Body

chemistry 100, Exam 3 (12/5/01)

(modified Friday Dec 7 -- part II now shows class responses)

Part I-- Short Answers (points indicated by number in brackets, [2] = 2 points)

50 points (50% of the exam)

Class average on this section: 25 out of 50 points

(answers and comments are in bold type)

1. The Big Six dominate the world of synthetic polymers-- list three of them by name

[2]_low density polyethylene LDPE
[2]high density polyethylene HDPE
[2] polyvinyl chloride (PVC)
[2]polystyrene
[2] polypropylene
PETE polyethylene terephthalate ester

2. The starting material for all six of these polymers is [2]_petroleum (or oil)_.

3. A polymer is a [2]_ macro (1 pt for very large )__-molecule that consists of many small units, called [2]__ monomers__, linked together.

4. Polymers are typically classified as thermoplastic or [2]__ themosetting___ materials.

5. A the term "plastic" in "thermoplastic" means what? [5]

flexible, pliable, moldable (in this case, when heated)

6. Nitrocellulose was used to make the plastic backing for movie film. What are two important problems with nitrocellulose based motion picture films.

a. _very flammable, explosive, burns __ [3]
b not stable, slowly decomposes and crumbles; old films are rarely preserved [3] <
once decomposed, film breaks, image deteriorates, etc., but this is part of the same problem
several answers talked about color fading... color film is a much later development and nitrate film had been abandoned long before color reached the theater

7. The electrolysis of water can produce hydrogen for use as a fuel. What circumstances are necessary if the use of hydrogen fuel is to cause a reduction in CO₂ emissions.

(Hint: why would hydrogen fuel be associated with CO₂ emission?) [5]

The electricity must be produced by a technology that doesn't rely on fossil fuels.
Nuclear power, solar power, etc. would qualify.
Otherwise, we merely shift CO2 production to the power plant.

8. It can be argued that rechargeable batteries are no more environmentally friendly than disposable batteries, even though you might throw out 100 disposable batteries for every rechargeable battery. Why is this so? [6]

Conventional batteries contain materials that are not particularly hazardous. Rechangable batteries often contain cadmium, lead and other highly hazardous materials.
Several papers argued that you still need to spend power to recharge, so there is CO2, SO2, etc at your regional power plant. True, but you need much more power and cause more environmental damage in the manufacture of new batteries.

9. In an ordinary flashlight battery one of the electrodes is made from Zinc.

The reaction at the electrode is Zn + 2OH^- ---> Zn(OH)₂ + 2 electrons
this type of reaction is labeled as _oxidation___[3]
and the electrode made of Zinc is considered a __ anode__[3].

10. A fuel cell would typically use hydrogen and air (oxygen) to convert chemical energy into

___electrical energy (power, current)________[2] and the only by product would be _ water__[2] . A hydrogen powered engine or flame would also be likely to produce some air pollution in the form of _Nitrogen oxides__[2].

11. Nuclear fusion is the energy source of _sun's energy / stars / also accept H-bomb__[2]

but it has not been an important commercial energy resource.

Part II-- Multiple Choice (25 questions, 50 points)

