1. Ch. 15 & 16 - Acids & Bases
II. pH (p )
C. Johannesson

2. A. Auto-Ionization of Water
Water molecules react with other water molecules to IONIZE (make ions). + -
H2O + H2O
H3O+ + OH-
base
acid
LPChem:Wz

3. H2O + H2O H3O+ + OH- A. Ionization of Water
“Pure” water contains hydronium and hydroxide ions.
Note the equilibrium arrow!
Auto-ionization only happens to one out of every quarter-billion molecules, so water doesn’t contain enough ions to be an electrolyte.
LPChem:Wz

4. H2O + H2O H3O+ + OH- Kw = [H3O+][OH-] = 1.0  10-14
A. Ionization of Water
H2O + H2O H3O+ + OH-
The product of the concentrations of H3O+ and OH- in aqueous solution will always equal the equilibrium constant, Kw.
Kw = [H3O+][OH-] = 1.0  10-14
C. Johannesson

5. HCl is a strong acid, [HCl] = [H3O+]
A. Ionization of Water
Find the hydroxide ion concentration of 3.0  10-2 M HCl.
[H3O+][OH-] = 1.0  10-14
[3.0  10-2][OH-] = 1.0  10-14
[OH-] = 3.3  M
Acidic or basic?
HCl is a strong acid, [HCl] = [H3O+]
[H3O+] > 1x10-7 Or
[H3O+] > [OH-]
 acidic
Acidic
C. Johannesson

6. Write answers in Scientific Notation!
A. Ionization of Water
Find the hydronium ion concentration of 2.5  10-5 M NaOH.
[H3O+][OH-] = 1.0  10-14
[H3O+][2.5  10-5]= 1.0  10-14
[H3O+] = 4.0  M
Acidic or basic?
NaOH is a strong base, [NaOH] = [OH-]
Write answers in Scientific Notation!
Basic
[H3O+] < 1x10-7
Or , [H3O+] < [OH-]
C. Johannesson

7. pouvoir hydrogène (Fr.)
B. pH Scale 14 7
INCREASING
ACIDITY
INCREASING
BASICITY
NEUTRAL
pH = -log[H3O+]
pouvoir hydrogène (Fr.)
“hydrogen power”
C. Johannesson

8. pH of Common Substances
B. pH Scale
pH of Common Substances
C. Johannesson

9. pH = -log[H3O+] pOH = -log[OH-] pH + pOH = 14
B. pH Scale
pH = -log[H3O+]
pOH = -log[OH-]
pH + pOH = 14
C. Johannesson

10. B. pH Calculations [H+] pH [OH-] pOH -log[H3O+] 10^(–pH) 14 = pH + pOH
Kw = [H3O+][OH-]
14 = pH + pOH
-log[OH-]
[OH-]
pOH
10^(–pOH)
LPChem:Wz

11. B. pH Scale What is the pH of 0.050 M HNO3? pH = -log[H3O+]
strong acid  [HNO3] = [H3O+]
pH = -log[H3O+]
pH = -log[0.050]
pH = 1.30
Acidic or basic?
__  2 sig figs
__  2 sig figs
after the decimal
Acidic
pH < 7
C. Johannesson

12. B. pH Scale What is the pH of a 1x10-9 M HNO3 solution? Basic
HNO3 is a strong acid
Therefore [HNO3] = [H3O+]
pH = -log[H3O+]
pH = -log[1x10-9] = 9.0
Basic
LPChem:Wz

13. B. pH Scale What is the [H3O+] of a solution with pH = 7.45?
pH = -log[H3O+]
Therefore 10^ -pH = [H3O+]
10^ = [H3O+]
= 3.6 x 10-8 M
LPChem:Wz

14. B. pH Scale
What is the molarity of HBr in a solution that has a pOH of 9.6?
Given:
Find:
HBr is a:
[HBr] =
pOH
Molarity of HBr
Strong Acid
[H3O+]
How do we solve from pOH to [H3O+] ?
C. Johannesson

15. B. pH Calculations [H+] pH [OH-] pOH -log[H3O+] 10^(–pH) 14 = pH + pOH
Kw = [H3O+][OH-]
14 = pH + pOH
-log[OH-]
[OH-]
pOH
10^(–pOH)
LPChem:Wz

16. B. pH Scale 10^ -pH = [H3O+] 10^ -4.4 = [H3O+]
What is the molarity of HBr in a solution that has a pOH of 9.6?
pH + pOH = 14
pH = 14
pH = 4.4
pH = -log[H3O+] or
10^ -pH = [H3O+]
10^ -4.4 = [H3O+]
= 4.0  10-5 M HBr
Acidic
C. Johannesson

17. B. pH Scale
What is the OH- concentration of a solution whose pH is 1.94?
Given:
Find: pH
[OH-]
How do we solve from pH to [OH-] ?
C. Johannesson

18. B. pH Calculations [H+] pH [OH-] pOH -log[H3O+] 10^(–pH) 14 = pH + pOH
Kw = [H3O+][OH-]
14 = pH + pOH
-log[OH-]
[OH-]
pOH
10^(–pOH)
LPChem:Wz

19. B. pH Scale 10^ -pOH = [OH-] 10^ -12.06 = [OH-]
What is the OH- concentration of a solution whose pH is 1.94?
pH + pOH = 14
pOH = 14
pOH = 12.06
pOH = -log[OH-] or
10^ -pOH = [OH-]
10^ = [OH-]
= 8.7  M OH-
Acidic
LPChem:Wz

20. B. pH Scale What is the pH of a 0.055 M KOH solution? Given: [OH-]
Find:
[OH-] pH
How do we solve from [OH-] to pH?
C. Johannesson

21. B. pH Calculations [H+] pH [OH-] pOH -log[H3O+] 10^(–pH) 14 = pH + pOH
Kw = [H3O+][OH-]
14 = pH + pOH
-log[OH-]
[OH-]
pOH
10^(–pOH)
LPChem:Wz

22. B. pH Scale pH + pOH = 14 What is the pH of a 0.055 M KOH solution?
KOH is a strong base
Therefore [KOH] = [OH-]
pOH = -log[OH-]
pOH = -log[0.055]
pOH = 1.26
pH + pOH = 14
pH = 14
pH = 12.74
Basic
LPChem:Wz