UNDERSTANDING THE MOLE
INTRODUCTION
    The relative mass of anything is actually how many times heavier the object is compared to the lightest 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 on 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 actually 12 times heavier than hydrogen.  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.

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

MATERIALS
    Part 1:    4 different types of beans, paper cup, balance
    Part 2:    one mole of each of 5 elements (sulfur, iron, aluminum, zinc, and copper)

Part 1
PROCEDURE
1.)  Zero your balance with the paper cup on it.
2.)  Count out exactly 100 beans of one type.  Discard any beans which differ greatly from an "average" bean. 
      This is important because if you do not do this, your results will not be accurate.  Mass the beans.
3.)  Calculate the mass of one bean by dividing the total mass of 100 beans by 100.  Do this for each type of
      bean.  Record in the data table.
4.)  Determine the relative mass of each type of bean by comparing it to the lightest type of bean.  The
      calculation should look like this:   
            relative mass =      average mass of bean    _
                                   average mass of lightest bean
5.)  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 get a mass of 3.4
      grams.)  Do not throw away any of the relative mass piles of beans because you will be asked questions
      about them later.
6.)  Now 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 = ___ (one relative mass/average mass of one bean)
      Compare this number to the number you got in step 5.

DATA TABLE

 

 

Kidney

Pinto

Navy

Lentil

1.)

Mass of 100 beans (g)
(See steps 1-2 in procedure.)

 

 

 

 

2.)

Average mass of one bean (g)
(See step 3 in procedure.)

 

 

 

 

3.)

Relative mass of beans
(See step 4 in procedure.)

 

 

 

 

4.)

Measured number of beans in one relative mass
(See step 5 in procedure.)

 

 

 

 

5.)

Calculated number of beans in one relative mass (round to whole #)
(See step 6 in procedure.)

 

 

 

 

 QUESTIONS (Part 1)
1.)  What did you find out about the number of beans in one relative mass?  Was it the same for each type of
      bean or different?

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

3.)  Compare the volume of the relative mass piles.  Are they the same or different?  Why?

4.)  What is the average mass of the lightest bean?  What is the relative mass of the lightest bean?

5.)  Think very hard on this one and give a real logical answer.  Why are there always the same number of beans
      in the relative mass?

6.)  Hydrogen is the lightest element and each atom has an average mass of 1.66 x 10-24 grams.  This is a very
      small number, but remember
that it is only one atom.  What is the relative mass of hydrogen if it is the
      lightest element?

Part 2
Below is a chart reporting the average masses of individual atoms of different elements.  Calculate the relative mass of each element and record it in the chart.  Then look up the atomic mass on the Periodic Table and record it in the table.

Atom

Mass of one atom (g)

Relative mass (to hydrogen)
(See #4 in Part 1 Procedure.)

Atomic Mass
(Periodic Table)

# of atoms in one relative mass
(See #3 below.)

hydrogen

1.66 x 10-24

 

 

 

sulfur

5.31 x 10-23

 

 

 

iron

9.30 x 10-23

 

 

 

aluminum

4.49 x 10-23

 

 

 

zinc

1.08 x 10-22

 

 

 

lead

3.44 x 10-22

 

 

 

copper

1.05 x 10-22

 

 

 

QUESTIONS (Part 2)
1.)  How do the atomic masses found on the Periodic Table compare to the relative masses you calculated?
      Were they the same or different?

2.)  What do you know about the number of atoms of each element in one relative mass?  Was it the same or
      different?

3.)  For each of the above elements, find out how many atoms there are in the relative mass you discovered.
      You will have to divide the relative mass in grams by the mass of one atom in grams.  Express your answers
      in scientific notation.

4.)  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 would have the same number.  The number,
      however, is equal to one mole.)

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