1. The battery in a traditional automobile [class overall = 21% correct]
- a. provides part of the power that turns the wheels
- b. is an important source of lead (and lead poisoning) if not disposed of properly
- c. is basically a fuel cell, with diluted sulfuric acid as the fuel
- d is considered an electrolytic cell
2. A fuel cell [class overall = 72% correct] differs from a traditional flashlight battery in that
- a. a flashlight battery can be recharged but a fuel cell cannot
- b. a fuel cell can be recharged by reversing the current but a flashlight cell cannot
- c. the flashlight battery converts chemical energy into electrical energy
- d. the fuel cell could be operated as long a fuel is supplied; a flashlight battery soon runs out of chemical resources and goes dead.
3. The Crowfoot cell used by early telegraph operators [class overall = 64% correct]
- a. was recharged from the power lines when not in use
- b. was completely sealed like today's flashlight cells
- c. was named because the electrolyte was often made from an extract of bird bones
- d. was named for the shape of the electrodes
4. Hydrogen is an attractive fuel because [class overall = 62% correct]
- a. vast untapped natural deposits are available
- b. it is easily stored and distributed
- c. it can be produced inexpensively from water
- d. it burns with no significant pollution or CO₂ production
5. Reduction involves [class overall = 58% correct]
- a. reaction with oxygen
- b. release of oxygen in chemical reaction
- c. release of one or more electrons per molecule
- d. capture of one or more electrons by a molecule
6. The two electrodes in a fuel call are [class overall = 84% correct]
- a. anode and cathode
- b. ampere and voltage
- c. catalyst and separating membrane
- d. n-doped and p-doped semiconductors
7. Hydrogen gas can be stored (as a fuel) for later use [class overall =39% correct]
- a. as a hydride, by reaction with a metal
- b. by reaction with oxygen to produce water
- c. as a hydrocarbon
- d. by conversion to deuterium
8. The hybrid automobiles that recently reached the market are called hybrids because
- a. they can burn a wide range of fuels
- b. they use nonpolluting fuels
- c. they are electric vehicles, relying on batteries to store the electricity they need
- d. during operation they use batteries connected to electrical motors and a gasoline engine
9. Silicon is considered [class overall = 45% correct]
- a. a metallic conductor
- b. a semiconductor
  This is the corect answer
- c. an insulator
  - Technically, Si is not an insulator. However the notes use that phase to suggest that pure silicon is a terrible electrical conductor. As a result, we find it necessary to dope it to make it a useful semiconductor.
  - Since the notes did use the phrase "insulator", I will certainly accept that as an acceptable response.
  - if this situation applies, you will get credit for response "c"
- d. a nonmetallic oxide
10. Look at the periodic table to answer this
Silicon can be P-doped to increase its electrical conductivity. This can be done by incorporating traces of ____ into otherwise pure silicon. [class overall = 36% correct]
- a. carbon
- b. gallium
  - Gallium is correct for P-doped material
  - Grades were scored with c in error and this will be corrected.
  - if you said Gallium, you get 2 more points
  - if you said Phosphorus, sorry, but we will take back 2 points
- c. phosphorus
  - an n-doped material has extra electrons (n=negative)
  - you need an element with more than 4 valence electrons (column 5A is good place to look)
  - Gallium, above is used to produce p-doped material (it has fewer electrons so it created bonds deficient in electrons (or p=positive holes)
- d. gas bubbles
11. Solar Cells are also known by the name [class overall = 72% correct]
- a. photoconductive films
- b. photovoltaic devices
- c. photogenic panels
- d. electrolytic cells
- .
12. Crosslinking [class overall = 49% correct]
- a. is the process that forms long linear polymer chains
- b. involves chemical bonds between long polymer chains
- c. means that the polymer contains some double bonds between carbon atoms
- d. means that molecules that become polymers must contain two reactive sites
13. Nylon is an example of [class overall = 32% correct]
- a. a naturally occurring protein
- b. a polyester
- c. a polyamide
- d. a modified form of cellulose
14. Two examples of naturally occurring polymers are [class overall = 70% correct]
- a. silk and cellulose
- b. Bakelite and celluloid
- c. carboxylic acids and amines
- d. rayon and nylon
15. Which molecule below is likely to become part of a protein: [class overall = 85% correct]
- a. amino acid
- b. hydrocarbon
- c. alcohol
- d. terephthalic acid
16. Thermoplastic polymers are heavily used because [class overall = 68% correct]
- a. they hold up to higher temperatures than other polymers
- b. they are generally less expensive than other polymers
- c. they are easier to use to form objects
- d. they are mechanically stronger than other polymers
17.A foamed coffee cup is likely to be made of [class overall = 83% correct]
a. polyethylene
b. polystyrene
c. PETE
d. freon

18. Which of the molecules in the box is an amine? (sorry box/figure didn't transfer to the web site)

[class overall = 48% correct] answer=C (amine has Nitrogen, similar to ammonia)

19. Of the four molecules in the box, which type of molecule is NOT included? [class overall = 29% correct]

a. a carboxylic acid
b. an alcohol
c. a hydrocarbon
d. a glycol
- a glycol has two -OH groups
- even if you didn't remember what a glycol is, you should recognize that all molecules had oxygen or nitrogen and were therefore not hydrocarbons.

20. Which of these is the oldest synthetic polymer [class overall = 80% correct]

a. Bakelite
b. Nylon
c. Polyvinyl chloride
d. ethylene glycol

21. Plastique (or plastic explosive, C4) is a high explosive often used by terrorists and military demolition specialists. The name suggests the important difference between this and other explosives [class overall = 79% correct]

a. it is more powerful
b. it can be shaped to fit into an irregular space
c. it is less likely to accidentally detonate
d. it produces less pollutants

22. In a modern landfill [class overall = 33% correct]

a. plastics and paper will breakdown over a period of about 20 years
b. plastic will break down through biodegradation, but paper will not
c. paper will quickly decompose but plastics seem to last forever
d. neither paper nor plastic are likely to decompose in the next 20 years.
- This seems unreasonableat first , since everyone knows paper is biodegradable
- but the discussion in text and class point out that landfills do not permit material to degrade properly and paper lasts for a very long time under these circumstances.

23. The FDA is in charge of policing the pharmaceutical industry. The letters stand for [class overall = 94% correct]

a. Food and Drug Administration
b. Federal Drug Agency
c. Federation of Drug Assessment
d. Fatal Drug Avoidance

24. Many drugs are isolated from naturally growing plants, microorganisms or animals.. Which of these was NOT first derived in that manner [class overall = 20% correct]

a. aspirin
aspirin is a modification of the material found in elm or willow bark, but asprin is not a natually occuring material.
b. penicillin
c. digitalis
- Not in text, but reatured axample in my notes-- from the floxglove, used to treat heart ailments (or as a poison) for centuries
d. quinine

25. In drug vocabulary, an ANALOG is [class overall = 37% correct]

a. a cheaper version of drug that can be substituted for a prescribed brand name drug
b. a chemical modification of a known drug
c. a drug used to reduce fever
d. a drug in the early testing stage, not yet available for sale