Name:
Inside of each beaker, write down your individual observations on pH and conductivity. 2) After the demo, discuss in groups of 3 the possible identity of each container. Prove your reasoning using calculations, e.g. expected pH or expected conductivity, etc...
Use the space provided for your discussion below each beaker. 3) Discuss with Amit and Zack and hand-in after class.
1 2 3 4
5
Solvent “blank” 1) 0.1 M solute A, 2) AgNO
3
0.1 M solute B 0.1 M solute C 0.1 M solute D
6
Solvent + some B
7
0.1 M E
8
0.1 M E + some B
9
0.1 M E + some D
10
0.05 M G

Name 1:
Name 2:
Name 3:
Discuss in groups of three the following topics. Choose one topic of your like and write down in group a final answer. Use drawings, schematics, graphs, beaker notation, whatever you need to get your points across.
A) You are a group of physicians trying to develop a universal buffer solution for medical purposes. You want this solution to buffer the pH over a range of 7 pH units, from pH 3 to pH 10. How would you do that? What complications do you foresee in making this buffer work?
B) Prof. Howard “High-Voltage” Malmstadt made a career in the 1950’s at the University of Illinois developing an electronic automatic titrator. Sloppy Joe thinks this might work based on conductimetric measurements, but Tim thinks that simply using a pH meter would be better. What is your expert opinion and why? How would you build it and how would it work?
C) Why is it a bad idea to try to prepare a buffer from a strong acid or base? There is such a concept called “the Leveling effect” which states that you cannot have in aqueous solution a base stronger than hydroxide or an acid stronger than the proton, explain why.

In all solutions, measure pH and conductivity. Display on-screen using the projector. Rinse well the pH meter. Do not reveal the identity of the containers until the end of the activity. 1) Demonstrate, 2) let them discuss and ask about their conclusions, 3) reveal and verify that the system performed as “expected”
DI water
0.1 M NaCl then add
AgNO3 until complete prec.
0.1 M HCl 0.1 M HOAc 0.1 M NaOH
1 2 3 4
5
DI water then add
10 ml HCl 0.1 M
6
0.1 M NaOAc
7
0.1 M NaOAc
10 ml HCl 0.1 M
8
0.1 M NaOAc then add
10 ml NaOH 0.1 M
0.05 M Na
3
PO
4 add HCl dropwise to see two buffer waves until pH ~ 3
9 10