Rationale by taoyni


									                       Materials and the Environment, Part 2

       Rationale: According to the new California Science Standards,
                                                                       rd   th
       students begin learning formally about ecosystems in the 3 and 4
       grades. In the 5 grade, students learn that substances may be
       separated using their chemical and physical properties. The idea that
       substances combine via chemical reactions to form products having
       different properties is introduced. In the 6 grade, students study natural
       resources. They learn about the ecology of the food web and how
       matter is transferred between organisms and the environment.
       Disclaimer: These activities were adapted from the book : “The
       Extraordinary Chemistry of Ordinary Things, 3 Ed.” written by Carl. H.

                                   Part 2: Pollution
    introduces the idea of concentration and uses this idea to explore extent of pollution

                                   Activity Summary:
    Introduction to pollution
    Concentration and the extent of pollution         Part 2 Worksheet Items 1, 2, and 3
    Acid rain demonstration                           Part 2 Worksheet Items 4, 5, and 6

                                      File Summary:
                                      envir_2_doc
                                      envir_2_teachers
                                      envir_2_wksht
                                      envir_2_wksht_key

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               Materials and the Environment, Part 2

Part 2: Pollution
After participating in the program Materials and the Environment, Part 2,
students will be able to:
     explain that pollution is a relative term
     demonstrate how to calculate the concentration of a solution
     describe the origin of acid rain

   pollution - contaminating substance(s) that makes another
       substance (especially water, air, or the environment) unclean or
   concentration - amount (mass or weight) of one substance found in
       a given volume of another substance, usually a solution (e.g.,
   acid - an acid is characterized by a sharp or sour taste, turns blue
       litmus paper pink, and reacts with a base to form salt and water
   base - a base is characterized by a slippery feel, turns red litmus
       paper blue, and reacts with an acid to form salt and water
   neutral - a substance which does not react as would and acid or
   pH - a scale used to indicate the relative basic or acidic nature of a
       solution; low pH numbers (0 to 7) indicate acids and high
       numbers (7 to 14) indicate bases; 7.0 is the pH of a neutral
   sulfur - a pale yellow, non-metallic element that burns with a blue
       flame and a very characteristic odor

Lesson Plan:
   For each small group:
         8 plastic cups or glasses, preferably with straight sides
         water
         set of measuring spoons
         unknown substance (salt or sugar)
         craft sticks for stirring
         ruler
         marker
   For each student:
         16 small tasting cups
         worksheet
   For the teacher/volunteer:
         concentrated red cabbage juice
         diluted ammonia solution
         vinegar
         2 small beakers
         paper towels (white)
         candle
         matches

Teacher/Volunteer Preparation:
1. Make the concentrated red cabbage juice pH indicator solution:
Break up a few leaves of red cabbage into small pieces. Place the
pieces in a pot and add enough water to barely cover the leaves. Boil

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                Materials and the Environment, Part 2

the leaves for a few minutes. The water should have turned a nice deep
blue color. Allow the water to cool and then strain to remove the
cabbage leaves. You now have an acid/base indicator solution. The dye
extracted from the cabbage leaves is an anthocyanin. The structure of
the dye changes with pH. That is why the solution will be green when
basic, deep blue when neutral, and bright pink when acidic.

2. Make a diluted ammonia solution: Add a few drops of ordinary
household ammonia to a glass of water. Try this solution with your
acid/base indicator. If it takes more than a few drops to change a small
amount of indicator from blue to green, add a few more drops of
ammonia to your diluted solution. The smell should not be
overpowering. Important! Mark the container in which you put this
solution as ammonia is poisonous. Keep this container out of reach of
children at all times. Ammonia solutions are not to be drunk or allowed
to come in contact with skin or clothing.

activity 1: 5 minutes
activity 2: 70 minutes
activity 3: 15 minutes

1. (5 minutes)
     What is pollution? Have students offer suggested definitions.
     Can you give some examples of polluting substances? Make a
         list on the blackboard of the responses.
     Is anything really pure?
     What would you consider pure to be? Is pollution when one
         substance is contaminated with a bit of some other substance?
         What about just one molecule?
     Students should be brought to the conclusion that pollution is
         unavoidable so that it is the extent of pollution that matters, not
         that it exists.
     How do we decide on acceptable levels of pollution?

