Chem 112  Exam I  ::::::  Spring 1999:  Day/Whelan

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  • The multiple choice portion of this exam has 17 questions totaling 80 points. 
  • The written portion of this exam has 5 questions totaling 20 points. 
          •  
          Information for your use:
        • K = °C + 273 
        • R = 0.08206 Latm/mol· K = 8.314 J/mol· K
        • 1 atm = 760 mm Hg 
        • Normal b. pt. H20 = 100.00 °C
        • ln P2/P1 = (-DHvap/R)(1/T2 - 1/T1) 
        • PV = nRT 
        • P1V1/T1=P2V2/T2 
        • XA = nA / (nA + nB) 
        • PA = XAP°A 
        • DTb = Kbmi 
        • DTf = Kf mi 

1.    (4 Points)
According to the ideas of the kinetic theory, a substance that is a liquid at room temperature and pressure has intermolecular attractive forces that are: 

weak compared to those of a substance which is a gas at the same temperature and pressure.
strong compared to those of a substance which is a gas at the same temperature and pressure.
strong compared to those of a substance which is a solid at the same temperature and pressure.
very weak compared to the average kinetic energy of the molecules.
very strong compared to the average kinetic energy of the molecules.
2.    (4 Points)
For which of the following substances would both dipole-dipole and dispersion forces have a pronounced effect on physical properties. 

KMnO4
I2
HF
NaF
ICl

3.    (5 Points)
Which of the following is not a consequence of hydrogen bonding?

The boiling point of CH4 is lower than the boiling point of SiH4.
The density of ice is lower than the density of water. 
The boiling point of NH3 is higher than the boiling point of PH3. 
The freezing point of C2H5OC2H5 is lower than the freezing point of (CH3)3COH. 
All of the above are consequences of hydrogen bonding.

4.    (4 Points)
The boiling points of the halogens is observed to increase in the order  F2 < Cl2 < Br2 < I2 . An explanation for this observation is that 

the larger the atoms the higher the permanent dipole moment 
the larger the atoms the higher the nuclear charge 
the larger the atoms the more polarizable the molecule 
the larger the atoms the stronger the ion-ion forces 
the larger the atoms the stronger the ion-dipole forces

5.    (5 Points)
The heat of fusion of HI (s) is 2.87 kJ/mol and the heat of vaporization of HI(l) is 19.8 kJ/mol. A reasonable value for the heat of sublimation of HI (s) in kJ/mol would be: 

1.52.911.319.922.7

Use the following information to answer questions 6 and 7 :
  • The vapor pressure of liquid methanol is 640 mm at 60 °C and 920 mm at 70 °C.

6.    (5 Points)
A sample of methanol maintained in a rigid container at 70°C has a pressure of 900 mm Hg. Under these conditions the sample is in the form of : 

a gasa liquida solida gas-liquid mixturenot possible to decide

7.    (5 Points)
The temperature of the container in the preceding problem is reduced to 60 °C. When all changes have taken place, the contents of the container will be: 

a gas at a pressure of 771 mm 
a gas and a liquid at a pressure of 874 mm 
a gas at a pressure of 874 mm 
a gas and a liquid at a pressure of 640 mm 
a gas at a pressure of 640 mm

8.    (5 Points)
Which one of the following is not always endothermic? 

melting a solid
subliming a solid
dissolving a solid
warming a liquid
vaporizing a liquid 

9.    (4 Points)
Which of the following would illustrate the concept of "like dissolves like"? 

NaCl (s) is soluble in CCl4
KMnO4 (s) is soluble in CCl4
I2 (s) is soluble in CCl4
NaOH (s) is not soluble in water 
KMnO4 (s) is not soluble in water 

Use the following data to answer questions 10 and 11:
  • A solution made by dissolving 288 grams of the non-volatile non-electrolyte sucrose (MW = 342)
  • in 820 grams of water (MW = 18.0) 
  • has a volume of 1.00 L. Assume ideal  behavior.

