PURPOSE: To better understand the mole system and the table of atomic masses by comparison with a model system.

DISCUSSION: The relative mass of anything is actually how many times heavier the object is compared to the lighter object. The atomic masses of the atoms are all relative masses. They are relative to the lightest element, which is hydrogen. Although modern atomic masses are based in the Carbon- 12 isotope, hydrogen is still assigned a mass of one and the comparison is still valid for our purposes. Carbon, which has a relative mass of 12, is 12 times heavier than the hydrogen and so on. In this lab you will be dealing with the relative mass of beans and then you will be asked to draw a parallel to the atomic masses of the elements.

MATERIALS:

  • 4 different types of beans (100 count of each)
  • Styrofoam cup
  • A balance
  • One mole of each of five substances to be located around the room: sulfur, iron, aluminum, zinc, copper

PROCEDURE:

  1. zero your balance with the paper cup on it (or any other suitable container)
  2. Count out exactly 100 beans of one type discarding any beans, which differ greatly from an average bean. This is important because if you do not do this or your results will not be accurate. Mass the beans.
  3. Calculate the mass of one bean by dividing the total mass of 100 of them by 100 do this for each type of bean and record in a data table.
  4. Determine the relative mass of each type of bean by comparison to the lightest type of bean the work should look like this:

Average mass of bean

Relative Mass = ------

Average mass of lightest bean

Mass out (do not calculate) the relative mass (in grams) of each kind of bean and count the beans massed. In other words if the relative mass is 3.4 then find out how many beans it takes to mass 3.4 grams. Do not throw away your relative mass piles of beans because you will be asked questions about them later.

DATA TABLE

Bean 1 Bean 2Bean 3 Bean 4

Mass of 100 beans

Aver. Mass of 1 bean

Relative mass

# of beans in relative mass

WRITE UP: Your write up should follow the standard form and should include the above data table. In addition all of the following questions should be answered in complete sentences and all calculations should be shown.

Your conclusions should be in the form of a paper entitled "The Mole". This paper should include what the mole is and how the mole works. In other words why do relative masses of atoms (atomic masses) contain the same number of atoms? Why do the volumes of the relative masses vary? Also include anything that you may have discovered by doing this lab.

THOUGHT QUESTIONS:

  1. What did you find out about the number of beans and the relative mass?
  2. Think very hard on this and give a real logical answer. Why are there always the same numbers of means in the relative mass?
  3. Compare the volume of the relative mass piles. Are they the same, different? Why or why not?
  4. Compare the mass of the relative mass piles of beans. Are they the same? Why or why not?
  5. What is the mass of the lightest bean? What is the relative mass of the lightest bean?
  6. Hydrogen is the lightest element and each atom masses 1.66 10 -24 grams. Very small because we are dealing with only one atom. But, what is the relative mass of hydrogen if it is the lightest element.
  7. Following is a chart with the masses of individual atoms. These masses are actually calculated. Figure out the relative masses and put them on the chart. In other words, compare to the lightest atom.

AtomMass of one atomRelative Mass

Hydrogen 1.66  10-24

Sulfur5.31  10-23

Iron9.30  10-23

Aluminum4.49  10-23

Zinc1.08  10-22

Lead3.44  10-22

Copper1.05  10-22

  1. Now look up the atomic masses and comment.
  2. What are the atomic masses and how were they determined?
  3. What do you know about the number of atoms in a relative mass of atoms?
  4. For each of the above elements find out how many atoms there are in the relative masses you discovered. You will have to divide the relative mass in grams by the mass of one atom in grams. Express your answers in powers of 10.
  5. So. How many atoms are there in an atomic mass of any atom if the unit is grams? (Remember this number was not really known for many years. The actual number is not important but what is important is that it was always known that in the same relative masses you have the same number.) The number, however, is equal to one mole.

On a table in the room you will see the relative masses (moles) of several elements. Go over and look at these masses as you answer the following questions:

  1. Why do the size (volumes) of the relative masses of the elements vary if they have the same number of atoms?
  2. Why does the mass of the relative masses of the atoms vary if they have the same number of atoms?