NAME:
Midterm Exam 4
Chemistry 211
Dec. 3, 1998
PAGE 1 0f 6
- Show all work or NO CREDIT will be awarded.
- Work problems to proper number of significant figures.
- Be sure to include units in your answers.
- Circle your final answers.
- Put your name on ALL pages.
- Multiple choice questions are worth 4 pts. each.
1. Using the VSEPR model, predict the geometry of the following molecules or ions:
I. AsH3
II. CS2
III. NO3-
I
II
III
a) tetrahedral
b) triagonal
c) trigonal pyramidal
d) tetrahedral
e) trigonal pyramidal
bent
planar linear
tetrahedral
bent
linear
trigonal pyramidal
trigonal planar
tetrahedral
trigonal pyramidal
trigonal planar
2. Which of the following molecules or ions does NOT have a tetrahedral shape
according to VSEPR theory?
a) SiF4
c) SeF4
e) BF4-
b) NF4+
d) CF4
3. Which of the following bond angles in the respective molecules has the smallest angle?
(If more than one angle exist in a compound, use the smallest angle.)
a) HCH angle in CH4
c) HNH angle in NH3
e) HOH angle in H2O
b) FIF angle in [IF4]d) OCO angle in [CO3]-2
4. A unit of pressure is the
a) Newton
c) Pascal
e) Manometer
b) Joule
d) Tortelini
5. A balloon has a volume of 0.30 L at one atmosphere pressure (760 torr). When it is
placed in a vacuum chamber with pressure = 1/5 atmosphere (152 torr), its volume will
be:
a) 0.060 L
b) 0.30 L
c) 1.5 L
d) 3.0 L
e) 5.0 L
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6. Potassium reacts rapidly with water to liberate hydrogen gas according to the equation,
2 K(s) + 2 H 2O(l) ----> 2 KOH(aq) + H2(g)
One might consider this process to design an airbag (i.e., potassium is mixed with water
on impact). How many grams of potassium would be needed (with excess water) to
produce 50 L of hydrogen gas at 1.0 atm pressure and 25 oC?
a) 80 g
c) 40 g
f) 1900 g
b) 160 g
e) 950 g
7. The oxygen gas generated in the thermal decomposition of potassium chlorate is
collected over water.
2 KClO3 (s) ----> 2 KCl(s) + 3 O2 (g)
At 24 oC and atmospheric pressure of 762 mm Hg, the volume of gas collected is
0.128 L. The vapor pressure of water at 24 oC is 22.4 torr. The mass of oxygen collected
is:
(a) 0.082 g
(c) 0.169 g
(e) none of the above
(b) 0.163 g
(d) 2.03 g
8. Which of the following graphs is not a straight line for an ideal gas?
a) V versus T (n and P constant)
b) T versus P (n and V constant)
c) P versus 1/V (n and T constant)
d) n versus 1/T (P and V constant)
e) n versus 1/P (V and T constant)
9. Which of the following is an assumption of the kinetic theory of gases that we know is
not a true statement of the behavior of a real gas at 25 oC and 1 atm?
a) Gases consist of a large number of tiny particles in constant random motion.
b) Gas particles move in a straight line until they collide with another gas particle or
the walls of the container.
c) The distance between gas particles is large compared with their diameters, and
therefore most of the volume of a gas is empty space.
d) The average kinetic energy of the particles in a gas is proportional to the
temperature of the gas and that factor alone.
e) There is no force of attraction between the particles in a gas.
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10. The same amount of solid iodine is added to two identical glass tubes, which are then
stoppered and heated to the same temperature. The color in the two tubes is seen to be the
same and solid iodine is still present in the bottom of the tubes. When a lot of additional
iodine crystals are added to one of the tubes
a) the color of the vapor in the tube with more solid iodine will become darker
b) there is no change in the color of the vapor in either tube
c) the color of the vapor in the tube with more solid iodine will become lighter
11. Hydrogen bonding would not exist in which of the following molecules?
a) H2O
b) CH4
c) HF
e) It is in fact important in all four molecules
d) NH3
12. The critical pressure of a substance is defined as:
a)
b)
c)
d)
e)
The pressure above which a gas cannot be liquified.
The pressure at which a gas no longer behaves as an ideal gas.
The pressure necessary to liquify a gas at the critical temperature.
