Download Unit 1. Materials: Formulating Matter A. How do chemists describe

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Unit 1. Materials: Formulating Matter
A. How do chemists describe matter?
The U.S. Mint is promoting the use of dollar coins instead of dollar bills. In what ways might coins be superior
to bills? How do the properties of each form of currency depend upon their composition? In this unit, you will
consider the benefits and drawbacks of using a dollar coin. You will make recommendations for dollar
production and use, as well as strategies to convince U.S.consumers to adopt our choice of currency.
A.3 Physical and Chemical Properties
Classify each statement as a describing either a physical property (P) or a chemical property (C). [Hint: Decide
whether the chemical identity of the material does or does not change when the property is observed.]
1. Pure silver has a high luster (is shiny and reflects light).
2. The surfaces of some metals become dull when exposed to air.
3. Nitrogen gas, which is a relatively nonreactive element at room temperature, can form nitrogen oxides at the
high temperatures of an operating automobile engine.
4. Milk turns sour if left too long at room temperature.
5. Diamonds are hard enough to be used on drill bits.
6. Metals are typically ductile (can be drawn into wires).
7. Bread dough increases in volume if it is allowed to “rise” before baking.
8. Argon gas, rather than air, is used in many light bulbs to prevent oxidation of the metal filament.
9. Generally, metals are better conductors of heat and electricity than are nonmetals.
10. For each of the following settings or situations, write a statement similar to those in Questions 1-9 and then
identify whether your statement describes a physical or chemical property.
a. One of your observations in Lab Investigating Matter.
b. Your everyday experiences.
c. One desirable property of a dollar coin.
A.4 Properties Matter: Designing the Penny. Concept Check
11. You found the density of post-1982 pennies in the lab, Investigating Matter to be about 7.30 g/cm3.
Compare your experimentally determined coin density to that of pure copper (8.94 g/cm3) and pure zinc
(7.14 g/cm3).
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12. Based on this comparison, estimate the relative quantities of zinc and copper in post-1982 pennies. (For
instance, do you think pennies are composed of 50:50 of zinc and copper or more of one or the other?)
13. Briefly describe your reasoning, or show mathematically how you arrived at your estimation.
Classification of Matter POGIL
Look at the things in this room. They are all matter. That matter may be pure or it may be a mixture. Can you tell
by looking at it? What if you looked at it under a microscope? Then could you tell? Something that looks pure may
not really be pure. It depends on what type of particles that thing is made of. In this activity we will explore how
the smallest chemical units of matter determine whether something is an element, a compound, or a mixture.
Model
C
Box 1
T & CSq & C
atom
8 particles
?
Box 3
Sq2
Box 6
molecule
Box 4
?
Box 2
CSq
Box 5
molecule
molecule
atoms
5 particles
?
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Box 7
TCSq2
Box 8
C3Sq & TSq
Box 9
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Part 1 – Observing the Model
14. Look at Boxes 1 and 5 in Model 1. How is C different from CSq?
15. Look at Boxes 1 and 4 in Model 1. How many particles are in each box?
16. Compare the codes listed at the top of each drawing in Model 1 with the shapes in that box. What do the
letters C, Sq and T in the codes represent?
17. Circle a molecule of CSq in Model 1. How many shapes (atoms) are in a molecule of CSq?
18. a) What does it mean when two shapes are touching in the drawings of Model 1?
b) What does it mean when two shapes or molecules are not touching in the drawings of Model 1?
19. Circle a molecule of TCSq2 in Model 1. How many different types of shapes (atoms) are found in a
molecule of TCSq2?
a) How many Sq shapes are in a molecule of TCSq2?
b) What do the small numbers (subscripts) in the codes represent?
c) When atoms are touching, how is that communicated in the code?
d) When atoms or molecules are not touching, how is that communicated in the code?
e) In Model 1 there are three drawings that are labeled “?”. Write codes to properly label these drawings.
20. a) Can a particle be a single atom?
b) Can a particle be a molecule?
c) How many particles are in Box 2 in Model 1?
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Part 2 – Exploring Pure Substances and Mixtures
Matter is classified as a pure substance when all of the particles are the identical. Matter is classified as a mixture
if there are different particles present.
21. Identify which set of drawings from #9 are pure substances and which set are mixtures. List the codes for each
set here.
Pure Substances
Mixtures
____________
____________
____________
____________
____________
____________
____________
____________
____________
22. How are the codes (chemical formulas) for pure substances different from those for mixtures?
23. As a team, look at the set of pure substances from #10 and separate them into those containing only one type of
atom, and those with two or more types of atoms.
