1. Acids
Lesson 12
Calculating
Kbs

2. You can calculate the Kb using the Ka from the data package page 6 and the equation below.
Ka x Kb = 1.0 x 25 oC
Kb = Kw
Ka(conjugate) or
Ka = Kw
Kb(conjugate)

3. Calculate the Kb for CN-.
Kb(CN-) = Kw
Ka(HCN)
= 1 x x
= 2.0 x 10-5

4. 2. Calculate the Kb for K2HPO4.
Kb(HPO42-) = Kw
Ka(H2PO4-)
= 1 x x 10-8
= 1.6 x 10-7

5. 3. Calculate the Kb for K2HC6H5O7.
Kb(HC6H5O72-) = Kw
Ka(H2C6H5O7-)
= 1 x x 10-5
= 5.9 x

6. 4. 200.0 mL of 0.200 M H2SO4 is mixed with 400.0 mL of
0.250 M NaOH. Calculate the pH of the new solution.
H2SO NaOH
L x mole L x mole
1 L 1 L
I moles moles
C moles moles
E moles note the loss of 1 sig fig
Final volume = mL mL = mL
[NaOH] = moles = M L
pOH = 1.48
pH = 12.52

7. 5. What is the pH of a solution that is amber in neutral red and
5. What is the pH of a solution that is amber in neutral red and yellow in thymol blue?
Look at page 7
amber in neutral red pH is 8 or higher
yellow in thymol blue pH is 8 or less
pH = 8

8. 6. What is the pH of a solution that is blue in Indigo carmine and
6. What is the pH of a solution that is blue in Indigo carmine and thymolphthalein?
Look at page 7
blue in indigo carmine pH is 11.4 or less
blue in thymolphthalein pH is 10.6 or greater
pH = 11

9. HCl
1 M H+
H2O
NaCl
OH-
NaOH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
100
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
10-14
[H+] pH
The pH Scale
For each change 1 unit of pH the [H+] and [OH-] change by a factor of
10 x. This is the nature of the logarithm.
1. If [H+] increases by 100 x

10. HCl
1 M H+
H2O
NaCl
OH-
NaOH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
100
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
10-14
[H+] pH
The pH Scale
1. If [H+] increases by 100 x

11. HCl
1 M H+
H2O
NaCl
OH-
NaOH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
100
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
10-14
[H+] pH
The pH Scale
1. If [H+] increases by 100 x pH decreases by 2
2. If [H+] decreases by 1000 x

12. HCl
1 M H+
H2O
NaCl
OH-
NaOH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
100
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
10-14
[H+] pH
The pH Scale
1. If [H+] increases by 100 x pH decreases by 2
2. If [H+] decreases by 1000 x

13. HCl
1 M H+
H2O
NaCl
OH-
NaOH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
100
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
10-14
[H+] pH
The pH Scale
1. If [H+] increases by 100 x pH decreases by 2
2. If [H+] decreases by 1000 x the pH increases by 3
3. If [OH-] increases by 100 x

14. HCl
1 M H+
H2O
NaCl
OH-
NaOH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
100
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
10-14
[H+] pH
The pH Scale
1. If [H+] increases by 100 x pH decreases by 2
2. If [H+] decreases by 1000 x the pH increases by 3
3. If [OH-] increases by 100 x

15. HCl
1 M H+
H2O
NaCl
OH-
NaOH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
100
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
10-14
[H+] pH
The pH Scale
1. If [H+] increases by 100 x pH decreases by 2
2. If [H+] decreases by 1000 x the pH increases by 3
3. If [OH-] increases by 100 x the pH increases by 2
4. If [OH-] decreases by 1000 x

16. HCl
1 M H+
H2O
NaCl
OH-
NaOH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
100
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
10-14
[H+] pH
The pH Scale
1. If [H+] increases by 100 x pH decreases by 2
2. If [H+] decreases by 1000 x the pH increases by 3
3. If [OH-] increases by 100 x the pH increases by 2
4. If [OH-] decreases by 1000 x

17. HCl
1 M H+
H2O
NaCl
OH-
NaOH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
100
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
10-14
[H+] pH
The pH Scale
1. If [H+] increases by 100 x pH decreases by 2
2. If [H+] decreases by 1000 x the pH increases by 3
3. If [OH-] increases by 100 x the pH increases by 2
4. If [OH-] decreases by 1000 x the pH decreases by 3
5. If the pH increases by 2 units

18. HCl
1 M H+
H2O
NaCl
OH-
NaOH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
100
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
10-14
[H+] pH
The pH Scale
1. If [H+] increases by 100 x pH decreases by 2
2. If [H+] decreases by 1000 x the pH increases by 3
3. If [OH-] increases by 100 x the pH increases by 2
4. If [OH-] decreases by 1000 x the pH decreases by 3
5. If the pH increases by 2 units the [H+] decreases by 100 x
6. If the pH decreases by 3 units

19. HCl
1 M H+
H2O
NaCl
OH-
NaOH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
100
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
10-14
[H+] pH
The pH Scale
1. If [H+] increases by 100 x pH decreases by 2
2. If [H+] decreases by 1000 x the pH increases by 3
3. If [OH-] increases by 100 x the pH increases by 2
4. If [OH-] decreases by 1000 x the pH decreases by 3
5. If the pH increases by 2 units the [H+] decreases by 100 x
6. If the pH decreases by 3 units

20. HCl
1 M H+
H2O
NaCl
OH-
NaOH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
100
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
10-13
10-14
[H+] pH
The pH Scale
1. If [H+] increases by 100 x pH decreases by 2
2. If [H+] decreases by 1000 x the pH increases by 3
3. If [OH-] increases by 100 x the pH increases by 2
4. If [OH-] decreases by 1000 x the pH decreases by 3
5. If the pH increases by 2 units the [H+] decreases by 100 x
6. If the pH decreases by 3 units the [OH-] decreases by 1000 x