d.
5%
D. 5%
10. Which plastic is relatively the most expensive?
a.
Polytetrafluoroethylene (PTFE)
b.
Polystyrene (PS)
c.
Polyethylene (PE)
d.
Polycarbonate (PC)
A. (PTFE)
11. Which currently manufactured consumer product does not typically contain
plastic components?
a.
Sewing machines
b.
Automobiles
c.
Home furnishings
d.
Athletic equipment
e.
None of the above
E. None of the above
12. Wallace Carothers was commissioned by DuPont in the early 20th century to
develop a new synthetic giant molecule that could be used as a replacement for
natural materials such as silk. Carothers’ research yielded which synthetic
material?
a.
Polyethylene (PE)
b.
Polyamide (Nylon)
c.
Polytetrafluoroethylene (PTFE)
d.
Polypropylene (PP)
B. (nylon)
Chapter 2
1. Describe the differences between the carbon and oxygen atoms.
Carbon has six protons in the nucleus and six electrons. (the number of neutrons
determines the isotope of carbon but is unimportant for the differences in
behavior between carbon and oxygen.) Oxygen has eight protons and eight
electrons.
2. Why is an octet of electrons a stable configuration?
When both the s and p orbitals of an atom are filled, a certain stability is
achieved. There are two electrons which fill the s orbitals and six electrons that
fill the p orbitals. Therefore, eight electrons will fill both, giving a stable
configuration.
3. Identify the type of bond and the product formula expected between potassium
(K) and bromine (Br), and explain the basic nature of this bond. Show the
resulting outer electron configurations of K and Br after the bond is formed.
The materials will form an ionic bond since one is a metal (loses electrons) and
the other is a nonmetal (gains electrons). The product formed will be KBr. After
the bond is formed, K will have transferred its outer electron to Br. Potassium
16
4.
5.
6.
7.
8.
will then have a stable octet and a net charge of +1. Bromine will have a stable
octet and have a net charge of -1.
Identify the type of bond and the product formula expected between magnesium
(Mg) and chlorine (Cl), and explain the basic nature of this bond. Show the
resulting outer electron configurations of Mg and Cl after the bond has formed.
The compounds will form an ionic bond since one is a metal (loses electrons) and
the other is a non-metal (gains electrons). The product formed will be MgCl2.
After the bond is formed, Mg will have transferred its outer shell electrons to two
Cl atoms. Two Cl atoms are required because Mg wants to lose two electrons to
have the stable octet outer electron configuration. Each Cl will accept one
electron and so two chlorines are needed for both electrons. The resulting Mg ion
will have a charge of +2 and each of the Cl ions will have a charge of -1.
Describe the type of bonding between carbon and chlorine.
Carbon and chlorine are both nonmetals and will therefore share electrons to
form covalent bonds. Carbon will always form four bonds by sharing its outer
four electrons. Since each chlorine needs only one electron to complete its octet,
four chlorines are required to give carbon its four bonds. The resulting material
is CCl4.
What is an initiator and why is it important in a polymerization reaction?
Initiators are materials that start a chemical reaction. In the case of polymers, the
reaction is usually either a polymerization or a crosslinking reaction. The most
common initiator is a peroxide which breaks apart, usually when heated or
through certain chemical reactions, to form free radicals (chemical groups
containing an unshared, and therefore very reactive, electron).
Why is it harder to make very long polymer chains using the condensation
polymerization method than by using the addition polymerization method?
In the condensation reaction every monomer molecule can react with equal
probability upon encountering any monomer of the opposite type. This situation
favors the formation of many small chains which grow simultaneously. As the
chains get larger, their ability to continue reacting is slightly less than small
chains because the large chains have less mobility and, therefore, less chance to
encounter a monomer with which it can react. Also, in condensation
polymerization the byproduct of water is formed as the monomers react. The
presence of water molecules in the reaction will hinder chain formation by
diluting the reactants. In addition polymerization, encounters between monomers
do not form bonds unless one of the monomers has been initiated, that is, reacted
with an initiator so that the monomer contains a free radical. Therefore, in
addition polymerization, since only a few of the monomers are initiated, the
growth of the chains will be largely at the sites that are on the already formed
polymers, thus making those polymer chains even longer.
Describe the bonding in a carbon-carbon double bond. Include in this description
an explanation of the mechanism by which the various bonds are formed. What
does the existence of a double bond tell about the other atoms bonded to the
carbon atoms?
17
A carbon-carbon double bond assumes that each carbon is bonded to three atoms
(the other carbon with the double bond and two additional atoms). All carbons
must have four bonds. The approach of the three atoms creates a rearrangement
of the carbon atomic orbitals to accommodate the three bonds. This means that
the s atomic orbital and two of the p atomic orbitals will be oriented in space at
120o angles from each other in a flat trigonal arrangement. The atomic p orbitals
on each of the carbon atoms are dumbbell-shaped and will not be forced to
rearrange, but will overlap and create a second bond between the carbons. Each
carbon will, therefore, have four bonds. Three of these bonds are sigma bonds.
And one of these bonds is a pi bond. One of the sigma bonds and the pi bond are
between the carbons.