Read This!
Elements are defined as substances made from only one type of atom. Compounds are defined as substances
made from two or more types of atoms chemically combined in a fixed ratio.
24. Identify which set of drawings (from #12) are elements and which set are compounds. List the codes for each
set here.
Elements
Compounds
____________
____________
____________
____________
____________
____________
25. How are the codes (chemical formulas) for elements different from those for compounds?
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A.7 Chemical Symbols and Formulas Go to: http://www.webelements.com/ and click on History
Name
Symbol
1. aluminum
Al
2. bromine
Br
3. calcium
Ca
4. carbon
C
5. chlorine
Cl
6. cobalt
Co
7. copper
Cu
8. gold
Au
9. hydrogen
H
10. iodine
I
11. iron
Fe
12. lead
Pb
13. magnesium
Mg
14. mercury
Hg
15. nickel
Ni
16. nitrogen
N
17. oxygen
O
18. phosphorus
P
19. potassium
K
20. silver
Ag
21. sodium
Na
22. sulfur
S
23. tin
Sn
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Name comes from . . .
Latin “alumen” for alum, a medicine
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26. Group the Elements to Learn in 4 groups, according to how the symbol relates to the element name. One
example of each type is shown.
First letter of name
First 2 letters of name
C
First letter +
predominant letter
Al
Cl
Latin or other language
name
Cu
27. Which is more likely to be the same throughout the world—the element’s symbol or its name?
28. For each formula, name the elements present and give the number of atoms of each element. The first one is
done for you.
3 carbon atoms + 8 hydrogen atoms
a. C3H8
propane
b. CO2
carbon dioxide:
c. H2O2
hydrogen peroxide (antiseptic)
d. CaCl2
calcium chloride (sidewalk de-icer)
e. NaHCO3
sodium hydrogen carbonate (baking soda)
f.
sulfuric acid (battery acid)
H2SO4
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A.8 Pictures in the Mind
Use the following key to draw and interpret models of elements and compounds containing hydrogen, carbon,
nitrogen, oxygen, and chlorine:
Ÿ Ÿ
Ÿ Ÿ Ÿ
Ÿ Ÿ Ÿ
Ÿ Ÿ
Model:
Atom:
H
C
N
O
Cl
Sample Problem 1: Draw a particulate level model of carbon dioxide (CO2). (Hint: Carbon is in the center of
the molecule.)
The chemical formula CO2 shows one carbon atom and two oxygen atoms. We’re told that
carbon is in the middle, so we’ll draw a model that looks like:
Sample Problem 2: Write the chemical formula for the element represented by this particulate-level model:
Using the key above, we identified the atoms as nitrogen. Two nitrogen atoms make up
the molecule, so the chemical formula for elemental nitrogen must be N2.
Now it's your turn to create and interpret particulate-level models of elements and compounds.
29. In Investigating Matter A.1, you mixed ammonia solution and vinegar solution.
a. Draw a molecular-level model of ammonia, which has chemical formula NH3.
b. The substance in vinegar that reacted with the ammonia is called acetic acid. Below is a molecular-level
model of acetic acid. Write its chemical formula. (Hint: Write the symbol for carbon first.)
30. Draw molecular-level models of these compounds:
a. Methane (CH4): The primary component of natural gas. (Hint: Carbon is in the center of the molecule.)
b. Water (H2O): The most abundant substance on Earth. (Hint: Oxygen is in the center of the molecule.)
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c. Elemental chlorine (Cl2): poisonous gas used to make plastics and disinfect water.
d. Hydrogen chloride (HCl): important industrial chemical also sometimes used in pure form to etch
semiconductor crystals.
e. Carbon monoxide (CO): toxic gas used in many industrial processes, including purifying nickel.
31. You melted and burned paraffin wax in the Lab Investigating Matter. Write the chemical formula of
paraffin wax given its model below. (Note: The carbon and hydrogen atoms are smaller than in the key so
that this molecule can fit on the page.)
So far, none of the models you have drawn or interpreted are of metals. How
can you visualize solid metals? The following picture shows a common use
of aluminum foil. Although we use the chemical symbol "Al" to represent
aluminum, what we visualize is actually a large collection of aluminum
atoms. Like this:
This model, like all models, has some limitations. It is really only showing one small
segment of the aluminum foil; the atoms extend outward from what is shown. The
main point, though, is that we still only use a single symbol, Al, without any
subscripts, to represent an entire collection of aluminum atoms. Think about how
that is different from the molecular compounds you worked with in Questions 1-3.
