1. Chem. Concepts: Buffers A General Overview Eric Liu Mr. Michael Gangluff Chemistry AP

2. What is a “Buffer”? A buffer is a solution that resists changes in pH when small amounts of acid or base are added to it. when small amounts of acid or base are added to it.

3. What is it made of?  Acidic buffers  Consists of a weak acid and a salt of its conjugate base  e.g. CH 3 COOH and CH 3 COONa  pH less than 7  Basic buffers  Consists of a weak base and a salt of its conjugate acid  e.g. NH 3 and NH 4 Cl  pH greater than 7 Buffers can be placed into two categories: acidic buffers and basic buffers Our blood is a buffer, as cells can only survive within a narrow pH range The pH of a buffer can be changed by altering the ratio of acid and its conjugate base or base and its conjugate acid. The amount of acid/conjugate base or base/conjugate acid determine its buffer capacity, or amount of acid or base that can be added for it to still maintain constant pH

4. How does it work? Buffers follow one of the following equilibriums: There are both products and reactants present in both cases Buffers use Le Chatelier’s Principle, which states that a system will relieve stress put on a system by “shifting” to the left or right side of the equation accordingly. In other words, if you add reactant to the equilibrium, the system would respond by removing reactant (and thus creating product), and vise versa

5. How does it work?  The H 3 O + from the acid will cause the system to shift left  Or react with OH - to form H 2 O If acid is added to the system… + + + + +

6. How does it work?  The OH - from the base will cause the system to shift to the left  Or react with H 3 O + to form H 2 O If base is added to the system… + + + + +

7. Summary Buffers are solutions that resist changes in pH with the addition of small amounts of acid or base weakweak They consist of a weak base and its conjugate acid salt or a weak acid and its conjugate base salt They work through Le Chatelier’s Principle, shifting to the left or right to counterbalance the addition of acid or base