1. Unit 13 – 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
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
Acidic
more [H3O+] than [OH-]
Basic
more [OH–] than [H3O+]

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

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

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

10. C. Determining pH
or [H3O+]
Acidic or
Basic
Neutral

11. C. Determining 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

12. 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

13. 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

14. 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

15. Determining pOH pOH is a measure of the concentration of OH- ions
pOH = -log[OH-]
pH + pOH = 14
What is the pOH of a solution with a OH- concentration of 2.30 x 10-2?
What is the pH of the above solution?
1.64
pH = 14 – 1.64 =
12.4

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

17. 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 17

18. 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 18

19. 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 19

20. 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+] 20