32. Earlier, we learned about the composition of current pennies. Examine this figure, which
shows a cross-section of a penny.
a. What chemical symbols represent copper and zinc?
b. Zero in on a small area of the cross-section in the figure. Draw a particulate-level
model of what you think the copper and zinc atoms look like in that small area.
c. Describe in words how you decided to draw your model.
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33. In chemistry, we often try to relate the atomic and molecular structure of materials to their properties. One
property of metals is that they can be pounded into thin sheets.
a. Consider the particulate-level model of aluminum foil and other metals. Does this model help you to
explain why metals can be pounded into thin sheets? [Could you predict from this model that aluminum
is malleable?]
b. Describe your reasoning.
A.11 It’s Only Money
Part I:
Apply your knowledge of existing currency, as well as what you have learned about properties of materials, to
answer the following questions.
34. For a suitable coin:
a. What physical properties must the material have?
b. What other physical properties are desirable?
c. What chemical properties are required of the material?
d. What other chemical properties are desirable?
35. For a suitable banknote (bill):
a. What physical properties must the material have?
b. What other physical properties are desirable?
36. What chemical properties are required of the material?
37. What other chemical properties are desirable?
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38. Which would make the best primary material for a new coin: a metal, nonmetal, or metalloid? Explain.
Part II:
To make knowledgeable decisions, it is useful to collect information from several reliable sources. As you
consider the use and sustainability of U.S. currency, it will be helpful to find the composition of dollar coins and
bills now in circulation.
39. How will you find the composition of current U.S. dollar bills and coins? (Hint: Think about the
organizations that are responsible for producing money in the U.S.)
40. How will you decide whether the information you find is reliable?
41. What materials are found in the U.S. one-dollar coin? Write the name and symbol of each element in this
coin.
42. What materials compose the U.S. dollar bill?
Section A Summary. Reviewing the Concepts
The physical properties of a material can be determined without altering the material's chemical
makeup; physical properties. Chemical properties describe how a material reacts chemically through
its transformation into one or more different materials.
43. Classify each as a chemical (C) or a physical (P) property:
a. Copper has a reddish brown color.
c. Carbon dioxide gas extinguishes a candle.
b. Propane burns readily.
d. Honey pours more slowly than does water.
44. Classify each as a chemical or a physical property:
a. Metal wire can be bent.
c. Paper is flammable.
b. Ice floats in water.
d. Sugar is soluble in water.
45. Classify each as a chemical or a physical change:
a. A candle burns.
c. Hair curls as a result of a "perm."
b. An opened carbonated beverage fizzes.
d. As shoes wear out, holes appear in the
soles.
46. Classify each as a chemical (C) or a physical (P) change. For each answer, give some evidence.
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a. A cut apple left out in the air turns brown.
b. Flashlight batteries lose their "charge" over time.
c. Dry cleaning removes oils from clothing.
d. Italian salad dressing separates into layers over time.
An element is composed of only one type of atom; compounds consist of two or more types
of atoms. Both elements and compounds are considered substances.
47. Classify each of these substances an element (E) or a compound (C).
a. CO
e. NaHCO3
b. Co
f.
NO
c. HCl
g. I2
d. Mg
48. Look at these models.
(i)
(ii)
(iii)
a. Which represent elements?
(iv)
(v)
b. Which represent compounds?
(vi)
A chemical formula indicates the composition of a substance.
49. What two pieces of information does a chemical formula provide?
50. Distinguish between chemical symbols and chemical formulas.
51. Name the elements and list the number of each atom in the following formulas for substances:
a. phosphoric acid, H3PO4 (used in soft drinks and fertilizers)
b. sodium hydroxide, NaOH (found in some drain cleaners)
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c. sulfur dioxide, SO2 (a by-product of coal combustion)
52. Classify each property as characteristic of metals (M) or nonmetals (NM):
a. shiny in appearance
c. shatters easily
b. does not react with acids
d. electrically conductive
53. List the names and symbols of two elements that are metalloids.
54. What would you expect to happen if you tapped a sample of nickel with a hammer?
55. List two properties that make nonmetals unsuitable for electric wiring.
56. List three properties that make metals suitable for coins.
Models help in visualizing and understanding particles and phenomena that cannot be directly observed.
57. Using the key on page 7, draw a molecular-level model of oxygen (O2).
58. Draw a molecular-level model of carbon tetrachloride (CCl4), a toxic compound once used in the production
of refrigerants.
59. Write the formula of the compound represented by this model:
60. Draw a particulate-level model to show how copper can be drawn into a wire.
61. .Describe a model that is used outside of chemistry class to visualize or understand phenomena.
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