1. Updated 9/27 - See slides 2 and 3
Chem. 1B – 9/27 Lecture
Updated 9/27
- See slides 2 and 3

2. Announcements I Exam #1 Next This week on Thursday (9/29)
Same format as last year
Covers material covered through buffers (covered Thursday)
Help Session Tues., 4:00 to 5:00 in Sequoia 452
Lab Sect. 2-6 here
Lab Sect. 7 in Sequoia 426
Need to bring Scantron Form SC982-E, No. 2 pencil and calculator

3. Announcements II Exam #1 – cont. Today’s Lecture
Will give constants (e.g. R), equation for converting Kp to KC, quadratic equation, Henderson-Hasselbalch equation
Today’s Lecture
Exam 1 Review
Titrations (Chapter 16 + not on Exam 1)

4. Exam 1 Review General Advice Multiple choice questions:
Read full question and all answers before selecting (some answers may “sound right” until you see the actual right answer)
If it is taking time to calculate or if you are uncertain how to proceed, skip that problem and get back to later (circle question so you know you still need to do it)
General Question (12 pts):
Will be multiple parts and involve calculations (e.g. like determination of equilibrium concentrations on quiz)
Need to show work (don’t just punch numbers into your calculator and write answer)
I will give partial credit for parts done correctly

5. Exam 1 Review Topics – Chapter 14
Understand how equilibrium relates to kinetics (dynamic view of equilibrium)
Understand how to get equilibrium equations from equilibrium reactions (chemical equations)
Understand what the K value tells you about equilibrium conditions
Know the difference and be able to convert between KP and KC (for given reaction with R and T given)
Know how equilibrium reaction “manipulation” affects K values (e.g. reversing reaction leads to Knew = 1/Kold)

6. Exam 1 Review Topics – Chapter 14 – cont.
Be able to determine K from all equilibrium concentrations or from initial and equilibrium conditions
Be able to determine equilibrium concentrations from “at equilibrium” conditions and K values or from initial conditions and K values
Be able to determine whether reaction will proceed to products or reactants from K and initial concentrations

7. Exam 1 Review Topics – Chapter 14 – cont. Chapter 15
Know how to apply Le Châtelier’s principle to systems initially at equilibrium with the following changes:
reactant/product addition/subtration
increase/decrease in volume (including dilutions)
changes in T (with DH known)
Chapter 15
Know all three definitions of acids and bases and be able to identify them in examples
Know differences between weak and strong acids and bases and the meaning of Ka and Kb

8. Exam 1 Review Chapter 15 – cont.
Know what autoionization is and how to determine pH and pOH
Be able to calculate the pH when a strong or weak acid is added to water
Be able to calculate the pH when a strong or weak base is added to water
Be able to calculate Ka from Kb (or visa versa)
Be able to calculate % ionization of weak acids
Know differences between weak and strong acids and bases and the meaning of Ka and Kb

9. Exam 1 Review Chapter 15 – cont.
Be able to predict if ions or salts are acidic, neutral or basic
Understand how polyprotic acids react and how to determine the pH and related species concentrations
Be able to calculate pH of buffer solutions (prepared or modified by addition of acid or base) or to determine the amount of weak acid or base to add to make desired pH
Know why buffer solutions are useful
Understand useful range of buffers and buffer capacity

10. Chem 1B – Aqueous Chemistry Titrations (Chapter 16)
Review from 4.8
Titrations are a way to accurately tell when we have reached a stoichiometric point in a reaction
Generic reaction: aA + bB → products
The equivalence point is defined where
(moles A)/(moles B) = a/b
mL of titrant (either A or B) are carefully measured (usually to determine the concentration of B or A)
The end point is where the equivalence point is observed (color change from indicator or inflection point in measured titration curve)

11. Chem 1B – Aqueous Chemistry Titrations (Chapter 16)
Review from 4.8
Example question: An unknown H2SO4 solution is pipeted (25.00 mL) into a flask. It is titrated with KOH until reaching an endpoint (where the equivalence point is observed). It requires 39.1 mL of M KOH. What is the concentration of H2SO4 in the unknown solution?

12. Chem 1B – Aqueous Chemistry Titrations (Chapter 16)
Titrations – pH behavior
Review material covered how we can use titrations, but not the exact behavior during the titration
In Chapter 16, we cover, through calculations, the pH of the full titration curve
The most valuable titrations are accurate (observed end point gives the equivalent point) and precise (reproduceable)
This occurs when change in pH in a titration is rapid

13. Chem 1B – Aqueous Chemistry Titrations (Chapter 16)
Strong Acid – Strong Base Titration
How does pH change as NaOH is added?
3 regions to titrations (different calculations in each region):
before equivalence point
at equivalence point
after equivalence point
Show pH at 5 mL, 12.5 mL, and 15 mL
0.100 M NaOH
0.050 M HCl, 25 mL

14. Chem 1B – Aqueous Chemistry Titrations (Chapter 16)
Titration Plot
0.100 M NaOH
0.050 M HCl, 25 mL
Extremely sharp titration (large slope at equivalence point)

15. Weak Acid – Strong Base Titration
How does pH Change as NaOH is added?
Reaction:
HA + OH- ↔ A- + H2O K = 1/Kb
Example – acetic acid:
Ka = 1.76 x 10-5
4 regions to titrations (different calculations in each region):
initial pH (skipping calculation)
before equivalence point
at equivalence point
after equivalence point
Show pH at 5 mL, 12.5 mL, and 15 mL
0.100 M NaOH
0.050 M HA, 25 mL 15