February 2011 Teacher's Guide Table of Contents


Answers to Student Questions

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Answers to Student Questions

Recycling to Survive


      1. What do “rag pickers” do?

Rag pickers” collect plastic objects from wastewater and deliver them to shops for recycling.

      1. Why do so many people in India recycle plastics?

Many in India recycle plastics as perhaps the only way they can earn enough to survive (see article title).

      1. What are the three types of structures for plastics?

The three structural types of plastics are linear, branched and cross-linked.

      1. What is the difference between thermoplastics and thermoset plastics?

Thermoplastics, usually linear of slightly branched polymers, can be reheated and reshaped into different shapes; thermoset plastics, once produced and shaped—and thus crosslinked, cannot be reheated and reshaped. They decompose upon extreme heating, rather than softening.

      1. List two thermoplastics and two thermoset plastics.

Polyvinyl chloride and polyethylene terephthalate are thermoplastics, and polyurethane and epoxy are thermosets.

      1. Name at least 5 uses for plastics in our everyday lives.

Plastics are used in electronic equipment, CDs, DVDs, clothing, cars, and packing for food, beverages and pharmaceuticals, just to name a few.

      1. What is the term for the source materials for almost all plastics?

The source material for almost all plastics is petrochemicals, derived from petroleum and natural gas.


      1. Name the two factors that drive the recycling industry worldwide.

The two factors driving recycling are the decreasing availability of petroleum and natural gas globally, and the almost infinite lifetime of plastics when placed in landfills.

      1. Name and describe the three recycling methods.

a) Physical recycling involves chopping the plastic into small pieces, washing the pieces, and melting them down so they can be molded or spun into new products;

b) Chemical recycling involves reversing the chemical process that produced the plastic in the first place, producing the original raw materials, treating them to remove impurities, usually mixing these recycled raw materials with virgin raw materials, and using them to produce new plastic of the same type; and

c) Thermal recycling involves heating the plastic with hot water and detergent to clean it, to prepare it for molding into new pieces.

      1. What are the health hazards that Ramzan faces in his work?

Ramzan faces possible bodily injury with the sharp blades of the machinery and he faces possible long-term health problems arising from inhalation of the plastic dust mentioned in the article.

Sewage: The Hottest New Resource?


      1. What are the different sources or constituents of wastewater (sewage) that leave a home?

The sources or constituents of sewage include human waste, food, grease, soaps, water from sinks, showers, bathtubs, toilets, washing machines and dishwashers.
      1. What are the four stages of wastewater treatment?


The four stages of treatment are:
a. physical treatment,
b. biological treatment,
c. filtration and
d. disinfection


      1. What three properties of waste material in sewage allow for separation in the physical treatment stage?

The three properties of waste material that allow for separation include size of particles, solubility of various constituents, and the density of the waste material.

      1. What are the three steps used by bacteria to convert nitrogen-containing compounds into free nitrogen gas (N2) that escapes into the atmosphere?

Different types of bacteria first convert the compound ammonia (NH3) into the nitrite ion, NO2 by reacting with oxygen. The nitrite ion is changed into the nitrate ion, NO3 again by reacting with oxygen. Finally, the nitrate ion is converted to nitrogen gas by reacting with an organic (carbon-containing) molecule.

      1. What uses are made of non-potable wastewater that has undergone final treatment?

The wastewater can be used for non-drinking purposes such as irrigation, parks and roof gardens, boat-washing and cleaning tasks in the treatment plant itself.

      1. How is non-potable wastewater used to generate electricity?

In Santa Rosa California, treated wastewater is pumped up into the mountains where it is injected into mile-deep cracks in the earth, re-supplying dried-up geysers. Here the water is heated to boiling by the underground rocks producing steam that can be used to turn generators for electricity production.


      1. What is reverse osmosis as used in the treatment of disinfected effluent?

Reverse osmosis is a process in which water containing viruses and ions of common salts is forced by pressure to pass through a very fine membrane against a concentration gradient.

      1. What is removed from disinfected effluent using reverse osmosis?

Reverse osmosis is used to remove various dissolved inorganic salts.

      1. What is meant by “recharging” through the use of sanitized (disinfected) effluent water?

Recharging involves using perfectly drinkable water from treated effluent to either percolate down through soil that acts as an additional filter or is added to large bodies of water.

      1. What is one of the drawbacks in using chlorine as a disinfectant for wastewater treatment?

Chlorine can react with organic matter (carbon-containing molecules) to form cancer-causing molecules called trihalomethanes.
Drugs Down the Drain: The Drugs You Swallow, the Water You Drink


      1. How does the concentration of pharmaceuticals detected in U.S. drinking water compare to the therapeutic dose of any of the pharmaceuticals?

The highest concentration of any pharmaceutical detected in U.S. drinking water was approximately 5 million times lower than the therapeutic dose.

      1. What are some examples of how pharmaceuticals dissolved in freshwater have affected fish?

Studies have revealed traces of common pharmaceuticals in the brains, livers, and muscles of freshwater fish. In another study, fish exposed to synthetic female hormones from birth-control pills developed both male and female reproductive organs. Another study showed that minnows exposed to antidepressants lost their instinct to avoid predators.


      1. What happens to the active ingredients in a drug when you take it?

When you take a drug, your body uses only a portion of the active ingredients. The rest is excreted and is released into the sewer system when you flush the toilet.

