Name: Professor Key
Chemistry
3600
First
Examination
October
2, 2002
Directions: There are 4 questions, each worth equal points. Some are more difficult than others. Read over all questions before you start to answer. Answering the harder questions last will insure that you obtain the maximum score. You must show your work and pertinent formula's to get full credit. The final number answer is only ten percent of the total score.
Statistics formulas:
Useful data:
Values of Q @ 90% confidence
|
Q |
0.94 |
0.74 |
0.64 |
0.56 |
0.51 |
0.47 |
0.44 |
0.41 |
|
N |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
Values of Student's t @ 95% confidence
|
t |
12.71 |
4.303 |
3.182 |
2.776 |
2.571 |
2.447 |
2.365 |
2.306 |
2.262 |
2.228 |
|
d.f. |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
1. Analysis, Concentrations, and Concepts
A) List the major steps in a chemical analysis.
1. Understand problem
2. Sampling
3. Separation into components
4. Conversion to measurable form
5. Measurement
6. Data Analysis
7. Report
B) A 48.0% (w/w) aqueous HBr (FW 80.91) solution has a density of 1.5 g/mL. What is the formal concentration of HBr?
Why is it more accurate to state concentration in formal than molar in this case?
Because the HBr dissociateds in solution. The concentration of Br- is about 8.9 M.
HBr is a strong acid. What is the approximate molar concentration of HBr solution?
Since the HBr has gone to H+ and Br-, the [HBr] is about 0 M.
C) State whether the shot patterns below are accurate, precise, both, or neither.
2. Statistics
A) Use the Q test to determine if the largest value can be dropped from the following data set
0.529, 0.765, 0.439, 0.530, 0.565, 0.521
Since Qcalc>Qtable, datum may be rejected from the set
B) Report the mean, standard deviation, and relative standard deviation based on the following data set. Be sure to show your work.
74.85, 74.93, 75.02, 74.83, 75.12
C) Calculate the confidence interval and report the statistically probable mean value at the 95% confidence level
D) A nano-sample contains 1 atom of potassium out of every 100 atoms. How many atoms have to be sampled to get a standard 1% RSD in a potassium analysis?
3. Chemical Equilibrium
A) Name and give an example of the four (4) main types of chemical equilibria found in aqueous chemistry using balanced chemical equations..
1 - Acid/Base
2 - Redox
3 - Precipitation
4 - Complex-forming
B) Calculate the concentrations of zinc species listed below in a solution with solid Zn(OH)2(s) buffered at pH=7.00 The solubility product and formation constants are given below.
1- Zn2+(aq) Ksp=3.0´10-16
2 - Zn(OH)+(aq) b1=2.5´104
3 - Zn(OH)3-(aq) b3=7.2´1015
4 - Zn(OH)42-(aq) b4=2.8´1015
4. Solubility Equilibrium
Lanthanum iodate, La(IO3)3, (F.W. 663.62) has Ksp=1.0´10‑11. How many grams lanthanum iodate will dissolve in...
A) 1.00 L pure water ?
The equilibrium equation is
La(IO3)3 (s) « La3+ (aq) + 3IO3- (aq)
Using the table method,
|
|
La(IO3)3 (s) |
La3+ (aq) |
IO3- (aq) |
|
initial |
Solid |
0 |
0 |
|
change |
-x |
+x |
+3x |
|
final |
Solid |
x |
3x |
Solve the Ksp equation for the molar solubility, x
Now find the weight in dissolved in 1.00 L pure water
B) 1.00 L of a 0.050 M (F) solution of soluble LiIO3?
Using the table method,
|
|
La(IO3)3 (s) |
La3+ (aq) |
IO3- (aq) |
|
initial |
Solid |
0 |
0.050 |
|
change |
-x |
+x |
+3x |
|
final |
Solid |
x |
0.050 + 3x |
Solve the Ksp equation for the molar solubility, x
Now find the weight in dissolved in 1.00 L pure water
