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 7.7-7.9 (at least) Monday (2/25): Finish Chapter 7 Start Chapter 8 on Wednesday, 2/24

Acids Vary in Strength

Acids Vary in Strength

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.

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

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

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.

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)?

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

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.

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