1. pH Scale

3. pH scale Logarithmic scale expressing the H+ concentration, [H+].
If the pH changes by a factor of 1, the [H+] changes by a factor of 10.
pH = -log[H+]

5. If the pH changes from 5 to 7, how do the [H+] compare?
Difference in pH = 2, which means the [H+] differ by 102 or The pH of 5 solution has an [H+] that is 100 X greater than that of the pH 7 solution.
If the pH changes from 5 to 7, how do the [H+] compare?

6. Molarity to pH To determine pH: Express [H+] in scientific notation.
Remember, [ ] means concentration of whatever is inside the brackets.
The log is the power of 10.

7. Molarity to pH for Pure water
a tiny bit of ionization:
H2O  H+ + OH-
[H+] = [OH-] = 1 X 10-7 M
pH = -log[H+] = -(-7) = 7

8. pH [H+] 1 M or 1X100 M 0.1 M 1 X 10-1 M 0.01 M 1 X 10-2 M .001 M1 2 3

10. pH to Molarity pH = -log[H+]. Solve for [H+]. -pH = log[H+]
Antilog(-pH) = [H+]
Say pH = 5. Then –pH = -5.
Antilog(-5) = 10-5.
The –pH becomes the power of 10!

11. pOH By analogy, pOH is defined as –log[OH-].
Express [OH-] in scientific notation.
If [OH-] = 1.0 X 10-3 M
Then pOH = -log(10-3) = -(-3) = 3.

12. pH + pOH = 14 pH = 3, pOH = 11 pH = 7, pOH = pH = 10, pOH = 75 13

14. ACID or BASE?
Acids, [H+]  [OH-]
Bases, [OH-]  [H+]

16. 0 is most acidic; 14 is most basic

17. pH range
0 to is neutral.
pH = 0, strongly acidic
pH = 14, strongly basic

20. If the pH = 4 The [H+] = ? The pOH = ? The [OH-] = ? 10
Antilog(-pH) = [H+]
Antilog(-4) = 10-4 10
Antilog(-10) = [OH-]
10-10 = [OH-]

21. If the [OH-] = 1 X 10-3 The pOH = ? The pH = ? The [H+] = ?
pOH = -log[OH-]
= -log(10-3) = --3 = 3
The pOH = ?
The pH = ?
The [H+] = ?
14 – 3 = 11
Antilog(-11) = M

22. The pH = ? The pOH = ? The [OH-] = ? 5 14 – 5 = 9
If the [H+] = 1 X 10-5 M
The pH = ?
The pOH = ?
The [OH-] = ? 5
14 – 5 = 9
Antilog(-9) = 10-9

23. [H+] pH
[OH-]
pOH
Acidic or
Basic 3
10-5 M
10-2 M 6
10-3
10-11 11 A 9 5 B
10-9 A 2
10-12 M 12 B
10-8 M 8
10-6 M

24. How to safely test pH Instrumental – use a pH meter
Indicators – use a series of indicators
See if the substance reacts with a metal other than Cu, Ag, or Au.
Do NOT say “taste.”

26. Indicator A substance that changes color over a narrow pH range.
Use several indicators to narrow down the pH range of the substance.