      1. Describe the path wastewater takes when it leaves your home, to when drinking water enters your home again.

Wastewater travels through underground pipes to a sewage treatment plant, where it is treated to remove harmful bacteria and toxins. Liquid discharge from sewage treatment plants is released into rivers, lakes, and reservoirs, where the water eventually is taken up by water treatment plants. The water treatment plants treat water to remove bacteria and other contaminants and produce potable water that is piped to your home.

      1. What did stream testing in 1999 and 2000 in the U.S. reveal?

Water sampling revealed that 80% of the waterways tested contained detectable levels of pharmaceuticals, insecticides, and fire retardants.

      1. What are some drawbacks to using chlorine to disinfect wastewater?

While chlorine completely removes some drugs present in water, others escape chlorine treatment. Another drawback is that chlorine can react with pharmaceuticals and personal-care products to form more toxic compounds.

      1. What are some of the methods scientists are working on to remove pharmaceuticals from drinking water?

Some potential solutions are adjusting the pH of water being treated to improve the effectiveness of chlorine disinfection, the use of activated charcoal filters, ozone treatment, cultivating bacteria to gobble up drugs, and educating consumers on proper disposal.


      1. What are some pros and cons of using ozone as a water disinfectant?

Pros include: Ozone is a more potent disinfectant than chlorine, works over a wide range of temperature and pH levels, and leaves no chemical residue in treated water. Cons include: A lack of a residual effect leaves water susceptible to contamination after treatment and its high energy cost.

      1. Describe the guidelines for disposing of unused medications.

Never flush or pour drugs down the drain unless the accompanying patient instructions advise you to. If no take-back drug programs are available locally, remove drugs from their containers, crush, and mix with an unappetizing substance, then seal in a plastic bag, and throw in the garbage.

Cleaning Up the Air


      1. What is meant by the Carbon Cycle?

The carbon cycle is the movement of carbon within the Earth’s system.

      1. Other than the burning of fossil fuels (coal, oil, natural gas), what are the two other “natural” or biological sources of carbon dioxide in the movement of the gas within the biosphere?

The two natural or biological sources of carbon dioxide are respiration and photosynthesis.

      1. What biological process removes carbon dioxide produced by respiration and decay?

The biological process that removes carbon dioxide is photosynthesis in plants.

      1. How is the respiration chemical equation related to the photosynthesis chemical equation?

The respiration chemical equation is the reverse of the photosynthesis equation with a net energy input for photosynthesis and a net energy output for respiration.


      1. What are the names and chemical formulas for the main greenhouse gases?

The main greenhouse gases are water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3).

      1. Why are the gases listed in question #5 called greenhouse gases?

These gases in the atmosphere are called greenhouse gases because they act like the glass in a greenhouse in which light passes through, is absorbed by various surfaces to become heat (infrared) and is unable to pass back out of the greenhouse glass (or the atmospheric gases).

      1. What human activities have increased the amount of carbon dioxide in the atmosphere?

The primary sources for increasing the amount of carbon dioxide include burning of coal, natural gas and gasoline (in automobiles).

      1. Why does the burning of coal not produce water compared with the burning of other fossil fuels such as natural gas and gasoline?

Coal does not contain the element hydrogen that is found in the molecules of natural gas and gasoline (see the formulas in the article).

      1. To produce the greenhouse effect in the atmosphere, what types of solar radiation (visible, invisible) are involved.

The types of radiation in the atmosphere that are involved in producing the greenhouse effect include most wavelengths of infrared and three types of UV including –C, –B, and –A.
      1. What prevents much of the heat produced at the earth’s surface (land, water, and atmosphere) from escaping into outer space (beyond our upper atmosphere)?


The heat, as infrared, is absorbed by greenhouse gases in the atmosphere where some of the infrared radiation is re-emitted back to earth rather than out into space.

      1. How can the injection of liquefied carbon dioxide gas into old oil wells produce more oil?

The pressure from the carbon dioxide can force more oil up into oil-drilling rigs at the earth’s surface.

      1. What chemical reactions can be used to store carbon dioxide in rock formations rich in magnesium and calcium?

The carbon dioxide can chemically react with magnesium and calcium to form carbonates of the two elements, permanently locking in the carbon dioxide as part of new compounds.

Kilimanjaro: Peering Through Disappearing Ice


      1. The article describes “fossils” for climate and weather. Name three of them.

The article mentions tree rings, pollen, marine sediments, and ice samples. Other acceptable answers, not described in the article, would be corals and microbial life.

      1. Where in the world have most ice cores been collected, and why these locations?

Greenland and Antarctica, because they are relatively easy to access and there is a lot of ice. Lonnie Thompson’s research, described in this article, is important because much of it has taken place in mountainous regions of the tropics in locations difficult to access.
      1. Name the two “greenhouse” gases that are trapped in air bubbles in ice cores and that are of interest to paleoclimatologists. Methane and carbon dioxide are the two greenhouse gases of interest to paleoclimatologists.


      2. Name the sub-atomic particles that a) are the same in all isotopes of a given element and b) are different in these isotopes.

          1. Isotopes of a given element have the same number of protons (because all atoms of a given element have the same number of protons) and electrons (since all atoms are neutral, the number of electrons must match the number of protons) and

          2. isotopes of a given element differ in the number of neutrons.

      1. There are two isotopes of oxygen described in the article. Water made of which of these isotopes vaporizes most easily?

Water made of the more abundant isotope O-16 vaporizes more easily, because it is lighter.

      1. Aerial photographs of Mt. Kilimanjaro show that much of its ice sheet has been lost. What percent has been lost since 1912?

About 85% of Mt. Kilimanjaro’s ice sheet has been lost since 1912.


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