Chemistry 152 Exam I Winter, 1997
Name______
All notes, books, etc., must be placed out of sight. Please read each of the problems carefully. If something is not clear, please ask.
The exam consists of 9 problems on 4 pages. Make sure your exam is complete. The exam is worth 100 points with each of the problems labeled as to its point value.
Answers should be placed in the space provided and written legibly. If I cannot read it -- it is wrong. You MUST show your work clearly for each problem in order to receive full credit. Please include an explanation whenever asked to or whenever necessary to make your answer clear. If I cannot understand it -- it is wrong. Please put your name on every page of the exam.
There are scratch papers and periodic tables available for your use. If you require more data, please ask. As usual, no cheating is allowed. Good Luck!
DATA
(liter atm) Joule 760 mm Hg = 760 Torr = 1 Atm R = 0.0821 = 8.31 2.54 cm = 1 inch 12 inch =1 ft (mole K) (mole K) 5280 ft = 1 mile 1 picture = 1 kiloword
Solvent Boiling Point KBP Melting KFP P(20 C) Hvap (C) Point (C) Pure Vapor Pressure
Benzene 80.2 2.53 5.45 5.07 80 -
Water 100 0.512 0 1.86 17.5 43.9 kjoule/mole Chemistry 152 Exam I Page 1 Name
1.(15) The percentage by mass of concentrated hydrochloric acid is 37.0% HCl. This solution has a density of 1.19 g/ml. Calculate... (and show your work for full credit)
A. Molarity
B. Molality
C. Mole fraction of HCl
2.(10) Lysozyme is an enzyme that cleaves cell walls. A 0.100 L sample of a solution of lysozyme that contains 0.0750 g of the enzyme exhibits an osmotic pressure of 1.32 x 10-3 atm at 25C. What is the molecular mass of lysozyme? Show all work clearly to receive full credit. Chemistry 152 Exam I Page 2 Name
3.(15) Phase diagrams for some substances can be quite complex. Shown here at the right is the phase diagram for sulfur. Use the phase diagram to answer the following questions.
A. How many triple points are in the phase diagram.
B. What phases are in equilibrium at each of the triple points?
C. What phase is stable at room temperature and 1.0 atm pressure?
D. Can monoclinic sulfur exist in equilibrium with sulfur vapor?
E. Is the normal boiling point of sulfur above or below 119C? Explain briefly how you know.
4.(15) When equal masses of two compounds, A and B, are dissolved in equal amounts of a solvent, the solution of A freezes at the lower temperature. Which of the following statements are true?
T F a. If A and B are both non-electrolytes, A has a larger molecular weight than B.
T F b. If A and B have the same molecular weight, A is molecular and B is ionic.
T F c. If A and B are both non-electrolytes, solution A must be a greater concentration than solution B.
T F d. Solution A will have a lower boiling point than solution B.
T F e. The vapor pressure of above solution B will be greater than the vapor pressure above solution A. Chemistry 152 Exam I Page 3 Name
5.(10) What is the freezing point of a solution of dibromobenzene, C6H4Br2 (MW = 235.8), in
0.250 kg of benzene, C6H6 (MW = 78), if the solution boils at 83.5C? Show all work.
6.(10) The temperature inside a pressure cooker is 115C. Calculate the vapor pressure of water inside the pressure cooker. Show all work carefully for full credit.
7.(10) A 1 m solution of HCl (MW = 36.5) in benzene, C6H6 (MW = 78), has a freezing point of 0.4C. Is HCl an electrolyte in benzene? Explain your reasoning clearly.
8.(5) Ethyl chloride (BP = 13C) is used as a local anesthetic. When the liquid is sprayed on Chemistry 152 Exam I Page 4 Name
the skin, it cools the skin enough to freeze and numb it. Explain the cooling effect of liquid ethyl chloride. Convince me you really understand.
9.(10) A solution is prepared by mixing 50.0 g of glucose, C6H12O6 (MW = 180), with 600.0 g
of water, H2O (MW = 18). What is the vapor pressure of this solution at 25C if the vapor pressure of pure water is 23.8 torr at 25C and glucose is a non-electrolyte?