IIC.3 Understanding the Mole

[Adapted from: Laboratory Manual accompanying Chemical Principles by Masterton and Slowinski. Modifications by Norma Mackenzie of Charlotte Country Day School, Charlotte, NC. Further modifications by Kathy Kreidler, Thornridge High School., Dolton, IL}


The relative mass of an object is how many times more massive the object is than a standard object. The atomic masses of atoms are all relative masses. They can be considered relative to any particular element. Historically, both oxygen and carbon have served as the reference standard. For our purposes we can also consider atomic masses relative to the least massive element--hydrogen, with an atomic mass of approximately one. Fluorine, with a relative mass of 19, is 19 times more massive than hydrogen, etc. In this laboratory exercise you deal with the relative masses of beans. Then you will be asked to draw a parallel to the atomic masses of elements.


To develop an understanding of the mole concept and molar masses of elements through an analogy with a model system.


Just don't spill the beans!


Part I. Be sure to use the same balance for the entire activity.

  1. In a beaker, count out exactly 100 beans of one type. Discard any beans that differ greatly from an average bean. If you fail to do this, your results will not be accurate.
  2. Put a plastic cup on the electronic balance. Hit the tare button.
  3. Add the beans to the cup; record their mass to the nearest 0.01 g.
  4. Each team member is responsible for one type of bean provided.


  5. Calculate (do not weigh) the mass of one bean of each type. Record the value in the data table. [Note: "Calculate" means to take the total mass of 100 beans and divide by 100 rather than weighing one particular bean.]

  6. Determine the relative mass of each type of bean.

    Relative Mass = (Average mass of one bean/Average mass of the lightest type of bean)

  7. Calculate the number of beans in one relative mass of each bean. Do this by dividing the relative mass by the average mass of one bean.

    Number of beans is = ( one Relative mass/Average mass of one bean)

  8. Check your calculated results in Step 7 by following these steps:

Data Analysis and Concept Development:


  1. What did you find out about the number of beans in one relative mass?
    ( ) same ( ) different

  2. How do your calculated values compare to your measured values?
    ( ) same (within one bean) ( ) different

  3. Compare the volume of the relative mass piles.
    ( ) same ( ) different Why?___________________________

  4. a. What is the average mass of the lightest bean?______________g

    b. What is the relative mass of the lightest bean?_____________g

  5. Among the elements, hydrogen has the least massive atoms an atom of hydrogen has an average mass of 1.66 x 10--24 g. This is very small, but remember it is only one atom! What is the relative mass of hydrogen if it is the least massive element? _____________g

Part II.

Below is a chart reporting the average masses of individual atoms. Calculate the relative mass of each element and record it in the chart. Then look up the molar mass (atomic mass) of each element on a periodic table and record it in the table.

  1. How do the atomic masses found on the periodic table compare to the relative masses you calculated?
    ( ) same ( ) different

  2. What did you find out about the number of atoms of each element in one relative mass?
    ( ) same ( ) different

  3. One mole of atoms contains how many atoms? See page 124 in your text.

  4. How many atoms are in one mole of uranium atoms?

  5. How many grams are in one mole of uranium atoms?

Author: Kathy Kreidler ( our web page at Thornridge High School.