Chapter 9 More on buffers

Buffers A buffer is a solution whose pH changes very little when acid or base is added Most buffers are solutions composed of roughly equal amounts of: A weak acid The salt of its conjugate base A salt is usually a positive metal ion bound to a negative non-metal ion The buffer resists change in pH because Added base, OH−, reacts with the weak acid Added acid, H3O+, reacts with the conjugate base

Buffer example: HF Most buffers are solutions composed of roughly equal amounts of: A weak acid: example HF Some will dissociate to H3O+ and F- which will result in an acidic pH The salt of its conjugate base: example F- from NaF Na+ will also be in solution but it is a spectator ion that does not contribute to pH F- When acid (H3O+) is added: H3O+ + F-  HF + H2O H3O+ + F- interact to make HF and water, so there is only a slight change in pH F- HF F- HF HF F- HF F- HF F- HF F- HF F- F- F- F- HF HF When base (OH-) is added: OH- + HF  F- + H2O OH- + HF interact to make F- and water, so there is only a slight change in pH F- HF F- HF HF F- HF HF

Buffers - generalized Most buffers are solutions composed of roughly equal amounts of: A weak acid, HA The salt of its conjugate base, A- A- When H3O+ is added it interacts with the conjugate base to form more of the weak acid A- HA A- HA HA A- HA A- HA A- HA A- HA A- A- When OH- is added it interacts with the weak acid to form water and more of the conjugate base A- A- HA HA A- HA A- HA HA A- HA HA