Body

chemistry 100, Exam 2

October 31, 2001

distribution of grades will be posted as they become available
there were three versions of the exam; the numbering of the questions may be different on your exam. Part I -- Short Answers(40 pts)

1. (6) Acid rain is said to be a regional problem (as contrasted to a global or a local problem)

Explain why it is regional...

Source--SO2 mostly from burning coal
gas travels 100-1000 miles (no longer local, but hardly world wide)
dissolves and appears in rain elsewhere
source of problem and apparent effect are separated--typically in different states or adjacent countries

2. (8) Give a brief definition of an acid and a base

An acid is a chemical compound that

an acid is a species that produces H+ ions (or H3O+) when dissolved in water
(need both H+ and water for a full answer)

A base is a chemical compound that

a base is a species that produces OH- ions (hydroxyl) when dissolved in water
(need both OH- and water for a full answer)

3. (6) The word aqueous (as in aqueous solution) means __in water (the solvent)_____

The word _ solute___ is used to refer to the material dissolved to form a solution.

A reaction that produced heat is said to be _ _exothermic___.

4. (6) What is meant by the electronegativity of an atom?

tendency to retain or control electrons in a covalent bond
atoms with a high electronegativity value will be partially negatively charged in the molecule

5. (8) Give two examples of the negative effect of acid rain:

corrosion of limestone statues, gravestones, buildings
failure of paint or early rusting of metals
kill off or weaken trees and other plants that can't take an acidic environment
kill off life forms in lakes (fish, amphibians, etc.); weaken species or alter the population in a lake.

6. (6) Radioactive materials produce three forms of radiation. Name and briefly describe each.

alpha -- (core of He atoms)
beta -- high energy electrons
gamma-- electromagentic radiation(similar to X-rays but more energetic)

Part II-- Multiple Choice
Answer all 30 questions (60 points) ; there is no penalty for incorrect answers.

1. Gasoline for automobiles often contains 5-15% ethanol or ethyl alcohol, C₂H₅OH because

a. Petroleum is a mixture of compounds including alcohols and hydrocarbons. Distillation of petroleum thus produces a mixture of hydrocarbons and alcohol.
b. Routine processing (catalytic "cracking") of petroleum converts some of the hydrocarbons into alcohols
c. Ethanol is added because it provides much more energy than hydrocarbons-- it is the easiest way to boost the octane rating of gasoline (gasoline is a better energy source)
d. Ethanol is much less expensive than petroleum; adding it makes fuel less expensive. (alcohol is usually more expensive; the lower cost is artifical because of exemption from fuel taxes and other governmental support for alcohol.)
E.. Added ethanol can reduce the amount of CO produced when cars burn gasoline

2. The molecule hexane is a hydrocarbon with six carbon atoms and no double or triple C-C bonds. The formula of hexane is:

a. C₆H₆
b. C₆H₁₂
c. C₆H₁₄ ....... this is correct
d. C₆H₁₈
e. C₆H₂₄

3. How much energy is needed to heat 100 grams of water from 20^oC to 50^oC?

a. 30 calories
b. 100 calories
c. 2000 calories
d. 3000 calories
- 30 degree temperature change-- need 30 calories per gram
- 100 grams
- 30x100 = 3000
e. 5000 calories

4. The table below lists the energy of some simple bonds

H₂ bond 432 kJ/mole; H-O bond 459 kJ/mole; O₂ bond 494 kJ/mol

How much heat is produced when 1 mole of H₂ burns?

a. 239 kJ
- reaction is H2 + (1/2) O2 ---> H2O
- before: 1 H-H bond and 1/2 (O2 bond)
- before: 432 + (1/2)(494) = 679 kJ
- after: two OH bonds
- after 2 x (459) kJ=918
- difference is 239 kJ
b. 459 kJ
c. 470 kJ
d. 918 kJ
e. 1385 kJ

5. In the U.S. , more energy is produced from ____ than any other source.

a. coal
b. hydroelectric power
c. oil
d. natural gas
e. nuclear power

6. Water hardness affects the ability of soap to clean properly. It is generally caused by:

a. acids in the water
b. bases in the water
c. addition of chlorine to water
d. dissolved Calcium ion
e. bad soap

7. An aquifer is

a. a region of salty water
b. a surface water supply
c. an underground water supply
d. an ancient Roman structure for transporting water (is an aquaduct)
e. a slide at a water park

8 The Bowling Green water supply is subject to periodic episodes of high nitrate and nitrite

content. The water treatment plant deals with such episodes through the use of

a. dilution with other water
- built a reservoir
- filled during safe periods
- used during alterts to keep piped water within safe limits
b. distillation
c. chlorination
d. charcoal treatment
e. warning customers of the high nitrate level, but simply waiting it out.

