CHM 123
EXAM 2 – PRACTICE PROBLEMS
*It is the students’ responsibility to study all other topics that was discussed from the lecture.
Question I – Multiple choice
2.
Which of the following statements is not correct when balancing a nuclear equation?
I. The mass numbers must be conserved on both sides of the reaction arrow.
II. The ionic charges must be conserved on both sides of the reaction arrow.
III. The atomic numbers must be conserved on both sides of the reaction arrow.
IV. The elements must be the same on both sides of the reaction arrow.
A) II only
B) II and III
C) I and III
D) II and IV
3.
When a substance decays by beta emission, the mass number of the nucleus ________ and the atomic
number ________.
A) decreases by 1, remains the same
B) increases by 1, remains the same
C) remains the same, decreases by 1
D) remains the same, increases by 1
4.
When more than 3000 known nuclides are plotted on a neutron/proton grid they make up a group called
A) the "island of stability."
B) the "peninsula of nuclear stability."
C) the "sea of instability."
D) none of these
5.
Which one of the following statements about isotopes is false?
A) The ratio of neutrons to protons is about 1:1 for stable elements lighter than Ca.
B)The ratio of neutrons to protons is > 1:1 for stable elements heavier than Ca.
C) Nonradioactive isotopes generally have an odd number of neutrons.
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D) All isotopes heavier than bismuth-209 are radioactive.
6.
A radioisotope which is neutron poor and very heavy is likely to decay by
A) alpha emmission, electron capture, or positron emission.
B) only alpha emission.
C) only electron capture.
D) only positron emission.
7.
Elements with ________ atomic mass are best possible candidates for a fusion reaction.
A) very low
B) moderate
C) moderate to heavy
D) very heavy
8.
What geometric arrangement of charge clouds is expected for an atom that has four charge clouds?
A) trigonal bipyramidal
B) octahedral
C) tetrahedral
D) square planar
9.
Which of the following compounds exhibits hydrogen bonding?
A) CH3Cl
B) HI
C) H3C-O-CH3
D) NH3
10.
When a liquid is heated at its boiling point, the
A) covalent bonds are broken, allowing vaporization to occur.
B) temperature of the liquid increases.
C) temperature of the liquid remains the same as long as any liquid is present.
D) temperature of the vapor phase increases
11.
The normal boiling point for HBr is higher than the normal boiling point for HCl. This can be explained by
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A) larger dipole-dipole forces for HBr.
B) larger dispersion forces for HBr.
C) larger hydrogen-bond forces for HBr.
D) larger dipole-dipole forces, larger dispersion forces, and larger hydrogen-bond forces for HBr.
Question II - Nuclear chemistry
1.
Uranium-238 decays very slowly, with a half-life of 4.47 billion years. What percentage of a sample of
uranium-238 would remain after 13.4 billion years? Use an appropriate equation to solve for it or no credit.
12.5 %
2.
A sample of Francium-212 will decay to one sixteenth of its original amount after 80 minutes. What is the
half-life of Francium-212.
20 mins
1. Mt-266 was prepared in 1982 by bombardment of Bi-209 atoms with Fe-58 atoms. Identify the other
product that must have formed, and write a balanced nuclear equation assuming no other products were
formed.
2. Californium-246 is formed by bombardment of uranium-238 atoms. If four neutrons are formed as by
products, what particles is used for the bombardment?
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3. Complete the following nuclear equations
35Cl
229
+ 1n 
Th 
20O

20F
35S
4He
+ _________
+ _________
104Ag

0e
+ _______
________ + 0e 
238U
+ _________
+
12C
54Cr

246Cf
+ _____
Question IV – VSEPR Theory and Hybridization
Draw the dots Lewis structure and determine the real geometric shape and angle of the following
BO33-
SF5-
1) What is the hybridization and geometry angle at all atoms, except hydrogens, in these compounds?
a.
b.
2) Use heavy and dashed wedge lines to show the shapes of the following molecules. Show the bond dipole of
each polar bond and show the overall dipole of each molecule.
a.
b.
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Question V – Intermolecular forces and phase diagram
While mercury is very useful in barometers, mercury vapor is toxic. Given that mercury has a ΔHvap of 56.9 kJ/mol
and its normal boiling point is 356.7°C, calculate the vapor pressure in mm Hg at room temperature, 25°C.
3.29
x 10-3 mm Hg
Ethyl chloride, C2H5Cl, is used as a local anesthetic. It works by cooling tissue as it vaporizes. The heat of
vaporization is 26.4 kJ/mol. How much heat could be removed by 10.0 g of ethyl chloride?
4.09 kJ
For questions a-c, refer to the phase diagram below of a pure substance.
(A)
(B)
(C)
(D)
(E)
Sublimation
Condensation
Vaporization
Melting
Deposition
a.
If the pressure decreases from 1.5 to 0.5
a constant temperature of 50˚C, which of the processes occurs?
b.
If the temperature increases from 10°C to 50°C at a constant pressure of 0.5 atmospheres, which of the
processes occurs?
c.
If the temperature decreases from 110°C to 40°C at a constant pressure of 1.1 atmospheres, which of the
processes occurs?
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atmospheres at