Chemistry 11 Spring 2008
Examination #2 ANSWER KEY
For the first portion of this exam, select the best answer choice for the questions below
and mark the answers on your scantron. Then answer the free response questions that
follow (100 pts. total; multiple choice 2 pts. each).
1.
A 2.48 g sample of a noble gas is stored in a 3.50 L vessel at 157 torr and 25 ºC.
What is the identity of the gas?
A.
B.
C.
D.
E.
2.
When a liquid is in dynamic equilibrium with its vapor in a closed container:
A.
B.
C.
D.
E.
3.
a change in temperature will not change the pressure in the container.
the amount of gas in the container must exactly equal the amount of liquid.
molecules cannot completely go from the liquid phase to the gas phase
because the amount of liquid in the container is constant.
the vapor will gradually change back to the liquid state; that is, no vapor
will be left.
the rate at which molecules from the liquid phase enter the gas phase
exactly equals the rate at which molecules from the gas phase pass
into the liquid phase.
Determine the mass (in g) of 2.71 x 1024 atoms of sulfur.
A.
B.
C.
D.
E.
4.
He
Ne
Ar
Kr
Xe
144
7.13
95.1
32.1
257
When pure water is heated to 100 ºC, bubbles form in the water. Is this evidence
of a chemical reaction?
A.
B.
C.
D.
E.
Yes, the formation of a gas is proof a new compound has been made.
No, the formation of gas bubbles is a secondary chemical reaction which
is ignored.
Yes, the formation of a gas is evidence of a chemical reaction.
No, boiling water is a physical change.
None of the above
5.
What is the theoretical yield of a reaction if 25.0 grams of product were produced
from a reaction that has an 88% yield?
A.
B.
C.
D.
E.
6.
28.4 g
22.0 g
3.52 g
352 g
88.0 g
When the equation below is balanced using smallest whole number integers,
determine the sum of the coefficients:
Al(s) + HCl(aq) → AlCl3(aq) + H2(g)
A.
B.
C.
D.
E.
7.
Which of the following compounds is most miscible in water?
A.
B.
C.
D.
E.
8.
butyl alcohol (CH3CH2CH2CH2OH)
ethylene glycol (HOCH2CH2OH)
hexane (CH3CH2CH2CH2CH2CH3)
carbon dioxide (CO2)
iodine (I2)
How many grams of oxygen atoms are found in 1.00 x 102 g of K2Cr2O7?
A.
B.
C.
D.
E.
9.
11
13
18
19
21
14.9 g
38.1 g
5.44 g
11.3 g
78.8 g
A solution prepared by dissolving 3.00 g NaBr in 12.0 g H2O is said to be:
A.
B.
C.
D.
E.
6.67% (w/w) NaBr by mass
8.30% (w/w) NaBr by mass
20.0% (w/w) NaBr by mass
25.0% (w/w) NaBr by mass
33.3% (w/w) NaBr by mass
10.
Consider the molecular equation shown below:
NaCl(aq) + AgNO3(aq) → AgCl(s) + NaNO3(aq)
If 45.8 mL of 3.14 M NaCl(aq) is titrated with 50.0 mL of AgNO3(aq), what is the
molarity of AgNO3(aq)?
A.
B.
C.
D.
E.
2.88 M
1.50 M
3.14 M
3.42 M
1.71 M
For Questions 11 – 12, consider the following: 6.0 M H2SO4(aq) of unknown volume is
required for the preparation of 500.0 mL of a 0.30 M H2SO4 solution.
11.
What volume (in mL) is initially required of the more concentrated solution?
A.
B.
C.
D.
E.
12.
Determine how much water must be added to the 6.0 M solution in order to make
the required dilution.
A.
B.
C.
D.
E.
13.
100.0 mL
50.0 mL
40.0 mL
30.0 mL
25.0 mL
475.0 mL
470.0 mL
460.0 mL
450.0 mL
400.0 mL
According to the kinetic molecular theory of gases, molecules of different gases at
the same temperature always have the same ________.
A.
B.
C.
D.
E.
molecular mass
pressure
average kinetic energy
volume
average density
14.
Two identical, open beakers at 1 atm and 25 ºC initially contain the same volume
of liquid unknowns. One beaker contains unknown compound X; the other
beaker contains unknown compound Y. Over time, the beaker with compound X
has a smaller volume than the beaker with compound Y. Based on this
information, one can assume that compound X:
A.
B.
C.
D.