9 Desalination refers to

a. boiling water and condensing the steam
b. the process that occurs in a water softener
c. dissolving ionic compounds in water
d. passage of water through a semipermeable membrane
e. all processes that making drinkable water from salty water (such as sea water.)

10. Molarity is

a. a unit of concentration (moles per liter)
b. a unit of energy in a reaction (joules per mole)
c. an amount of material (moles of a reactant)
d. the volume of a solution, measured in liters
e. the value of Avogadro's number

11. If you were to cool a bottle of wine until it was half frozen, the remaining liquid

a. would also contain half of the alcohol
b. would contain nearly all of the alcohol
- the ice is pure H2O (solid)
- so all solutes, like alchol, remain in the liquid
c. would contain almost none of the alcohol
d. ...you couldn't do this-- the contents of the bottle would never freeze since alcohol
acts as antifreeze.
e. (no answer)

12. A solution of Hydrochloric Acid has a concentration of 0.0010 Molar H⁺ (or H₃O⁺)

a. The pH is 0.0010
b. the pH is -3
c. the pH is 3
- H+ = 1 x 10-3 M
d. the pH is 7.0
e. the pH is greater than 7

13. Adding lemon juice (which is mainly citric acid) to water will

a. cause the pH of the water to become larger
b. will cause the pH of the water to become smaller
c. will probably not affect the pH
d. has no predictable effect on the pH
e. will change the pH to H₃O⁺

14. Which of the following species is best described as having polar covalent bonds?

a. water, H₂O
b. sodium chloride crystals, NaCl
c. oxygen, O₂
d. Helium, He
e. octane (C₈H₁₈)

15. Acid rain appears to be a less serious problem in the Midwest than in New England because...

a. SO₂ is a major source of acid rain and the Midwest produces less SO₂
b. Volcanoes are a major source of SO₂ and there are no volcanoes in the US Midwest
- there are, of course, no active volcanoes in New England either
c. The Midwest tends to rest on a layer of limestone (a base) that neutralizes
acid rain after it falls.
d. Acid rain is mainly caused by nitrogen oxides associated with automobile traffic and
the Midwest has a lower concentration of vehicles.
e. Both areas experience comparable acid rain and acidic water lands, but the plants and fish found in the Midwest are less susceptible than those in the east.

16. Water quality standards are set by a federal agency known as the EPA. The P in the name

a. comes from the word "Purity"
b. comes from the work "Protection"
- Envionmental Protection Agency
c. comes from the word "Pollution"
d. comes from the Latin word for Lead, Plumbum
e. comes from the word "Public"

17. Beta radiation is

a. the most penetrating of the three forms of radiation
b. is too weak to pose a health risk
c. consists of high energy electrons
d consists of high energy Helium nuclei
e. consists of high energy electromagnetic radiation

18. If the half life of an isotope is 3000 years, how much will remain after 9000 years?

a. 3 times the starting amount
b. 1/3 of the starting amount
c. 1/4 of the starting amount
d. 1/8 of the starting amount
- 1/2 remains after 3000 yrs
- 1/2 of that (or 1/4) remains after another 3000 years
- 1/2 of that (1/8) remains after an additional 3000 years
e. none of it will remain

19. A nuclear reactor contains control rods of Cadmium or similar material

a. the rods absorb neutrons and slow (or stop) the fission reactions
b. the rods are used to absorb heat and transfer it to water, producing steam
c. the cadmium is the fuel and it undergoes fission
d. The cadmium is used to trap radioactive isotopes which would otherwise
escape from the reactor chamber
e. the cadmium rods are actually the product from nuclear reactions

20 The used fuel from a nuclear reactor

a. is highly radioactive; will need to be stored away from people for thousands of years
b. is mildly radioactive, but the radiation only lasts for a period of about five years and then the used fuel can be safely disposed of in an ordinary landfill.
c. consists only of the unfissionable isotopes (like ²³⁸U) that are not radioactive
d. is normally processed, recycled, used indefinitely; thus there is no waste to store
- not that much is actually recycled
- even then, one removes fission prodcuts that are highly radioactive
- those must be stored somewhere
e. since a reactor converts mass entirely into energy (E = mc²), there is no waste remaining from normal operation.

