practice exam 2 - Chemistry at Winthrop University

Dr. Harris
Chemistry 105-002
Exam 2 10/17/13
Directions: Show all work. Show all units.
1. Determine the number of pi and sigma bonds in the following molecule: NH2CH2CO2CN (2)
a.) 9σ, 2π
b.) 10σ, 3π
c.) 10σ, 2π
d.) 9σ, 3π
2. Which of the following are weak electrolytes? (Select all that apply) (2)
a.) FeCl3
b.) MgCO3
d.) NH3
e.) CsClO4
c.) (NH4)2SO4
3. A five coordinate molecule containing 2 bonding domains and 3 lone pair would assume which of
the following geometries? (2)
a.) seesaw
b.) t-shape
d.) bent
e.) linear
c.) trigonal bipyramid
4. When four atomic orbitals are hybridized, four hybrid orbitals are formed. (2)
a.) true
b.) false
c.) can not determine
5. An atom with four hybrid orbitals must make four sigma bonds. (2)
a.) true
b.) false
c.) can not determine
6. 100 mL of HBr is mixed with 100 mL of LiOH. A base indicator is added to the resulting solution,
causing it to turn pink. Which of the following statements are correct: (2)
a.) [HBr] = [LiOH]
b.) [HBr] > [LiOH]
c.) [HBr] < [LiOH]
d.) can not determine
7. In the reaction: H2 (g) + Cl2 (g)
H2O (L)
2HCl (aq), hydrogen is: (3)
a.) oxidized, reducing agent
b.) oxidized, oxidizing agent
c.) reduced, oxidizing agent
d.) reduced, reducing agent
8. The number of hydrogen atoms in 1 g of ammonium hydroxide. (3)
a.) 1.72 x 1021
b.) 3.44 x 1021
c.) 5.16 x 1021
d.) 6.88 x 1021
e.) 8.60 x 1021
f.) none of the above
9. In full detail, explain the differences between ionic and covalent bonding. (4)
10. Why is it necessary for an atom to hybridize its lone pair (e.g. H2O) ? (4)
11. A methane molecule (CH4) has four electron domains, and its geometry is tetrahedral. The
bond angles within the methane molecule are 109.5o. An ammonia molecule (NH3) also has four
electron domains, but its geometry is trigonal pyramidal, with bond angles of 107.5o. Why are these
structures different? (4)
12. Review Lewis Structure Quiz.
13. A sample of a substance containing only aluminum and sulfur is found to be 36% aluminum by
mass. Given that the molecular mass of the substance is 450 g/mol, determine the molecular
formula. (7)
14. 120 mL of 0.20M aqueous cobalt (III) acetate is added to 125 mL 0.24 M potassium sulfide. The
system immediately undergoes a double replacement reaction. A solid, cobalt (III) sulfide, is
formed. The remaining species are aqueous spectators.
a. Write a balanced reaction, including phases. Given that 0.73g of cobalt (III) sulfate form,
determine the percent yield of the reaction. (15)
b. Determine the molarity of the aqueous product. (7)
15a. As part of a community service project, you spend a day at a local middle school, assisting 7th
graders in chemistry lab. A student needs to prepare 100 mL of an aqueous 0.50M stock solution of
lithium chlorate. How would you have the student prepare this solution? Keep in mind that you
are explaining this to a 7th grader. (6)
15b. Using the stock solution above, the student must then create an additional 100 mL of a 0.10M
solution. How would you have the student prepare this solution? (6)BONUS
16. Consider the molecule nitrate. Draw the orbital diagram of the atoms, making sure to clearly
indicate any energetic differences between the valence atomic orbitals. Illustrate the hybridization
of the atoms by showing the orbitals involved, and their merger to form hybrid orbitals. Sketch the
overlap of these orbitals. Label the sigma and pi bonds. (7.5)
17. Arrange the following in order of increasing boiling temperature: SO3, I2, SO2, LiF, HCN, ClF3,
Equations and constants
π‘šπ‘œπ‘™π‘’π‘  π‘ π‘œπ‘™π‘’π‘‘π‘’
πΏπ‘–π‘‘π‘’π‘Ÿπ‘  π‘œπ‘“ π‘ π‘œπ‘™π‘’π‘‘π‘–π‘œπ‘›
moles = MV
M1V1 = M2V2
NA = 6.02 x 1023 mol-1
%yield =
π‘₯ 100%