2. (70) minutes
Let’s explore how the extent of pollution with an exercise on
     Split the students into two large groups, A and B.
     Within each large group, students will work in smaller groups
        determined by the instructor. (For a class of 32 students, the
        large groups could be divided into 4 smaller groups of 4 each. If
        work space is a premium, the experiment might work better with
        2 smaller groups of 8 each.)
     Each small group will be provided with eight clear (or
        translucent) plastic cups or glasses (straight sides make this
        experiment more straightforward), a ruler, marker, and an
        unknown substance (group A gets salt and group B gets sugar).
        The directions given below are illustrated in Figure environ_2_1.
         Step 1: Students prepare a standard measure by making a
             mark near the top of one cup. This cup is labeled S.
         Step 2: Label the remaining 7 cups A through G.
         Step 3: Place 1 tsp of the unknown into the standard cup,
             then fill to the mark with water (warm water makes the

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              Materials and the Environment, Part 2

           dissolution go faster but is not necessary). Stir until the
           unknown is completely dissolved.
          Step 4: Pour this solution from cup S into cup A. Calculate
           and record in the table the concentration of cup A. At this
           point concentration may need to be discussed. Students will
           record something like “1 tsp/cup” as the concentration of cup
           A. Here “cup” would mean the volume of the standard cup
           S. If this actual volume is known or is measured (let’s
           pretend the students used 250 ml in their standard cup),
           students could then write “1 tsp/250 ml” as the concentration
           of cup A.
          Step 5: With the ruler, make a mark on cup A that is 1/10 of
           the way down from the water level. Pour this amount of
           solution back into standard cup S. Go over and have
           students record in their worksheets the answers to the
           following question. How much of the unknown is now in cup
           S? (1/10 tsp) Has the concentration in cup A changed?
          Step 6: Fill the standard cup S up to the mark with water
           and stir. Pour this solution into cup B. Calculate and record
           in the table the concentration of cup B. (Students will now
           write answers such as “1/10 tsp/cup” or “1/10 tsp/250 ml”.
           Cup B contains a solution that has been diluted from the
           concentration in cup A by a factor of 10.)
          Step 7: Repeat these steps (make mark 1/10 down from the
           water level, transfer 1/10 of the solution back to cup S, fill
           cup S to the standard mark, stir, pour into new cup, record
           concentrations in the table) five more times, using all the
          Step 8: Prepare tasting cups for the members of the other
           team (match small groups from large group A to those from
           large group B). Each small group will pour some of the
           solution from each cup into a small tasting cup, one tasting
           cup for each member of the other team. Make sure the
           small tasting cups are kept with the larger cups so that they
           don’t get mixed up. For each tasting trial, fill another tasting
           cup for each taster with plain water. The taster should not
           know which cup contains the test solution and which
           contains the plain water.
          Step 9: Have the teams taste each other’s solutions. Start
           with the cup G (most dilute) samples. For example, a taster
           will taste both cups from sample G (one containing cup G
           water and the other containing plain water). This will help
           the taster determine when he/she begins to taste the
           substance. Record in the table when you can taste the
           added substance. Proceed from sample G to F, then E, then
           D, etc. (i.e., from most dilute to most concentrated). When
           do you become able to sense the presence of the added
           substance. What is the substance? When would you
           consider the solution undrinkable?
          Step 10: Discard all solutions and containers. Discuss
           results with the class. Does this experiment help you to
           understand that the extent of pollution is the real issue?

3. (15 minutes)
     Have you heard about acid rain?

