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CHE1031
CHE1031 Chapter 1 Homework Problem Key
Homework problems are organized by topic, in the same order that topics are covered in
lecture. Once we cover a topic in lecture, the problems for that topic are due at our next class
meeting. If you have questions about which questions are due, please ask!
Homework format: Problems must be solved, or written out, in their entirety with all work
shown on engineering graph paper. You must label each set in the upper left hand corner
with your name, the date and the chapter. Problems must be identified by number and all
work must be shown with answers boxed. Be sure your handwriting is legible.
1.1 Science and chemistry
1. What is the difference(s) between science and engineering?
Science is the systematic study of the physical world by observation and
experimentation; any systematic collection or body of knowledge about a certain
subject.
Engineering is the practical application of knowledge in the construction of machines,
buildings, infrastructure etc.
2. What’s the essential difference between physics and chemistry? [Use any resource you
need to pin this down.]
Physics is the study of matter and its behavior. Chemistry is the study of the changes
matter undergoes.
3. The scientific method is “iterative” in nature. What does iterative mean and how does it
apply to the scientific method.
Iterative means that a process must be applied again and again (repeatedly) in order to
learn and solve a problem. The scientific method involves observing a phenomenon,
forming a hypothesis, designing and executing experiments to test the hypothesis, and
finally supporting or disproving the hypothesis; supported hypotheses become theories.
Most hypotheses are not supported, so scientists must engage the method in an iterative
fashion until they develop a hypothesis that can be supported by experimentation.
1.2: What is matter?
States of matter
4. In which physical state is matter most:
a. Dense
solid
b. Energetic
gas
c. most compressible
gas
5. What is unusual about the solid physical state of water? [Imagine a pond of water with ice
and compare it to a pond of molten steel with solid steel chunks.]
Solid ice is less dense than liquid water and floats on liquid it. The solid state of most
substances is more dense than the liquid state, and will sink through it.
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CHE1031
Pure substance vs. mixture
6. Classify each of the following as a pure substance or as a mixture. If a mixture, is it
homogeneous or heterogeneous?
a. air
mixture; homogeneous
b. tomato juice
mixture; heterogeneous if you can see pulp
c. iodine crystals
pure substance; element
d. sand
mixture of granules, largely silicon dioxide
Physical vs. chemical change
7. Label each as a physical or chemical property of Zn:
a. Zn is a silver-gray metal.
physical
b. Zn melts at 420°C.
physical
c. Zn “disappears” when added to acid, and hydrogen gas is produced. chemical
d. Zn has a hardness of 2.5 Mohs.
physical
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e. Zn has a density of 7.13 g/cm .
physical
f. Zn reacts with oxygen, at elevated temperatures, to produce zinc oxide, ZnO.
chemical
8. Identify each as a chemical or physical change:
a. the match burns
chemical
b. the metal gets warmer
physical
c. water condenses on the metal
physical – change of state
d. soot is deposited on the metal
chemical – soot is formed by combustion
1.3: Measurement, metric units & prefixes
Units
9. What exponential notation do the following abbreviations represent:
a. d
-1
b. c
-2
c. f
-15
d. μ
-6
e. M
+6
f. k
+3
g. n
-9
h. m
-3
i. p
-12
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CHE1031
Density
10. The label fell off a bottle of clear liquid. The lab tech thinks that it’s benzene – a nasty
carcinogen – and measures its density to try and confirm this. A 25.0-mL volume of the
liquid has a mass of 21.95 g. The density of benzene is 0.8787 g/mL at 15°C. Was the tech
right?
ρ = m/v = 21.95 g = 0.878 g/mL
So density is a match for benzene.
25.0 mL
11. The density of titanium metal is 4.51 g/cm3 at 25°C. What mass of Ti displaces 125.0 mL of
water at that temperature?
m = ρv = (4.51 g/cm3)(125.0 cm3) = 564 g
Exact vs. inexact numbers
12. Which are exact numbers?
a. Mass of a 16-oz. bag of coffee from Vermont Coffee Company
b. Number of students in class
c. The temperature of the surface of the sun
d. The mass of a postage stamp
e. The number of millimeters in a cubic meter of water
f. the average height of students at the college
inexact
exact
inexact
inexact
exact
inexact
Uncertainty precision & accuracy
13. You are using a graduated cylinder calibrated in one mL intervals. The volume of liquid in
your cylinder looks to be halfway between 20 and 21 mL. How would you report this
volume with proper uncertainty?
