Sample Exam Problems

This is simply a collection of the kinds of questions I may ask. For short essay type questions, I have not included full answers, but rather tried to describe the characteristics of a full credit answer.

Some potentially useful constants:

• h= 6.626 x 10^-34 J s
• c=3.00 x x 10⁸ M S
• 1 nm = 10^-9 m
• 1 m = 10⁹ nm

1. Write down the correct chemical name for the following chemical formulas:
   1. N₂O
   2. SiCl₄
   3. NBr₃
   4. KF

   1. dinitrogen oxide
   2. silicon tetrachloride
   3. nitrogen tribromide
   4. potassium fluoride

2. What is the chemical formula for phosphorus pentachloride?

   PCl₅

3. What is the name for the compound formed from bromine (Br) and barium (Ba)?

   barium bromide

4. What is the name for the compound formed from sodium (Na) and sulfur (S)?

   sodium sulfide

5. Classify each of the following as an element (E), a mixture (M) or a compound (C):
   1. nitrogen dioxide Compound
   2. lead Element
   3. orange juice Mixture
   4. selenium Element

6. Describe one problem associated with incomplete combustion of gasoline in automobile engines.

   Many potential answers. Here are some: Incomplete combustion results in the formation of CO (carbon monoxide) and unburnt hydrocarbon fragments. CO is a criteria pollutant regulated by the EPA and has a variety of health effects. Hydrocarbon fragments are involved in the formation of photchemical smog, which has a variety of health and environmental effects. Specific health problems associated with either of these would also be acceptable answers.

7. Choose one of the following pollutants and indicate one major source of this pollutant in the air we breathe.
   1. NO_x (nitrogen oxides)
   2. CO (carbon monoxide)
   3. O₃ (ozone)
   4. SO_x (sulfur oxides)

   Many potential answers, such as:

   • NO_x : transportation, industrial combustion
   • CO : transportation, power gerneration
   • O₃ : transportation, through photochemical smog
   • SO_x : power generation (electric utilities, such as coal power plants)

8. (3 pts) Ozone absorbs radiation in the UV-B (320-242 nm wavelength) range. Why are we so concerned with this wavelength range?

   Several reasons: The UV-B range consists of light (photons) with enough energy to do biological damage. Also, human skin is particularly sensitive to UV-B radiation. At the same time, this range of UV light is not screened out by O₂ and N₂, two major components of out atmosphere (which screen out UV-C light).

9. Explain how the ozone layer protects us from ultraviolet radiation.

   Ozone is able to absorb radiation with wavelengths smaller than 320 nm. Light with this wavelength (or shorter) has enough energy to break bonds in ozone through the following process:

   O₃ + photon --> O₂ + O

10. The National Ambient Air Quality Standard for a particular pollutant is 0.053 ppm. What would this value be in terms of a percent of air ``particles''?

            
         0.053         x          (where
       --------- = ----------      x = %)      -->     x = 0.0000053
       1,000,000      100
    
    or
    
       0.053 ppm        1 %
       ---------  x ------------  = 0.0000053 %
                     10,000 ppm           
    
    
    

11. What two substances make up most of our atmosphere?

    nitrogen and oxygen

12. Name any one criteria air pollutant regulated by the EPA other than ozone and carbon monoxide:

    particulates, NOx, SOx, lead.

13. Describe one reason it is desirable to keep ozone (O₃) levels low in the air we breathe.

    Many different answers. Sample response : ozone is very reactive and has been shown to premature age lung tissue.

14. In the earth's atmosphere, is the atmospheric pressure higher in the troposphere or the stratosphere?

    higher in the troposphere

15. Balance the following equation:

    C₅H₁₂ + O₂ --> CO₂ + H₂O

    C₅H₁₂ + 8O₂ --> 5CO₂ + 6H₂O

16. Balance the following equation:

    SO₂ + O₂ --> SO₃

    2SO₂ + O₂ --> 2SO₃

17. (2 pts) Write 1257 in scientific notation.

    1.257 x 10³

18. Write 7 x 10^-5 in conventional notation.

    0.0000735

19. Name any one product of photochemical smog.

    ozone, NO₂

20. If the AQI (Air Quality Index) value is in the 51-100 range, this corresponds to an air quality rating of:
    1. Good
    2. Moderate ****
    3. Unhealthly
    4. Very Unhealthy
    5. Hazardous

21. (10 points) Fill in the following table for electrically neutral atoms of the isotopes in column 1

    	# protons	# neutrons	# total electrons	# valence electrons	would expect this element to be similar to what other element?
    carbon-14
    chlorine-35

    	# protons	# neutrons	# total electrons	# valence electrons	would expect this element to be similar to what other element?
    carbon-14	6	8	6	4	Si, Ge, Sn etc
    chlorine-35	17	18	17	7	F, Br, I, etc

22. The bright yellow light emitted by a sodium vapor street lamp has a wavelength of 589 nanometers (nm). Convert this to meters.

