What's Out There?
(Based on an idea by Stacie Kreitman, Kilmer Middle School, Falls Church, VA)
This exercise allows students to calculate the abundance of elements in different substances.
Materials and Preparation:
Each element is represented by a different food found in a kitchen. Below are suggested items for different elements. Different colored candy sprinkles also work well. Each item should be approximately the same size.
|H -White Rice ||He - Green Split Peas ||O - Brown Rice|
|C - Black Beans ||Fe - Red Lentils ||N - Brown Lentils|
|Ar - Blue Sprinkles ||Si - Pearl Barley ||Mg - Wild Rice|
Prepare mixtures of these items according to the following recipes for the substances we are modeling. Note that these abundances are by number, not weight. Because these items are approximately the same size, using dry measure (which measures volume) is equivalent to measuring numbers of atoms.
For each substance, the recipe gives the abundance and the amount of each element. The measured amounts total to approximately 1.25 cups, where 1/8 cup represents 10% abundance, and 1 teaspoon represents 1 % abundance. Note that the percentages may not add to 100% due to excluding less significant elements. Place each mixture into a separate jar or bottle. (11 oz. plastic water bottles work well). Cap all the jars/bottles. Seal some of them using superglue, but leave others that can be opened.
|Carbonaceous Chondrite ||Supernova ||Human Body|
|O: 44.3% 1/2 c + 4 1/4 tsp ||O: 42.2% 1/2 c + 2 tsp ||H: 61.6% 3/4 c + 1 1/2 tsp|
|H: 30.8% 3/8 c + 3/4 tsp ||Fe: 36.7% 3/8 c + 6 3/4 tsp ||O: 26.3% 1/4 c + 6 1/2 tsp|
|Mg: 6.2% 6 tsp ||C: 11.1% 1/8 c + 1 tsp ||C: 10.0% 1/8 c|
|Si: 5.5% 5 1/2 tsp ||Si: 3.7% 3 3/4 tsp ||N: 1.5% 1 1/2 tsp|
|Fe: 4.9% 5 tsp ||Mg: 2.8% 2 3/4 tsp|| |
|C: 4.2% 4 tsp|| || |
|The Sun ||Earth's Atmosphere|| |
|H: 92.1% 1 1/8 c ||N: 78.0% 1 c|| |
|He: 7.8% 7 3/4 tsp ||O: 21.0% 1/4 c|| |
|Ar: 1.0% 1 tsp|| || |
Give the bottles to the students, with each pair of students working on one bottle. Also give them a copy of the key as to what element each type of object represents. Have the students estimate the composition of the bottles by giving the fraction of hydrogen, fraction of helium, etc. Note that students with bottles that can be opened can directly sample the material, but those with sealed bottles must estimate visually.
Now give the students the abundances for the different objects. Have the students determine what type of object their bottle represents. You may choose to leave the Human Body off the list and treat it as a "mystery." The students should determine what it could be.
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