20.5 + 0.5 where the ‘0.5’ after the 20 is the digit of uncertainty, and the + 0.5 is one-half
of the instrument’s least count (smallest calibration) and tells the reader about the
instrument’s quality.
14. The US government issues monthly statistics for job growth, unemployment,
manufacturing productivity, etc. The numbers are usually revised a few weeks after they
are first announced. Is the purpose of the revision to increase:
a. accuracy; or  Revised statistics use complete and checked data.
b. precision?
Significant figures
15. How many significant figures in each of these numbers:
a. 3.774 km
4
2
b. 205 m
3
c. 1.700 cm
4
d. 350.00 K
5
e. 307.080 g
6
3
f. 1.3 x 10 m/s
2
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CHE1031
16. The diameter of the Earth at the equator is 7926.381 miles. Round that to 3 sig figs and
express it with scientific notation.
7.93x103 miles
17. Express the answer to each problem with the correct number of significant figures.
a. 320.5 – (6104.5/2.3) =
= 320.5 – 2600 = -2280 (none after decimal)
b. ((285.3 x 105) – (1.200 x 103)) x 2.8954 =
= (2.99 x 104 – 124)(2.8954) = 8.62x104
c. (0.0045 x 20,000.0) + (281.3 x 12) =
= 90. + 3.4 x 103 = 35. x 102
d. 863 x (1255 – (3.45 x 108)) =
= (863)(882) = 7.61 x 105
Scientific notation
18. Convert these numbers into scientific notation:
a. 25030000
2.503 x 107
b. 0.00000042600
4.2600 x 10-7
1.5: Dimensional analysis
Single conversion factor
19. A blue whale has a lung capacity of 5.0 x 103 L. Convert that to gallons.
5.0x103 L
1 gallon = 1.3x103 gallons
3.7854 L
With multiple conversion factors
20. In 2007, it’s estimated that 31 billion tons of CO2 was emitted worldwide due to fossil fuel
combustion and cement production. Express this mass in grams using a metric prefix
without scientific notation.
31x109 tons 2000 lb
1 ton
453.59 g = 2.81x1016 g = 28100000 Gg
1 lb
21. Bamboo can grow up to 60.0 cm per day. Convert that to inches per hour.
60.0 cm
1 in
1 day = 0.984 in/hour
1 day
2.54 cm 24 hr
22. The recommended adult dose of Elixophyllin, an asthma drug, is 6 mg/kg of body weight.
What’s the dose (mg) for a 185-lb person?
185 lb 453.59 g 1 kg 6 mg = 503 mg
1 lb
103 g
1 kg
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CHE1031
With cubed unit volumes
23. Silicon for computer chips is grown in large cylinder called “boules”. One boule is 300 mm
in diameter and 2 m tall. The density of Si is 2.33 g/cm3. Silicon wafers for making
integrated circuits are sliced from a 2.0 m boule and are 0.75 mm thick and 300 mm in
diameter.
a. How many wafers can be cut from a single boule?
b. What is the mass of one wafer?
a. 2.0 m 1000 mm
1 slice = 2.7 x 103 slices
1m
0.75 mm
b. volume of a slice = (h)(πr2) = (0.75 mm)(π)(150 mm/2)2 = 5.3 x 104 mm3
5.3 x 104 mm3
13 cm3
103 mm3
2.33 g = 1.2 x 102 g
1 cm3
24. The concentration of carbon monoxide in an urban apartment is 48 μg/m3. What is the
mass (g) of CO in room that measures 11.0 x 11.5 x 20.5 ft?
Room volume = (11.0)(11.5)(20.5) = 2.59 x 103 ft3
2.59 x 103 ft3
123 in3 2.543 cm3 13 m3
13 ft3
13 in3
1003 cm3
48 μg
1g
= 3.52 x 10-3 g
1 m3 106 μg
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