              1 x 10-9 m
    589 nm x ------------ = 5.89 x 10-7 m
                1 nm
    
    

23. Convert the wavelength above into a frequency v.

        3.00 x 108 m/s 
    v = ----------------- = 5.09 x 1014 /s
        5.89 x 10-7 m
    
    

24. Infrared (IR) photons have less energy than visible photons. A photon with wavelength 700nm corresponds to red (visible) light. Do IR photons have wavelenths shorter than 700nm or longer than 700nm?

    E(IR photons) < E(visible)

    so wavelength(IR photons) > wavelength(visible)

    so:

    IR photons have wavelenths longer than 700nm.

25. 1. How many valence electrons are there in CH₂Cl₂?
    2. Draw the Lewis dot structure for CH₂Cl₂ (C is the central atom).

       CH₂Cl₂ has (1)(4) + (2)(1) + (2)(7) = 20 valence e-

        
               ..
             : Cl :
               | 
           H - C - H
               |
             : Cl :
               ..
       
       
       

26. Draw the Lewis dot structures for O₂ and Cl₂.

       ..    ..           ..   ..
     : O  :: O :        : Cl : Cl :
                          ..   ..
    
    or:
    
       ..   ..           ..   ..
     : O  = O :        : Cl - Cl :
                         ..   ..
    
    
    
    

27. Draw the Lewis dot structures for a neon (Ne) atom.

             ..
           : Ne :
             ..
    
    

28. Using the periodic table as a guide, give the name and symbol of the element that has 6 protons.

    carbon, C

29. Which of the following species is a free radical?
    1. a neon atom (Ne)
    2. a chlorine atom (Cl)
    3. a nitrogen molecule (N₂)
    4. a chlorine molecule (Cl₂)

    a chlorine atom (Cl)

30. A higher frequency of light means:
    1. shorter wavelength and lower energy
    2. shorter wavelength and higher energy
    3. longer wavelength and higher energy
    4. longer wavelength and lower energy

    longer wavelength and higher energy

31. Which of the following species is least likely to be involved in the depletion of the ozone layer by the destruction of O₃ molecules? Hint: consider what you know about ozone destruction and also consider the number of valence electrons.
    1. nitrogen oxide: NO
    2. dichlorodifluoromethane: CCl₂F₂
    3. carbon dioxide: CO₂
    4. an H atom: H

    Carbon dioxide is the least likely. H and NO have unpaired electrons and are free radicals - thus they can destroy ozone. When CCl₂F₂ is exposed to ultraviolet light in the stratosphere, C-Cl bonds are broken and Cl atoms are released. Cl atoms contribute to ozone destruction.

32. Describe a potential health problem associated with the destruction of the ozone layer.

    Many possible answers: increased incidence of skin cancer, effects on the human immune system, environmental effects in plants and animals, etc.

33. What are some of the limitations of the Chapman Cycle in terms of using it to model stratospheric ozone concentration? Specifically, does it over or underestimate stratospheric ozone concentration and why (give 2 primary reasons)?

    The Chapman Cycle overestimates stratospheric ozone concentration due to its failue to include natural processes (such as the influence of the OH radical or NO from natural sources) as well as man-made issues like CFC induced ozone depletion. A full credit answer will include details of the Chapman Cycle as well as information about two specific chemicals or class of chemicals that contribute to lower ozone levels than predicted by Chapman

34. Describe how CFC's destroy ozone. As part of this question, mention how one Cl atom can be responsible for destroying up to 100,000 ozone molecules. Be as specific as possible, using chemical formulas and equations if necessary.

    Many different approachs are possible here. For full credit, there must be some reference to the chemical equations involved in the main ozone depletion cycle, the active species, and reference to or description of the regeneration of Cl* by the cycle. A full credit answer will also indicate the mechanism by which CFC's release Cl atoms in the stratosphere.

35. Describe the major factors involved in the formation of the ozone hole over Antarctica in the Antarctic Spring.

    Many different approachs are possible here. For full credit, there must be some reference to the four main features: the vortex formed in the fall, stratospheric clouds, chlorine containing compounds, and the need for sunlight. The specific chemical equations involved are not neccessary, though reference to sunlight's role in activating chlorine containing compounds is necessary.

36. What advantages does a CFC replacement like HCFC-141b have over CFC-12? How does does the chemical makeup of HCFC-141b influence the molecule's properties compared to similar CFCs? Can HCFC-141b destroy ozone, why or why not?

    Many different approachs are possible here. For full credit, there would be some reference to the lifetime of the gases (see graph page 98), acknowledgment that replacing Cl's with H's influences the molecules properties, a description of those properties and recognition that HCFC-141b still incorporates Cl, and is thus capable of destroying ozone.

37. Describe two of the principles of green chemistry.

    Six of the Twelve Principles of Green Chemistry are described in the text (see page 13).

38. Identify the three components of the Triple Bottom Line

    See section 0.3 in the text, beginning on page 7.

    
    

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