1. Bell Ringer
Which of the following aqueous solutions will cause litmus paper to turn red?
A NaOH
B NaCl
C HCl
D H2O pH
1-6 7
8-14
Solution Added
Acid
Neutral
Base
Litmus paper changes from
Blue to Red
Does not Change
Red to Blue
Source: 2003 VA EOC Exam

2. pH
Acids and
Bases

3. A Quick Reminder… Reactions can stop at an EQUILIBRIUM NO2 + NO2 N2O4
Image source:

4. The Equilibrium Constant, Keq
For the reaction:
aA bB cC + dD
Where:
a, b, c, d are coefficients
A, B, C, D are substances
(products)
[C]c [D]d
Keq =
[A]a [B]b
(reactants)
[ ] = concentration in M

5. The Equilibrium Constant, Keq
For the reaction:
NO2 + NO N2O4
[N2O4]1
[N2O4]
Keq = =
[NO2]1 [NO2]1
[NO2]2
2 NO N2O4
[N2O4]1
[N2O4]
Keq = =
[NO2]2
[NO2]2

6. A Special Equilibrium Constant, Kw
For the reaction:
H2O H2O H3O OH-
[H3O+] [OH-]
[H3O+] [OH-] =
Kw =
[H2O]2
“hydronium”
“hydroxide”
[1.00 x 10-7] [1.00 x 10-7]
= 1.00 x 10-14
Kw =
Image source:

7. Practice Problems
Using the knowledge that Kw = 1.00 x 10-14, solve for the missing piece of information:
1. Calculate the hydroxide ion concentration in a solution whose hydronium ion concentration is 1 x 10-5 M
Kw = [H3O+] [OH-]
1.00 x = [1 x 10-5 M] [OH-]
[OH-] = x 10-14 =
1 x 10-9 M
1 x 10-5 M

8. Practice Problems Kw = [H3O+] [OH-] 1.00 x 10-14 = [H3O+] [0.0010 M]
2. Calculate the hydronium concentration for a solution whose hydroxide concentration is M.
Kw = [H3O+] [OH-]
1.00 x = [H3O+] [ M]
[H3O+] = x 10-14 =
1 x M M

9. Practice Problems
3. What is the hydroxide concentration of a solution if grams of NaOH are dissolved in 2.0 L of solution?
What is the hydronium ion concentration of this solution?
M OH-
1.0 x M H3O+
1 mol NaOH
1 mol OH-
0.080 g NaOH
mol OH- x x =
40.00 g NaOH
1 mol NaOH
[OH-] =
mol OH- =
M OH-
2.0 L
Kw = [H3O+] [OH-]
1.00 x = [H3O+] [ M]
[H3O+] = x 10-14 =
1.0 x M H3O+ M

10. Practice Problems
4. What is the hydroxide ion concentration of a solution if grams of Ca(OH)2 are dissolved in 2.0 L of solution?
What is the hydronium ion concentration of this solution?
M OH-
9.3 x M H3O+
1 mol Ca(OH)2
2 mol OH-
0.080 g Ca(OH)2
mol OH- x x =
74.10 g Ca(OH)2
1 mol Ca(OH)2
[OH-] =
mol OH- =
M OH-
2.0 L
Kw = [H3O+] [OH-]
1.00 x = [H3O+] [ M]
[H3O+] = x 10-14 =
9.3 x M H3O+ M

11. pH – the POWER of H+! pH = the negative logarithm of [H3O+]
These numbers represent the POWER of H+
pH = the negative logarithm of [H3O+]
Image source:

12. Log-o-rhythms Logarithm Exponent POWER = = pH – the POWER of H+!
pH = the negative logarithm of [H3O+]
POWER
pH = - log [H3O+]
Answer the following questions without using a calculator:
What is the pH of a solution with [H3O+] = 1.0 x 10-4 M?
pH = 4.00
ACID
What is the pH of a solution with [H3O+] = 1.0 x M?
pH = 12.00
BASE

13. My Kingdom for a Calculator!
To solve for pH, given hydronium molarity
On TI-83:
push “(-)” key
push “log” key
type in number
On Scientific Calculators:
type in number
push “log” key
push +/- key

14. Practice Problems pH = - log [H3O+] pH = - log (1.0 x 10-2) pH = 2.00
1. What is the pH of a solution if the concentration of hydronium ions is 1.0 x 10-2 M? Is the solution acidic or basic?
pH = - log [H3O+]
pH = - log (1.0 x 10-2)
pH =
ACIDIC
SIG FIG RULES: Put the correct number of Sig Figs BEHIND the decimal point.

15. Practice Problems pH = - log [H3O+] pH = - log (1.0 x 10-10)
2. What is the pH of a solution if the concentration of hydroxide ions is 1.0 x 10-4 M? Is the solution acidic or basic?
Kw = [H3O+] [OH-]
1.00 x = [H3O+] [1.0 x 10-4 M]
[H3O+] = x 10-14 =
1 x M
1.0 x 10-4 M
pH = - log [H3O+]
pH = - log (1.0 x 10-10)
pH =
BASIC

16. My Kingdom for a Calculator (again)!
To solve for hydronium molarity, given pH
On TI-83:
push “10x” key
push “(-)” key
type in pH
On Scientific Calculators:
type in number
push +/- key
push “2nd” key
push “log” key

17. Practice Problems pH = 8.00 = - log [H3O+] -8.00 = log [H3O+]
3. What is the concentration of hydronium ions in a solution whose pH is 8.00?
pH = = - log [H3O+]
= log [H3O+]
10–8.00 M = [H3O+]
[H3O+] = x 10-8 M

18. Practice Problems Kw = [H3O+] [OH-]
4. For Question #3, what is the concentration of hydroxide ions?
Kw = [H3O+] [OH-]
1.00 x = [1.0 x 10-8 M] [OH-]
[OH-] = x 10-14 =
1 x 10-6 M
1.0 x 10-8 M

19. Practice Problems pH = - log [H3O+] pH = - log (0.0584) pH = 1.234
5. What is the concentration of hydronium ions in a solution that has a volume of 2.50 L and 5.33 g of HCl? What is the pH of this solution?
1 mol HCl
1 mol H+
5.33 g HCl
0.146 mol H+ x x =
36.46 g HCl
1 mol HCl
[H+] =
0.146 mol H+ =
M H+
2.50 L
pH = - log [H3O+]
pH = - log (0.0584)
pH =

20. Homework
Complete the practice problems on the worksheet. Due next class