1. The pH Scale Hydronium & Hydroxide Ions (H3O+) (OH–) pH Scale
Calculations
Print 1-12

2. auto-ionization of water:
H2O molecules ionize to H3O+ & OH– ions by proton (H+) transfer
auto-ionization constant of water, Kw :
Kw = [H3O+] x [OH–]
= 1.0 x 10–14
[H3O+] = [OH–]

3. [H3O+] & [OH–] =
Acidic
Neutral
Basic

4. pH Scale
pH is…
measure of acidity/basicity by conc. of H3O+ ions, or [H3O+] , or [H+]
[H3O+] pH
[H3O+] pH

5. pH Scale
pH is…
measure of acidity/basicity by conc. of H3O+ ions, or [H3O+] , or [H+]
pure water (pH =7)
[H+] = [OH–]
WHY?
Kw = [H3O+] x [OH–] = 1.0 x 10–14
(1 x 10–7 M)
(1 x 10–7 M)

6. Calculating pH
or [H3O+]
Acidic or
Basic
Neutral

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

8. 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

9. Neutral [H+] pH pOH [OH–] Kw = [H+]x[OH–] 1 x 10–14 1 x 10–14
0.0
14.0
1 x 10–14
1 x 10–1
1.0
13.0
1 x 10–13
1 x 10–2
2.0
12.0
1 x 10–12
1 x 10–3
3.0
11.0
1 x 10–11
1 x 10–4
4.0
10.0
1 x 10–10
1 x 10–5
5.0
9.0
1 x 10–9
1 x 10–6
6.0
8.0
1 x 10–8
1 x 10–7
7.0
Kw = [H+]x[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
Neutral
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

10. Neutral [H+] pH pOH [OH–] Kw = [H+]x[OH–] 1 x 10–14 1 x 10–14
0.0
14.0
1 x 10–14
1 x 10–1
1.0
13.0
1 x 10–13
1 x 10–2
2.0
12.0
1 x 10–12
1 x 10–3
3.0
11.0
1 x 10–11
1 x 10–4
4.0
10.0
1 x 10–10
1 x 10–5
5.0
9.0
1 x 10–9
1 x 10–6
6.0
8.0
1 x 10–8
1 x 10–7
7.0
Kw = [H+]x[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
Neutral
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

11. Neutral [H+] pH pOH [OH–] Kw = [H+]x[OH–] 1 x 10–14 1 x 10–14
0.0
14.0
1 x 10–14
1 x 10–1
1.0
13.0
1 x 10–13
1 x 10–2
2.0
12.0
1 x 10–12
1 x 10–3
3.0
11.0
1 x 10–11
1 x 10–4
4.0
10.0
1 x 10–10
1 x 10–5
5.0
9.0
1 x 10–9
1 x 10–6
6.0
8.0
1 x 10–8
1 x 10–7
7.0
Kw = [H+]x[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
Neutral
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

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

13. 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 13

14. 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 14

15. 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 15

16. 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+] 16