The document discusses the pH scale and how it is used to measure acidity and basicity in solutions. It defines pH as the negative log of the hydrogen ion concentration. Solutions with pH < 7 are acids, pH = 7 are neutral, and pH > 7 are bases. It also discusses how water can act as both an acid and base and how the pH, pOH, [H+], and [OH-] of any solution are related through water's ionization constant, Kw.

1. pH Scale Representation of the acidity of a solution Acids have a pH < 7 Bases have a pH > 7 Neutral solutions have a pH = 7 (pure water)

2. Calculating pH pH = - log [H + ] where [ ] indicate molarity To find [H + ], use the inverse log function [H + ] = 10 -pH

3. Examples Find pH if [H + ] = 1 x 10 -3 M Find pH if [H + ] = 4.55 x 10 -5 M Find [H + ] if pH = 8.5

4. Water Water is amphiprotic Can act as an acid or a base according to the BL Theory Water can donate a proton to NH 3 and act as an acid Water can accept a proton from HCl and act like a base

5. Water Water can autoionize Acts as a proton donor and a proton acceptor towards itself Equation: Only happens to a very small extent and allows pure water to have a small electrical conductivity

6. Derivations of pH Since water is neutral, pH = 7 and [H + ] = [OH - ] Therefore, [H + ] = 1 x 10 -7 = [OH - ] We can define pOH as a measure of the basicity of a solution pOH = -log [OH - ] and [OH - ] = 10 -OH For pure water, since [H + ] = [OH - ] = 1x 10 -7 , pH + pOH = 14 (this holds true for any solution)

7. Derivations of pH Also, [H + ] [OH - ] = 1 x 10 -14 This is called the dissociation of water constant or the ion-product constant of water (K w ) and relates the concentration of H + and OH - for any solution Given these derivations, we can calculate the pH, pOH, [H + ], and [OH - ] for any solution given one of the above!

8. Examples Find [H + ], pH, and pOH if [OH - ] = 3.4 x 10 -6 M

9. Examples Find [H + ], [OH - ], and pOH if pH = 8.32