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Chemistry Assessments
QUARTER ONE
Unit 1
C2.5a Determine the age of materials using the ratio of stable and unstable isotopes of a
particular type.
1. The isotope Np-238 has a half-life of 2.0 days. If 84 grams are produced on Monday, how
much will be remaining 4.0 days later?
A.
B.
C.
D.
E.
18 grams
21 grams
35 grams
42 grams
84 grams
Answer: B
2. The isotope Np-238 has a half-life of 2.0 days. If 96 grams are produced on Monday, how
much will be remaining 6.0 days later?
A.
B.
C.
D.
E.
8 grams
12 grams
24 grams
48 grams
96 grams
Answer: B
3. The half-life of a radioactive substance is 2.5 minutes. What fraction of the original
radioactive substance remains after 10 minutes?
A.
B.
C.
D.
1/2
1/4
1/8
1/16
Answer: D
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4. The half-life of 131I is 8.07 days. What fraction of a sample of 131I remains after 24.21 days?
A.
B.
C.
D.
1/2
1/4
1/8
1/16
Answer: C
5. What does the half-life of an isotope mean?
A.
B.
C.
D.
It means that ½ of the atoms are isotopes
It is the time it takes for ½ of the isotope atoms to decay into another material
It is ½ of the age of the isotope
It is ½ of the atomic mass of the atom
Answer: B
6. Which of the following best explains why a large amount of energy is released in this
reaction?
A.
B.
C.
D.
The hydrogen converts the light into energy.
Some of the reactant mass is converted into energy.
All of the hydrogen isotopes undergo radioactive decay.
The temperature of the products is lower than that of the reactants.
Answer: B
C3.5a Explain why matter is not conserved in nuclear reactions
1. Conservation of mass is not true for nuclear reactions because:
A.
B.
C.
D.
mass lost in a nuclear reaction is not destroyed, cut converted into energy
alpha particles are converted into beta particles
energy lost in a nuclear reaction is converted into mass
the reactants of a nuclear reaction are neutrons
Answer: A
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C4.7b Compare the density of pure water to that of a sugar solution.
1. The density of water is 1.0 g/cm3, the density of a 10% sugar solution is:
A.
B.
C.
D.
less than the density of water
greater than the density of water
equal to the density of water
none of the above
Answer: B
C4.8A Identify the location, relative mass, and charge for electrons, protons, and neutrons
1. What is the nuclear charge of an iron atom?
A.
B.
C.
D.
+26
+30
+56
+82
Answer: A
e
e
e
e
e
13P
14N
e
e e
e
e
e
e
e
Using the diagram above and a periodic table, answer the following questions:
2. What is the atomic number of this element?
A.
B.
C.
D.
E.
2
3
8
13
25
Answer: D
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3. Which symbol represents this element?
A.
B.
C.
D.
E.
He
Li
O
Al
Mn
Answer: D
4. What is the mass number of this element?
A.
B.
C.
D.
E.
2
3
8
13
27
Answer: E
C4.8B Describe the atom as mostly empty space with an extremely small, dense nucleus
consisting of the protons and neutrons and an electron cloud surrounding the nucleus
Using the diagram above, answer the following questions:
1. What can be inferred from the diagram about the structure of the atom?
A.
B.
C.
D.
E.
the atom is very small
the electrons are moving very fast
the atom is mainly empty space
the electrons are very heavy
the nucleus is composed of protons and neutrons
Answer: C
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2. Experiments performed to reveal the structure of atoms led scientists to conclude that an
atom’s
A.
B.
C.
D.
positive charge is evenly distributed throughout its volume
negative charge is mainly concentrated in its nucleus
mass is evenly distributed throughout its volume
volume is mainly unoccupied
Answer: D
3. An experiment in which alpha particles were used to bombard thin sheets of gold foil led to
the conclusion that an atom is composed mostly of
A.
B.
C.
D.
empty space and has a small, negatively charged nucleus
empty space and has a small, positively charged nucleus
a large, dense, positively charged nucleus
a large, dense, negatively charged nucleus
Answer: B
4. Which of these conclusions can be drawn from Rutherford’s experiment?
A.
B.
C.
D.
Each atom contains electrons.
The nucleus of an atom can be split.
Each atom contains protons.
Atoms are mostly empty space.
Answer: D
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5. Ernest Rutherford performed an experiment in which he shot alpha particles through a thin
layer of gold foil. He predicted that the alpha particles would travel straight through the gold
atoms, as shown below
However, Rutherford observed that although most of the alpha particles passed straight
through the foil, a few alpha particles were deflected, as shown below.
Which of the following statements about the atom did Rutherford’s experiment support?
A.
B.
C.
D.
An atom contains protons, neutrons, and electrons.
An atom’s nucleus is small and has a positive charge.
Electrons follow a predictable path around the nucleus.
Different isotopes of an element have different masses.
Answer: B
C4.8C Recognize that protons repel each other and that a strong force needs to be present to
keep the nucleus intact.
1. A nucleus consists of protons and neutrons that are tightly bound together by
A.
B.
C.
D.
the strong nuclear force
repulsion of the protons
attraction of the electrons
the positive charge of the protons
Answer: A
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2. The neutrons in the nucleus of an atom produce a net attractive force to
A.
B.
C.
D.
repel the protons
produce a strong nuclear force
attract the electrons
release energy
Answer: B
C4.8D Give the number of electrons and protons present if the fluoride ion has a -1 charge.
1. To change F to F-, you need to:
A.
B.
C.
D.
Add one electron
Remove one electron
Remove one neutron
Add one neutron
Answer: A
C4.10A List the number of protons, neutrons, and electrons of any given ion or isotope.
1. As a Ca atom undergoes oxidation to Ca2+, the number of neutrons in its nucleus:
A. decreases
B. increases
C. remains the same
Answer: C
2. An atom of carbon-12 and an atom of carbon-14 differ in:
A.
B.
C.
D.
atomic number
atomic mass
nuclear charge
number of electrons
Answer: B
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3. All the isotopes of a given atom have:
A.
B.
C.
D.
the same atomic mass and the same atomic number
the same atomic mass but different atomic numbers
different atomic mass but the same atomic number
different atomic mass and different atomic numbers
Answer: C
4. Atoms of the same element that have different numbers of neutrons are classified as:
A.
B.
C.
D.
charged atoms
charged nuclei
isomers
isotopes
Answer: D
5. What are isotopes?
A.
B.
C.
D.
Atoms that only have neutrons in their nucleus
Atoms that have lost or gained electrons
Atoms with different numbers of neutrons for that element
Atoms that only have neutrons in their nucleus
Answer: C
6. What is the atomic number of an element that has six protons and eight neutrons?
A.
B.
C.
D.
6
2
8
14
Answer: A
7. Why is one isotope of an element so much more common that the others?
A.
B.
C.
D.
The less common isotopes are usually unstable
The heavier the isotope, the more common it is
All isotopes are common
All isotopes are uncommon
Answer: A
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C4.10B Recognize that an element always contains the same number of protons.
1. Is it possible for an element to have isotopes with different numbers of protons?
A.
B.
C.
D.
Yes, that is the definition of an isotope
It depends on the number of electrons the element has
No, because the element is defined by a specific number of protons
No, because the element is defined by a specific number of neutrons
Answer: C
2. Which statement about the mass of an electron is correct?
A. The mass of an electron is equal to the mass of a proton.
B. The mass of an electron is less than the mass of a proton.
C. The mass of an electron is equal to the mass of a neutron.
D. The mass of an electron is less than the mass of a neutron.
Answer: B
C4.10e Write the symbol for the isotope , where Z is the atomic number, A is the mass
number and X is the symbol for the element.
1. What is the structure of a krypton-85 atom?
A.
B.
C.
D.
49 electrons, 49 protons, 85 neutrons
49 electrons, 49 protons, 49 neutrons
36 electrons, 36 protons, 85 neutrons
36 electrons, 36 protons, 49 neutrons
Answer: D
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C5.2C Draw pictures to distinguish the relationships between atoms in physical and chemical
changes.
H2SO4 + 2NaOH 
2SO4
+ 2H2O
1. The illustrations show a conservation-of-mass experiment. The solution in the beaker lost
mass because:
A.
B.
C.
D.
materials have less mass at high temperatures
the mass of the reactants and products was less than 100 g
sodium sulfate (Na2SO4) is lighter than air
some of the water molecules turned into gas
Answer: D
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Unit 2
C4.9A Identify elements with similar chemical and physical properties using the periodic table.
1. Elements in the Periodic Table are arranged according to their
A.
B.
C.
D.
atomic number
atomic mass
relative activity
relative size
Answer: A
2. In which list are the elements arranged in order of increasing atomic mass?
A
B.
C.
D.
Cl, K, Ar
Fe, Co, Ni
Te, I, Sb
Ne, F, Na
Answer: B
3. Which element would you expect to have chemical properties similar to calcium (Ca)?
A.
B.
C.
D.
strontium, Sr
potassium, K
rubidium, Rb
sodium, Na
Answer: A
4. Which of the following elements has characteristics of some metals and also of some
nonmetals?
A.
B.
C.
D.
antimony ( 51Sb)
calcium ( 20Ca)
sulfur ( 16 S)
zinc ( 30 Zn)
Answer: A
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C4.9b Identify metals, non-metals, and metalloids using the periodic table.
1. Which elements are both classified as metalloids?
A.
B.
C.
D.
Ge and As
Bi and Po
B and C
Si and P
Answer: A
2. A characteristic of a nonmetal is
A.
B.
C.
D.
high melting points
high electronegativity
high electrical conductivity
the ability to form positive ions
Answer: B
3. Determine from the periodic table which set of elements represents exclusively metals.
A.
B.
C.
D.
E.
0, N, Cl, Br
Fe, Mn, Cl, He
Cu, Fe, Sn, Li
Rn, 0, P, S
Au, Ag, Na, Br
Answer: C
4. Determine from the periodic table which set of elements represents exclusively gases.
A.
B.
C.
D.
E.
O, N, Ne
Al, Na, Cl
Sr, Ar, Zn
C, P, O
S, Fe, Ra
Answer: A
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5. The table below contains a list of properties for an unidentified element, X.
Based on the properties in the table, to which of the following groups from the periodic table
does element X most likely belong?
A.
B.
C.
D.
(1A)
(2A)
(4A)
(6A)
Answer: A
C4.9c. Predict general trends in atomic radius, first ionization energy, and electronegativity of
the elements using the periodic table.
1. Arsenic and silicon are similar in that they both
A.
B.
C.
