2. Let’s take a look at water  2H 2 O  H 3 O + + OH -  [H 3 O + ][OH - ]= 1x10 -14 M 2  [H 3 O + ]= 1x10 -7 M  [OH - ]= 1x10 -7 M  K w = 1x10 -14 M 2

3. Example 1  An acid is added to water and gives a hydroxide ion concentration [OH - ] of 1.0x10 -12 M. What is the hydrogen ion concentration [H + ] ?

4. What is pH?  Pouvoir hydrogene: “hydrogen power”  pH = measure of [H 3 O + ]------- Acidity  [H 3 O + ] expressed in powers of 10  Ex. 10 -14 to 10 -1

5. pH Scale  Range from 0-14.  NEUTRAL, pH=7. (pure water)  BASE, pH > 7. (ocean water, milk of magnesia, baking soda)  ACID, pH < 7. (stomach acid/HCl, vinegar, soft drinks)

6. pH Scale

7. How do we measure the pH of a solution?  Acid-base indicators (ex. litmus paper)  pH meter

8. Equations  pH = -log[H + ]  pOH = -log[OH - ]  pH + pOH = 14  [H + ][OH - ] = 1x10 -14 M 2

9.  Example 2: What is the pH of a solution with a hydrogen ion concentration of 1x10 -4 M ? Is this solution acidic or basic ?

10.  Example 3: What is the hydrogen ion concentration of a solution with a pH of 11 ? Is this solution acidic or basic ?

11.  Example 4: Calculate the [H + ] and [OH - ] of a vinegar solution with a pH of 2.5.

12. Now, you try……  1) [H 3 O + ] = 1.5x10 -6 M. Find the pH.  2) A solution’s pH is 3.72. What are the [H 3 O + ] and [OH - ] concentrations in the solution?

13. Thought Question  When an acid is added to a beaker of water, what happens to the [H 3 O + ] and [OH - ] in the solution? Why? What happens to the pH? Why?