Chemistry 2604
L. S. Curtin
April 16, 200
Name: __________________________
Soc. Sec. #. ____________________
EXAMINATION II
INSTRUCTIONS:
Follow the instructions given to you below. Failure to follow these instructions will result in a significant
deduction of points from your exam score.
1) This exam consists of ten pages, the last three being a periodic table and tables of equilibrium constants
and reduction potentials. If any of the pages are missing bring your exam to me immediately.
2) Make sure to print your name and social security number in the top, right hand corner of the exam.
3) Answer five and only five of the six questions on the exam. Clearly indicate which question you do
not want to be graded by putting an X through the entire page the question is on.
4) You must show ALL of your work in order to receive credit for an answer. Show all of your units
in your calculations and pay attention to the number of significant figures in your responses.
5) Budget your time for each question and answer questions which you know how to work first. After you
have finished the entire exam, it is a good practice to review and check your work.
6) Potentials for reference electrodes are given at the bottom of the table of equilibrium constants.
7) Good luck!
Reduction potentials for reference electrodes (vs S.H.E.):
Ag/AgCl Eo = +0.222 V E = +0.197 V
S.C.E.
Eo = +0.268 V E = +0.241 V
1) Draw a block diagram of a Spec-20 including all of the internal parts, what they are used for and
how they perform their tasks.
2)
Explain how you would construct a calibration curve to generate a Beers’ law plot to determine
the concentration of an unknown. Be complete in your discussion.
3) 50.00 mL of an aqueous solution which is 0.0525 M in sodium phosphate is titrated with an aqueous
solution which is 0.100 M in ferrous chloride. Calculate the solubility of ferrous phosphate when
enough titrant has been added to be one milliliter past the equivalence point of the titration.
4) Consider the following electrochemical cell (assume that all solutions are aqueous based and that the
temperature is 25 oC):
Pt(s)/ Mn 2+ (0.0250 M), H+ (pH = 3.00), MnO4 -1 (0.453 M)//KCl (sat’d), AgCl (sat’d)/AgCl(s)/Ag(s)
a) Calculate the measured cell potential.
b) Calculate the potential of the cell vs S.C.E.
5) Consider Experiment 5: The Determination of Vitamin C in Tablets:
A student collects the following data:
Mass of potassium bromate dissolved in a 500.00 mL volumetric flask: 1.3134 g
Mass of 4 vitamin C tablets: 4.4894 g
Volume of potassium bromate solution: 25.00 mL
Volume of sodium thiosulfate required to reach the end-point of the titration: 39.85 mL
Sample mass of vitamin C tablet: 0.4459 g
Volume of potassium bromate solution added: 44.01 mL
Volume of sodium thiosulfate required to reach the end-point of the titration: 2.94 mL
Calculate the mg vitamin C/tablet. Note: You must show all of the necessary chemical
equations and stoichiometry.
6) Give the correct name or chemical formula for the following compounds.
a)
Potassium bromite
b) Ammonium persulfate (ammonium peroxydisulfate)
c)
HIO2
d) Calcium phosphite
Some Potentially Useful Equilibrium Constants
Acid
Acetic
Benzoic
Formic
Hydrocyanic
Hydrofluoric
Nitrous
Sulfurous
Salt
Aluminum hydroxide
Barium hydroxide
Calcium phosphate
Calcium sulfate
Iron(III) hydroxide
Iron(II) phosphate
Iron(III) phosphate
Lead chloride
Lead oxalate
Lead sulfate
Silver bromide
Silver carbonate
Silver chloride
Silver chromate
Silver cyanide
Silver iodide
Zinc sulfate
Ka
1.75 x 10-5
6.14 x 10-5
1.80 x 10 -4
4.9 x 10 -10
6.8 x 10 -4
5.1 x 10 -4
Ka1 = 1.23 x 10-2
Ka2 = 6.6 x 10 -8
Base
Ammonia
Aniline
Dimethylamine
Ethylamine
Hydroxylamine
Methylamine
Pyridine
THAM
Trimethylamine
Kb
1.75 x 10 -5
3.94 x 10 -10
5.9 x 10 -4
4.28 x 10 -4
1.07 x 10 -8
4.8 x 10 -4
1.7 x 10 -9
1.19 x 10 -6
6.25 x 10 -5
Ksp
2 x 10 -32
3.0 x 10 -4
2.0 x 10 -29
4.0 x 10 -38
1.0 x 10 -36
4.0 x 10 -27
1.6 x 10 -5
4.8 x 10 -10
1.6 x 10 -8
5.2 x 10 -13
1.82 x 10 -10
1.1 x 10 -12
7.2 x 10 -11
1.5 x 10 -5
Reduction potentials for reference electrodes (vs S.H.E.):
Ag/AgCl Eo = +0.222 V E = +0.197 V
S.C.E.
Eo = 0.268 V E = +0.241 V