D.
have the same ionization energy
have the same covalent radius
are transition metals
are metalloids
Answer: D
2. Which Group of the Periodic Table contains atoms with a stable outer electron
configuration?
A.
B.
C.
D.
1
8
16
18
Answer: D
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3. The high electrical conductivity of metals is primarily due to:
A.
B.
C.
D.
high ionization energy
filled energy levels
mobile electrons
high electronegativities
Answer: C
4. According to the periodic table, which element most readily accepts electrons?
A.
B.
C.
D.
Fluorine
Nitrogen
Arsenic
Aluminum
Answer: A
5. Which of the following trends in the periodic table should be expected as the atomic number
of the halogens increases from fluorine (F) to iodine (I)?
A.
B.
C.
D.
Atomic radius decreases.
Electronegativity decreases.
Atomic mass decreases.
Electron number decreases.
Answer: B
C4.10c Calculate the average atomic mass of an element given the percent abundance and mass
of the individual isotopes.
1. The percent composition of Hydrogen is 99.98% found in nature. The percent abundance of
Deuterium is .0156%. The mass of Hydrogen is 1.00794 amu and the mass of Deuterium is
2.01664amu. Calculate the average atomic mass of Hydrogen.
Answer: 1.00805
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C4.10d Predict which isotope will have the greatest abundance given the possible isotopes for an
element and the average atomic mass in the periodic table.
1. The average atomic mass of Chlorine is 35.453 amu. The isotopes of Chlorine are Chlorine35 and Chlorine-37. Determine which isotope will be found in greatest abundance given the
atomic mass.
Answer: Chlorine exists as two common isotopes. Chlorine-35 has an atomic mass of about 35
amu, Chlorine-37 has an atomic mass of about 37amu. The fractional abundance of Chlorine-35
in nature is 75 percent, while Chlorine-37 is found to be 25 percent. The average mass of
Chlorine atoms is somewhere between 35 and 37, closer to 35, because Chlorine-35 is more
abundant than Chlorine-37.
C5.2g Calculate the number of atoms present in a given mass of element.
1. How many atoms of Calcium are there in 80 grams?
A.
B.
C.
D.
6.02 x 10 23
12.04 x 10 23
18.06 x 10 23
24.08 x 10 23
Answer: D
2. How many atoms of carbon are there in 36 grams?
A.
B.
C.
D.
6.02 x 10 23
12.04 x 10 23
18.06 x 10 23
24.08 x 10 23
Answer: C
3. How many atoms of Oxygen are there in 64 grams?
A.
B.
C.
D.
6.02 x 10 23
12.04 x 10 23
18.06 x 10 23
24.08 x 10 23
Answer: D
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C5.5A Predict if the bonding between two atoms of different elements will be primarily ionic or
covalent.
1. Element X is in Group 2 and element Y is in Group 17. What happens when a compound is
formed between these two atoms?
A.
B.
C.
D.
X loses electrons to Y to form an ionic bond.
X loses electrons to Y to form a covalent bond.
X gains electrons from Y to form an ionic bond.
X gains electrons from Y to form a covalent bond.
Answer: A
2. Which atom will form an ionic bond with a Br atom?
A.
B.
C.
D.
N
Li
O
C
Answer: B
3. Which elements combine by forming an ionic bond?
A.
B.
C.
D.
sodium and potassium
sodium and oxygen
carbon and oxygen
carbon and sulfur
Answer: A
4. Which type of bond is formed when an atom of potassium transfers an electron to a bromine
atom?
A.
B.
C.
D.
metallic
ionic
nonpolar covalent
polar covalent
Answer: B
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C5.5B Predict the formula for binary compounds of main group elements.
Use a polyatomic ion table with oxidation numbers to answer the following questions.
1. What is the formula for the compound named sodium sulfate?
A.
B.
C.
D.
E.
NaSO
Na2SO
Na2SO4
S2SO4
SSO4
Answer: B
2. What is the formula for the compound named potassium nitrate?
A.
B.
C.
D.
E.
KNO
KNO3
kno
PN
PNO
Answer: B
Rules for Naming Transition Metal Salts
1. The name of the metal is unchanged.
2. For metals having more than one oxidation state, a Roman numeral in parenthesis indicates
the oxidation state of the metal.
3. The anion is named by adding -ide to the stem of the element.
Using the rules above, answer the following questions:
1. What is the proper name for Cr2O3?
A.
B.
C.
D.
E.
Chromium (II) oxide
Chromium (III) oxide
Chromium trioxide
Dichromium trioxide
Chromium oxide
Answer: A
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2. What is the formula for Iron (II) sulfide?
A.
B.
C.
D.
E.
FeS
Fe2S
FeS2
Fe2S2
Fe2S3
Answer: A
3. What is the proper name for ZnCl2?
A.
B.
C.
D.
E.
Zinc chloride
Zinc (I) chloride
Zinc (II) chloride
Zinc (III) chloride
Zinc chlorine
Answer: A
C5.5c Draw Lewis structures for simple compounds
1. Which Lewis dot structure for NO2+ has the lowest energy?
Answer: A
2. Which of the following elements has the same Lewis dot structure as silicon?
A. germanium (Ge)
B. aluminum (Al)
C. arsenic (As)
D. gallium (Ga)
Answer: A
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3. Which of the following Lewis dot structures represents the compound methane (CH4)?
A.
B.
C.
D.
Answer: A
C5.5d Compare the relative melting point, electrical and thermal conductivity, and hardness for
ionic, metallic, and covalent compounds.
A chemist performs the same tests on two white crystalline solids, A and B. The results are show
in the table below.
Melting Point
Solid A
High, 801≈C
Solid B
Low, decomposes
at 186≈C
3.2
Solubility in H2O
35.7
(grams per 100.0 g in H2O at 0≈C)
Electrical Conductivity
Good conductor Nonconductor
(in aqueous solution)
1. The results of these tests suggest that:
A.
B.
C.
D.
both solids contain only ionic bonds
both solids contain only covalent bonds
solid A contains only covalent bonds and solid B contains only ionic bonds
solid A contains only ionic bonds and solid B contains only covalent bonds
Answer: D
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2. What type of bond is used when hydrogen is bonded to oxygen in a water molecule?
A.
B.
C.
D.
E.
covalent
non-polar
hydrogen
ionic
polar
Answer: A
3. Which are the properties of metals?
A.
B.
C.
D.
E.
conductor, brittle low melting point, lustrous
non conductor, brittle low melting point, lustrous
malleable, conductor, high melting point, lustrous
non conductor, brittle, high melting point, lustrous
non conductor, brittle, high melting point, non lustrous
Answer: C
4. Several chemists examined a pure, unknown substance and observed and measured its
physical properties. Their results are shown below.
Unknown Substance
Based on the data recorded in the table, answer the following.
a. What is the physical state of this substance at room temperature? Explain how the
information in the table is used to make this classification of the substance’s state.
b. The substance is unreactive in water. What will happen if 10.00 g of this
substance is added to 200.0 g of water at 20°C and standard pressure? Explain
your response.
Answer: a. The unknown substance is a liquid at room temperature, since its melting point is –
22.9oC. The substance is a solid below –22.9oC. The substance is a gas above 76.74oC.
b. Since the solubility of the substance is .08g/100g water, then .16 g of the substance will
dissolve in 200 g water.
Chemistry Assessments – May 2008
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Unit 3
C2.4a Describe energy changes in flame tests of common elements in terms of the
(characteristic) electron transitions.
1. The color of light emitted by an atom is most related to
A.
B.
C.
D.
E.
energy release by the electron
mass of the electron
potential energy of the electron in the ground state
size of the electron
strength of charge on the electron
Answer: A
2. What causes the emission of radiant energy that produces characteristic spectral lines?
A.
B.
C.
D.
neutron absorption by the nucleus
gamma ray emission from the nucleus
movement of electrons to higher energy levels
return of electrons to lower energy levels
Answer: D
3. The characteristic bright-line spectrum of an element is produced when electrons
A.
B.
C.
D.
absorb quanta and return to lower energy levels
absorb quanta and move to higher energy levels
release quanta and return to lower energy levels
release quanta and move to higher energy levels.
Answer: C
4. During a flame test, ions of a specific metal are heated in the flame of a gas burner. A
characteristic color of light is emitted by these ions in the flame when the electrons
A.
B.
C.
D.
gain energy as they return to lower energy levels
gain energy as they move to higher energy levels
emit energy as they return to lower energy levels
emit energy as they move to higher energy levels
Answer: C
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5. Of the particles listed here, which is most involved with quantum theory?
A.
B.
C.
D.
E.
electron
proton
neutron
nucleus
quark
Answer: A
C2.4b Contrast the mechanism of energy changes and the appearance of absorption and emission
spectra.
1. The light produced by signs using neon gas results from electrons that are:
A.
B.
C.
D.
moving from a higher to a lower principal energy level
moving from a lower to a higher principal energy level
being lost by the Ne(g) atoms
being gained by the Ne(g) atoms
Answer: A
C2.4c Explain why an atom can absorb only certain wavelengths of light.
Electromagnetic radiations are photons traveling in waves at the speed of light. The
wavelength is the distance from the crest of one wave to the crest of another. Frequency is
the number of waves that pass a given point in one second (waves/sec).
Answer the following questions using the above diagram and statement.
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1. The electromagnetic spectrum shows the relationship between:
A.
B.
C.
D.
E.
the mass of light and its force
the forces caused by light and the wavelength
the amount of energy and wavelength
the electrical power and strength of energy
gamma and radio waves only
Answer: C
2. Which of the following occurs as energy of electromagnetic radiation increases?
A.
B.
C.
D.
E.
wavelength increases
wavelength decreases
frequency increases
frequency decreases
both b and d are correct
Answer: E
3. Of the colors listed below, which one has the highest energy?
A.
B.
C.
D.
E.
blue
green
orange
red
yellow
Answer: A
4. When an excited electron drops from the 4th orbital to the 2nd orbital, a photon that exhibits
the color green. What would the color be of a photon emitted when an electron drops from
the 3rd to the 2nd orbital?
A.
B.
C.
D.
E.
blue
green
purple
yellow
white
Answer: D
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C2.4d Compare various wavelengths of light (visible and non-visible) in terms of frequency and
relative energy.
Frequency
Frequency
Wavelength
Energy
1. From the above graphs, describe the relationship between energy, wavelength, and
frequency.
A.
B.
C.
D.
as the wavelength increases, the frequency and energy decrease
as the frequency increases, the wavelength and energy decrease
as the energy increases, the frequency and wavelength decrease
as the energy increases, the frequency and wavelength increase
Answer: A
2. From the above graphs, describe how you could increase the energy of light the most.
A.
B.
C.
D.
increase the wavelength
decrease the wavelength
decrease the frequency
increase the wavelength while decreasing the frequency
Answer: B
3. The proper relationship of wavelength (8) to light energy (E) is:
A.
B.
C.
D.
increased wavelength correlates to increased energy
increased wavelength correlates to decreased energy
wavelength is independent of energy
wavelength is independent of frequency
Answer: B
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C4.8e Write the complete electron configuration of elements in the first four rows of the periodic
table.
1. 1s22s22p63s23p64s1 is the electron configuration for which element?
A.
B.
C.
D.
aluminum (Al)
argon (Ar)
potassium (K)
sodium (Na)
Answer: C
C4.8f Write kernel structures for main group elements.
1. Sodium has an atomic number of 11 and a mass number of 23.
A. Identify the types of subatomic particles located in the nucleus of a sodium atom.
Compare the properties of each type of particle.
B. Where is most of a sodium atom’s mass located? Explain your answer.
C. Identify the subatomic particles that are found in the energy levels outside the
nucleus of a sodium atom.
D. Describe the number and arrangement of these particles, including valence and
nonvalence (kernel) electrons.
Answers:
a. Sodium has 12 neutrons and 11 protons.
b. Most of the mass of a sodium atom is found in the nucleus.
c. 11 electrons are found in the energy levels of the atom.
d. The atom has 10 non-valance electrons and 1 valance electron. The configuration is 1s2 2s2
2p6 3s1.
C4.8g Predict oxidation states and bonding capacity for main group elements using their electron
structure.
Use the diagram below to answer question 1.
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1. Which element will gain only one electron during a chemical reaction?
A.
B.
C.
D.
silicon
phosphorus
sulfur
chlorine
Answer: D
C4.8h Describe the shape and orientation of s and p orbitals.
1. What is the shape of the s orbital?
A.
B.
C.
D.
doughnut
dumbbell
spherical
elliptical
Answer: C
2. What is the shape of the p orbital?
A.
B.
C.
D.
doughnut
dumbbell
spherical
elliptical
Answer: B
C4.8i Describe the fact that the electron location cannot be exactly determined at any given time.
1. What is an electron cloud and why can’t an exact electron location be determined?
Answer: In atomic theory, an electron cloud is a visual prediction of where an electron may be
located in respect to the nucleus, at a given time. Electrons do not travel in circular paths and it is
impossible to predict where an electron is at a given time. Instead, scientists now describe
electrons in terms of their probable location around the nucleus.
Chemistry Assessments – May 2008
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QUARTER TWO
Unit 7
C2.2A Describe conduction in terms of molecules bumping into each other to transfer energy.
Explain why there is better conduction in solids and liquids than gases.
1. Increasing the temperature increases the rate of a reaction by:
A.
B.
C.
D.
lowering the activation energy
increasing the activation energy
lowering the frequency of effective collisions between reacting molecules
increasing the frequency of effective collisions between reacting molecules
Answer: C
2. As the concentration of reacting particles increases, the rate of reaction generally
A. decreases
B. increases
C. remains the same
Answer: B
3. A 1.0-gram sample of powdered Zn reacts faster with HCl than a single 1.0-gram piece of Zn
because the surface atoms in powered Zn have
A.
B.
C.
D.
higher average kinetic energy
lower average kinetic energy
more contact with the H+ ions in the acid
less contact with the H+ ions in the acid
Answer: C
C2.2B Describe the various states of matter in terms of the motion and arrangement of the
molecules (atoms) making up the substance.
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27
C2.2c Explain changes in pressure, volume, and temperature for gases using the kinetic
molecular model.
1. Four different gases are all observed to have the same temperature. Which of the following
conclusions is supported by this observation?
A.
B.
C.
D.
All four gases must have the same mass.
All four gases must have the same pressure.
All four gases must have equal numbers of particles.
All four gases must have equal average kinetic energies.
Answer: D
2. The illustration below shows four containers. Each container is full of helium gas at a
different temperature.
If all of the containers are closed and have a pressure of 1 atm, which container has helium
particles with the greatest average kinetic energy?
A.
B.
C.
D.
1*
2
3
4
Answer: A
C2.2f Compare the average kinetic energy of the molecules in a metal object and a wood object
at room temperature.
Chemistry Assessments – May 2008
28
1. What probably causes water to have the highest specific heat of the substances listed above?
A.
B.
C.
D.
Molecule size
Molecular mass
Strong hydrogen bonds
High density of ice
Answer: C
C3.3A Describe how heat is conducted in a solid.
1. Heat convection occurs in gases and liquids. Heat convection does not occur in solids
because solids are unable to —
A.
B.
C.
D.
absorb heat by vibrating
transfer heat by fluid motion
emit radiation by reflecting light
exchange heat by direct contact
Answer: A
C3.3B Describe melting on a molecular level.
1. Which of the following phase changes results in an overall increase in randomness of
particles over the course of the change?
A.
B.
C.
D.
freezing
condensation
melting
deposition
Answer: D
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29
Matter can exist in three phases. A solid has a definite shape and volume. A liquid has a definite
volume, but takes on the shape of a container. A gas takes on both the volume and shape of a
container. The differences in the physical properties of the three phases of matter can be
explained by differences in how the particles (atoms or molecules) that make up matter interact,
as in Figures A, B, and C.
2. A student took a small ice cube and heated it in a large, closed container. First, the ice cube
melted and then the water boiled into steam. According to the information given, how would
the volume of the water and the volume of the steam compare to the volume of the original
ice cube?
A. water: about the same; steam: much greater
B. water: about the same; steam: about the same
C. water: much greater; steam: much greater
D. water: much greater; steam: about the same
Answer: A
3. If a liquid is heated, what happens to both its energy content and the speed of its particles?
A. The energy increases; the speed decreases.
B. The energy increases; the speed increases.
C. The energy remains the same; the speed remains the same.
D. The energy remains the same; the speed increases.
Answer: B
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30
4. You stir a glass of milk with a spoon. Which of the following best explains why the spoon
keeps its shape while it passes through the milk?
A. In the spoon, the particles vibrate back and forth; in the milk, the particles
maintain their relative positions.
B. In the spoon, the particles randomly move in all directions; in the milk, the
particles are close together.
C. In the spoon, the particles maintain their relative positions; in the milk, the
particles can only vibrate back and forth.
D. In the spoon, the particles maintain their relative positions; in the milk, the
particles move in all directions.
Answer: D
C4.3A Recognize that substances that are solid at room temperature have stronger attractive
forces than liquids at room temperature, which have stronger attractive forces than gases at room
temperature.
1. If the attractive forces among solid particles are less than the attractive forces between the
solid and a liquid, the solid will:
A. probably form a new precipitate as its crystal lattice is broken and re-formed.
B. be unaffected because attractive forces within the crystal lattice are too strong for
the dissolution to occur.
C. begin the process of melting to form a liquid.
D. dissolve as particles are pulled away from the crystal lattice by the liquid
molecules.
Answer: C
2. Compared with the particles in a solid, the particles in a liquid usually are:
A.
B.
C.
D.
Closer together
Less fluid
More massive
Higher in energy
Answer: D
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31
3. The higher the temperature of a liquid, the greater the average speed of its molecules.
What would happen to the temperature of an evaporating liquid if the molecules with higher
speed are escaping the liquid and no energy is applied (like perspiration on skin)?
A.
B.
C.
D.
The temperature of the liquid will increase.
The temperature of the liquid will remain unchanged.
The temperature of the liquid will decrease.
The temperature of the liquid will decrease briefly and then increase.
Answer: B
C4.3B Recognize that solids have a more ordered, regular arrangement of their particles than
liquids and that liquids are more ordered than gases
The graph below compares three states of a substance
1. Which of the following choices is the best label for the y-axis?
A.
B.
C.
D.
molecular density
molecular motion
neutron density
neutron motion
Answer: B
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C4.5a Provide macroscopic examples, atomic and molecular explanations, and mathematical
representations (graphs and equations) for the pressure-volume relationship in gases.
1. Which of the following best illustrates a graph of pressure versus volume for a gas at a
constant temperature?
Answer: A
C4.5b Provide macroscopic examples, atomic and molecular explanations, and mathematical
representations (graphs and equations) for the pressure-temperature relationship in gases.
1. Which of the following correctly describes molecules of two different gases if they are at the
same temperature and pressure?
A.
B.
C.
D.
They must have the same mass.
They must have the same velocity.
They must have the same average kinetic energy.
They must have the same average potential energy.
Answer: C
2. A cylinder of gas particles is shown below.
The cylinder is fitted with a movable piston that can be raised and
lowered. Which of the following would result in an increase in the
pressure of the gas below the piston?
A.
B.
C.
D.
increasing the volume of the cylinder
removing some of the gas from the cylinder
decreasing the volume of the cylinder
decreasing the pressure outside the cylinder
Answer: C
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3. Which of the following occurs when a rigid container of gas is heated?
A.
B.
C.
D.
The pressure inside the container increases.
The pressure inside the container decreases.
The pressure inside the container stays the same.
The pressure inside the container changes the composition of the gas.
Answer: A
4. The graph shows the pressure of an ideal gas as a function of its volume. According to the
graph, increasing the volume from 100 mL to 150 mL:
A.
B.
C.
D.
decreases the pressure by 160 kPa
increases the pressure by 80 kPa
increases the pressure by 160 kPa
decreases the pressure by 80 kPa
Answer: D
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C4.5c Provide macroscopic examples, atomic and molecular explanations, and mathematical
representations (graphs and equations) for the temperature-volume relationship in gases
1. Assuming pressure is held constant, which of the following graphs shows how the volume of
an ideal gas changes with temperature?
A.
B.
C.
D.
Answer: A
2. According to Charles’s law, what will happen to the piston when the gas is heated?
A. The piston will move up because the gas particles get larger.
B. There will be no change because heat will not affect the system.
C. The piston will move up because the gas particles move faster and get farther
apart.
D. The piston will move down because the gas particles move slower and get closer
together.
Answer: C
Chemistry Assessments – May 2008
35
Unit 4
INTRODUCTION TO BONDING
C2.1a Explain the changes in potential energy (due to electrostatic interactions) as a chemical
bond forms and use this to explain why bond breaking always requires energy.
1. Because we can observe two types of electrostatic interactions, attractive and repulsive, we
postulate that there are two kinds of charge. Do you think that there are also two types of
mass? Why do you think this? Do you think that there are two types of magnetic poles? Why
do you think this?
