1. pH

2. Aim: How is the pH of a solution determined? Objectives: 1.Students should be able to identify if a substance is an acid, a base or neutral when provided with its pH. 2.Students should know what is being measured when pH is determined. 3.Students should know the relationship between H + concentration and pH.

3. Strong Weak Weak Strong Acid Neutral Base pH vs H + Concentration 10 0 10 -1 10 -2 10 -3 10 -4 10 -5 10 -6 10 -7 10 -8 10 -9 10 -10 10 -11 10 -12 10 -13 10 -14 10 -14 10 -13 10 -12 10 -11 10 -10 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 OH - ion concentration H + ion concentration 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

4. pH ACID Low pH = ___________ [H + ] ___________ [OH - ] BASE High pH = ___________ [H + ] ___________ [OH - ] Compare [H + ] to [OH - ] at the following pHs: pH = 1 [H + ] =[OH - ] = pH = 2 [H + ] =[OH - ] = pH = 3 [H + ] =[OH - ] = pH = 7 [H + ] =[OH - ] = pH = 10 [H + ] =[OH - ] = pH = 14 [H + ] =[OH - ] =

5. What is the relationship between changes in H + concentration and changes in pH? When pH changes by 1 point, H + concentration changes by 10X (ten-fold). When pH increases, [H + ] __________________. When pH decreases, [H + ] ___________________. Examples: pH increases from 1 to 2, what happens to [H + ]? pH increases from 7 to 10, what happens to [H + ]? pH decreases from 4 to 3, what happens to [H + ]? pH decreases from 9 to 5, what happens to [H + ]? [H + ] increases by 1000, what happens to pH? [H + ] decreases by 10,000, what happens to pH?

6. Exit 1.Identify the following as an acid, a base or a neutral solution based on the given pH. 2.What quality of a solution is being measured when we measure pH? 3.What are the H + ion and OH - ion concentrations in the solutions listed in question 1? SolutionpH 17 212 36 When the pH of an aqueous solution is changed from 1 to 2, the concentration of hydronium ions in the solution is (1) decreased by a factor of 2 (2) decreased by a factor of 10 (3) increased by a factor of 2 (4) increased by a factor of 10

7. Acid-Base Indicators colorless (Acid) pink (Base)

8. Indicators Table M: Common Acid- Base Indicators Examples: methyl orange 3.2 and below = red 4.4 and above = yellow bromthymol blue 6.0 and below = yellow 7.6 and above = blue http://www.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/D-Video-e.htm

9. 1 3.2 4.4 14 1 3.8 5.4 14 1 8.2 10 14 1 8.9 9.6 14 Indicator Scales 1 5.5 8.2 14

10. Indicator Questions pH is 6.0 and the indicator is yellow. Yellow in thymol blue, pink in phenolphthalein. What is the possible pH range? Red in litmus, yellow in methyl orange. What is the possible pH range?

11. 49.Three samples of the same solution are tested, each with a different indicator. All three indicators, bromthymol blue, bromcresol green, and thymol blue, appear blue if the pH of the solution is (1) 4.7 (2) 7.8 (3) 6.0 (4) 9.9 48. What is the color of the indicator thymol blue in a solution that has a pH of 11? (1)Red (2) pink (3) blue (4) yellow Regents Questions HW: Pg. 177-178, 1-16 Pg. 187, 61-75