10
(need ~1.0 M of weak base and 1.0 M of weak acid) - 15 min

7. Homework:
Pg. 181 # and
5 min