21. The acronym NIMBY is used with respect to nuclear storage sites. In this term, the N stands for

a. Nitrogen
b. Nuclear
c. Neighborhood
d. National
e. Not
- Not in My Back Yard

22. Yucca Mountain (in Nevada) is best known as

a. the site of the first atomic bomb test
b. an underground repository where highly radioactive nuclear wastes have been buried for the past twenty years.
c. an underground repository that is designated for the storage of nuclear wastes but has not been used for that purpose.
- government designated site, yes
- still questions about safety
- has not been completed and has never stored waste (except for some testing)
d. an underground storage site for nuclear wastes that was selected because it has adequate sources of ground water for cooling hot materials.
- no-- clearly want to avoid ground water that would spread radioactivity
e. a highly radioactive thrill ride planned for Cedar Point

23. Which reaction below is typical of the reaction that powers a nuclear power plant?

(All of the equations are balanced and refer to real reactions. Sorry the subscripts and superscripts for isotopes don't line up correctly.)

a. ²³⁵₉₂U -----> ²³³₉₀Th + ⁴₂He
b. ²³⁵₉₂U + ¹_on ----> ¹⁴¹₅₆Ba + ⁹²₃₆Kr + 3 ¹_on
- correct, fission reaction
- caused by neutron
- produces more than one neutron
c. ²³⁸₉₂U + ¹n_o -----> ²³⁹₉₄Pu + 2 ⁰_-1e
d. ²₁H + ²₁H---> ⁴₂He
e. U + O₂ ---> UO₂

24. The radioactive decay of Thorium-234 follows the following reaction.

What is "X" in the reaction?

²³⁴₉₀Th ----> ²³⁴₉₁Pa + X

a. a neutron
b. a beta particle
- upper superscrits (mass ) must balance-- so X has superscript 0
- lower subscripts must balance (charge) -- so X has subscript -1
- that's an electron (very tiny mass, negative charge)
- a beta ray/particle is another way to express X
c. an alpha particle
d. a gamma ray
e. a proton

25. The primary purpose of the Containment Vessel in a nuclear reactor is

a. to hold the water as it is heated to produce steam
b. to cool the steam after it passes through the turbine
c. to keep the rate of nuclear reaction slow and controlled
d. to keep radioactive materials from escaping in the event of failure in the reactor core
e. to keep terrorists from reaching critical regions of a reactor

26. The textbook and the Web page illustrated how we could form images of the thyroid gland by

injecting radioactive iodine into a patient. This works because...

a. The iodine collects in the thyroid and shows up on X-rays
b.The iodine collects in the thyroid and can be detected by radiation from the isotope
c. The iodine is taken up throughout the body, but much less shows up in normal thyroids.
d. Radioactive iodine collects in the thyroid and the radiation damages thyroid tissue; the resulting swelling can be used to locate the thyroid gland.
- that generally sounds like a bad idea just to form an image
- some radioiodine treatment is done to damage (turn down activity) of overactive thyroids
e. Iodine reacts with starch in the body and stains the thyroid blue.

27. Which of the statements below is FALSE

a. Radioactivity was first discovered by darkening of photographic film.
b. Treatment of cancerous tumors with radiation is effective because tumor cells grow
much more rapidly than normal cells and are more easily damaged by radiation.
c. The unit that measures the dosage of radiation is the rem.
d. Over half of the Nuclear Reactors in the US were built after 1980.
e. Separating nuclear isotopes (like ²³⁵U and ²³⁸U) is a difficult and expensive process.

28. Aluminum is a commonly used metal for window and exterior door frames because

a. metallic Al is quite inert and the metal is not subject to oxidation
b. although metallic Al is actually quite reactive, the oxide film that forms protects it from further oxidation
c. metallic Al simply does not form oxides or nitrides and so exposure to air and water causes no reaction
d. all commercial Al products are coated with an inert species such as tin or with
a thin paint-like coating that provides protection.
e. Aluminum reacts as quickly as iron, but it's cheaper and is easily recycled and replaced.

29. Which chemical reaction below best describes the process by which bauxite (aluminum ore) is converted into metallic aluminum

a. 2Al₂O₃ + 3C ----> 4Al +3CO₂
b. 2Al + 6HCl ---> 2AlCl₃ +3 H₂
C. Al⁺³ + 3 electrons^- ---> Al (in an electrolysis cell)..
- true, All Al is manufactured electochemically
- the Hall Process
- (dissolved in a fairly mean solvent, it is true)
d. Al₂O₃ + 2Fe ---> 2Al + Fe₂O₃
e. Aluminum ore contains metallic aluminum which is mechanically separated from rocks and other particles in the ore .

30. Most carbon is the ¹²₆C isotope, but the radioactive ¹⁴₆C isotope is useful because

a. the best quality natural diamonds are nearly pure ¹⁴₆C.
b. C-14 makes the best quality graphite for pencils
c. C-14 is continuously formed in the atmosphere and absorbed by plants and allows us to date ancient wood.
- that's how radiation gets into plant tissue
- after death of plant, no new C (or C-14) is added to that material
- so loss of C-14 can measure age (1/2 gone every 5700 years)
d. no new C-14 has been produced since the universe was formed and the amount remaining lets us date the age of the universe.
e. Buckminsterfullerene (Bucky Balls, C₆₀) only forms from the C-14 isotope
- answers a, b, e must be false
- seldom see any difference in chemical properties based on specific isotope
- all Carbon is equal
- physical properties also virtually identical (cost of isotope separation is high.)

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