1. Chem. 31 – 12/6 Lecture

2. Announcements I AA regrades Remaining Lab Due Dates
Won’t be ready until Monday
I had planned to get feedback to students about how this could affect formal lab (students should still have a copy of spreadsheet and data)
Remaining Lab Due Dates
Formal Lab Report – part B – due today
Soda Ash – due 12/8
IC #2 – due 12/8
All Resubmissions – due 12/8

3. Announcements II
New Posted Material (Exam 2 key, HW solutions, working on S17 Final key)
Final Exam
Dec. 11, 10:15-12:15
Will allow you to bring in 1 sheet of notes (8.5”x11” or smaller) with notes
175 points; about half new material
New material
Starting with relative retention and band broadening in Ch. 23
Ending with Chapter 10 (ran out of time to get to titrations)

4. Announcements III Today’s Lecture Review for Final Exam
Chapter 10
Polyprotic acids used to make buffers
Monoprotic and Polyprotic acids in buffer solutions (if time)
Review for Final Exam
Bonus Point for completing evaluation on new lab:
Teaching Evaluations

5. Chapter 10 – Polyprotic Acids
Use as Buffers
Similar to buffers covered in Chapter 9
With most polyprotic acids where Ka1 >> Ka2 >> Ka3, the Henderson-Hasselbalch equation can be used with a single pKa selected)
The only difficulty can be in deciding which species exist and how to get to those species
Example 1: A mixture of mol NaH2PO4 and mol Na2HPO4 in 1.00 L solution. Determine the pH
Example 2: How many mL of 1.00 M HCl needs to be added to 500 mL of M Na3PO4 to get a pH = 6.5 buffer?

6. Chapter 10 – Polyprotic Acids
Distribution of forms at fixed pH (e.g. when in a buffer)
Let’s start with monoprotic acid HA
HA H+ + A-
Fraction present as HA = a(HA) = [HA]/[HA]total = [HA]/([HA] + [A-])
Can calculate ratio ([A-]/[HA]) using Henderson-Hasselbalch equation, but other method calculating a values is more general
Go over method on board
a(A-) = Ka/([H+] + Ka) (can do derivation yourself)

7. Chapter 10 – Polyprotic Acids
On to a diprotic acid H2A
From H2A form
From HA- form
From A2- form
Notice that denominator is the same
Can you guess a(A2-)?

8. Chapter 10 – Polyprotic Acids Alpha Plot
pKa2
pKa1

9. Chapter 10 – Polyprotic Acids Example Problems
What is the concentration of CO32- if 1.0 x 10-4 moles of CO2 are dissolved into 1.0 L of a buffer at pH = 8.80? (for H2CO3, pKa1 = 6.35, pKa2 = )

10. Final Exam – Review of New Topics
Chapter 23
How to determine relative retention (a) from chromatogram and what it is a measure of*
How relative retention can be changed
How to determine N and H for a column from chromatogram*
How to determine resolution from chromatogram*
What factors can be adjusted to improve resolution

11. Final Exam – Review of New Topics
Chapter 8
Basis for effects of solution ionic strength on equilibrium
Calculation of ionic strength*
Calculation of activity and activity coefficients*
Solution of equilibrium problems including activity*
Predict effects of ionic strength on shifting reaction direction
Determination of pH (including activity)*

12. New Topics on Final Exam
Chapter 8
Rationale as to why the ICE method can fail
Be able to set up solutions to equilibrium problems using steps 1 to 5 of systematic method*
Be able to solve simple equilibrium problems (up to 3 unknowns) using systematic method*
Qualitative understanding of how secondary reactions affect primary reactions

13. New Topics on Final Exam
Chapter 9
Be able to solve strong acid/strong base problems*
Solution of weak acid problem (using ICE method)*
Solution of weak base problem (using ICE method)*
Determination of fraction of association/dissociation*
Knowledge of when ICE method fails
Solution of buffer problems (both weak acid/conjugate base and weak acid/strong base or weak base/strong acid types)*
Identification of combinations that make a traditional buffer

14. New Topics on Final Exam
Chapter 10
Identification of type (e.g. H2A vs. H2L+ vs. H2L2+) and form (acid, intermediate, or base) of polyprotic acids (including charge on groups)
Determination of pH buffer problems involving polyprotic acids*
Determination of fractions of acid present in each form (monoprotic to diprotic acids) or concentration of each form when pH is known*