1. Welcome

2.  Saturday School: 10-11ish  Monday: Cold Call Quiz

4.  I have two beakers  Beaker 1 – 1 L of pure water  Beaker 2 – 1 L of human blood  I pour 5 mL of NaOH in the pure water and the pH goes from 7 up to 13.2  I pour 5 mL of NaOH into the blood and it goes from a pH of 7.2 to 7.3

5.  I have the same two beakers  Beaker 1 – 1 L of pure water  Beaker 2 – 1 L of human blood  I pour 5 mL of HCl in the pure water and the pH goes from 7 up to 2.2  I pour 5 mL of NaOH into the blood and it goes from a pH of 7.2 to 7.1

6.  A buffer is any solution that resists changes in pH  Two components of a buffer: 1. A component that neutralizes an acid 2. A component that neutralizes a base  A weak acid or a weak base are capable of creating a buffer because they have both of these components, but a strong acid or base cannot create a buffer.

7.  A weak acid or base make an excellent buffer because they have a component that can react with an acid and a component that can react with a base. CH 3 COOH + H 2 O CH 3 COO - + H + ⇌ Can react with a base! Can react with an acid! Therefore, reacting each component produces a part of the equilibrium and little change in pH is observed!

8.  The best buffers have close to equal concentrations of the conjugate acid/base pair.  We can think about the K a expression for a weak acid  Therefore, pH is determined by the ratio of conjugate acid/base pair and the value of K a.  As long as the change in ratio of [HA]/[A - ] is small, the change in pH will be small.

9.  Adding base to a buffer shows minimal change  Adding base to a neutral solution causes huge changes

10.  Could each of the following solutions can be classified as buffer systems? Why/why not? 1. KH2PO4/H3PO4 2. NaClO4/HClO4 3. C5H5N/C5H5NHCl(C5H5N is a base)

11.  Students explore using http://www.mhhe.com/physsci/chemistry/ess entialchemistry/flash/buffer12.swf

12.  Calculate the pH of a buffer that is 0.12 M lactic acid and 0.10 M sodium lactate. The K a for lactic acid is 1.4 x 10 -4

13.  Calculate the pH of a buffer composed of 0.12 M benzoic acid and 0.20 M sodium benzoate. The K a for the solution is 6.4 x 10 -5

14.  The pH at which any buffer works most effectively is when pH = pK a  This is known at the ½ equivalence point  Buffers usually have a useable range within ±1 pH unit of the pK a