Constants you may need : c=2.998x10
8 m/s, h = 6.626x10
-34 Js
1A. (5 points) What is the frequency associated with green light that has a wavelength of 400 nm?
B. (5 points)What is the energy of this light?
2. (10 points) A substance has an , of 375 M -1 cm -1 . I known my spectrometer is most accurate between 0.4 and 0.9 absorbance units. If I am using a 1 cm pathlength cell, what range of concentrations can I measure most accurately on my spectrophotometer?
3. (10 points)I have a solution that is .1M NaOH, .05M NaCl, .03M K
2
SO
4
. What is the ionic strength of this solution?

4. (15 points) I have a solution with an ionic strength of 0.04. What is the solubility of
BaF
2
in this solution? (K sp
BaF
2
is 1.6x10
-6
, " (Ba) = 500pm " (F) = 350pm) Use the extended Debye-Hückel equation: log
.
51
2 z u u
1
305
2
5. I have 250 mL of .05M HCN.
A. (3 points) What is the p[CN ] of this solution?
B. (4 points) I would like to remove the cyanide before I pour this solution down the drain. Since the K sp
of AgCN is 2.2x10
CN
-
with Ag
+
. How much .035 M AgNO
3
-16
I think I can do this by precipitating the
do I need to add to be equivalent to the CN
-
in my solution?
C. (3 points) What is the p[CN ] after this addition?
6. (10 points) When ammonium acetate dissolves, both the anion and the cation have acid-base properties as seen in the following equilibria:
(NH
4
)
2
SO
4
(s) W 2NH
4
+ + SO
4
2K sp
= 276
NH
4
+ W
NH
3
+ H
+
K a
=5.7x10
-10
SO
4
2 + H
2
O W HSO
4
+ OH . K b
= 9.8x10
-13
Write a charge balance equation for this system.
Write a mass balance equation for this system.

3

4
7(15 points) (A). A 0.1 M solution of an acid has a pH of 1, is this a strong or weak acid.
If it is a weak acid, what is its pK a
?
(B) A 0.1M solution of an acid has a pH of 2, is this a strong or weak acid? If it is a weak acid, what is its pK a
8.(10 points) In our experiment to determine the pK a
of methyl red I wanted a solution that was well buffered around pH 3.0, the pK a
of the indicator. I chose acetic acid (pK a
= 4.757) Other acids I might have tried are: 2-aminobenzoic acid (pK a
2.08) or citric acid (pK a
3.13).
A. Given these choices, what is the best acid for this buffer?
B. Given a .1M solution of this acid and a 0.1M solution of its conjugate base, how would I make up a .1M buffer solution at pH 3. (How many mLs of acid and conjugate base solution would I use?)
9. (10 points) If I have a 0.35 M solution of a weak base that is 94% in the free base form (B) and 6% in the charged form (BH), what is the K b
of the base?