CHEMISTRY 102A Fall, 1999

HOUR EXAM #1

Hour Exam #2

Hour Exam #3

NAME (Please Print) _______________________________________________________________

Name of your Professor ____________

Lecture Section _______ ( List-1, Ekman-2, Hall-3, Phillips-4 )

School (A&S, Eng., Other) ________

 

I pledge on my honor that I have neither given nor received improper aid on this examination.

_______________________________________________
Signature

You will have exactly two hours to complete your exam.

Before you begin, CAREFULLY READ AND FOLLOW THE INSTRUCTIONS BELOW.

Instructions

  1. Check to see that your exam contains all seven pages.
  2. Show all work neatly and completely to receive partial credit.
  3. Write your answers clearly and legibly. Answers not clearly written will be marked wrong.
  4. Include units with answers.
  5. Direct any questions to the supervising instructor or graduate student proctors.

I. True/False-check the appropriate blank (2 points each, 10 points total)

True False

1. Chemical reactions result in the transformation of one element into another.

 ________ ________

2. For molecular compounds the empirical formula is never equivalent to the molecular formula.

 ________ ________

3. The mass number of an isotope does not include the mass of the electrons.

 ________ ________

4. A covalent bond between atoms of two different elements would be polar.

 ________ ________

5. According to the VSEPR theory, all of the electron pair-electron pair repulsions about the central atom in PCl3 are of equal strength.

 ________ ________

 

II. Select the one best match for the following terms. (2 points each 10 points total)

  1. the total number of electrons in Mg2+ion _________
  2. mass of oxygen (g) in one mole of NaHCO3 (84 g/mol) _________
  3. name of Mg(ClO3)2 _________
  4. common units of density ________
  5. percent of nitrogen in hydrazine, N2H4 (32 g/mol) _________
a. 14 j. magnesium perchlorate o. magnesium dichloroheptoxide
b. 3 k. O p. 12%
c. (14.0/32.0) X 100 l. magnesium chlorate q. g/mL
d. 44% m. C r. N
e. manganese chlorate h. (28.0/32.0) X 100 s. 12
f. 48 i. 16 t. g/mol
g. mol/L n. 10

III. Multiple choice. For the following questions pick the best possible answer (5 points each, 25 points total). If you circle two answers, one of which is correct, you will receive 2 points.

1. Which of the following sets of atoms is ranked correctly from Most electronegative to Least electronegative?

  1. Na>K>F>Cl
  2. F>Cl>Na>K
  3. K>Na>Cl>F
  4. Cl>F>K>Na
  5. F>Na>Cl>K

2. Which of the following does not have a steric number of 4 for the central atom?

  1. NH3
  2. SF4
  3. BH4-
  4. CH4
  5. NH4+

3. Borazine is a ternary compound composed of 40.31% boron, 52.18% nitrogen, and 7.51% hydrogen. Determine the empirical formula for borazine.

  1. BNH2
  2. BN2H2
  3. B2NH2
  4. B2N2H3
  5. none of the above

4. In the gaseous reaction, 2H2S(g) + 3O2(g) 2SO2(g) + 2H2O(g)
6.0 L of H2S was reacted with 8.7 L of O2 yielding 5.0 L of SO2. The percent yield of this reaction is equal to

  1. (5.0/6.0) X 100%
  2. (5.0/8.7) X 100%
  3. (5.0/12.0) X 100%
  4. (5.0/5.8) X 100%
  5. (6.0/8.7) X 100%

5. Which contains the largest number of molecules?

  1. 1.0 g CH4 (molar mass = 16)
  2. 1.0 g H2O (molar mass = 18)
  3. 1.0 g HNO3 (molar mass = 63)
  4. 1.0 g N2O4 (molar mass = 92)
  5. 1.0 g Mn3O4 (molar mass = 229)

IV. Short answers (6 points each 36 points total) SHOW UNITS WITH ANSWER!

  1. Isocyanic acid (HNCO) reacts with gaseous nitrogen monoxide (NO), an air pollutant, to form nitrogen gas, carbon dioxide, and water. Write a balanced chemical equation to represent the reaction. (No partial Credit)
  2. A new super heavy element has been discovered, Vandium (symbol: Vu). There are three stable isotopes having the masses and percentage abundances listed below. Determine the relative atomic mass of naturally occurring Vu.

    Isotope

    Abundance

    Atomic Mass

    151 Vu

    48.22%

    150.9823

    152 Vu

    12.67%
    151.9234

    153 Vu

    39.11%

    152.852





  3. Chalcopyrite (CuFeS2) is a principal mineral of copper. Calculate the number of kilograms of Cu contained in 2,000 g of chalocopyrite.
  4. Give the name or chemical formula for the following substances.
    1. sodium hydrogen sulfate _____________
    2. HCN _______________________________
    3. CuSO4 _____________________________





  5. Draw the Lewis structure for PCl6-. Be sure to include formal charge.




  6. Briefly, but accurately, explain:
    1. Why chemists refer to MgCl2 as magnesium chloride and not magnesium dichloride.
    2. The difference between the atomic mass of oxygen and the molecular mass of oxygen.

V. PROBLEM

  1. A laboratory manual calls for 169 g of chromite (FeCr2O4, MWT = 224 g/mol), 298 g of potassium carbonate (MWT = 138 g/mol), and 75.0 g of oxygen gas as reactants in the preparation of potassium chromate (MWT = 194 g/mol).

4FeCr2O4 + 8K2CO3 + 7O2 8K2CrO4 + 2Fe2O3 + 8CO2

A student following these directions obtains 194 g of potassium chromate.

a) What is the theoretical yield of the reaction? (6 points)




b) What is the percent yield of the reaction? (3 points)