E.
15.
A sample of a gas originally at 25 ºC and 1.00 atm pressure in a 2.5 L container is
allowed to expand until the pressure is 86.1 kPa and the temperature is 15 ºC.
Determine the final volume of the gas (in L).
A.
B.
C.
D.
E.
16.
is less volatile, has a lower vapor pressure, and possesses weaker
intermolecular forces than compound Y.
is more volatile, has a higher vapor pressure, and possesses stronger
intermolecular forces than compound Y.
is less volatile, has a lower vapor pressure, and possesses stronger
intermolecular forces than compound Y.
is more volatile, has a higher vapor pressure, and possesses weaker
intermolecular forces than compound Y.
is the same as compound Y.
3.0
2.8
2.6
2.1
0.38
Consider the structure of the benzene (C6H6) molecule shown below:
H
C
H
benzene =
C
C
H
H
C
C
C
H
H
Which of the following substances is most miscible in benzene?
A.
B.
C.
D.
E.
H2SO4
MgCl2
CHBr3
HF
C2H4
17.
Which of the following represents the expected trend in increasing boiling points
of the liquid states for the chemical species shown?
A.
B.
C.
D.
E.
18.
Determine the pH of a 2.8 x 10-3 M NaOH(aq) solution.
A.
B.
C.
D.
E.
19.
dipole moment
polarity
polarizability
vapor pressure
surface tension
Which of the following INCORRECTLY describes an ideal gas?
A.
B.
C.
D.
E.
21.
2.55
2.80
11.20
11.45
7.00
When the electron cloud of an atom is easily distorted, the atom has a high
________?
A.
B.
C.
D.
E.
20.
He < CO < H2O < SO2 < NaCl
He < CO < SO2 < H2O < NaCl
NaCl < SO2 < H2O < CO < He
SO2 < NaCl < H2O < CO < He
CO < He < SO2 < NaCl < H2O
An ideal gas is one whose pressure, volume, and temperature behavior can
be completely described by the equation PV = nRT.
Attractive and repulsive forces between gas molecules are significant
only at short distances.
The volume of all molecules of the gas is negligible compared to the
total volume in which the gas is contained.
Gases consist of large numbers of molecules that are in continuous,
random motion.
Gases behave ideally under conditions of low pressure and high
temperature.
Which of the following is NOT a strong electrolyte?
A.
B.
C.
D.
E.
NaOH(aq)
HCl(aq)
Mg(OH)2(aq)
H2SO4(aq)
NaCl(aq)
22.
Determine the FALSE statement about buffer solutions:
A.
B.
C.
D.
E.
23.
Choose the TRUE statement below:
A.
B.
C.
D.
E.
24.
HClO3(aq) and HClO4(aq) are equally strong acids.
Blood pressure is measured at the pulmonary artery in the arm using a
sphygmomanometer.
As blood moves down the arteries and the heart prepares for another beat,
the blood pressure drops temporarily, and the lowest pressure reached is
called the systolic pressure.
A blood pressure reading of 152/96 indicates pre-hypertension.
When the temperature is raised to the point at which the vapor
pressure is equal to the atmospheric pressure, vaporization occurs
throughout a liquid.
Which of the following will react with HCl(aq) to produce a gas?
A.
B.
C.
D.
E.
25.
A buffer solution is one that resists a drastic change in pH when either an
acid or a base is added.
The most important example of an acid/base buffer system in the body is
carbonic acid/sodium bicarbonate.
The second most important example of an acid/base buffer system in the
body is a phosphate buffer made up of hydrogen phosphate ion, HPO4-2,
and dihydrogen phosphate ion, H2PO4-.
A blood pH between 7.0 and 7.3 is called alkalosis, which causes the
person to feel tired and disoriented and have difficulty in breathing.
A buffer solution consists of a weak acid and its salt or a weak base and its
salt.
Fe, Al, and Cu
Cu, Ag, and Hg
Pb, Na, and Ag
Li, K, and Sn
Hg, Au, and Ni
What volume of 0.11 M H2SO4(aq) is required to exactly neutralize 10. mL of
0.085 M NaOH(aq)?
A.
B.
C.
D.
E.
7.7 mL
1.9 mL
0.39 mL
3.9 mL
0.19 mL
26.
(16 pts. total) In a particular oganic synthesis, one of the series of chemical
reactions conducted in the laboratory involves combusting a mass of 15.1 g
glucose (C6H12O6) with 16.0 g of oxygen.
