Chemistry 60/68 Mock Exam #1 ANSWERS pp. 1
Los Angeles City College
Chemistry 60/68 Mock Exam #1 ANSWER KEY
Professor Torres
Multiple Choice
1.
If you have a sample of aluminum (density = 2.70 g/cm3) and a sample of iron
(density = 7.87 g/cm3) and the samples have equal masses, then the following
inference can be made about the relative volumes of these two samples.
A.
B.
C.
D.
2.
A student took a beaker containing a colorless liquid and evaporated the liquid.
After the liquid was evaporated, she observed a white residue in the beaker. From
these observations, she would conclude that the original liquid was a _______.
A.
B.
C.
D.
3.
compound
element
mixture
pure substance
Melting is to freezing as boiling is to _________.
A.
B.
C.
D.
4.
The volumes of the metal samples cannot be compared due to lack
of information.
The volume of the iron sample is greater than the volume of the
aluminum sample.
The volume of the aluminum sample is greater than the volume
of the iron sample.
The volumes of the metal samples are equal.
sublimation
solidification
evaporation
condensation
How many cubic centimeters are in one cubic meter?
A.
B.
C.
D.
1 x 10-6
1 x 10-3
100
1 x 106
Chemistry 60/68 Mock Exam #1 ANSWERS pp. 2
5.
Which of the following is NOT an example of an extensive property?
A.
B.
C.
D.
6.
When an 80 mg sample of iron is allowed to sit in the air in an open container, a
reddish powder forms on its surface. The sample now weighs more than the
original iron because
A.
B.
C.
D.
7.
They are solutions.
They are mixtures.
They are always composed of only one element.
They have a constant boiling point.
Which of the following is an example of the law of multiple proportions?
A.
B.
C.
D.
10.
condensation of steam
rusting of iron
shredding a piece of paper
dissolving sugar in water
Which of the following is characteristic of pure substances?
A.
B.
C.
D.
9.
the law of conservation of mass does not directly apply.
a portion of the air has combined chemically with the iron.
the element iron has changed to a more dense phase.
the iron has decomposed into simpler components.
An example of a chemical change is
A.
B.
C.
D.
8.
density
volume
weight
mass
two compounds of carbon and oxygen with different amounts
of each element in each compound
a mixture of 20 g Fe, 10 g Cu, and 40 g Al
a solution of NH3 and H2O that cannot be completely separated
a compound containing 4 atoms of H, 2 atoms of C, and 2 atoms of
O
The modern periodic table contains elements arranged by increasing
A.
B.
C.
D.
atomic number
atomic mass
mass number
metallic character
Chemistry 60/68 Mock Exam #1 ANSWERS pp. 3
11.
Which of the following is NOT characteristic of most nonmetals?
A.
B.
C.
D.
12.
Which of the following is characteristic of all metals?
A.
B.
C.
D.
13.
gain protons
gain electrons
lose protons
lose electrons
Anions are formed when atoms ______________.
A.
B.
C.
D.
16.
metals
transition metals
metalloids
noble gases
Cations are formed when atoms ______________.
A.
B.
C.
D.
15.
poor conductors of heat and electricity
form ionic compounds
do not reflect light
have low malleability
Elements that can possess multiple oxidation states are ____________.
A.
B.
C.
D.
14.
poor conductors of heat and electricity
low melting points
do not reflect light
can be bent or hammered flat
gain protons
gain electrons
lose protons
lose electrons
What idea(s) did Rutherford propose about atoms after his alpha-particle
scattering experiment?
A.
B.
C.
D.
Nearly all the mass of an atom is concentrated at the center of the
atom.
The positive charge of the atom is located in the nucleus.
Electrons orbit the nucleus.
All of the above were proposed by Rutherford.
Chemistry 60/68 Mock Exam #1 ANSWERS pp. 4
17.
Which of the following is NOT part of Dalton’s original theory of atoms?
A.
B.
C.
D.
18.
Atoms that have an atomic mass of 93 and contain 40 electrons make up one
isotope of what element?
A.
B.
C.
D.
19.
number
electrons
25
25
30
30
Atomic
Number
25
30
25
30
Atomic
Mass
55
55
55
60
Which of the following statements is true?
A.
B.
C.
D.
21.
I
Nb
Th
Zr
What are the number of electrons, atomic number, and atomic mass of atoms
known to contain 25 protons and 30 neutrons?
A.
B.
C.
D.
20.
Atoms of different elements are different.
Compounds are formed by the joining of atoms of two or more
elements.
