1. Acid / Base and pH / pOH
Chemistry Unit 10

2. Key Topics Water is amphoteric: H2O + H2O acts as an acid and a base.
Chemistry Unit 10

3. Key Topics Water is amphoteric: H2O + H2O H3O+ + OH-
acts as an acid and a base.
Donates H+
H2O + H2O H3O+ + OH-
Chemistry Unit 10

4. Key Topics Water is amphoteric: H2O + H2O H3O+ + OH-
acts as an acid and a base.
Accepts H+
H2O + H2O H3O+ + OH-
Chemistry Unit 10

5. Key Topics Water is amphoteric: H2O + H2O H3O+ + OH- BASE ACID
acts as an acid and a base.
Accepts H Donates H+
H2O + H2O H3O+ + OH-
BASE ACID
Chemistry Unit 10

6. Key Topics Water is amphoteric: H2O + H2O H3O+ + OH-
acts as an acid and a base.
Accepts H Donates H+
H2O + H2O H3O+ + OH-
BASE ACID ACID BASE
Chemistry Unit 10

7. Key Topics H2O + H2O H3O+ + OH- BASE ACID ACID BASE CONJUGATE PAIRS:
Accepts H Donates H+
H2O + H2O H3O+ + OH-
BASE ACID ACID BASE
Chemistry Unit 10

8. Opposite sides of equation, Opposite acid vs. base,
CONJUGATE PAIRS:
BASE ACID ACID BASE
Opposite sides of equation,
Opposite acid vs. base,
Opposite STRENGTHS ( weak vs strong)
Chemistry Unit 10

9. Key Topics Water is amphoteric: Self-ionization of water
acts as a WEAK acid and a WEAK base.
It’s acid dissociation constant, Ka , is low.
Self-ionization of water
H2O + H2O H3O+ + OH-
Chemistry Unit 10

10. Key Topics Self-ionization of water Ion Product Constant for Water, Kw
H2O + H2O H3O+ + OH-
Ion Product Constant for Water, Kw
Like the Dissociation Constant: Measure of STRENGTH
Kw = [H3O+][OH-]
Concentrations of hydronium and hydroxide in molarity
Chemistry Unit 10

11. Key Topics Ion Product Constant for Water, Kw Kw = [H3O+][OH-]
Concentrations of hydronium and hydroxide in molarity
Kw = 1 x at 25 oC
Chemistry Unit 10

12. Using Kw Calculate the concentration of
hydronium and hydroxide ions in neutral water.
First, we know Kw = [H3O+][OH-]
AND we know Kw = 1 x 10-14
ALSO, we know the balanced equation for the self ionization of pure water:
H2O + H2O H3O+ + OH-
Therefore, we know [H3O+]= [OH-] according to reaction coefficients.
Rest is algebra!
Chemistry Unit 10

13. Using Kw Kw = [H3O+][OH-] = 1 x 10-14
Substitute in “x” for both [H3O+]and [OH-]
x . x = 1 x 10-14
x2 = 1 x 10-14
x = 1 x 10-7
Chemistry Unit 10

14. Using Kw Kw = [H3O+][OH-] = 1 x 10-14
[H3O+] = 1 x 10-7 M [OH-] = 1 x 10-7 M
H2O + H2O H3O+ + OH-
In water, ALL three species:
H2O, H3O+ and OH- exist!
Chemistry Unit 10

15. Using Kw Kw = [H3O+][OH-] = 1 x 10-14
Substitute in “x” for both [H3O+]and [OH-]
The molarity for both [H3O+]and [OH-] are:
x = 1 x 10-7
[H3O+] = 1 x 10-7 M [OH-] = 1 x 10-7 M
Chemistry Unit 10

16. Calculations with the Kw constant
Calculate the concentration of hydronium, if the hydroxide ion concentration is 1 x 10-8 M.
Chemistry Unit 10

17. Calculations with the Kw constant
Calculate the concentration of hydronium, if the hydroxide ion concentration is 1 x 10-8M.
First, we know Kw = [H3O+][OH-]
AND we know Kw = 1 x 10-14
ALSO, we know the [OH-] = 1 x 10-8M.
Rest is algebra!
Chemistry Unit 10

18. Using Kw Kw = [H3O+][OH-] = 1 x 10-14
Substitute in “x” for [H3O+] and known value for [OH-], 1 x 10-8
x . 1 x 10-8 = 1 x 10-14
x = 1 x 10-14
1 x 10-8
x = 1 x 10-6
Chemistry Unit 10

19. What pH and pOH Mean
pH is a numeric measurement of the hydronium ion concentration.
pH = -log[H3O+]
Remember the hydronium concentration must be in molarity!
Hydrogen ion concentration[H+] is the same thing as the hydronium ion concentration!
Chemistry Unit 10

20. What pH and pOH Mean
pOH is a numeric measurement of the hydroxide ion concentration.
pOH = -log[OH-]
Remember the hydroxide concentration must be in molarity!
Keep checking if the question asks or gives hydroxide, hydrogen, hydronium,
pH or pOH!
Chemistry Unit 10

21. What pH and pOH Mean pH plus pOH always equal 14. Example:
If the pH = 7 then the pOH must equal 7.
If the pH = 5 then pOH = 9.
If the pOH = 13.2 the pH = 0.8
Chemistry Unit 10

22. Calculations
What is the pH of a solution with a concentration of 1 x M H3O+
Chemistry Unit 10

23. Calculations
What is the pH of a solution with a concentration of 1 x M OH-
Chemistry Unit 10

24. Calculations
What is the pH of a solution with a concentration of 4.5 x 10-3 M H3O+
Chemistry Unit 10

25. Calculations
What is the pH of a solution with a concentration of 6.8x 10-5 M OH-
Chemistry Unit 10

26. Next Steps Make sure you READ the chapter! Complete pH and pOH table
Chemistry Unit 10

27. Neutralization
The reaction of an acid with a base to produce a salt and water.
HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)
If we prepare a standard solution of NaOH, we can then use it to determine the concentration of HCl in a sample.
This is an example of Analytical Chemistry.

28. Titration Method based on measurement of volume.
You must have a solution of known concentration - standard solution.
It is added to an unknown solution while the volume is measured.
The process is continued until the end point is reached - a change that we can measure.
Acids and bases are commonly measured using titrations.

29. Titrations Buret volumetric glassware used for titrations.
It allows you to add a known amount of your titrant to the solution you are testing.
An indicator will give
the endpoint.

30. Titrations
Note the color change which indicates that the ‘endpoint’ has been reached.
Start
End

31. Indicator examples
Acid-base indicators are weak acids that undergo a color change at a known pH. pH
phenolphthalein

32. Indicator examples
bromothymol
blue
methyl red