1. Unit 14 – Acid, Bases, & Salts
The pH Scale
Hydronium & Hydroxide Ions
(H3O+) (OH–)
pH Scale
Calculations
Print 1-12

2. A. Hydronium & Hydroxide Ions
H3O+ & OH– Ions
auto-ionization of H2O by
proton (H+) transfer

3. Kw – Ionization Constant for Water
A. Hydronium & Hydroxide Ions
Kw – Ionization Constant for Water
In pure water at 25 C:
[OH-] = [H3O+] = 1 x 10-7 M
Kw is a constant at 25 C:
Kw = [H3O+][OH-]
Kw = (1 x 10-7)(1 x 10-7) = 1 x 10-14
[H3O+][OH-] = 1 x 10-14

4. A. Hydronium & Hydroxide Ions
[H3O+][OH-] = 1 x 10-14
1. If [H3O+] is 1 x 10-9, what is [OH-]?
(1 x 10-9) [OH-] = 1 x 10-14
[OH-] = 1 x =
1 x 10-9
1 x 10-5 M

5. A. Hydronium & Hydroxide Ions
[H3O+][OH-] = 1 x 10-14
2. If [H3O+] is 4.5 x 10-5, what is [OH-]?
(4.5 x 10-5) [OH-] = 1 x 10-14
[OH-] = 1 x =
4.5 x 10-5
2.2 x M

6. A. Hydronium & Hydroxyl Ions
Acidic
more [H3O+] than [OH-]
Basic
more [OH–] than [H3O+]

8. B. pH Scale pH
a measure of the concentration of H3O+ ions in solution, or [H3O+]
[H+] same as [H3O+]

9. B. pH Scale pH
a measure of the concentration of H3O+ ions in solution, or [H3O+]
[H+] same as [H3O+]
pH [H3O+]
pH [H3O+]

10. pH of Common Substances
B. pH Scale
pH of Common Substances
acidic pH < Neutral basic pH > 7
WHY?
pure water pH =7
[H+] = [OH–]

11. C. Calculating pH
or [H3O+]
Acidic or
Basic
Neutral

12. C. Calculating pH or [H3O+]
What is the pH of a solution with a H+ concentration of 1.0 x 10-10?
pH = - log (1.0 x 10-10)
pH = 10
Acidic or
Basic

13. C. Calculating pH or [H3O+]
What is the pH of a solution with a [H+] = M ?
pH = - log (0.045)
pH = 1.35
Acidic or
Basic

14. C. Calculating pH or [H3O+]
What is the pH of a solution with a [H+] = 6.35 x 10-6 M ?
pH = - log (6.35 x 10-6)
pH = 5.20
Acidic or
Basic

15. C. Calculations pH = –log [H+] pOH = –log [OH–] [H+] = 10–pH
[OH–] = 10–pOH
pH + pOH = 14
Kw = [H+] x [OH–] = 1 x 10–14
(auto-ionization constant of water)

16. Kw = [H+][OH–]
1 x 10–14
1 x 10–14
1 x 10–14
1 x 10–14
1 x 10–14
1 x 10–14
1 x 10–14
1 x 10–14
1 x 10–14
1 x 10–14
1 x 10–14
1 x 10–14
1 x 10–14
1 x 10–14
1 x 10–14

17. OH– H+ pH pOH C. Calculations [OH–] = 1 x 10–14 [H+] [H+] = 1 x 10–14
pH = –log[H+]
[OH–] = 10–pOH
pOH = –log[OH–]
pOH = 14 – pH pH
pOH
pH = 14 – pOH

18. Quick Quiz! 1) Which one of the following solutions is the most basic?
A) soap
B) milk
C) vinegar
D) ammonia
E) tomato juice
F) blood
pH ≈ 10
pH ≈ 6.5
pH ≈ 2.5
pH ≈ 11
pH ≈ 4.0
pH ≈ 7.4 18

19. Quick Quiz
2) The [H3O+] for four solutions is given below. Which one of the solutions is the most acidic?
A) 1 x 10-3M
B) 1 x 10-7M
C) 1 x 10-9M
D) 1 x 10-14M 19

20. Quick Quiz.
3) What is the pH of a solution with a [H+] concentration of x 10-11M ?
A) 12.93
B) 10.60
C) 8.92
D) 5.50 20

21. Quick Quiz.
4) What is the pH of a solution with a [OH–] concentration of x 10-3M ?
A) 2.82
B) 11.18
C) 6.67 x 10–12
D) 1.50 x 10–12
pOH = –log[OH–]
pH = 14 – pOH OR
[H+] = 1 x 10–14
[OH–]
pH = –log[H+] 21