9. Define monomer and polymer. Write typical polymeric repeating unit structures
for both addition and condensation polymerization, and explain the various
symbols contained therein.
[ ─C—C─ ] ethylene mer unit
[ ─C—C─ ] propylene mer unit
/
C
A monomer is a molecule that can be chemically reacted to form a long chain. A
polymer is that long chain of monomer units. In a typical repeating unit structure
for a polymer made by addition polymerization, the polymer unit is represented
without the carbon-carbon double bond and with two bonds extending beyond the
basic monomer unit. These bonds indicate that the basic unit bonds to additional
units on either side of the unit shown. The entire basic unit is enclosed in
parentheses (which normally go through the lateral bonds) to indicate that the
basic unit exists as a group that is repeated many times down the chain. A
subscripted n follows the second parenthesis and represents the number of times
the basic unit is repeated down the chain. For polymers made by the condensation
polymerization method, the basic unit is the combination of the two monomers
with the monomers joined at the active sites but with the small, condensate
molecule removed. All the other symbols are the same as for the addition
polymerization case.
10. Which polymerization method, addition or condensation, is expected to result in
branched molecules? Why?
Addition polymerization will give branched polymers. This branching results from
the loss of an atom, usually hydrogen, during the polymerization process which
causes a free radical to form at the site where the hydrogen atom was previously
located. This free radical is then able to bond with other free radicals, as on the
end of a growing polymer chain, or with a monomer and begin a chain which
grows as a branch off the main backbone. Condensation is less likely to branch
because there is no mechanism that will create a reactive site in the middle of a
chain.
11. Describe crosslinking and the resultant properties that it will create.
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Crosslinking is the process of connecting polymer chains with covalent bonds.
When this occurs, the total length of the polymer chains (or molecular weight)
increases tremendously which raises the melting point of the polymer, usually
beyond the decomposition temperature. Therefore, polymers that have been
crosslinked will decompose before they melt.
12. What is a copolymer and how are copolymers formed?
A copolymer is formed when more monomers are mixed together than are
required for normal homopolymer formation. For addition polymerization this
means that two different monomer types are required. For condensation
polymerization three different monomer types are required. When these
monomers are mixed, the resultant polymer has some of each of the monomers
within it. These monomers can be arranged in four different patterns. The
properties of the copolymer are normally intermediate between the properties of
the homopolymers that would have been formed from pure, single-type monomers.
13. What is the molecular difference between thermoset and thermoplastic materials?
The thermoset materials are crosslinked and thermoplastics are not. This
crosslinking raises the total length (molecular weight) of the thermoset and
thereby prevents the material from being remeltable.
14. Achieving a high molecular weight was a major problem in the development of
the nylon polymerization process. Why was this so? Suggest a method to
overcome the problem.
Nylon is made through the condensation polymerization process. Water is a
byproduct of the polymerization. After a certain point in the process, the reaction
begins to slow because of the abundance of water. Continued reaction becomes
increasingly more difficult and chain growth is halted. This gives shorter chain
length and lower molecular weight. One method to overcome the overabundance
of water in the reaction vessel is to apply a vacuum to the polymerization
chamber. By removing the water from the reaction, the molecular weight can
continue to grow.
15. Define a free radical and explain why it is so reactive.
A free radical is an atom or molecule which has at least one electron which is not
paired with another electron. It is so reactive because the natural state of matter
is for that unpaired electron to form a bond.
Supplementary (non-text book) questions
16. Most polymers in use today are molecules with a backbone consisting primarily
of which basic element?
a.
Silicon
b.
Nitrogen
c.
Hydrogen
d.
Carbon
d. carbon
17. Every covalent bond is made up of how many electrons?
a.
One
b.
Two
c.
Three
19
d.
Eight
b. two
18. When naming organic compounds, the prefix but- (or buta-) is used to indicate
which quantity?
a.
Four
b.
Five
c.
Six
d.
Seven
a. four
19. Which of the following means basic repeating unit in organic chemistry
nomenclature?
a.
Monob.
Polyc.
–mer
d.
–ene
c. -mer
20. Step-growth polymerization is also known as which?
a.
Addition polymerization
b.
Subtraction polymerization
c.
Condensation polymerization
d.
Evaporation polymerization
c. condensation polymerization
21. When high temperatures or direct flame is applied to a plastic part that is made
from a thermoset material the typical response is what?
a.
Bursting into flames
b.
Blackening and charring
c.
Melting
d.
Nothing, thermosets are impervious to heat
b. blackening and charring
Chapter 3
1. Contrast the interatomic or intermolecular forces present in solids, liquids and
gases. Explain the consequences of these forces and how these forces are
normally overcome.
In solids the inter-atomic and intermolecular forces are very strong. The particles
(atoms or molecules) are relatively fixed in relation to all the surrounding
particles. These materials resist movements of the particles. Hence, solids are
rigid. In liquids the inter-particle forces are less strong than in solids, but there is
still some association between the particles. The particles can move freely to take
the shape of the container but will not fill the entire volume of the container. In
gases the inter-particle forces are nearly non-existent. Gases can take both the
shape and fill the volume of the container. The inter-particle forces are normally
overcome by adding thermal energy to the material. This thermal energy causes
20