Answer: Mass is the quantity responsible for gravitational interactions. Since all gravitational
interactions are attractive, we can assume that there is only one type of mass. Magnetic poles are
responsible for magnetic interactions. We find that magnetic interactions can be attractive or
repulsive. Therefore, there must be two types of magnetic poles (called North and South).
2. Imagine having a collection of electrically charged marbles which retain their charge even if
they touch other objects. Red marbles are positively charged, blue marbles are negatively
charged.
What happens if you place (a) a bunch of red marbles, (b) a bunch of blue marbles, or (c) an
equal mixture of red and blue marbles close together on a flat horizontal surface? (d)
What happens in (c) if you have few more red marbles than blue ones? (e) As a whole, is the
collection of marbles in (d) positively charged, negatively charged, or neither?
ANSWER: (a) The red marbles, all carrying a positive charge, exert repelling forces on each
other and so they fly apart so as to get as far away as possible from each other, see Figure
S26.10a. (b) The blue marbles, all carrying a negative charge, also exert repelling forces on each
Chemistry Assessments – May 2008
36
other and so they, too, spread out as illustrated in Figure S26.10b. (c) Red and blue marbles are
attracted to each other and so they form red-blue pairs. A red-blue pair carries no net charge and
so it does not interact with other red-blue pairs of marbles. Consequently the marbles organize
themselves in pairs; because the pairs don’t interact they do not spread out, see Figure S26.10c.
(As we will see later, because the positive and negative charges do not overlap completely — a
red and a blue marble cannot be at the same place — some residual interaction is left). (d) Each
blue marble forms a red-blue pair; the left-over red marbles repel each other and spread out. (e)
Because of the surplus of positively-charged red marbles, the entire collection of marbles carries
a positive charge. Remember it is not the type of charge present in an object that determines the
net charge, but the type of charge causing the surplus.
C2.1b Describe energy changes associated with chemical reactions in terms of bonds broken and
formed (including intermolecular forces).
1. Given the reaction:
Cl(g) + Cl(g)  Cl2(g) + energy
Which statement best describes the reaction?
A.
B.
C.
D.
A bond is formed and energy is absorbed.
A bond is formed and energy is released.
A bond is broken and energy is absorbed.
A bond is broken and energy is released.
Answer: B
Use the following equation to answer the question:
Energy +
2C
+
3H2

carbon
hydrogen
C2H6
ethane
2. On the right hand side of the equation are two carbons and six hydrogens. On the left hand
side are two carbons and six hydrogens. This is because:
A.
B.
C.
D.
E.
Only two carbons can react with six hydrogens.
The conservation of matter is reflected in this model.
The conservation of volume is reflected in this model.
The formation of ethane requires small amounts of energy.
The formation of ethane requires large amounts of energy.
Answer: B
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37
3. Which of the statements given concerning chemical bonding is FALSE?
A.
B.
C.
D.
E.
Energy is required to break any chemical bond.
Energy must be released if two atoms are to form a chemical bond.
A chemical bond occurs only if the potential energy is lowered.
All chemical reactions require a transfer of electrons in forming new bonds.
Chemical bonds are due to electrostatic forces of attraction and repulsion.
Answer: D
C3.2b Describe the relative strength of single, double, and triple covalent bonds between
nitrogen atoms.
1. What is the formal charge on a triply-bonded oxygen?
A.
B.
C.
D.
+1
0
-1
Cannot be determined
Answer: A
2. Which of the following statements is correct?
A.
B.
C.
D.
the C(triple bond)C bond is three times as strong as a C-C bond.
the C(triple bond)C bond is composed of two sigma bonds and one pi bond.
the C(triple bond)C bond is composed of one sigma bond and two pi bonds.
the pi bond is stronger than the sigma bond in an alkyne.
Answer: C
3. Which of the following is a correct explanation of why it is difficult to draw the Lewis
structure for NO.
A.
B.
C.
D.
As an odd electron molecule, it is impossible to complete the octet on both atoms
One can only draw structures with high formal charges.
It is impossible to tell where to place the odd electron.
None of the above
Answer: A
Chemistry Assessments – May 2008
38
4. The Lewis structure of NO is difficult to draw due to its odd number of electrons. Use
molecular orbital theory to predict which atom has the odd electron.
A.
B.
C.
D.
O
N
Neither
Cannot be determined
Answer: B
C3.3c Explain why it is necessary for a molecule to absorb energy in order to break a chemical
bond.
1. The molar entropies of NO(g), N(g) and O(g) at 298oK are 210.6, 153.2, and 161.0 J mole-1
K-1 respectively. Using the Go given below calculate the bond energy of NO.
NO(g)
N(g) + O(g)
Go = 600.1 kJ
A.
B.
C.
D.
609.0
620.0
631.0
639.0
Answer: C
2. The entropies of CH4(g), C(g) and H(g) are 186.2, 158.0, and 114.6 J mole-1 K-1 respectively
at 298oK. Using the Go given below calculate the bond energy of CH4.
CH4(g)
C(g) + 4 H(g)
o
G = 1535.2 kJ
A.
B.
C.
D.
440.0
422.6
415.8
406.9
Answer: C
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39
3. The entropies of I2(g) and I(g) are 260.6 and 180.7 J mole-1 K-1 respectively at 298oK. Using
the data given below calculate the bond energy of I2.
I2(g)
2 I(g)
Go = 121.2 kJ
A.
B.
C.
D.
145.2
148.3
151.2
153.5
Answer: C
C4.4a Explain why at room temperature different compounds can exist in different phases.
The table below shows some characteristics of four substances at 1 atm pressure.
1. Which of the following substances is a liquid at temperatures ranging from -50°C to 0°C?
A.
B.
C.
D.
bromine
chlorine
ethanol
mercury
Answer: C
C4.4b Identify if a molecule is polar or nonpolar given a structural formula for the compound.
1. Consider the following molecules.
Which compound has the most polar bonds?
A.
B.
C.
D.
CH4
NCl3
BF3
CS2
Answer: C
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40
2. Which compound has the most polar bonds?
A. SiCl4
B. SSl2
C. PCl3
Answer: C
3. What type of bond is formed when a highly electronegative element and an electropositive
element form a bond?
A. Nonpolar covalent
B. Polar covalent
C. Nonpolar ionic
D. Ionic
Answer: B
C5.8A Draw structural formulas for up to ten carbon chains of simple hydrocarbons.
1.
The diagram shows the structural formula of benzene. The empirical and molecular formulas
of benzene are, respectively –
A.
B.
C.
D.
CH, C2H2
CH, C3H3
C3H3, C6H6
CH, C6H6
Answer: D
C5.8B Draw isomers for simple hydrocarbons.
1. How would the bond strength of the double bond in an alkene compare to that of a single
bond in the corresponding alkane?
A. The double bond would have the same strength as the single bond.
B. The double bond would have less than twice the strength than the corresponding
single bond.
C. The double bond would have exactly twice the strength of the single bond.
D. The double bond would have more than twice the strength of the single bond.
Answer: B
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2. The enolate anion of ethyl acetate has the following structure:
Which resonance structure has the lowest energy?
A.
B.
Answer: A
C5.8C Recognize that proteins, starches, and other large biological molecules are polymers.
1. Which of the following best describes polymers?
A. large molecules made up of smaller organic molecules, called isomers, that are
linked together to form new bonds
B. hydrocarbons in which some of the carbon atoms form double or triple covalent
bonds with other carbon atoms
C. proteins, carbohydrates, and lipids
D. large molecules made up of smaller organic molecules, called monomers, that are
linked together to form new bonds
Answer: D
2. Both lipids and carbohydrates are hydrocarbon polymers that contain carbon, hydrogen, and
oxygen. What quality distinguishes lipids from carbohydrates?
A.
B.
C.
D.
Lipids are a type of protein while carbohydrates are a type of sugar.
For a balanced diet, you should eat more lipids than carbohydrates.
Lipids are a more concentrated source of energy for the body than carbohydrates.
Your body can break down lipids but cannot break down carbohydrates.
Answer: C
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Unit 8
ADVANCED BONDING CONCEPTS
C4.3c Compare the relative strengths of forces between molecules based on the melting point
and boiling point of the substances.
1. The temperature at which a liquid boils is the boiling point of the liquid. The boiling point is
an indication of the submicroscopic forces that hold the matter in the liquid state. Water,
H2O, boils at 100oC. Ethanol, C2H6O boils at 78oC. Ammonia, NH3, boils at -33oC. Which
one of the following ranks the submicroscopic forces in these liquids from the strongest to
the weakest?
A.
B.
C.
D.
Water > Ammonia > Ethanol
Ammonia > Ethanol > Water
Ethanol > Water > Ammonia
Water > Ethanol > Ammonia
Answer: D
C4.3d Compare the strength of the forces of attraction between molecules of different elements.
(For example, at room temperature, chlorine is a gas and iodine is a solid.)
1. At room temperature, chlorine exists as a gas, bromine exists as a liquid, and iodine exists as
a solid. The physical states of these elements indicate that melting point —
A.
B.
C.
D.
decreases from top to bottom with group17 elements
is independent of periodic position
increases from top to bottom within group 17 elements _
is constant within group 17 elements
Answer: C
C4.3e Predict whether the forces of attraction in a solid are primarily metallic, covalent, network
covalent or ionic based upon the elements’ location on the periodic table.
1. Which of the pairs of elements listed will NOT form an ionic solid?
A.
B.
C.
D.
E.
barium and iodine
calcium and oxygen
lithium and chlorine
oxygen and hydrogen
cesium and fluorine
Answer: D
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43
2. Which combination(s) is/are most likely to form predominantly covalent bonds?
A. Potassium-Chlorine
B. Oxygen-Oxygen
C. Hydrogen-Carbon
D. More than one of the above
E. None of the above
Answer: D
3. Which combination(s) is/are most likely to form predominantly ionic bonds?
A.
B.
C.
D.
E.
Potassium-Chlorine
Oxygen-Oxygen
Hydrogen-Carbon
More than one of the above
None of the above
Answer: A
4. In reactions to form ionic compounds, metals generally:
A.
B.
C.
D.
lose electrons
gain electrons
become non-metals
do not react
Answer: A
C4.3f Identify the elements necessary for hydrogen bonding (N, O, F).
1. What type of bond is used when hydrogen is bonded to oxygen in a water molecule?
A.
B.
C.
D.
E.
covalent
non-polar
hydrogen
ionic
polar
Answer: A
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44
2. What type of bond forms between carbon and hydrogen in a molecule of methane?
A.
B.
C.
D.
E.
covalent
non-polar
hydrogen
ionic
polar
Answer: A
C4.3g Given the structural formula of a compound, indicate all the intermolecular forces present
(dispersion, dipolar, hydrogen bonding).
1. What type of bond is formed when a highly electronegative element and an electropositive
element form a bond?
A. Nonpolar covalent
B. Polar covalent
C. Nonpolar ionic
D. Ionic
Answer: D
2. Which of the following molecules has a net dipole?
A.
B.
C.
D.
NH3
SF6
CCl4
SiH4
Answer: A
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C4.3h Explain properties of various solids such as malleability, conductivity, and melting point
in terms of the solid’s structure and bonding.
A chemist performs the same tests on two white crystalline solids, A and B. The results are show
in the table below.
Melting Point
Solid A
High, 801≈C
Solid B
Low, decomposes
at 186≈C
3.2
Solubility in H2O
35.7
(grams per 100.0 g in H2O at 0≈C)
Electrical Conductivity
Good conductor Nonconductor
(in aqueous solution)
1. The results of these tests suggest that:
A.
B.
C.
D.
both solids contain only ionic bonds
both solids contain only covalent bonds
solid A contains only covalent bonds and solid B contains only ionic bonds
solid A contains only ionic bonds and solid B contains only covalent bonds
Answer: D
2. Which element has the highest electrical conductivity when a large amount of it is present?
A.
B.
C.
D.
Mg
H
He
Cl
Answer: A
C4.3i Explain why ionic solids have higher melting points than covalent solids. (For example,
NaF has a melting point of 995°C while water has a melting point of 0° C.)
1. Which of the following observations about a certain pure solid would indicate most strongly
that the solid is ionic?
A.
B.
C.
D.
Its water solution is a good conductor of electricity.
It is composed of small white crystals.
It has a density greater than 1.0 gram/cm3.
It has a high melting point.
Answer: D
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C5.4c Explain why both the melting point and boiling points for water are significantly higher
than other small molecules of comparable mass (e.g., ammonia and methane).
1. Water has unique properties because of its interparticle forces. Thinking about this property,
why does water have significantly higher melting and boiling points than other small
molecules of comparable mass such as ammonia and methane?
Answer: Water has strong interparticle forces, (strength of the attractive forces between
particles) which are held together tightly. A large amount of energy is required to break these
forces, allowing the particles to evaporate. This results in a low vapor pressure and a high normal
boiling point.
C5.4d Explain why freezing is an exothermic change of state.
1. Which of the following processes is exothermic?
A.
B.
C.
D.
water boiling
photosynthesis
ice melting
a car battery charging
Answer: C
2. Which phase change is exothermic?
A. H2O(s)  H2O(l)
B. H2O(l)  H2O(s)
C. H2O(s)  H2O(g)
D. H2O(l)  H2O(g)
Answer: A
3. Distinguish between exothermic and endothermic reactions, and give an example of each,
using the three states of water (H2O).
C5.4e Compare the melting point of covalent compounds based on the strength of IMFs
(intermolecular forces)
1. Which of these substances has the lowest melting point?
A.
B.
C.
D.
LiBr
CaO
CO
CH3OH
Answer: C
Chemistry Assessments – May 2008
47
QUARTER THREE
Unit 5
NOMENCLATURE AND FORMULA STOICHIOMETRY
C4.1a Calculate the percent by weight of each element in a compound based on the compound
formula.
1. Calculate the percent composition of Calcium in CaCO3 .
A.
B.
C.
D.
30%
40%
60%
80%
Answer: B
2. Calculate the percent composition of Phosphorus in P2O5.
A.
B.
C.
D.
25.8%
30.2%
38.7%
43.6%
Answer: D
3. Calculate the percent composition of Sodium in NaN3.
A.
B.
C.
D.
28%
35%
42%
58%
Answer: B
4. Calculate the percent composition of Nitrogen is NH3.
A.
B.
C.
D.
45.7%
56.2%
68.5%
82.3%
Answer: D
Chemistry Assessments – May 2008
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C4.1b Calculate the empirical formula of a compound based on the percent by weight of each
element in the compound
1. Calculate the empirical formula of a compound composed of 38.67 % C, 16.22 % H, and
45.11 %N.
Answer: 3.220 mole C, 16.09 mole H, 3.219 mole N - therefore: CH5N
2. A compound is 43.64 % P and 56.36 % O. What is the empirical formula?
Answer: P2O5
3. Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula?
Answer: C4H5N2O1
C4.1c Use the empirical formula and molecular weight of a compound to determine the
molecular formula.
1. A compound is known to be composed of 71.65 % Cl, 24.27% C and 4.07% H. Its molar
mass is known (from gas density) to be 98.96 g. What is its molecular formula?
Answer: Cl2C2H4
2. The empirical formula for a substance is CH2. If the molecular mass of the substance is 56,
the molecular formula is –
A. C2H4
B. C3H6
C. C4H8
D. C5H10
Answer: C
C4.2A Name simple binary compounds using their formulae.
1. What is the name of the compound, Na2S:
A.
B.
C.
D.
Sodium sulfate
Sodium sulfide
Sodium persulfate
Sodium trisulfide
Answer: B
Chemistry Assessments – May 2008
49
2. What is the name of the compound, BaO:
A.
B.
C.
D.
Barium Hydroxide
Barium dioxide
Barium oxide
Barium oxylate
Answer: C
3. What is the name of the compound, CsCl:
A.
B.
C.
D.
Cesium chloride
Cesium dichloride
Cesium chlorate
Cesium trichloride
Answer: A
4. What is the name for the compound, Al2O3
A.
B.
C.
D.
Aluminum dioxide
Aluminum oxide
Aluminum oxylate
Aluminum dioxide
Answer: B
C4.2B Given the name, write the formula of simple binary compounds.
1. What is the formula for Calcium fluoride?
A.
B.
C.
D.
CaF
CaF2
Ca2F3
Ca3F4
Answer: B
2. What is the formula for Potassium phosphide?
A.
B.
C.
D.
KP2
K2P3
K3P
K3P2
Answer: C
Chemistry Assessments – May 2008
50
3. What is the formula for Lithium oxide:
A.
B.
C.
D.
LiO
LiO2
Li2O
LiO3
Answer: C
4. What is the formula for Magnesium chloride:
A.
B.
C.
D.
MgCl2
Mg2Cl
Mg2Cl3
MgCl
Answer: A
C4.2c Given a formula, name the compound.
1. The chemical name of Mg3(PO4)2 is:
A.
B.
C.
D.
Magnesium phosphate
Magnesium phosphide
Magnesium phosphite
Magnesium phosphotate
Answer: A
2. The chemical name of Cd(MnO4)2 is:
A.
B.
C.
D.
Cadmium manganate
Cadmium manganite
Cadmium phosphate
Cadmium permanganate
Answer: D
3. The chemical name of Al(NO3)3 is:
A.
B.
C.
D.
Aluminum nitrate
Aluminum nitride
Aluminum nitrite
Aluminum trinitrate
Answer: A
Chemistry Assessments – May 2008
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4. Which of the following is the formula for Ammonium hydroxide?
A.
B.
C.
D.
Al2O3
AmO2
NH3OH
NH4OH
Answer: D
C4.2d Given the name, write the formula of ionic and molecular compounds.
Which of the following is the balanced chemical equation for the reaction shown above?
C4.2e Given the formula for a simple hydrocarbon, draw and name the isomers.
1. The formula for pentane is C5H12, draw two isomers.
Answer: 2-methylbutane and 2,2 dimethylpropane
C4.6a Calculate the number of moles of any compound or element given the mass of the
substance.
1. If you weigh out 20 grams of NaOH and place it in a 250 ml volumetric flask. Fill the flask
up to the designated mark on the neck. Determine the Molar concentration of this solution.
Answer: 1M NaOH
2. A sample of NaNO3 weighing 8.5 grams is placed in a 500 ml volumetric flask and distilled
water was added to the mark on the neck of the flask. Calculate the Molarity of the resulting
solution.
Answer: 0.2M NaNO3
Chemistry Assessments – May 2008
52
3. How would you prepare 100 mL of 0.25 M KNO3 solution?
Answer: Add 2.7 g of KNO3 to 100 ml distilled water
4. A chemist dissolves 98.4 g of FeSO4 in enough water to make 2.000 L of solution. What is
the molarity of the solution?
Answer: (98.4g) / (2,000 g H2O)(1 mol) / (151.8 g/mol) = 0.324 molarity
C4.6b Calculate the number of particles of any compound or element given the mass of the
substance.
1. How many atoms are contained in 97.6 g of platinum (Pt)?
A.
B.
C.
D.
30
5.16 × 10
23
3.01 × 10
24
1.20 × 10
28
1.10 × 10
Answer: B
2. How many atoms are in a chromium sample with a mass of 13 grams?
23
A. 1.5×10
23
B. 3.3×10
26
C. 1.9×10
24
D. 2.4×10
Answer: A
Chemistry Assessments – May 2008
53
Unit 6
EQUATIONS & STOICHIOMETRY
C3.4A Use the terms endothermic and exothermic correctly to describe chemical reactions in the
laboratory.
1. Which of the following are examples of an exothermic chemical reaction? Check all that
apply.
A.
B.
C.
D.
photosynthesis
burning a piece of wood
freezing water into ice
none of the above
Answer: B
C3.4c Write chemical equations including the heat term as a part of equation or using H
notation.
1. Which of the following equations correctly shows the reaction of methane and oxygen?
A.
B.
C.
D.
CH4 + O→CH4O ∆H -890.3 KJ/mol
CH4 +O2→CO2 + H2O ∆H 890.3 KJ/mol
CH4 +O2→CO2 + H2O ∆H -890.3 KJ/mol
CH4 + O→CH4O ∆H 890.3 KJ/mol
Answer: C
C5.2A Balance simple chemical equations applying the conservation of matter
1. __CCl4 +__ HF =>__ CCl2F2 +__ HCl
Answer: 1CCl4 + 2HF  1CCl4 + 2HCl
2. __ HCl +__ Na3PO4 =>__ H3PO4 +__ NaCl
Answer: 3HCl + Na3PO4  H3PO4 + 3NaCl
3. __A1 + __C12 =>__A1C13
Answer: 2Al + 3Cl2  3Cl2 + 2AlCl3
4. __HNO3 +__ NO =>__ NO2 +__ H2O
Answer: 2HNO3 + 1NO  3NO2 + 1H2O
Chemistry Assessments – May 2008
54
5. C3H6 + O2 CO2 + H2O
When the equation above is balanced and all coefficients are reduced to their lowest wholenumber values, the coefficient for H2O is:
A.
B.
C.
D.
2
3
4
6
Answer: D (2C3H6 + 9O2  6CO2 + 6H2O)
C5.2B Distinguish between chemical and physical changes in terms of the properties of the
reactants and products.
1. When performing an experiment which of the following would ensure that chemical changes
have occurred?
A.
B.
C.
D.
the product is a different shape than the reactant
the product and the reactant are different physical states
the product has no odor the reactant has a strong odor
the product has a greater volume than the reactant
Answer: B
2. Which of the following is a way to recognize a chemical change?
A.
B.
C.
D.
the substance has changed shape
the substance has changed from liquid to gas
a new substance has formed
the change is reversible
Answer: C
3. Which of the following indicates a chemical change has occurred?
A.
B.
C.
D.
a gas forms when two liquids are mixed
a powder dissolves in a liquid
a solid has melted into a liquid
a piece of clay has a new shape
Answer: A
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55
C5.2d Calculate the mass of a particular compound formed from the masses of starting materials.
1. For the following balanced chemical reaction: H2O + C => H2 + CO
How many grams of H2 will be produced by the reaction of 82.48 grams of H2O?
Answer: 9.16g H2
2. For the following balanced chemical reaction: 2Na + 2H2O => 2NaOH + H2
How many grams of NaOH will be produced, if 0.39 grams of H2 are produced?
Answer: 15.6g NaOH
3. For the following balanced chemical reaction: CaCN2 + 3H2O => CaCO3 + 2NH3
How many grams of NH3 will be produced, if 12.23 grams of CaCO3 are produced?
Answer: 4.16 g NH3
4. For the following balanced chemical reaction: 4KO2 + 2CO2 => 2K2CO3 + 3O2
How many grams of O2 will be produced by the reaction of 72.78 grams of KO2?
Answer: 24.6 g O2
C5.2e Identify the limiting reagent when given the masses of more than one reactant.
1. For the following balanced chemical reaction, if 84.32 grams of Na2O2 are reacted with
18.22 grams of H2O, what is the limiting reagent?
2Na2O2 + 2H2O => 4NaOH + O2
A. Na2O2
B. H2O
Answer: B
2. For the following balanced chemical reaction, if 24.46 grams of CaCN2 are reacted with
19.32 grams of H2O, what is the limiting reagent?
CaCN2 + 3H2O => CaCO3 + 2NH3
A. CaCN2
B. H2O
Answer: B
Chemistry Assessments – May 2008
56
3. For the following balanced chemical reaction, if 68.13 grams of C8H18 are reacted with
296.28 grams of O2, what is the limiting reagent?
2C8H18 + 25O2 => 16CO2 + 18H2O
A. C8H18
B. O2
Answer: A
4. For the following balanced chemical reaction, if 23.04 grams of C4H10 are reacted with 62.65
grams of O2, what is the limiting reagent?
2C4H10 + 13O2 => 8CO2 + 10H2O
A. C4H0
B. O2
Answer: B
C5.2f Predict volumes of product gases using initial volumes of gases at the same temperature
and pressure.
1. Blaise decides to build a barometer. He can’t find any mercury in his workshop and decides
to use water instead. Assume that the density of water is 1.00×103 kg/m3. If the atmospheric
pressure is 7.60×102 torr, how tall must his barometer be in order to obtain an accurate
reading?
Answer: First, convert the atmospheric pressure to Pascals. 7.60×102 torr = 101, 325 Pa. Now
that all the variables are in SI units, rearrange P = ghρ to P/(gρ) = h and plug the variables into
the equation.
=
= 10.3 m
Chemistry Assessments – May 2008
57
Thus Blaise’s barometer must be taller than 10.3 meters. A comparable mercury barometer
would be 0.76 m tall.
2. In a fit of inspiration and hot air, you have blown the world’s largest balloon. Your two
cousins, Bongo the 300 lb. gorilla and Jeeves the 70 lb. weakling, both want to climb to the
top of your balloon. When Bongo goes, he goes in style. He wants to lay down on his 1 m by
5 m air bed at the summit. Jeeves proposes to bounce on the top of the balloon on his pogo
stick, whose head has an area of 0.001 m2. Assume that the masses of the bed and pogo stick
are negligible, and that their occupants’ weights are evenly distributed upon them.
You know that your balloon can sustain 200 more kPa of pressure on its surface before it
pops. Assuming both can make it to the top without damaging the balloon (or themselves),
which cousin(s) should you allow to climb?
Answer: P = F/A, so the first thing we need to do is convert everything to the appropriate units.
Let’s use SI units. 1 lb = 0.454 kg, and F = (mass)×(9.8 m/s2), so Bongo and Jeeves exert forces
of 1330 and 311 Newtons, respectively. P = F/A, so Bongo has a pressure of PBongo =
= 270 Pa. Jeeves exerts a pressure of PJeeves = (311 N)×(0.001 m2) = 310 kPa. You should
allow Bongo on, but not Jeeves.
3. A sample of an element has a volume of 78.0 mL and a density of 1.85 g/mL. What is the
mass of the sample (measured in grams)?
Answer: .025 g
4. The graph shows the pressure of an ideal gas as a function of its volume. According to the
graph, increasing the volume from 100 mL to 150 mL –
A.
B.
C.
D.
decreases the pressure by 80 kPa
decreases the pressure by 160 kPa
increases the pressure by 80 kPa
increases the pressure by 180 kPa
Answer: A
Chemistry Assessments – May 2008
58
C5.6b Predict single replacement reactions.
1. Given the reactants: Fe + CuSO4, predict the products in a single replacement reaction:
A.
B.
C.
D.
Fe2SO4 + Cu
FeSO4 + 2Cu
FeSO4 + Cu
Fe3SO4 + Cu
Answer: C
2. Given the reactants Cd + 2HCl predict the products in a single replacement reaction:
A.
B.
C.
D.
CdCl + H2
CdCl2 + H2
CdCl3 + 2H2
CdCl + 2H2
Answer: B
3. The figure below represents a reaction.
What type of reaction is shown?
A.
B.
C.
D.
synthesis
decomposition
single displacement
double displacement
Answer: A
4. The equation, Fe + CuSO4 → FeSO4 + Cu is an example of:
A.
B.
C.
D.
decomposition reaction
oxidation
single replacement
double replacement
Answer: C
Chemistry Assessments – May 2008
59
Unit 9
THERMOCHEMISTRY SOLUTIONS
C2.1c Compare qualitatively the energy changes associated with melting various types of solids
in terms of the types of forces between the particles in the solid.
1. The melting point for salt is 800.8°C and the melting point for sugar is 146°C. What can be
concluded from this information?
A.
B.
C.
D.
The intermolecular forces in sugar release more energy than those of salt
Sugar molecules require more energy than salt to break apart
The intermolecular forces of salt release more energy than those of sugar
Salt molecules require more energy than sugar to break apart
Answer: D
C2.2d Explain convection and the difference in transfer of thermal energy for solids, liquids, and
gases using evidence that molecules are in constant motion.
1. The illustration below shows a hot-air balloon. The pilot can change the altitude of the hot-air
balloon by changing the temperature of the gas inside the balloon. When the gas is heated,
the balloon rises.
Which of the following best explains this phenomenon?
A. Heating the gas reduces its pressure.
B. Heating the gas decreases its density.
C. Heating the gas decreases its molecular
motion.
D. Heating the gas reduces the frequency of the
gas molecules’ collisions.
Answer: B
Chemistry Assessments – May 2008
60
C3.1c Calculate the ΔH for a chemical reaction using simple coffee cup calorimetry.
1. When 12.29 g of finely divided brass (60% Cu, 40% Zn) at 95.0oC is quickly stirred into
40.00 g of water at 22.0oC in a calorimeter, the water temperature rises to 24.0oC. Find the
specific heat of brass.
A.
B.
C.
D.
334.7 J
-334.7 J
0.38 J g-1 oC-1.
0.98 J g-1 oC-1.
Answer: B
C3.1d Calculate the amount of heat produced for a given mass of reactant from a balanced
chemical equation.
Figure A
Figure B
1. Which of the figures is depicting an endothermic reaction?
A.
B.
C.
D.
Figure A
Figure B
Both Figures A and B
Neither Figure A nor B
Answer: B
Use this balanced equation to answer the following question: Fe2O3 + 2Al → Al2O3 + 2Fe
2. 18.2 g of Aluminum (Al) reacts with Fe2O3 according to the reaction: ∆Hrxn = -853.2 kJ/mol
Fe2O3. How much heat is produced?
Answer: 18.2g(1m Al/27g Al)(-853.2kJ/1mAl) = -575.12kJ heat
Chemistry Assessments – May 2008
61
C3.4g Explain why gases are less soluble in warm water than cold water.
1. When stirred in 30°C water, 5 g of powdered potassium bromide, KBr, dissolves faster than
5 g of large crystals of potassium bromide. Which of the following best explains why the
powdered KBr dissolves faster?
A. Powdered potassium bromide exposes more surface area to water molecules than
large crystals of potassium bromide.
B. Potassium ions and bromide ions in the powder are smaller than potassium ions
and bromide ions in the large crystals.
C. Fewer potassium ions and bromide ions have been separated from each other in
the powder than in the crystals.
D. Powdered potassium bromide is less dense than large crystals of potassium
bromide.
Answer: A
C4.7a Investigate the difference in the boiling point or freezing point of pure water and a salt
solution.
1. At which temperature do KBr and KNO3 have the same solubility?
A.
B.
C.
D.
27°C
48°C
65°C
80°C
Answer: B
Chemistry Assessments – May 2008
62
The freezing point of a liquid is the temperature at which a liquid changes to a solid. The table
below lists the freezing point of four liquids.
Table adapted from Leonard Bernstein, Martin Schachter, Alan Winkler, and Stanley Wolfe,
Concepts and Challenges in Physical Science, 3rd edition. ©1991 by Globe Book Company.
2. Which of the liquids in the table would be LEAST likely to freeze outside during the winter
in Michigan?
A.
B.
C.
D.
water
glycerin
seawater
ethyl alcohol
Answer: D
3. An ice-skating rink has tubes under its floor to freeze the water. Salt water is cooled well
below the freezing point of water and pumped through the tubes to freeze the water in the
rink. Why can the salt water be cooled so low without freezing?
A.
B.
C.
D.
Salt has a very low freezing point.
Adding salt to water lowers its freezing point.
Movement of the salt water through the tubes keeps it in the liquid state.
The salt water is constantly absorbing energy from its surroundings.
Answer: B
C5.4A Compare the energy required to raise the temperature of one gram of aluminum and one
gram of water the same number of degrees.
1. In order to raise the temperature of 200g of water and 200g of aluminum 5 degrees each:
A.
B.
C.
D.
The same amount energy is required for each
More energy is needed to raise the temperature of water
More energy is needed to raise the temperature of aluminum
It is impossible to determine which needs more energy
Answer: C
Chemistry Assessments – May 2008
63
C5.4B Measure, plot, and interpret the graph of the temperature versus time of an ice-water
mixture, under slow heating, through melting and boiling.
1. Between points 2 and 3, energy is being used to:
A.
B.
C.
D.
heat water
evaporate water
heat water vapor
melt ice
Answer: D
C5.5e Relate the melting point, hardness, and electrical and thermal conductivity of a substance
to its structure.
1. Rank the following compounds by increasing melting point:
(I)C2H6,
(II)C2H5OH,
(III)C2H5F
A.
B.
C.
D.
E.
I, II, III
II, III, I
III, I, II
II, I, III
None of the above
Answer: A
Chemistry Assessments – May 2008
64
QUARTER FOUR
Unit 10
ACIDS-BASES
C5.7A Recognize formulas for common inorganic acids, carboxylic acids, and bases formed
from families I and II.
1. Which of the following is an example of a base
A.
B.
C.
D.
HCl
HC2H3O2
NaOH
H2O
Answer: C
2. Which of the following is and example of an acid
A.
B.
C.
D.
HCl
NaOH
Mg(OH)2
H2O
Answer: A
C5.7B Predict products of an acid-based neutralization
1. If it takes 1.0 gram of solid NaOH (a strong base) to change the pH of a solution containing a
strong acid from 1 to 2, how much solid NaOH (in g) would be needed to change the pH of
this solution from 2 to 3? You may assume that there is no change in the volume of the
solution.
Answer: 1.0 x 10-1
2. Calculate the pH of a solution prepared by dissolving 2.13 g of NaOH (a strong base) in
enough water to produce 100 mL of solution.
Answer: 13.7:
3. Calculate the concentration (in M) of HCl that would be needed to make an aqueous solution
of HCl with a pH of 4.3.
Answer: 5.0 x 10-5
Chemistry Assessments – May 2008
65
4. Calculate the pH of a solution prepared by dissolving 5.9 x 10-5 moles of HCl in 1.0 L of
pure water.
A.
B.
C.
D.
3.77
4.77
4.23
10.23
Answer: D
Analyzing a Titration Experiment
Given: Becky is conducting an experiment in which she measures 30 ml of an acid of unknown
concentration. She adds an indicator solution to it, then slowly adds a basic solution of a known
concentration from a buret until the acid solution is neutralized. She measure and records the pH
of the solution periodically throughout the experiment.
1. What laboratory technique is Becky using?
A.
B.
C.
D.
electrolysis
distillation
titration
electrophoresis
Answer: C
2. Which reaction would fit this experiment?
A.
B.
C.
D.
E.
CuSO4 + 2NaCl --> Na2SO4 + CuCl2
2H2O --> 2H2 + O2
KOH + HCl --> H2O + KCl
2H2O + BaSO4 --> H2SO4 + Ba(OH) 2
All of the reactions listed
Answer: C
3. All bonds holding atoms together within both the reactants and products in Becky’s
experiment are of what type?
A.
B.
C.
D.
E.
Metallic
Ionic
Covalent
Ionic and Covalent
Hydrogen
Answer: D
Chemistry Assessments – May 2008
66
C5.7C Describe tests that can be used to distinguish an acid from a base.
1. Which is the best indicator for giving a color change at the equivalence point?
A.
B.
C.
D.
Bromocresol green
Indigo carmine
Neutral red
Phenolphthalein _
Answer: D
C5.7D Classify various solutions as acidic or basic, given their pH.
1. The table below contains data for water samples from four sources.
Nancy analyzed water samples from several sources: rainfall, a nearby creek, a swimming
pool, and her kitchen faucet. She recorded her data in the table.
Chemistry Assessments – May 2008
67
Which sample was most acidic?
A.
B.
C.
D.
rain
creek
pool
faucet.
Answer: A
2. If we gradually increase the concentration of a strong acid in water without changing the
volume significantly, then the:
A. concentrations of hydronium and hydroxide ion will both increase.
B. concentrations of hydronium and hydroxide ion will both decrease.
C. hydronium ion concentration will decrease and the hydroxide ion concentration
will increase.
D. hydronium ion concentration will increase and the hydroxide ion concentration
will decrease.
E. concentrations of hydronium and hydroxide ion will be unaffected.
Answer: D
5.7E Explain why lakes with limestone or calcium carbonate experience less adverse effects
from acid rain than lakes with granite beds.
1. Why do limestone lakes experience less adverse effects from acid rain than lakes with granite
beds?
A. limestone is more acidic and more likely to react
B. limestone is more basic and neutralizes the rain
C. granite is more basic and more likely to react
D. granite is more acidic and neutralizes the rain.
Answer: B
C5.7f Write balanced chemical equations for reactions between acids and bases and perform
calculations with balanced equations.
1. How many liters of 2.5 M HCl are required to exactly neutralize 1.5 liters of 5.0 M NaOH?
A.
B.
C.
D.
1.0 L
2.0 L
3.0 L
4.0 L
Answer: C
Chemistry Assessments – May 2008
68
2. How many milliliters of 0.600 M H2SO4 are required to exactly neutralize 100 milliliters of
0.300 M Ba(OH)2?
A. 25.0 mL
B. 50.0 mL
C. 100.0 mL
D. 200.0 mL
Answer: B
3. How many milliliters of a 0.20 M KOH are needed to completely neutralize 90.0 milliliters
of 0.10 M HCl?
A.
B.
C.
D.
25 mL
45 mL
90 mL
180 mL
Answer: B
C5.7g Calculate the pH from the hydronium ion or hydroxide ion concentration.
1. What is the pH of a solution that contains 2.5 x 10-5 M hydronium ion?
Answer: -log(2.5 x 10 – 5) = pH 4.602
2. What is the molar concentration of hydroxide ion, [OH-], in a water solution that contains 2.5
x 10-4 hydronium ion (H3O+)?
Answer: 4 x 10 – 11 (OH-)
3. What is the molar hydroxide ion concentration, [OH-], in a solution with pH = 7.63?
Answer: inverse log (7.63) = 2.3 x 10 –8
4. For each hydrogen/hydronium/hydroxide ion concentration given, determine the pH and
indicate whether the sample is acidic, basic, or neutral.
A.
B.
C.
D.
[H+] = 1 X 10-10 M
[H+] = 1 X 10-2 M
[OH-] = 1 X 10-8 M
[H3O+] = 1 X 10-7 M
Answer: a. 10 = basic
b. 2 = acidic
c. 8 = basic
d. 7 = neutral
Chemistry Assessments – May 2008
69
C5.7h Explain why sulfur oxides and nitrogen oxides contribute to acid rain.
Angie had heard that acid rain was due to coal burning power plants. these power plants heat
water to make steam that is then used to generate electricity. During the combustion (burning)
process, sulfur in the coal combines with oxygen to make sulfur dioxide (SO2). Upon leaning the
power plant smokestack, the sulfur dioxide combines with water vapor in the atmosphere to
make sulfurous acid (H2SO3). Angie wanted to investigate the acidity of rain samples downwind
from a coal burning power plant. She collected 100 milliliter (mL) rainwater samples from the
following locations:
Angie added 1 drop of phenolthalein solution to each rainwater sample to use as an endpoint
indicator. She then titrated each beaker with 0.1 M (molar) sodium hydroxide (NaOH) solution
until the phenolthalein turned pink in color. She gathered the following results from her
experiment:
Sample mL of NaOH needed to
reach endpoint
A
1.8
2.4
C
5.6
1. All of the following are reasons why acid rain concerns people. What would be the major
reason the results of Angie’s experiment would be of interest to an agricultural community
that was situated 75 kilometers downwind from the power plant?
A. Acid rain could increase the yield (pounds/acre) of crops by releasing nutrients
locked up in the soil.
B. Acid rain could have a long-term effect on materials and people’s health.
C. Acid rain could affect the population’s health for a few days if a bad storm
occurred.
D. Acid rain could cause weaknesses in concrete poured when it rained, creating
structural problems in new buildings.
E. Acid rain could slowly decay the limestone found in old buildings.
Answer: B
Chemistry Assessments – May 2008
70
2. Why did Angie use sodium hydroxide (NaOH) to titrate the rain water samples?
A. Because phenolthalein is a specific indicator for NaOH and not other bases.
B. Because NaOH would neutralize the acid present, allowing the indicator to
change color.
C. Because the large amount of acid present required a strong base.
D. Because NaOH, being a strong base, is not affected by the dust particles found in
rain water.
Answer: B
3. Based on the results, how much acid did sample "C" contain compared to normal rainwater?
A.
B.
C.
D.
About 5.6 times as much as normal rain.
About 3.8 times as much as normal rain.
About 3.2 times as much as normal rain.
Cannot be compared to normal rainwater because of inadequate sampling.
Answer: E
Chemistry Assessments – May 2008
71
Unit 11
REDOX-EQUILIBRIUM
C5.3a Describe equilibrium shifts in a chemical system caused by changing conditions (Le
Chatelier’s Principle).
1. The reaction for the synthesis of ammonia: N2(g) + 3H2(g) ↔ 2NH3(g) is exothermic.
Increasing the temperature applied to the system:
I.
II.
III.
IV.
A.
B.
C.
D.
increases the amount of NH3.
decreases the amount of NH3.
changes the value of Keq.
does not change the value of Keq.
I and III only
II and III only
I and IV only
II and IV only
Answer: B
2. Consider the system below at equilibrium. Which of the following changes will shift the
equilibrium to the right?
N2(g) + 3H2(g) → 2NH3(g) + 92.94 kJ
I. Increasing the temperature
II. Decreasing the temperature
III. Increasing the pressure on the system
A.
B.
C.
D.
E.
I only
II only
III only
I and III
II and III
Answer: E
Chemistry Assessments – May 2008
72
3. The value of the equilibrium constant, K, is dependent on:
I.
II.
III.
IV.
A.
B.
C.
D.
E.
The
The
The
The
temperature of the system
concentration of the reactants
concentration of the products
nature of the reactants and products
I, II
II, III
III, IV
I and IV
I, II, and IV
Answer: D
C5.3b Predict shifts in a chemical system caused by changing conditions (Le Chatelier’s
Principle).
1. Which action will drive the reaction to the right?
A.
B.
C.
D.
heating the equilibrium mixture
adding water to the system
decreasing the oxygen concentration
increasing the system’s pressure
Answer: D
2. The reaction shown below occurs inside a closed flask. What action will shift the reaction to
the left?
A.
B.
C.
D.
pumping CO gas into the closed flask
raising the total pressure inside the flask
increasing the NO concentration in the flask
venting some CO2 gas from the flask
Answer: B
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C5.3c Predict the extent reactants are converted to products using the value of the equilibrium
constant.
1. If at a given temperature the equilibrium constant for the
reaction
is K p , the equilibrium constant for the
reaction
can be represented as:
A.
B.
C.
D.
E.
Answer: C
2. The value of the equilibrium constant, K, is dependent on:
V.
VI.
VII.
VIII.
A.
B.
C.
D.
E.
The
The
The
The
temperature of the system
concentration of the reactants
concentration of the products
nature of the reactants and products
I, II
II, III
III, IV
I and IV
I, II, and IV
Answer: D
C5.6a Balance half-reactions and describe them as oxidations or reductions.
1. __KClO4 +__H3ASO3 => __KCl +__H3AsO4
Answer: 1, 4, 1, 4, reduction
2. __H2S + __MnO4- + __H+ => __S + __Mn2++ __H2O
Answer: 1, 1, 2, 1, 1, 4, reduction
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C5.6c Explain oxidation occurring when two different metals are in contact.
1. Identify the oxidizing agent in the following reaction.
Cu2+ (aq) + Mg (s) → Cu (s) + Mg2+ (aq)
Answer: Cu loses e- (oxidizes)
2. Write the equation for the redox reaction that occurs when a piece of iron (Fe) metal is
dipped in a solution of copper (II) sulfate (CuSO4).
Answer: Fe2+ = CuSO4 → CuII2+ + SO4
3. Identify which reactant is reduced and which is oxidized in each of the following reactions.
a. 2Al (s) + 3Cu2+ (aq) → 2Al3+ (aq) + 3Cu (s)
b. 2Cr3+ (aq) + 3Zn(s) → 2Cr(s) + 3Zn2+ (aq)
Answers: a. Al oxidizes and Cu reduces
b. Cr oxidizes and Zn reduces
4. Silver (Ag) is a commonly used metal that easily tarnishes. The silver reacts with hydrogen
sulfide (H2S) in the air. This reaction produces silver sulfide (Ag2S), a dull brownish
compound, and hydrogen gas (H2).
a. Write a balanced equation for this reaction and identify the reaction type.
b. Explain why silver tarnishes faster in a heated room than in an unheated room.
c. Describe how you could slow down this reaction or prevent it from occurring.
Answers:
a. 2Ag + H2S  Ag2S + H2
b. Silver tarnishes faster in a heated room than an unheated room because particles have more
kinetic-molecular energy and as a result have more collisions.
c. The reaction could be slowed or prevented by lowering the temperature in the room.
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C5.6d Calculate the voltage for spontaneous redox reactions from the standard reduction
potentials.
1. Using the following equation calculate the voltage for the redox reaction
Zn  Zn2+ + 2e- 0.76v
Cu  Cu2+ + 2e- -0.34v
A.
B.
C.
D.
1.95v
-1.95v
.42v
-.42v
Answer: C
C5.6e Identify the reactions occurring at the anode and cathode in an electrochemical cell.
1. Which of the following half-cell reactions describes what is happening at the anode in the
diagram?
A. Zn  Zn 2+ + 2e B. H 2  2H + + 2e C. 2Cl -  Cl 2 + 2e D. SO 4 -  S + 2O 2 + 6e E. 2H + + 2e-  H 2
Answer: A
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Unit 12
THERMODYNAMICS
C2.2e Compare the entropy of solids, liquids, and gases.
1. Consider the combustion reaction between octane and oxygen in the cylinder of an
automobile. The reaction generates CO2, H2O and heat, and at the same time the expanding
gases push up the piston thereby powering the car. If the system is defined as the contents of
the cylinder (not including the piston or the cylinder) which of the following statements is
true for the system in this process?
A.
B.
C.
D.
The change in internal energy (ΔE) is negative
The change in internal energy (ΔE) is positive
The change in internal energy (ΔE) is zero
Not enough information is given to unambiguously determine the sign of ΔE
Answer: A
2. Which of the following processes is likely to have the most positive entropy change per mole
under standard conditions?
A. Freezing of water to ice
B. A sample of helium gas compressed to half its original volume at constant
temperature
C. The vaporization of liquid trichloromethane
D. The cooling of graphite from 77 K to 4.2 K
E. The transformation of graphite to diamond at room temperature
Answer: C
C2.3a Explain how the rate of a given chemical reaction is dependent on the temperature and the
activation energy.
1. Each of two solutions are mixed separately, and both solutions are found to be the same
temperature. The two solutions are mixed, and a thermometer shows that the mixture’s
temperature has decreased. Which of the following statements is true?
A. The chemical reaction is exothermic.
B. The chemical reaction is absorbing energy.
C. The chemical reaction is releasing energy.
D. The energy released could be found by multiplying the temperatures together.
E. The energy absorbed by the solution is equal to the difference in temperature of
the solutions.
Answer: B
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2. Which of the following events is least likely to occur with an increase in temperature for the
reaction given? (With ΔH = -45.9 kJ/mol.)
A. The gas particles will move more quickly.
B. The reaction will produce more ammonia in a shorter time.
C. The reaction will reverse and ammonia will decompose.
D. The entropy of the system will increase.
E. The equilibrium constant will become smaller.
Answer: B
3. Chemists determine the activation energy for a reaction by
A.
B.
C.
D.
measuring product amounts
measuring rates
calculating from bond dissociation energies
calculating from ΔH values
Answer: B
C2.3b Draw and analyze a diagram to show the activation energy for an exothermic reaction that
is very slow at room temperature.
1. Which letter corresponds to the activation energy of the reaction?
A.
B.
C.
D.
E.
A
B
C
Y
X
Answer: A
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2. Which letter corresponds to the change in energy for the overall reaction?
A.
B.
C.
D.
E.
A
B
C
Y
X
Answer: C
3. Which graph represents the reaction shown above?
A.
B.
C.
D.
Answer: B
C3.1a Calculate the ΔH for a given reaction using Hess’s Law.
1. The specific heat of copper is 0.4 joules/gramoC. How much heat is needed to change the
temperature of a 30-gram sample of copper from 20.0oC to 60oC?
A.
B.
C.
D.
1000 J
720 J
480 J
240 J
Answer: C
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2. A chemical reaction taking place in a calorimeter causes the temperature to rise 7.5° C. The
addition of 50 kJ of energy to the same calorimeter by an electrical heater increases its
temperature 2.5° C. What is ΔH of the chemical reaction?
A.
B.
C.
D.
16.7 kJ
-16.7 kJ
-150 kJ
150 kJ
Answer: C
3. Given the following thermodynamic data at 25° C:
2 HCl(g) + F2(g) --> 2 HF(l) + Cl2(g); ΔH° = -988 kJ/mol
H2(g) + F2 (g) --> 2 HF(l); ΔH° = -1200 kJ/mol
2 H2(g) + O2(g) --> 2 H2O(l); ΔH° = -572 kJ/mol
Calculate the ΔH° of the following reaction: 4HCl(g) + O2(g) --> 2 H2O(l) + 2 Cl2(g)
A.
B.
C.
D.
-148 kJ/mol
996 kJ/mol
-3748 kJ/mol
-2760 kJ/mol
Answer: A
C3.1b Draw enthalpy diagrams for exothermic and endothermic reactions.
1. The diagram above is a potential energy curve for a reaction. Which number represents the
effect of a catalyst on the reaction?
A.
B.
C.
D.
1
2
3
4
Answer: B
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C3.2a Describe the energy changes in photosynthesis and in the combustion of sugar in terms of
bond breaking and bond making.
1. What occurs during this change?
Given the equation representing a reaction:
carbon dioxide + water→ glucose + oxygen
A.
B.
C.
D.
Energy is absorbed and a bond is broken.
Energy is absorbed and a bond is formed.
Energy is released and a bond is broken.
Energy is released and a bond is formed.
Answer: B
C3.4B Explain why chemical reactions will either release or absorb energy.
2. Write the equilibrium expression for the following reaction:
A. [A] 2 [B][D]
B.
C.
D.
E.
Answer: D
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C3.4d Draw enthalpy diagrams for reactants and products in endothermic and exothermic
reactions.
1. The illustrations show a conservation-of-mass experiment. The solution in the beaker lost
mass because:
Intermediat
e
H2SO4 + 2NaOH 
A.
B.
C.
D.
2SO4
+ 2H2O
materials have less mass at high temperatures
the mass of the reactants and products was less than 100 g
sodium sulfate (Na2SO4) is lighter than air
some of the water molecules turned into gas
Answer: D
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C3.4e Predict if a chemical reaction is spontaneous given the enthalpy (ΔH) and entropy (ΔS)
changes for the reaction using Gibb’s Free Energy, ΔG = ΔH - TΔS (Note: mathematical
computation of ΔG is not required.)
1. Consider the following reaction at 50° C, given ΔH° = -57.2 kJ/mol and ΔS° = -175.8 J/molk:
2 NO2(g) --> N2O4(g)
A. This reaction is nonspontaneous at 50° C, but could be made spontaneous at
sufficiently high T.
B. This reaction is nonspontaneous at 50° C, but could be made spontaneous at
sufficiently low T.
C. This reaction is spontaneous at these conditions, but could be made
nonspontaneous by increasing the T.
D. This reaction is spontaneous at these conditions, but could be made
nonspontaneous by decreasing the T.
E. This reaction is spontaneous under all temperature conditions.
Answer: B
2. At constant pressure, the following reaction 2NO2 (g) → N2O4(g) is exothermic. The
reaction (as written) is:
A.
B.
C.
D.
always spontaneous.
spontaneous at low temperatures, but not high temperatures.
spontaneous at high temperatures, but not low temperatures.
never spontaneous.
Answer: B
C3.4f Explain why some endothermic reactions are spontaneous at room temperature.
The diagram shows an experiment in which crushed coal is heated in a test tube.
1. The flowchart represents what happens in this experiment.
The reaction shown above is –
A.
B.
C.
D.
an endothermic reaction
an exothermic reaction
a decomposition reaction
a double-replacement reaction
Answer: B
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