1. Schedule Today (2/20): Continue Chapter 7
Should have read up to Section 7.6 (at least)
New OWL assignments open
See new text assignments (Course Information)
Friday (2/22): Continue Chapter 7
Read Sections (at least)
Monday (2/25): Finish Chapter 7
Start Chapter 8 on Wednesday, 2/24

2. Acids Vary in Strength

3. Acids Vary in Strength

4. Clicker Question
Order the bases F–, Cl–, CN–, and H2O from strongest to weakest. HF (Ka = 7.2 x 10–4) HCN (Ka = 6.2 x 10–10) a) CN–, F–, Cl–, H2O b) H2O, F–, Cl–, CN– c) Cl–, H2O, F–, CN– d) CN–, F–, H2O, Cl– e) I am not sure how to do this.

5. Water is Amphoteric Kw = [H3O+][OH–] = constant at a given temperature
At 25°C, Kw = 1.0 x 10–14
pH = log[H3O+] = 7.00 for pure water at 25°C

6. Consider two samples of pure water at different temperatures.
The pH values are different.
The pH values are the same.
One sample is more acidic than the other. A B
The samples are both neutral. C D

7. Demo Question
Consider the conductivity demonstration showing the difference in the brightness of the bulb between a 0.10M solution of HCl and a 3.0M solution of HC2H3O2. a. What concentration of HC2H3O2 (Ka = 1.8 x 10–5) would make the bulb as bright as the 0.10M HCl? Note: this concentration would be technically impossible, but you can calculate it in theory.

8. Demo Question
Consider the conductivity demonstration showing the difference in the brightness of the bulb between a 0.10M solution of HCl and a 3.0M solution of HC2H3O2. b. What concentration of HCl would make the bulb as dim as the 3.0M HC2H3O2 (Ka = 1.8 x 10–5)?

9. Clicker Question
You add 1.00 x 10–7 mol of HCl to 1.0 L of water at 25°C. What is the pH of the solution? a) 6.70 b) 6.79 c) 7.00 d) 7.21 e) 7.30

10. Problem Solving: A Journey
Where Are We Going?: What are we trying to solve? What does this mean?
Where Have We Been?: What do we know? What is given in the problem, and what is our knowledge base?
How Do We Get There?: How do we connect what we know to what we are trying to solve? Diagrams and more questions can be useful.

11. Problem Solving: Acids-Bases
What are the major species?
HF in water: HF and H2O
HCl in water: H3O+, Cl–, and H2O
What are the reactions in solution?
Always: H2O + H2O H3O+(aq) + OH–(aq)
Weak acid: HA(aq) + H2O H3O+(aq) + A–(aq)
Which reaction dominates?
Look at K values for the reactions