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           Materials and the Environment, Part 2

   What kind of damage to the environment can be caused by acid
    rain? Students are given the opportunity to list acid rain damage
    in their worksheets.
   Does anyone know how air pollution causes acid rain? The
    teacher/volunteer will do a demonstration that will illustrate how
    acid rain is made.
   Do you know about acids and bases?
   Can you name some common acids? Have students list the
    ones they know in their worksheets.
   What are some characteristics of an acid? Have students make
    notes on their worksheets.
   Can you name some common bases? Students should list the
    ones they know in their worksheets.
   What are some characteristics of a base? Have students make
    notes on their worksheets.
   If you don’t know what a substance is, how could you tell if it
    were an acid or base?
   One way to do this is to use an indictor. Red and blue litmus
    paper are commonly used by chemists to test for acids and
    bases. We will use a different indicator in our demonstration.
   Show the students the concentrated cabbage juice and tell them
    it contains a natural dye (anthocyanin) whose color depends on
    the nature (acidity or basicity) or the solution it is in. We use a
    pH scale to tell us how acid or base a substance is. The blue
    color we see now indicates a neutral solution. Let’s see what
    happens when we add an acid to it.
   Pour some cabbage juice into a beaker and put a few drops of
    vinegar in it. The color should change to a bright pink. Since we
    know that vinegar is an acid, the pink color indicates the
    presence of acid.
   Have students fill in their pH/color charts as this discussion
   Now let’s see what happens with a base. Pour some cabbage
    juice into another beaker. Add a few drops of diluted ammonia
    solution to this beaker. The solution should turn a nice green
    color. Since we know that ammonia is a base, the green color
    indicates the presence of base.
   Now we know what our indicator is showing us. Let’s use it to
    see how acid rain is produced. Fold the paper towel into a long
    flat shape. Dip one end into the cabbage juice (get several cm
    wet). What color is the end of the paper towel with the cabbage
    juice on it?
   Light a candle. Hold the wet part of the paper towel just above
    the candle. Is there any change in the paper towel? (You are
    looking for a color change. There should be none.)
   Now put a match in the candle flame while holding the paper
    towel just above it. The idea is to ignite the match so that most
    of the fumes go directly to the wet part of the paper towel. After
    the initial flare of the match is over, blow out the match. What
    happened to the paper towel?
   If the students wish, a drop of vinegar can be placed on the
    paper towel in a new spot to confirm that acid is what makes the
    paper towel turn pink (make sure you do this in a place that has
    indicator or no color change will take place).

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               Materials and the Environment, Part 2

       How did the acid get on the paper towel? Students may have
        some ideas here.
       Was it the match paper (or wood) burning? To show that this is
        not the case, repeat the experiment over a different part of wet
        paper towel igniting the paper (or wooden) end of the previous
       The only thing left to produce the acid would be the head of the
        match. Do you remember the flare when the match was lit and
        the smell? Match heads often contain sulfur, S (and
        phosphorus, P) to help the match light easily and burn hot. The
        gas SO2 is often produced when the materials in the match head
        burns. This gas is what you smelled. When the SO2 gas is
        combined with the water on the paper towel, sulfurous acid is
        produced. That is where the pink spot came from. SO2 is
        released into the air by the burning of sulfur in petroleum and
        coal products. SO2 can react with oxygen in the air to form SO3.
        When this gas combines with water droplets in clouds, sulfuric
        acid rain can result. The main contribution of sulfur gases to the
        atmosphere are from human activities (90%) and most of that
        comes from energy generation.
       Do you think that concerns about this type of pollution would
        make energy generation an international issue?

               References and Extension Ideas:
These activities were adapted from the book : “The Extraordinary
Chemistry of Ordinary Things, 3 Ed.” written by Carl. H. Snyder.
Background information on acid rain may be found at the website listed
    1. The Extraordinary Chemistry of Ordinary Things, 3 Ed., Carl. H.
       Snyder, John Wiley & Sons, Inc., New York, 1998.
    2. http://pubs.usgs.gov/gip/acidrain/

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