“Quasi” Final Exam
Notes:
 Your final exam will count as 1/7 of your final grade in chemistry. Each
trimester counts 2/7.
 There will be 116 total points available on the exam. Your grade will be
determined by the percentage of those points that you earn.
 The exam will contain multi-part problems whereby the answer to one part of
the problem may depend on the answer to a previous part. If you can not
solve the previous part, then make up a reasonable answer that you can use
on the subsequent part. If you can show your work correctly using the
“estimated” answer, you can still earn full credit for that part.
 During a cumulative exam it is important that you relax. Accept the fact now
that you are probably not going to know everything and that you are going to
get something “wrong”. It will be OK! The key is to make your best showing by
getting all of them right that you do know and not getting rattled by the ones
that you don’t. When you get stuck or confused, skip that one and
concentrate on the ones that you immediately know how to solve or answer. If
you have time, come back to the others. You don’t want to spend 20 minutes
on one that you are not likely to earn points on anyway and then never get to
attempt four problems at the end of the test that you could have completed
easily.
Problem I:
(76 pts.)
Tool Box
Ethanol = C2H5OH
d = 0.789 g/mL
$1.12/gal
1 mile = 5280 ft
1 in = 2.54 cm
1.06 qt = 1 L
1 Quarter Pounder =
420 Cal
Macronutrients:
Fat = 21 g
CHO = 37 g
Protein = 23 g
carbon En = 2.50
hydrogen En = 2.20
H = -326.7 Kcal/mol C2H5OH
oxygen En = 3.50
Walking (3 mph) = 5 Kcal/min energy expenditure for a 150 lb. person
a) What type of compound is ethanol? How is it held together? (2 pts.)
b) Write an electron configuration for each element in the ethanol molecule. Draw
a Lewis structure for ethanol. Explain the reasoning for the number of electrons
you assigned to the carbon, oxygen, and hydrogen atoms. (4 pts.)
c) Identify the location of partial charges and dipoles in the compound. Is this
molecule polar or nonpolar? (3 pts.)
d) How are ethanol molecules held together in a liquid? (2 pts.)
e) Would ethanol molecules mix with water molecules? Why or why not? (2 pts.)
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f)
g)
h)
i)
j)
What is the molar mass of ethanol? (1 pts.)
What is the percent by mass of carbon in the compound? (2 pts.)
Write a balanced equation for the combustion of ethanol. (3 pts.)
What makes this a chemical change rather than a physical change? (2 pts.)
It is now the year 2025 and gasoline powered cars are outlawed and the U.S.
has finally adopted the metric system. The speedometer in your ethanolpowered sports car says (and it really does talk to you) that you are traveling
at a rate of 94 Km/hr. How fast are you going in mph? (2 pts.)
k) Your car’s fuel efficiency using ethanol is 19.5 Km/L. If you travel 300. Km,
how many liters of ethanol have you burned? . (2 pts.)
l) How many counting units of ethanol were used? How many molecules? (4 pts.)
m) How many molecules of oxygen were required in the reaction? (2 pts.)
n) How many molecules of carbon dioxide would be produced? (2 pts.)
o) Draw Lewis structures for the oxygen and carbon dioxide molecules. What is
similar about their structures and properties? (4 pts.)
p) How much potential energy was represented by the ethanol molecules in the
reaction? (3 pts.)
q) During the reaction, the potential energy of the ethanol molecules is
converted to what forms of energy? (2 pts.)
r) How many Quarter Pounders would be required to have the same amount of
potential energy as the ethanol molecules? (2 pts.)
s) How long would a 150 lb. person have to walk in order to expend the energy
present in one Quarter Pounder? How many miles have they traveled? (3 pts.)
t) What percent of the potential energy in the Quarter Pounder is supplied by fat
molecules? (2 pts.)
u) How much ethanol (in grams) would a person need to consume to supply the
potential energy they needed to fuel a day’s worth of activities? Assume they
require 3125 Kcal per day. (3 pts.)
v) How many milliliters of ethanol would they have to drink. (2 pts.)
w) How much would it cost this person per day to run on ethanol? (2 pts.)
x) What if the person consumed a little too much energy each day? Let’s
assume that the excess was the equivalent of 175 Kcal. How much
bodyweight will they gain in one year’s time? (2 pts.)
y) Your new ethanol-powered sports car is also “turbocharged”. A turbocharger
gives a car more horsepower by compressing the air that enters the engine.
The compressed air is more concentrated in oxygen, which causes the
combustion reaction to be more vigorous. If the turbocharger takes in 3.4 L of
air at standard pressure and increases the pressure to 5.5 atm, what will be
the new volume of the air? Assume the temperature remains constant. (3
pts.)
z) As you drive to the beach, your tires heat up from the sun and friction with the
road. What will happen to the gas molecules inside the tire as the tire heats
up? What will this change about the tire? (3 pts.)
aa) How many grams of oxygen would be in scuba tank that has a volume of 20.
L with a pressure of 125 atm at 22.5 *C? (3 pts.)
bb) What are the purposes of soap and wax molecules? (3 pts.)
cc) The aluminum atoms that form your engine are reacting with oxygen to form
aluminum oxide. Write a balanced equation for this reaction. (3 pts.)
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dd) How is the compound aluminum oxide structurally different from the ethanol
molecule? (3 pts.)
Problem II: (40 pts.)
A chemistry student obtains a chunk of aluminum and measures its mass on a
balance. The student pours some water in a graduated cylinder and reads the
volume. The chunk of metal is placed in the cylinder and the new volume is
recorded. The student masses out some zinc chloride and dissolves it in a flask
with water to make a solution. The aluminum is taken from the water and added
to the zinc chloride solution. Metallic crystals begin growing on the piece of
aluminum. The piece of aluminum dissolves and the flask seems to get warmer.
The student adds some hydrochloric acid to the flask and observes bubbles
being produced.
Data Table
Measurement
Reading
Mass of the aluminum piece
3.933 g
Initial volume of the water
23.7 mL
Final volume of the water
25.4 mL
Mass of zinc chloride
27.554 g
Observations: The aluminum piece begins to darken and then metallic looking
crystals begin to grow from its surface. The solution remains clear but gets
warmer. When acid is added, the metallic crystals begin to dissolve and bubbles
rise to the surface. The flask gets much warmer.
a) From the data, determine the density of aluminum. (3 pts.)
b) If the literature value for the density of aluminum is 2.70 g/mL, what is the
student’s percent error for the experiment? (2 pts.)
c) Write a total molecular equation for the reaction. Include the heat term to
show if the reaction was endothermic or exothermic. (3 pts.)
d) Write a net ionic equation for the reaction. (3 pts.)
e) Explain in detail what occurred during this chemical change. (4 pts.)
f) What type of reaction is this? (1 pts.)
g) Who has more potential energy, the reactants or the products? (1 pts.)
h) Write electron configurations for aluminum before and after the reaction. What
happened to the aluminum atoms and why? (3 pts.)
i) How many protons, neutrons, and electrons would be in the aluminum ion?
(3 pts.)
j) How many grams of zinc will be produced before the reaction runs out? (3 pts.)
k) What causes the reaction to stop? (2 pts.)
l) How many grams of the excess reactant will be left over when the reaction
stops? (4 pts.)
m) Write the total molecular equation for the second reaction. What type of
reaction is this? (3 pts.)
n) How many grams of hydrogen will form from this reaction? (3 pts.)
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