All atoms of the same element are exactly alike; they all have the
same mass.
Elements are composed of atoms which are divisible and
indestructible particles.
The atomic number is always greater than the mass number.
The mass number is the same for all atoms of the same element.
The difference between the atomic number and the mass
number is the number of neutrons.
The atomic number is the sum of the number of particles in the
nucleus.
Which of the following chemists was credited with discovering the electron?
A.
B.
C.
D.
John Dalton
William Crookes
J.J. Thomson
Ernest Rutherford
Chemistry 60/68 Mock Exam #1 ANSWERS pp. 5
For Questions 22 – 25, classify each of the following as a chemical change or a physical
change. Select “A” for chemical change or “B” for physical change.
22.
A solid is combined with hot water to produce a brown liquid. B
23.
Through exposure to air and moisture, iron turns reddish and cannot conduct
electricity. A
24.
Iron is heated. It turns red, then white, and then melts. B
25.
Sugar is heated to produce steam and a black solid. A
For Questions 26 – 31, determine which characteristics are physical properties and which
are chemical properties for an unknown substance. Select “A” for physical property or
“B” for chemical property.
26.
This substance is a silvery-white, lustrous metal. A
27.
It melts at 649 ºC and boils at 1105 ºC. A
28.
Its density at 20 ºC is 1.738 g/cm3. A
29.
The substance burns in air, producing an intense white light. B
30.
It reacts with chlorine to give a brittle, white solid. B
31.
The substance can be pounded into thin sheets or drawn into wires. A
32.
The total number of nonmetal atoms in Ca3(PO4)2 is:
A.
B.
C.
D.
33.
7
9
10
13
Write 0.000004506 in scientific notation.
A.
B.
C.
D.
4.5 x 1010
4.506 x 10-6
0.000005
5 x 106
Chemistry 60/68 Mock Exam #1 ANSWERS pp. 6
34.
How many significant figures are there in 0.010210 L?
A.
B.
C.
D.
35.
Convert 100.0 ºC to Kelvin.
A.
B.
C.
D.
36.
easily shattered
dull in appearance
conducts electricity
low melting points
Which one of the following elements is a metalloid?
A.
B.
C.
D.
39.
1500 mL
1560 mL
1559 mL
1559.1 mL
Which of the following properties is characteristic of most metals?
A.
B.
C.
D.
38.
173 K
273 K
373 K
212 K
The answer that should be reported for the total number of milliliters of a silver
nitrate solution when 39.10 mL of AgNO3 is added to 1.52 L of solution is
A.
B.
C.
D.
37.
1
3
5
6
Mg
Ne
C
Sb
An ion is:
A.
B.
C.
D.
an atom with a charge
an atom without a charge
a molecule
a neutron
Chemistry 60/68 Mock Exam #1 ANSWERS pp. 7
40.
What volume of alcohol (density = 0.800 g/mL) is needed to obtain 0.704 lb?
(note: 1 lb = 0.454 kg)
A.
B.
C.
D.
41.
When 8.44 g of calcium are heated in air, 11.82 g of calcium oxide are formed.
The percentage of oxygen in the compound is:
A.
B.
C.
D.
42.
KF
H2S
Na2O
MgS
Substance “X” has 13 protons, 14 neutrons, and 10 electrons. Determine its
identity.
A.
B.
C.
D.
45.
63.2 amu
64.8 amu
63.8 amu
64.1 amu
Which of the following is a molecular compound?
A.
B.
C.
D.
44.
28.6%
40.0%
71.4%
1.40%
The average atomic mass of copper is 63.5 amu. Copper has two naturally
occurring isotopes. One of the isotopes has an atomic mass of 62.9 amu and an
abundance of 69.1%. What is the atomic mass of the other isotope of copper?
A.
B.
C.
D.
43.
256 mL
400 mL
80 mL
320 mL
27
Mg2+
Ne
27
Al3+
27
Al
27
Which of the following compounds is ionic?
A.
B.
C.
D.
N2O3
SO2
ClF3
KCl
Chemistry 60/68 Mock Exam #1 ANSWERS pp. 8
46.
The correct name for Cu2SO3 is:
A.
B.
C.
D.
47.
copper(I) sulfate
dicopper sulfur trioxide
copper(I) sulfite
copper(II) sulfite
Which group of elements is most likely to react with calcium to form ionic
compounds with the general formula Ca3X2?
A.
B.
C.
D.
Group VII
Group VI
Group V
Group IV
Free Response
48.
