Chemistry 112                                          Exam 1                                                         3/01/01

 

Lecture 2, MWF 11:15                        Day

 

The multiple choice portion of this exam has 18 questions totaling 85 points.

The written portion of this exam has 3 questions totaling 15 points.

 

The multiple-choice questions are given below.

The answer key for the multiple-choice questions is given immediately following the questions.

 

Information for your use:

 

K = °C + 273              R  =  0.08206 Latm/mol·K  =  8.314 J/mol·K

1 atm = 760 mm Hg             Normal f. pt. H2O = 0.0 °C Normal b. pt. H2O = 100.0 °C

q = mass x specific heat x DT                   PV = nRT                  P1V1/T1=P2V2/T2

XA = nA / (nA + nB)                   PA = XAP°A             DTb = Kbmi                DTf = Kfmi    

 

1.      (5 points) At room temperature and pressure, substance A is a solid, substance B is a liquid, and substance C is a gas. According to the ideas of the kinetic theory, at room temperature and pressure, intermolecular forces in:

 

(A)  C are much stronger than those in B.

(B)  A are somewhat weaker than those in B.

(C)  C are somewhat stronger than those in A.

(D)  B are very strong compared to the average kinetic energy of its molecules.

(E)  C are very weak compared to the average kinetic energy of its molecules.

 

2.      (5 points) In which of the following pure substances would hydrogen bonding be expected?

 

(A)      all of them                          (C)  CH2F2                       (E) CH3OCH3

(B)       H2                                      (D)  CH3CH2OH

 

3.       (5 points) When NaCl dissolves in water, the solute-solvent interactions are best described as

 

(A)  dipole-dipole                           (C) ion-dipole                           (E) dispersion

(B)   dipole-induced dipole               (D) ion-ion

 

4.        (5 points) Intermolecular attractive forces are expected to be stronger in octane, C8H18 , than in hexane, C6H14 , because

 

(A)   dipole-dipole forces increase with molecular weight

(B)   dispersion forces increase with molecular weight

(C)   the larger the molecule the stronger the hydrogen bonding

(D)   the larger the molecule the larger the dipole moment

(E)    the larger the molecule the stronger the ion-dipole forces

 

5.      (4 points) Which of the following would you expect to be lower for octane, C8H18, than for hexane, C6H14?

 

(A)  the critical temperature

(B)  the normal boiling point

(C)  the heat of vaporization at the normal boiling point

(D)  the vapor pressure of the liquid at 25 oC

(E)   none of the above would be expected to be higher for hexane than for octane.

 

 

Use the following information to answer questions 6 and 7 :

The vapor pressure of liquid chloroform is 100 mm at 283 K and 400 mm at 316 K.

 

6.      (4 points) When a sample of chloroform is put in an evacuated rigid container and maintained at 283 K, it is found that both liquid and vapor are present at equilibrium. The pressure in the container:

 

(A)   is less than 100 mm                                          (D) is greater than 100 mm

(B)   is equal to 100 mm                                          (E) is unpredictable

(C)   could be less than or equal to 100 mm

 

7.      (5 points) A sample of gaseous chloroform in a rigid container at a pressure of 300 mm and a temperature of 316 K is cooled at constant volume to 283 K. When all changes have taken place, the contents of the container will be:

 

(A)  a gas at a pressure of 269 mm

(B)  a gas and a liquid at a pressure of 269 mm

(C)  a liquid at a pressure of 269 mm

(D)  a gas at a pressure of 100 mm

(E)   a gas and a liquid at a pressure of 100 mm

 

8.      (4 points) For a given substance, which one of the following transformations would require the most energy?

 

(A) solid to liquid                (C) liquid to gas            (E) liquid to solid

(B) solid to gas       (D) gas to solid

 

Use the following information for heptane (MW=100) for questions 9 and 10:

 

            normal boiling point = 98.4 oC            heat of vaporization = 34.1 kJ/mol

            specific heat liquid = 2.24 J/goC

 

9.       (5 points) What is the vapor pressure of heptane in mm Hg at 98.4 oC over a solution that contains 0.500 mol of a non-volatile non-electrolyte dissolved in 200 grams of heptane?