10.     (5 Points)
The molality of sucrose in this solution is: 

0.8421.031.431.662.23

11.     (5 Points)
The vapor pressure of water in mm Hg over this solution at 100 °C is calculated to be: 

687702746872888

12.    (5 Points)
Assuming ideal behavior, calculate the normal boiling point in °C of a solution that contains 0.200 moles of the non volatile non electrolyte glucose in 1000 grams of ethanol. For ethanol the normal boiling point is 78.40 °C and Kb = 1.22 °C/m 

78.16 
78.64
79.62
100.24
101.62

13.    (5 Points)
Assuming ideal behavior, arrange the following 0.10 molal aqueous solutions in order of decreasing freezing point. NaCl , CH3CO2H, urea, Cu(NO3)2

highest freezing point ® lowest freezing point
NaCl > CH3CO2H > urea > Cu(NO3)2
Cu(NO3)2 > NaCl > CH3CO2H > urea 
CH3CO2H > urea > Cu(NO3)2 > NaCl
urea > CH3CO2H > NaCl > Cu(NO3)2
ideally all would have the same freezing point

Use the following kinetic data for the reaction of bromine with formic acid in aqueous solution to answer questions 14 and 15:

Br2 (aq) + HCOOH (aq) ® 2Br- (aq) + 2H+ (aq) + CO2 (g)

Time, s 0 100 150
[Br2], M 0.00710 0.00500 0.00420


14.    (5 Points)
What is the average rate of disappearance of Br2 from t = 0 to t = 100 s in Ms-1? 

1.1 x 10-5
2.1 x 10-5
4.2 x 10-5
5.0 x 10-5
7.1 x 10-5

15.    (4 Points)
What is the average rate of appearance of Br- over the same time period ? 

1.1 x 10-5
2.1 x 10-5
4.2 x 10-5
5.0 x 10-5
7.1 x 10-5

16.    (5 Points)
At 230 ° C, the reaction 2ICl(g) + H2(g) ® I2(g) + 2HCl(g) is first order in ICl and second order overall. The rate law for the reaction is: 

Rate = k[ICl][H2]
Rate = k[ICl][H2]2
Rate = k[ICl]2[H2]
Rate = k[ICl]2[H2]2
Rate = k[ICl]2

17.    (5 Points)
At 273 ° C, the gas phase reaction 2NO + Br2 ® 2NOBr has a rate law given by Rate = k[NO]2[Br2] . If the rate constant is 1.2 x 104 M-2s-1, what is the rate of the reaction in Ms-1 when [NO] = [Br2] = 0.10 M ?

12
48
2.4 x 102
3.0 x 106
1.2 x 107

Esssay Portion
Use the following information for oxygen to answer 18 and 19.
      • Normal melting point = 54.8 K 
      • Normal boiling point = 90.2 K
      • Triple point = 54.0 K, 0.0015 atm 
      • Critical point = 155 K, 50 atm

        •  

18.    (6 Points)
Draw a phase diagram for oxygen. Label the axes and all points, lines and regions.
Answer:   

19.    (3 Points)
A sample of oxygen at a pressure of 0.9 atm and temperature of 40K is heated at constant pressure to a temperature of 100 K. Trace this path on your phase diagram and briefly describe what happens.
Answer:   

20.     (3 Points)
A sample of oxygen at room temperature (298K) is compressed at constant temperature until the pressure is 100 atm. Briefly describe what will happen and why?
Answer:   

21.    (5 Points)
At what temperature will water boil at the top of Mount Everest where the prevailing pressure is one third of an atmosphere? Assume the heat of vaporization of water to be 40.7 kJ/mol. 
Answer:   

22.    (3 Points)
A protozoan (a single celled animal) whose normal habitat is the ocean is placed in a fresh water pond. Briefly describe what might happen to this creature in the fresh water pond and explain why.
Answer: