2. pH = potential hydrogen
pH is a measure of the acidity of an aqueous solution.

3. Logarithms and the pH concept
definition: pH = -log[H+]
(Logarithms are powers of ten.)
Neutral solution: pH = 7
Acidic solution: pH = less than 7
Basic solution: pH= greater than 7

4. pOH = potential hydroxide
pOH is a measure of how basic a solution is.
pOH = -log [OH-]
pH + pOH = 14
Therefore, pOH scale is opposite of the pH scale.

5. Basic Solution: pOH = less than 7
Acidic Solution: pOH = greater than 7

6. Calculation Practice
What is the pH and pOH of a 1.2 x 10-3 M HBr solution? FIRST ASK YOURSELF: IS HBr AN ACID OR A BASE?

7. Calculation Practice:
What is the pH and pOH of a 2.34 x 10-5 M NaOH solution?
FIRST ASK YOURSELF: IS NaOH AN ACID OR A BASE?

8. Calculation Practice:
Determine the [H3O+] of a solution with a pH of 2.81
Determine the [OH-] of a solution with a pH of 11.21

9. Calculation Practice
Determine the pH of a magnesium hydroxide solution in which 17.1 grams are dissolved in 1L.

10. Measuring pH Why measure pH?
Everything from swimming pools, soil conditions for plants, medical diagnosis, soaps and shampoos, etc.
Sometimes we can use indicators, other times we might need a pH meter

11. Acid-Base Indicators
An indicator is an acid or base that undergoes dissociation in a known pH range, and has different colors in solution (more later in chapter)
Examples: litmus, phenolphthalein, bromthymol blue:

12. Acid-Base Indicators
Although useful, there are limitations to indicators:
usually given for a certain temperature (25 oC), thus may change at different temperatures
what if the solution already has color?
Ability of human eye to distinguish colors

13. Acid-Base Indicators A pH meter may give more definitive results
Gives numerical pH values
some are large, others portable
works by measuring the voltage between two electrodes
needs to be calibrated