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Chem 332
Analytical Chemistry
Exam I
Show all work for partial credit
1. One of the instruments we will talk about in Instrumental Analysis is the Inductively
coupled plasma-mass spectrometer. With this instrument you are capable of detecting
as little as .0003 ng of Mg+2 in 1 ml of solution.
A. (5 points) What is this concentration in ppb?
B. (5 points) What is this concentration in Molarity?
2. (10 points) I have two lab assistants, both making me a 0.1M solution of NaCl.
Assistant A is fast at making large quantities, so he made this solution by weighing out
5.844 grams of NaCl on a balance that reads to .001 g and putting the salt in a 1000 ml
graduated cylinder that can be read to +/- 10 ml.
Assistant B is slow and makes smaller quantities. She weighed out .0584 grams on a
balance that reads to .0001 g, and put the salt in a 10 ml volumetric flask with a +/- .02
ml tolerance.
Determine the uncertainty in the molarity for the solutions made by my two
assistants. Who made the more precise solution?
Assistant A
Assistant B
If I write the molarity as 0.100000...
How many zeros should follow the 1 to correctly express the uncertainty in the resulting
solution?
Assistant A molarity ____________
Assistant B Molarity ______________3A. (7 points) I have a set of data, where the mean is .5674 and the standard deviation
is 0.00051 What is the 95% confidence interval if n=5?
3B. (3 points) For the same set of data and the same confidence level, how large does
n have to be so that the confidence interval is smaller than the standard deviation?
4. (10 points) La(OH)3 has a Ksp of 2x10-21. How many grams of La(OH)3 are dissolved
as ions in 1 liter of a saturated solution of La(OH)3?
5. (10 points) Describe a Volhard and a Fajans titration.
6. (10 points) Calculate the pH of the following solutions
A. 0.00567 M Ca(OH)2
B. 5.7x10-8 M HCl
Take home portion (tear this page out)
7. (10 points) What is the pH of a .24 M solution of Hydrogen thiocyanate
8.( 10 points) I am going to mix 25 mls of .25M HCl, 35 mls of .45M NaOH, 45 mls of
.55M Acetic Acid and 50 mls .65M Sodium acetate. What is the pH of the solution?
9. (20 points) I make up a set of standards to make a calibration curve. Below is the
data I obtain:
Standards
Concentration (mM)
0
2
8
Absorbance
.11
.29
.81
A. I have an unknown with an absorbance of .30, what is its concentration, and what is
the uncertainty in the concentration?
B. I now make an additional set of standards, if I use these two sets of standards
together, and my unknown still has an absorbance of .30, what is its concentration, and
what is the uncertainty in the concentration?
Second Standards
0
.10
1
4
.18
.45
16
1.40
C. Rather than making a third set of standards, I just take a second and third
measurement of my standards and get the following data.
Total data set including first and second runs
0
.11, .10, .11, .09
1
.18. .19, .19
2
.29, .29, .29
4
.45, .40, .44
8
.81, .79, .79
16
1.40, 1.38, 1.37
If my unknown still has an absorbance of .30, what is its concentration, and what
is the uncertainty in the concentration?