1. C. Johannesson Ch. 18- Acids & Bases II. pH

2. C. Johannesson A. Ionization of Water H 2 O + H 2 O H 3 O + + OH - K w = [H 3 O + ][OH - ] = 1.0  10 -14

3. C. Johannesson A. Ionization of Water  Find the hydroxide ion concentration of 3.0  10 -2 M HCl. [H 3 O + ][OH - ] = 1.0  10 -14 [3.0  10 -2 ][OH - ] = 1.0  10 -14 [OH - ] = 3.3  10 -13 M Acidic or basic? Acidic

4. C. Johannesson pH = -log[H 3 O + ] B. pH Scale 0 7 INCREASING ACIDITY NEUTRAL INCREASING BASICITY 14 pouvoir hydrogène (Fr.) “hydrogen power”

5. C. Johannesson B. pH Scale pH of Common Substances

6. C. Johannesson B. pH Scale pH = -log[H 3 O + ] pOH = -log[OH - ] pH + pOH = 14

7. C. Johannesson B. pH Scale  What is the pH of 0.050 M HNO 3 ? pH = -log[H 3 O + ] pH = -log[0.050] pH = 1.3 Acidic or basic? Acidic

8. C. Johannesson B. pH Scale  What is the molarity of HBr in a solution that has a pOH of 9.6? pH + pOH = 14 pH + 9.6 = 14 pH = 4.4 Acidic pH = -log[H 3 O + ] 4.4 = -log[H 3 O + ] -4.4 = log[H 3 O + ] [H 3 O + ] = 4.0  10 -5 M HBr

9. C. Acid-Base Indicators  Why measure pH? 4Everyday solutions we use - 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

10. Acids Affect Indicators, by changing their color Blue litmus paper turns red in contact with an acid (and red paper stays red).

11. Bases Affect Indicators Red litmus paper turns blue in contact with a base (and blue paper stays blue). Phenolphthalein turns purple in a base.

12. How to measure pH with wide- range paper 1. Moisten the pH indicator paper strip with a few drops of solution, by using a stirring rod. 2.Compare the color to the chart on the vial – then read the pH value.

13. Some of the many pH Indicators and their pH range

14. C. Acid-Base Indicators  Although useful, there are limitations to indicators: usually given for a certain temperature (25 o C), thus may change at different temperatures what if the solution already has a color, like paint? the ability of the human eye to distinguish colors is limited

15. C. Acid-Base Indicators  A pH meter may give more definitive results some are large, others portable works by measuring the voltage between two electrodes; typically accurate to within 0.01 pH unit of the true pH Instruments need to be calibrated

16. Worksheet and bookwork  Complete worksheet 18.3  Bookwork p. 651 problem 22  p. 653 24, 25  p. 654 27 C. Johannesson