ANSWER KEY - Supplemental Unit 2 Worksheet

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Supplemental Unit 2 Worksheet
1. What is chemistry the study of?
Chemistry is the study of the properties, composition, and reactivity of matter.
2. What are the three different levels of representation in chemistry?
Macroscopic, sub-microscopic, symbolic
3. Susan is using a model of a water molecule to teach the class about the six-fold symmetry of a
snowflake’s structure.
a. What level of chemical representation is the model of the water molecule?
symbolic
b. What level of chemical representation is the observed six-fold symmetry of a
snowflake’s structure?
macroscopic
c. What level of chemical representation explains why a snowflake has a six-fold
symmetrical structure?
sub-microscopic
4. What are the two fundamental characteristics of chemistry?
Chemistry is both conceptual and computational.
a. Which characteristic describes an equation we could use to calculate how much energy
it takes to melt ice?
computational
b. Which characteristic describes an explanation we could give for why ice is less dense
than liquid water?
conceptual
5. Classify the following properties as intensive or extensive. Then, justify your classification for b,
d, e, and f.
a. Color - intensive
b. Mass – extensive; Mass is an extensive property because it depends upon the amount of
substance present. The more of a substance, the greater its mass.
c. Volume - extensive
d. Melting point – intensive; Melting point is an intensive property because it does not
depend upon the amount of substance present. 5.00 g of ice will melt at the same
temperature as 3.00 g of ice.
e. Luster – intensive; Luster is an intensive property because it does not depend on the
amount of substance present. For example, gold maintains the same shine whether or
not it is present in a small or large amount.
f.
Surface area – extensive; Surface area is an extensive property because it is dependent
upon the amount of substance present. The more substance, the greater the surface
area it occupies.
g. Density - intensive
6. Based on the following experimental data, justify why the boiling point of ethanol is intensive.
Then, explain what the data would have looked like if the boiling point of ethanol was an
extensive property instead. Why did the students have to test various masses of ethanol in
order to reach a conclusion?
Mas of Ethanol (g)
Boiling Point of Ethanol (°C)
2.00
77.8
4.00
78.0
6.00
78.1
The boiling point of ethanol is an intensive property because it remains close to 78.0°C even
when the mass of ethanol was varied from 2.00 to 4.00 to 6.00 g. Intensive properties remain
the same regardless of how much of the substance is present.
If the boiling point of ethanol was an extensive property, it would have varied significantly
between trials as the mass was increased instead of remaining the same.
The students had to test various masses of ethanol in order to reach a conclusion because they
needed to see how different amounts of ethanol would affect the boiling point. If different
amounts of ethanol resulted in different boiling points, then boiling point would be extensive. If
different amounts of ethanol resulted in the same boiling points, then boiling point would be
intensive.
7. Draw a brief sketch of a Bunsen burner. Label the (1) air vents and (2) gas control valve, and
explain what each of these parts do.
Air vents – increase or decrease the amount of air supplied to the flame;
affects flame color
Gas control valve – regulates the gas flow of the burner; affects flame
height
8. Two lab groups are performing an experiment using beakers. The first group’s beaker breaks,
but there is not enough time left in the experiment to start over. Can they simply substitute the
mass of the other group’s beaker into their data? Why or why not?
Different pieces of the same equipment can have different masses; therefore, they cannot
substitute the other group’s data. They will need to account for the mass of the new beaker by
using a balance.
9. Label the diagram with the following: stationary phase & mobile phase. Then, explain which
color dye was least attracted to the paper. Finally, explain which color dye was most attracted
to the paper.
Stationary
phase
Mobile
phase
The red dye was least attracted to the paper because it was the closest to the bottom of the paper. The
yellow dye was least attracted to the paper because it moved farthest from the bottom of the paper. It
was more attracted to the mobile phase than the paper.
10. During the sand and salt lab, what type of mixture occurred when…
a. The sand, salt, and water had not yet been separated heterogeneous
b. The salt water was left over after the sand had been filtered out
homogeneous
c. Only salt was left after the water was evaporated (Hint: Is this a mixture or something different
now?)
There is no longer a mixture since salt is a compound.
11. Based on previous lab observations, complete the following table.
Properties of Metals
Properties of Nonmetals
lustrous
non-lustrous
Malleable
brittle
Good conductors
Poor conductors
12. Based on your experience in the lab, how can the reactivity (a chemical property) of an element
be tested?
The reactivity of an element can be tested by reacting it with solutions of other chemicals. In this
lab, we reacted elements with hydrochloric acid (HCl) and copper (II) chloride (CuCl2).
13. Complete the following table.
State of Matter
Solid
Liquid
Gas
Properties
Regular arrangement of particles;
particles vibrate in place; fixed shape
and volume
Random arrangement of particles;
particles are close but can move past
one another; fixed volume, variable
shape
Random arrangement of rapidly
moving particles; particles are far
apart; variable volume and shape
Relative Strength of Forces
strong
medium
weak
14. Explain the difference between a chemical and physical change on the sub-microscopic level.
(i.e. What is going on at the tiny level during a physical/chemical change?)
During a physical change, there is no change to the structure of the particles at the sub-microscopic
level. The particles simply change their arrangement. During a chemical change however, there is a
structural change that occurs at the sub-microscopic level. This means that the structure of the particles
at the beginning is different from the structure of the particles at the end.
Physical change
chemical change
Construct a particulate drawing for each of the following.
Element
(monatomic)
See below:
Element
(diatomic)
Compound
Mixture
(homogeneous)
Mixture
(heterogeneous)
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