Chemistry 1212 Exam I Page 4 Name

Chemistry 1212

Exam I

Fall, 2001

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 6 problems on 4 pages with a Take-Home extra credit opportunity on the fourth page. 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

760 mm Hg = 760 Torr = 1 Atm

1 picture = 1 kiloword

Substance / Density / Freezing Pt / kfp / Boiling Pt / kbp / Hvap
H2O / 1.0 g/ml / 0.0 °C / 1.86 / 100.0 °C / 0.512 / 40.79 kJ/mole
Benzene / 0.8787 g/ml / 5.5 °C / 5.12 / 80.1 °C / 2.53 / 30.8 kJ/mole


1.(20) Estimate the molar heat of vaporization of a liquid whose vapor pressure doubles when the temperature is raised from 85°C to 95°C. Show all work clearly for full credit.

2.(20) A 1.20 g sample of water is injected into an evacuated 5.00 L flask at 65°C. What percentage of the water will be vapor when the system reaches equilibrium? Assume ideal behavior of water vapor and that the volume of liquid water is negligible. The vapor pressure of pure water at 65°C is 187.5 mm Hg. Show all work clearly for full credit.


3.(15) A solution is prepared by condensing 4.00 L of a gas, measured at 27°C and 748 mm Hg pressure, into 58.0 g of benzene, C6H6. Calculate the freezing point of this solution. Show all work clearly for full credit.

4.(20) A mixture of table salt, NaCl (MW = 58.5) and table sugar, sucrose, C12H22O11 (MW = 342), of combined mass of 10.2 g is dissolved in enough water to make up 250 ml of solution. The osmotic pressure of the solution is 7.32 atm at 23°C. Calculate the mass percentage of NaCl in the mixture. Assume ideal behavior of the components. Show all work clearly for full credit.


5.(10) This problem actually gives you a choice. Work either part A or part B, but not both. If both are attempted I will only grade part A.

Part A. The binary hydrogen compounds of the Group IVA elements and their boiling points are listed here:

Compound / Boiling Point
CH4 / -162 °C
SiH4 / -112 °C
GeH4 / - 88 °C
SnH4 / - 52 °C

Explain, in some detail (not just one or two words) the increase in boiling points from CH4 to SnH4.

Part B. Ammonia, NH3, is both a donor and an acceptor of hydrogen in hydrogen bond formation. Draw a diagram showing the hydrogen bonding of an ammonia molecule with two other ammonia molecules.

Dr. B., I am attempting Part ______


6. (20) How many grams of sucrose, C12H22O11 (MW = 342), must be added to 552 grams of water to give a solution with a vapor pressure 2.0 mm Hg less than that of pure water at 20°C. The vapor pressure of pure water at 20°C is 17.5 mm Hg. Show all work clearly for full credit.