Quiz 2 Answer Key
Each question is worth 2 points. Correct answers and annotations are in red.
1. Which of the following is most likely to form a substitutional impurity in a nickel’s crystal structure?
a. Copper (same crystal structure and most similar atomic radius, electronegativity, and valence)
b. Cobalt (different crystal structure)
c. Silver (same crystal structure and electronegativity, but >15% difference in atomic radius)
d. Aluminum (same crystal structure, different electronegativity)
2. Which of the following compounds would form a stable crystal structure with a coordination
number of 6?
a. Aluminum oxide (Al2O3) (rc/ra=0.38-> coordination number of 4. For those of you who may
have looked online or in other sources, many sources state that the coordination number of
aluminum is 6 in aluminum oxide, but this is not the coordination number of the oxygen atoms
in this crystal structure, so the overall coordination number is lower – remember to use the
rules and calculations laid out in the book to get answers with full credit.)
b. Silica (SiO2) (rc/ra=0.29 -> coordination number of 4)
c. Zinc oxide (ZnO) (rc/ra=0.52-> coordination number of 6)
d. Calcium fluoride (CaF2) (rc/ra=0.75-> coordination number of 8)
3. True or false: a molecule containing 8 ethylene groups is considered a polymer.
False (A molecule containing <10 mers is considered an oligomer).
4. What is the molecular weight of PCL, an FDA-approved synthetic polymer for sutures and drug
delivery applications?
a. 11,400 g/mole (many people selected this answer, but you MUST include the end capping
hydrogen atoms)
b. 6,602 g/mole
c. 11,402, g/mole (100*(16+5*12+10*1+12+16)+2*1=11,402)
d. 5,800 g/mole
5. True or false: the polymer shown below is unsaturated.
False (Nylon contains no double bonds between carbon atoms, therefore it is saturated).
6. You need a very stiff polymer for a device that you are designing. Which of the following properties
do you know would be a poor choice for your polymer?
a. Unsaturated
b. Low molecular weight (less potential for entanglement of polymer chains – more entanglement
leads to higher mechanical properties)
c. Highly crosslinked
d. Atactic configuration (this answer was also accepted because atactic polymers have lower
potential for crystallinity, and therefore may have less packing of polymer chains and lower
stiffness)
7. Which of the following types of copolymers would allow most dense packing of chains next to each
other:
a. Random copolymer (Randomness decreases crystallinity and the potential for tightly packing
chains.)
b. Block copolymer
c. Syndiotactic copolymer (Note that a “syndiotactic co-polymer” does not exist (it is not one of
the 3 types of copolymers discussed in the book), but the idea that ordered tacticity increases
crystallinity was awarded 1.5 points.)
d. Addition copolymer
8. Which of the following statements is false?
a. A screw dislocation with a dislocation line in the +y direction has a Burger’s vector in the +y
direction. (A screw dislocation has parallel dislocation line and Burger’s vector.)
b. Both edge and screw dislocations cause an increase in atomic density. (this is FALSE, see section
3.2.1.3 point #1 in textbook)
c. The Burger’s vector varies in space (x,y,z). (The Burger’s vector is invariant – see diagram p.
104)
d. None of the above.