Download Quiz #5 - Chemistry 108 - Design Thinking in Education

1.
Last Week's lab on Spectrophotometry
(a) What does a spectrophotometer measure?
(b) Light can be reflected, absorbed, or transmitted Be able to give an example of each, citing both the type of light and the
material that it hits. For example, as an example of transmission you might say that visible light is transmitted through glass,
but not through concrete.
(c) Rank these in order of wavelength: meter, millimeter, nanometer, centimeter, kilometer, micrometer.
(d) What type of UV light do all sunscreens protect against? What additional protection do some give and why?
(e) Briefly describe what is meant by the SPF on a sunscreen.
(f) Para-aminobenzoic acid (PABA) is an example of a sunscreen. Does PABA absorb, transmit or reflect UV light when it
hits your skin? PABA protects you from UV-B. Why is UV-B dangerous?
Your sunscreen also should protect you from UV-A. Why?
(g) Spectrophotometers contain one or more different light sources. The bulb of your visible light source was made of glass.
The bulb of the UV light source was not made from glass, but rather from quartz. Why the difference in composition?
2.
Ultraviolet radiation
(a) Is ultraviolet light higher or lower in energy than visible light? Does it have a longer or a shorter wavelength?
(b) Of UV-A, UV-B and UV-C, which is higher in energy? Which is longer in wavelength?
(c) The spectrophotometer that you are using in lab contains a UV source (actually UV-A and some UV-B) (a deuterium
lamp). Why is this made using a quartz bulb rather than a glass bulb? In contrast, the visible source (a halogen lamp) can be
made of glass. Why? (Note: you do not need to memorize the names of the two different light sources.)
(d) The Sun emits electromagnetic radiation of different wavelengths. Review all the figures in your text that we looked
at in lecture.
(e) When visible light hits your mirrored sunglasses, it can be absorbed, transmitted or reflected. Explain the difference.
(f) Can you get a sunburn through the glass windows in your house? Explain.
(g) Explain the process of fluorescence in general terms. Now get specific. When you shine UV-A on a $20 bill, the stripe in
the bill appears orange. What happened?.
(h) Now another example with pale green uranium glass. Under UV-A, this glass appears "fluorescent green." What
happened to the UV-A light when it struck the glass?
(i) Optical brighteners" are added to fabrics. Why? In your answer, explain 1) what makes a shirt look white.
2) what makes it look dingy.
3) what an optical brightener does to a dingy shirt, again making it appear white.
3.
Sunscreens
(a) How do zinc oxide and titanium dioxide function as sun blocks?
(Remember to review chemical formulas with the oxide ion) What is their drawback?
(b) Which part of the UV spectrum is associated with wrinkling and premature aging?
(c) Which part of the UV spectrum is associated with sunburn and skin cancer?
(d) What is the Earth's own sunscreen and from what does it protect us?
(e) PABA was one of the earliest sunscreens. Were early sunscreens for UV-A or UV-B? Why isn't PABA used today?
(f) UV radiation is more of a problem at higher altitudes. Although humans can wear sunscreen, plants cannot.
How has the silver sword plant (found at 10,000 ft) adapted to cope with the higher levels of UV?
4.
Molecules and light
(a) Review:
- What is a molecule (as compared to an atom)?
- How do X-rays, UV, visible and IR light compare in terms of wavelength and energy?
- What is ionizing radiation? What is an ion?
- The word "radiation" can refer to both nuclear radiation and electromagnetic radiation.
Explain the difference (and note why gamma rays and X-rays are a point of confusion).
(b) Light causes different events in a molecules, depending on its wavelength.
Give two examples of: light interacting with a molecule to (1) eject an electron (ionizing radiation) and
(2) to break a bond (non-ionizing radiation).
Actually, for the latter you should be able to give 3 examples.
(b) Oxygen and ozone both absorb UV light. Write equations for both processes.
Which molecule requires more energy to break the bonds?
(c) UV light is not ionizing radiation. What can UV light (especially UV-C) do when it interacts with some molecules?
(d) Write a balanced chemical equation for the formation of hydrogen chloride from chlorine and hydrogen caused by the
bright light made by burning magnesium. Also write a balanced chemical equation for the combustion (burning in oxygen)
of magnesium. Remember: the oxide ion is on your list of ions to know.
5.
More on UV light
(a) Do sunscreens protect against UV-A, UV-B and/or UV-C?
(b) Does the sun emit UV-C radiation? Should somebody market a sunscreen that protects against UV-C? Explain.
(c) Bottom line #1: UV radiation reaching the Earth's surface is not uniform. Explain why.
(d) Bottom line #2: Our skin responds differently to UV wavelengths. Explain the differences.
(e) Bottom line #3: The ozone layer in the stratosphere protects us. Explain how.
6.
The ozone layer and the ozone hole
(a) Explain where and why our ozone layer exists. Also explain what it protects us from and how.
(b) Approximately what is the concentration of the ozone in the ozone layer - 3%, 300 ppm or 300 ppb.
(c) In a word or two, how do satellites measure ozone concentrations?
(d) The ozone hole is not really a hole. Explain.
(e) Explain why the ozone hole forms in the south over Antarctica, but not at the north over Greenland.
(f) How does this year's ozone hole compare with those of the past few years? Were there ozone holes 50 years ago?
(g) In October, what season is it in Australia? Why do white Australians have to take special precaution against sunburn this
time of year, even though it is not summer?
7.
Hydrocarbons, chlorocarbons, and chlorofluorocarbons
(a) Memorize the names/chemical formulas for methane, ethane, propane and butane.
We will be referring to these compounds dozens of times before the semester is out.
(b) Give the names and the chemical formulas for any three chlorocarbons that contain only one carbon atom.
(c) Give the names and the chemical formulas for any three chlorofluorocarbons that contain only one carbon atom.
... stay tuned for more about CFCs and the ozone layer.
NOTE: questions from Chemistry in Context listed on the web site are also possibilities for showing up on this and future quizzes.