1. Buffered Solutions
A solution of a weak acid and a common ion is called a buffered solution.

2. Thus, the solution maintains it’s pH in spite of added acid or base.

3. Demo: buffered solution

4. Demo: tap water vs. dH2O
Both waters have Universal indicator in them (= pH indicator (changes color in the presence of ions), which is a type of weak acids)
The water will change pH, and therefore COLOR (which helps us determine if a solution is acidic or basic) with the addition of HCl (acid) and NaOH (base)

5. Universal Indicator Color Chart PAGE 602 fig 19.13
pH scale
Acid Neutral Base

6. Why does it take more drops of acid or base to make the tap water change color than it does for the distilled water?
What is distilled water made of? What is tap water made of?

7. pH and pOH
Pg. 596 (in section 19.2)

8. Ionization of water
Experiments have shown that pure water ionizes very slightly:
2H2O  H3O+ + OH-
Measurements show that:
[H3O+] = [OH-]=1 x 10-7 M
Pure water contains equal concentrations of H3O+ + OH-, so it is neutral.

9. pH pH = -log [H3O+] pH = -log [H+]
pH is a measure of the concentration of hydronium ions in a solution.
pH = -log [H3O+] or
pH = -log [H+]

10. Example: What is the pH of a solution where [H3O+] = 1 x 10-7 M?
pH = -log [H3O+]
pH = -log(1 x 10-7)
pH = 7

11. Example: What is the pH of a solution where [H3O+] = 1 x 10-5 M?
pH = -log [H3O+]
pH = -log(1 x 10-5)
pH = 5
When acid is added to water, the [H3O+] increases, and the pH decreases.

12. Example: What is the pH of a solution where [H3O+] = 1 x 10-10 M?
pH = -log [H3O+]
pH = -log(1 x 10-10)
pH = 10
When base is added to water, the [H3O+] decreases, and the pH increases.

13. The pH Scale PAGE 598 Table 19.5 & fig 19.10
*You must use pH to determine if something is acidic, basic or netural (not pOH)
Acid Neutral Base

14. pOH
pOH is a measure of the concentration of hydroxide ions in a solution.
pOH = -log [OH-]

15. Example: What is the pOH of a solution where [OH-] = 1 x 10-5 M?
pOH = -log [OH-]
pOH = -log(1 x 10-5)
pOH = 5

16. How are pH and pOH related?
At every pH, the following relationships hold true:
[H3O+] • [OH-] = 1 x M
pH + pOH = 14

17. Example 1: What is the pH of a solution where [H+] = 3.4 x 10-5 M?
pH = -log [H+]
pH = -log(3.4 x 10-5 M)
pH = 4.5

18. Example 2: What is the pH of a solution where [H+] = 5.4 x 10-6 M?
pH = -log [H+]
pH = -log(5.4 x 10-6)
pH = 5.3

19. Example 3: What is the [OH-] and pOH for the solution in example #2?
[H3O+][OH-]= 1 x 10-14
(5.4 x 10-6)[OH-] = 1 x 10-14
[OH-] = 1.9 x 10-9 M
pH + pOH = 14
pOH = 14 – 5.3 = 8.7

20. Example #4 ***MUST SOLVE FOR pH and use the pH scale basic basic
Classify each solution as acidic, basic, or neutral
***MUST SOLVE FOR pH and use the pH scale
a. [H+] = 6.0 x M
b. [OH-] = 3.0 x 10-2 M
c. [H+] = 2.0 x 10-7 M
d. [OH-] = 1.0 x 10-7 M
basic
basic
acidic
neutral

21. Example #5
Which is the MOST basic from question #4? B.