The pressure at which an ideal gas occupies 0 volume.
The pressure above which a substance can endure no more criticism.
13. What types of attractive forces are holding the many H 2O molecules together in ice?
a) London force
b) London force and dipole force
c) ionic bonding
d) covalent bonding
e) London force, dipole force, and hydrogen bonding
14. In which of the following gases do molecules have the highest average kinetic energy
at 25º C?
a) H2
d) Cl2
b) O2
e) All have the same.
c) N2
15. Deviations from the ideal gas law are greatest at
a)
b)
c)
d)
e)
low temperature and low pressure
low temperature and high pressure
high temperature and high pressure
high temperature and low pressure
No deviations occur--all gases are ideal and the world is better
because of it--particularly the free world.
16. A mixture of three gases has a total pressure of 1380 mm at 25º C. The mixture is
analyzed and is found to contain 1.27 moles of CO2, 3.04 moles of CO, and 1.50
moles of Ar. What is the partial pressure of Ar?
a) 0.258 atm
d) 1380 mm
b) 301 mm
e) 5345 mm
c) 356 mm
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17. Which molecular substance from the following list would have the highest boiling
point?
a) N2
d) Cl2
b) Br2
e) O2
c) H2
18. Which of the following gases has a density of 2.104 g/L at 303 K and 1.31 atm?
a) He
d) Kr
b) Ne
e) Xe
c)Ar
19. Arealgasdiffersfrom anideal gas inthat the molecules of a real gas:
a) Have no appreciable volumes and no molecular attractions for one another.
b) Have appreciable molecular volumes and have molecular attractions for one another.
c) Have no molecular attractions forone another.
d) Have no kinetic energy.
e) Have low molecular weights.
20. You have two balloons purchased at a recent carnival. One is filled with hydrogen,
one with helium. If you assume that both gases can pass through the pores of the balloon
material:
a) The hydrogen balloon will deflate 2 times faster than the helium balloon.
b) The helium balloon will deflate 2 times faster than the hydrogen balloon.
c) The hydrogen balloon will deflate 1.4 times faster than the helium balloon.
d) The hydrogen balloon will deflate 4 times faster than the helium balloon.
e) The helium balloon will deflate 1.4 times faster than the hydrogen balloon.
21. Consider the Lewis structure for glycine, the simplest amino acid:
(3 pts.) a) What are the approximate bond angles x, y and z?
What are the orbital hybridizations of:
(1 pts.) b) the nitrogen atom?
(1 pts.) c) the carbon atom bonded to the nitrogen?
(1 pts.) d) the carbon atom bonded to the two oxygen atoms?
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(1 pts.) e) the oxygen atom double bonded to a carbon atom?
(1 pts.) f) the oxygen atom bonded to both a hydrogen and a carbon atom?
(1 pts.) g) What is the total number of σ bonds in the glycine molecule?
(1 pts.) h) What is the total number of π bonds in the glycine molecule?
15. (5 pts.) a) Draw the phase diagram for water. Clearly indicate where each phase is
located on the diagram and what physical change is occurring at each boundary.
b) (2 pts.) Clearly indicate on the diagram at what temperature and pressure the melting
point for water occurs under standard conditions.
c) (1 pts.) What feature about this diagram indicates that ice is less dense than liquid
water?
d) (2 pts.) Label and BRIEFLY describe the triple point.
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(10 pts.) EXTRA CREDIT. List five major types of intermolecular forces in order of
increasing strength (weakest first).
USEFUL EQUATIONS:
ln P =
− ΔHvap
RT
µ =
3RT
M
E=
− µq
4 πε or2
+C
En =
λ =
− RH
n2
h
mv
ΔxΔ (mv) > h
Useful Constants:
Atomic mass unit
Avogadro's number
Boltzmann's constant
Electron Charge
Faraday's constant
Gas constant
1 amu
N
k
e
F
R
Planck's constant
Speed of light
h
c
= 1.66054 X 10-27 kg
= 6.0221367 X 10 23 /mol
= 1.38066 X 10-23 J/K
= 1.6021773 X 10-19 C
= Ne = 9.6485309 X 104 C/mol
=Nk = 8.314510 J/K-mol
= 0.08205783 L-atm/mol-K
= 6.6260755 X 10 -34 J-s
= 2.99792458 X 108 m/s
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