What is the density (g/mL) of a rectangular block of wood if it measures 4.0 cm
thick, 120 mm long, and 0.57 in wide and has a mass of 0.720 kg? Will it sink or
float in water? Briefly explain. (note: 1 in = 2.54 cm)
To solve this problem, first obtain the volume of the rectangular block using
consistent units: V = 4 cm x 12 cm x 1.45 cm (converted from in.) = 70. cm3
Density = mass/volume = 720 g/70. cm3 = 10 g/mL → SINK since the density
of water at room temperature is 1.0 g/mL!
49.
A piece of aluminum foil measuring 12.0 in by 15.5 in has a mass of 5.175 g.
Aluminum has a density of 2.70 g/mL. What is the thickness of the foil in
millimeters?
Density = Mass/Volume; Volume = Mass/Density ⇐ Solve for V!
Volume = 5.175 g/2.70 g/cm3 = 1.92 cm3
Volume (in3) = 1.92 cm3 x (1 in/2.54 cm)3 = 0.117 in3
Therefore, (12.0 in)(15.5 in)(thickness) = 0.117 in3
Thickness = 6.29 x 10-4 in
Thickness (mm) = 6.29 x 10-4 in x (2.54 cm/1 in) x (10 mm/1 cm)
= 0.0160 mm
50.
Convert 81 kilometers per hour to meters per second.
m = 81 km x 1000 m x 1 hr x 1 min
s
hr
1 km
60 min 60 s
= 22 m/s ⇐ Be careful with significant figures/rounding!
Chemistry 60/68 Mock Exam #1 ANSWERS pp. 9
51.
Naturally occurring bromine consists of two isotopes, 79Br and 81Br, whose
atomic masses are 78.918 and 80.916, respectively. Given that the observed
atomic mass of bromine is 79.904, calculate the percentages of 79Br AND 81Br in
naturally occurring bromine.
x = % abundance of 79Br; 1 – x = % abundance 81Br
79.904 = 78.918 x + 80.916 (1 – x)
x = 0.5065 or 50.7% 79Br; therefore, 49.3% 81Br
52.
Discuss Rutherford’s gold-foil experiment (use a schematic for detail if necessary,
but also explain). Is this model depicting the atom consistent with modern
physics? Explain why or why not.
Rutherford used a thin sheet of gold as a target, and alpha particles emitted
from a radioactive substance were directed towards the foil. This foil is
surrounded by a fluorescent screen coated with zinc-sulfide. Each time an
alpha particle hits this zinc-sulfide coating, a flash of light was produced at
the point of contact. By observing these flashes of light, it was possible to see
whether the alpha particles that passed through the foil had been deflected
from their straight-line path.
Rutherford’s model depicted the atom as having a positively charged nucleus
of relatively great mass. Moreover, traveling around the nucleus were one or
more negatively charged electrons of very small mass. According to classical
physics of the time, since an electron loses energy by giving off light, it would
eventually fall toward the nucleus. This apparent anomaly goes contrary to
the fact that atoms appear very stable. Therefore, an adequate atomic model
must be postulated to explain why the electrons do not give off energy and
collapse into the nucleus.
53.
A 27.7 g sample of ethylene glycol loses 688 J of heat. What was the initial
temperature of the ethylene glycol if the final temperature is 32.5 ºC (specific heat
of ethylene glycol is 2.42 J/g K)?
q = mC∆T
-688 J = (27.7 g)(2.42 J/g ºC)(32.5 – Ti)
Solve for Ti to obtain an initial temperature of 42.8 ºC.
54.
Write formulas for the following compounds:
A.
B.
C.
D.
lithium oxalate
ammonium sulfate
sodium acetate
xenon tetrafluoride
Li2C2O4
(NH4)2SO4
NaC2H3O2
XeF4
Chemistry 60/68 Mock Exam #1 ANSWERS pp. 10
E.
F.
G.
55.
cobalt(III) permanganate
copper(II) hydroxide
hydrofluoric acid
Co(MnO4)3
Cu(OH)2
HF(aq)
Name each of the following compounds:
A.
B.
C.
D.
E.
F.
G.
H.
FeNO3
CrClO2
BrI5
H2O2
AlPO4
HClO4(aq)
(NH4)2S
H2CO3(aq)
Iron(I) nitrate
Chromium(I) chlorite
Bromine pentiodide
Hydrogen peroxide
Aluminum phosphate
Perchloric acid
Ammonium sulfide
Carbonic acid