1. Review of pH and preparation for the pH Lab

2. CH2O3 What would the chemical formula be for this molecule?
Carbonic Acid
What would the chemical formula be for this molecule?
CH2O3

3. CO2 + H2O  H2CO3 H2CO3  HCO3- + H+
When you mix Carbon Dioxide and Water you make Carbonic Acid
CO2 + H2O  H2CO3
However, since Carbonic Acid does not hold tightly to the Hydrogen atoms you get a lot of free H roaming around (an acid).
H2CO3  HCO H+

4. This is in carbonated drinks.

5. C2H4O2 What would the chemical formula be for this molecule?
Acetic Acid
What would the chemical formula be for this molecule?
C2H4O2

6. C2H4O2
 (in water becomes)
C2H3O H+
Acid in
vinegar

7. pH = the number of H+ per liter of water.
So if pH = the amount of H+, then a large pH should be more H+
But it does NOT!
How can a bigger number mean less?

8. 1/2 1/3 1/10 Let us consider fractions. Which is the most pie?
1/ / /10
Which is the most pie?
Notice: as the bottom of the fraction gets bigger the amount gets smaller.

9. 1 pH The pH value goes on the bottom of a fraction.
So as the pH value goes up the amount of H+ goes down.

10. However: the pH number is not alone on the bottom of the fraction.
The pH value is actually a power of 10 on the bottom of the fraction. 1 pH

11. However: the pH number is not alone on the bottom of the fraction.
The pH value is actually a power of 10 on the bottom of the fraction. 1
10pH

12. 1
101 1 10
pH 1 = = 1
103 1
1,000 =
pH 3 = 1
1010 1
10,000,000,000
pH 10 = =

13. But this does not make any sense!
pH 1 = 1/10 H+ per liter of water.
How do you have 1 tenth of a H+ per liter of water?

14. = 6 x 1023 There is one thing forgot to tell you!
It is not 1/10 of a H+
It is 1/10 of a “gram” of H+
“gram” = 600,000,000,000,000,000,000,000
= 6 x 1023

15. 1 10pH 1 100 A 0 pH solution would have Gram of H+ per liter.

16. A pH 0 solution
Gram of H+ per liter. 1
100
Gram of H+ per liter. 1

17. A pH 0 solution
Gram of H+ per liter. 1
Gram of H+ per liter. 1

18. 1 1 x gram = 6 x 1023 A pH 0 solution Gram of H+ per liter.
6 x H+ per liter.
1 x

19. 1 x A pH 0 solution 6 x 1023 H+ per liter. So, a pH 0 solution has
6 x H+ in each liter.

20. Or 1 100 A pH 0 solution would have Gram of H+ per liter.
6 x H+ per liter.

21. x 6 x 1023 1 101 Any math people out there? pH of 1 =
1/101 grams of H+ per liter
x 6 x 1023 1
101
Any math people out there?

22. 1
x 6 x 1023
101 x x x

23. x 6 x 1023 x 1
101 x

24. x
6 x 1022
H+ per liter
60,000,000,000,000,000,000,000

25. Even a liter of pH 14 has a lot of H+ in it.
(a strong base)
has a lot of H+ in it.

26. pH 14
x x
1014 1 pH
6 x 1023
1014
6 x 109 1
6,000,000,000 H+ per liter of water.

27. 6 x 1016 H+ per liter A pH 7 (neutral) would have.
So how can something with so many H+ ions NOT be highly reactive,
how can it be neutral?
It is balanced out by an equal amount of OH- (hydroxide ions).

28. Measuring pH:
But
not
today

29. We are going to use Indicators: chemicals that change color based on the pH of the solution they are in.

30. Actually we are going to use papers that have be soaked in indicators = pH paper

31. measuring½ ml using the pipets.

32. 1. Using a pipit, put ½ ml of a solution in wells
1. Using a pipit, put ½ ml of a solution in wells #1,2,and 3 of your chem-plate.
(Be sure to put the same chemical in all three wells)

33. You should never have more than one chemical at your table.
All the same chemical.

34. If you have more than 1 ph paper at your table then I will subtract 10 from your score.

36. 2. Dip a small piece (about ½ cm) of pH paper into well # 1 (using tweezers) and then remove. Using the pH color card, determine the pH value before the strip has time to dry, and record the pH value in your chart above.
pH = 10

37. Do NOT use this big color chart with for determining pH.

38. pH = 10

39. 10

41. 10
Base

43. 10
Base
Medium

44. Phenolphthalein
Phen

45. D4

46. 10
Base
Medium D4

47. Bromthymol Blue
B B

48. A5

49. 10
Base
Medium D4 A4

50. Universal Indicator
U I

51. B7

52. 10
Base
Medium D4 A4 B7

53. 1 pH 3 = 103 grams of H+ per liter Sample had a measured pH of 3
Gram of Hydrogen = 1 mole 1
103
pH 3 =
grams of
H+ per liter

54. Sample had a measured pH of 31
103
X 6 x 1023
moles
H+ per liter

55. Sample had a measured pH of 31
103
6 x 1023 X
H+ per liter 1

56. Sample had a measured pH of 3
6 x 1023
103
H+ per liter

57. Sample had a measured pH of 3
H+ per liter
6 x 1020