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 RiceHe - Green Split PeasO - Brown Rice
C - Black BeansFe - Red LentilsN - Brown Lentils
Ar - Blue SprinklesSi - Pearl BarleyMg - Wild Rice

Prepare mixtures of these items according to the following recipes. Note that these abundances are by number, not weight. So measure using dry measure, not a scale.

Below are listed the percentages, and the amount of each element for a total of 10 oz for each substance (Note that the percentages may not add to 100% due to our excluding less significant elements.) In general, 1/8 cup represents 10% of the total amount, and 1 teaspoon represents 1% of the total amount. Place each 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

O -- 44.3% =1/2 c + 4 1/4 tsp
H -- 30.8% = 3/8 c + 3/4 tsp
Mg -- 6.2% = 6 tsp
Si -- 5.5% = 5 1/2 tsp
Fe -- 4.9% = 5 tsp
C -- 4.2% = 4 tsp

Supernova

O -- 42.2% = 1/2 c + 2 tsp
Fe -- 36.7% = 3/8 c + 6 3/4 tsp
C -- 11.1% = 1/8 c + 1 tsp
Si -- 3.7% = 3 3/4 tsp
Mg -- 2.8% = 2 3/4 tsp

Human Body

H -- 61.6% = 3/4 c + 1 1/2 tsp
O -- 26.3% = 1/4 c + 6 1/2 tsp
C -- 10.0% = 1/8 c
N -- 1.5% = 1 1/2 tsp

The Sun

H -- 92.1% = 1 1/8 c
He -- 7.8% = 7 3/4 tsp

Earth's Atmosphere

N --78% = 1 c
O -- 21 % = 1/4 c
Ar -- 1 % = 1 tsp
 

Procedure

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.

An extended version of this activity is still to come.