Section 19.2 Lecture for Honors & Prep Chemistry

1. BELLWORK- Label pairs
Identify the conjugate acid-base pairs
a. H2S + H2O  HS- + H3O+
b. HClO4 + H2O  ClO4- + H3O+
c. NH3 + H2O  NH4+ + OH-
d. H2O + HNO3  NO3- + H3O+

2. The pH scale measures the
hydrogen ion
concentration[H+] of a solution.

3. A pH of 7 is neutral
A pH less than 7 is acidic (litmus is red)
A pH greater than 7 is basic (litmus is blue)
The pH scale ranges from below zero (very acidic)
to above 14 (very basic)

4. The pH scale is not linear.
The pH scale is logarithmic.
pH = -log[H+]
[H+] = 1.0 x 10-2 pH = 2 very acidic
[H+] = 1.0 x 10-3 pH = 3 acidic
A solution with pH of 2 contains 10 times as
much H+ as a solution with pH of 3.

5. Calculate pH
pH = -log [H+]
[H+] = 1.0 x 10-7M
[H+] = 5.0 x 10-5M

6. Calculate pH
pH = -log [H+]
[H+] = 1.0 x 10-7M pH= -(exponent) =7
[H+] = 5.0 x 10-5M

7. Calculate pH
pH = -log [H+]
[H+] = 1.0 x 10-7M pH= -(exponent) =7
[H+] = 5.0 x 10-5M pH is between 4&5

8. Calculate pH
pH = -log [H+]
[H+] = 1.0 x 10-7M pH= -(exponent) =7
[H+] = 5.0 x 10-5M pH is between 4&5
to CHECK with calculator
1.Enter concentration in calculator
2.Press log key
3.Change sign to positive
OR in the reverse order depending on
your calculator!

9. Calculate [H+] given pH
pH = 7.0
pH= 8.5

10. Calculate [H+] given pH
pH = 7.0 [H+]= 1x10-7
pH= 8.5

11. Calculate [H+] given pH
pH = 7.0 [H+]= 1x10-7
pH= 8.5 [H+]= 3.2x10-9

12. Calculate [H+] given pH
pH = 7.0 [H+]= 1x10-7
pH= 8.5 [H+]= 3.2x10-9
= between 1x10-9
and 1x10-8
1. Enter pH value in calculator
2. Press the +/- key
3. Press the 10x key
OR in the reverse order depending on your calculator!

13. From pH0 to pH14 the H+ concentration
decreases 100,000,000,000,000 times!!

14. Relationship between [H+] and [OH-]
[H3O+][OH-] = 1.0 x 10-14
ALWAYS!!

15. Relationship between [H+] and [OH-]
[H3O+][OH-] = 1.0 x 10-14
ALWAYS!!
If [H+] = 1.0 x 10-5 then,
[OH-] = 1.0x10-14/ 1.0x10-5 = 1 x 10-9
SUBTRACT THE EXPONENTS!

16. Relationship between [H+] and [OH-]
[H3O+][OH-] = 1.0 x 10-14
If [H+] = 5.0 x 10-4 then,
[OH-] = 1.0x10-14/ 5.0x10-4 = 2 x 10-11

17. Acidic = more H+ than OH-
Basic = more OH- than H+
There is always some of each ion in water
no matter what the pH

19. Relationship between pH and pOH
pOH = -log[OH-]
pH + pOH = 14
Always!!

20. pH pH + pOH = 14 pOH
pH = pOH =
-log[H+] -log[OH-]
[H+] [H+][OH-]=1x10-14 [OH-]

21. pH pH + pOH = 14 pOH
[H+] = [OH-]=
10-pH 10-pOH
[H+] [H+][OH-]=1x10-14 [OH-]

22. Calculate pH ↔ pOH
What is the pH of a solution with pOH = 13?
Is the solution acidic or basic?
What is the pOH of a solution with pH = 8?
Is the solution acidic or basic?
What are the concentrations of H+ and OH-?

23. Calculate pH ↔ pOH
What is the pH of a solution with pOH = 13?
Is the solution acidic or basic?
pH= 1, acidic
What is the pOH of a solution with pH = 8?
Is the solution acidic or basic?
pOH = 6, basic
What are the concentrations of H+ and OH-?
[H+] = 1.0x10-1, [OH-] = 1.0x10-13
[H+] = 1.0x10-8, [OH-] = 1.0x10-6