 

(A)  152           (B)  323      (C)  507      (D)  608      (E)  950

 

10.   (6 points) How many kilojoules of energy are required to convert a 100 gram sample of pure liquid heptane at 20.0 oC to heptane vapor at 98.4 oC?

 

(A)  17.6          (B)  35.9      (C)  41.8      (D)  48.6      (E)  51.7

 

11.   (4 points) The solubility of sodium acetate in water at 0°C is 119 g per 100g water. A solution that contains 170 g sodium acetate per 100 g water at 0°C is

 

(A) unsaturated       (C) supersaturated                   (E) impossible

(B) saturated                      (D) hyposaturated

 

12.  (6 points) Assuming ideal behavior, calculate the normal boiling point in °C of a solution that contains 64.5 grams of the non-volatile non-electrolyte quinoline (MW = 129) in 500 grams of benzene. For benzene the normal boiling point is 80.10 °C and Kb = 2.53 °C/m

 

(A)  77.57        (B)  80.37      (C)  82.63      (D)  84.46      (E)  98.24

 

13.  (4 points) Assuming ideal behavior, which of the following solutions would have the lowest freezing point? Sucrose is a non-electrolyte.

 

(A) 0.20 m NaCl                (C) 0.20 m CH3COOH   (E) all would have the same f pt

(B) 0.20 m CaCl2               (D) 0.20 m sucrose

 

14.  (4 points) A 0.20 M aqueous sucrose solution is separated from a 0.10 M aqueous sucrose solution by a semi-permeable membrane. As time passes one would expect a net flow of _____ molecules from the _____ M solution to the other one.

 

(A) H2O, 0.10                 (C) sucrose, 0.10                 (E) both, 0.20

(B) H2O, 0.20                 (D) sucrose, 0.20

 

 

Use the following data for the decomposition of NO2 at 573 K for questions 15 and 16:

 

NO2 (g) ®   NO (g) + 1/2 O2 (g)

 

Time, s

0

100

200

300

[NO2], M

0.0100

0.0065

0.0048

0.0038

 

15.  (5 points) What is the average rate of disappearance of NO2 from t = 200 to t = 300 s in Ms-1?

 

(A) 1.0 x 10-5       (B) 2.4 x 10-5            (C) 1.3 x 10-5       (D) 4.3 x 10-3         (E) 4.3 x 10-5

 

16.  (4 points) What is the average rate of appearance of O2 over the same time period ?

 

(A) 5.0 x 10-6       (B) 1.0 x 10-5             (C) 2.0 x 10-5       (D) 5.0 x 10-5          (E) 8.6 x 10-3

 

17.  (5 points) The rate law for the NO2 decomposition reaction is given by Rate = k[NO2]2 . If the rate constant is 0.54 M-1s-1, what is the rate of the reaction in Ms-1 when [NO2] = 0.020 M ?

 

(A) 1.1 x 10-2      (B)  2.2 x 10-2            (C)  5.8 x 10-3        (D)  2.2 x 10-4         (E)  6.9 x 10-2

 

18.   (5 points) The reaction  2Cl-(aq) + 2H+ (aq) + H2O2 (aq) ®  Cl2(aq) + 2H2O(l)  is third order overall and first order in each reactant. The rate law for the reaction is:

 

(A)  Rate = k[Cl-]2[H+]2[H2O2]                   (D)  Rate = k[Cl-]3/2[H+]3/2[H2O2]3

(B)  Rate = k[Cl-]3[H+]3[H2O2]3                       (E)  Rate = k[Cl-]3[H+]3[H2O2]3/2

(C)  Rate = k[Cl-][H+][H2O2]

 

The following list gives the number of points for each answer, in the order ABCDE, for each question. The correct answer to each question is the one worth the most points.

1                    00005

2                    00050

3                    00500

4                    05000

5                    00040

6                    04000

7                    00005

8                    04000

9                    30050

10                30006

11                00400

12                30600

13                04000

14                40000

15                50000

16                40200

17                00050

18                00500