A.
(3 pts.) Write the balanced chemical equation for this process.
C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(g)
B.
(10 pts.) How many grams of carbon dioxide can be produced from this
reaction? Identify BOTH your limiting and excess reagents.
g CO2 = 15.1 g glucose x 1 mol glucose x 6 mol CO2 x 44.0 g CO2
180 g glucose 1 mol glucose 1 mol CO2
= 22.1 g CO2
g CO2 = 16.0 g O2 x 1 mol O2 x 6 mol CO2 x 44.0 g CO2
6 mol O2 1 mol CO2
32 g O2
= 22.0 g CO2
The limiting reagent is oxygen; the excess reagent is glucose.
C.
(3 pts.) If 31.8 g of CO2 are obtained by a particular student in this step of
the experiment, what is the percentage yield? How can this outcome be
justified?
% Yield = 100 * (Actual/Theoretical) = 100 * (31.8 g/22.0 g) = 145%
A carbon-containing contaminant or impurity must have been initially
mixed to result in a percentage yield higher than 100% when this
particular student conducted the experiment!
27.
(20 pts. total; 4 pts. each) Write BALANCED equations (net ionic where
appropriate) for each laboratory situation. Assume that solutions are aqueous
unless otherwise indicated. Write NR if no reaction occurs.
A.
Calcium metal is immersed in zinc chloride solution.
Ca(s) + ZnCl2(aq) → CaCl2(aq) + Zn(s)
Ca(s) + Zn+2(aq) → Ca+2(aq) + Zn(s)
B.
Ammonium phosphate is combined with mercury(II) sulfate.
2(NH4)3PO4(aq) + 3HgSO4(aq) → 3(NH4)2SO4(aq) + Hg3(PO4)2(s)
2PO4-3(aq) + 3Hg+2(aq) → Hg3(PO4)2(s)
C.
Nitric acid (HNO3) is mixed with strontium hydroxide.
2HNO3(aq) + Sr(OH)2(aq) → 2H2O(l) + Sr(NO3)2(aq)
H+(aq) + OH-(aq) → H2O(l)
D.
Solid aluminum is reacted with hydrochloric acid (HCl).
2Al(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2(g)
2Al(s) + 6H+(aq) → 2Al+3(aq) + 3H2(g)
E.
Methane gas (CH4) is burned in air.
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
28.
(8 pts.) Briefly explain the phenomenon of inhalation. Your description should
include the following terms: diaphragm, rib cage, thoracic cavity, pressure
gradient.
The process of taking a breath of air begins when the diaphragm contracts,
the rib cage expands, causing an increase in the volume of the thoracic
cavity. The elasticity of the lungs allows them to expand when the thoracic
cavity expands. According to Boyle’s law, the pressure inside the lungs will
decrease when their volume increases. This causes the pressure inside the
lungs to fall below the pressure of the atmosphere. This causes a pressure
gradient, where molecules flow from an area of greater pressure to an area of
lower pressure. Thus, we inhale as air flows into the lungs until the pressure
within the lungs becomes equal to the pressure of the atmosphere.
29.
(6 pts. total; 2 pts. each) Circle the substance below within each given pair which
most appropriately matches the listed description, and briefly explain your
selection utilizing the appropriate chemical principles.
A.
least volatile:
CCl4
CH2Cl2
Volatility increases with weaker intermolecular forces. The selected
molecule is polar, exhibiting dipole-dipole interactions in addition to
London dispersion forces, thereby making it less volatile compared to
the first molecule (which only exhibits LDF).
B.
most soluble in fatty tissue of the body:
Vitamin B2
H3C
C
C
H3C
H
C
C
H
O
C
C
N
N
C
C
N
H
N
O
OH
H2C
CH2OH
CH
CH CH
OH OH
Vitamin K1
O
HC
HC
H
C
C
H
C
C
C
C
O
CH
CH
CH3
CH2CH=C(CH3)CH2CH2CH2CH(CH3)CH2CH2CH2CH(CH3)CH2CH2CH2CH(CH3)2
Vitamin K1 is more soluble in the fatty tissue of the body (which is
predominantly nonpolar) as it consists of a long-chain hydrocarbon
with only slightly polar components within the structure.
C.
greatest surface tension:
CH3CH2OH
OHCH2CH2OH
The greater number of -OH groups on this molecule increases
the hydrogen bonding, resulting in greater surface tension compared
to the first molecule.