Chemistry Name:_______________________

Fall 2002

 

Isotope Abundance Using M&M’s

(It’s the Melts In Your Mouth, Not in Your Lab Activity)

Objective:

To demonstrate how isotope abundance and exact mass is used to determine average atomic mass.

Introduction:

According to Dalton’s atomic hypothesis, all atoms of the same element are identical. This notion of the atoms, however, is somewhat outdated, as not all atoms of the same element possess the same number of neutrons (possess a different atomic mass). It is in this spirit, a cavity-producing form of torture, involving candy, has been selected for you.

            J.J. Thomson was the first to note that atoms of an element can have different masses but behave chemically the same.  His student, F.W. Aston, developed the mass spectrometer and studied these atoms. These atoms are called isotopes.  They have the same number of protons, but a different mass due to a varying number of neutrons.  These isotopes can occur in different percents in nature.  The average atomic mass is determine by multiplying the abundance (percent) of the isotope as found in nature by the mass of that isotope for each isotope and then adding these results.

(%X1).(massX1) + (%X2).(massX2) + (%X3).(massX3) + (etc) = average atomic mass

 

Equipment:

M&M’s     Calculator     Graph Paper (Excel)

Procedure:

1. Pour a small bag of M&M’s on the paper towel on the desktop. Start by counting each color. Each  color represents an isotope of the same element, Escolarenium. Determine the isotopic abundance of each isotope (how many of each color are there?)

 

2. Given below are the exact masses of each isotope in CMU’s (Candy Mass Unit).

Isotope                 Red                 Green                 Brown    Orange   Yellow                 Blue                 Purple 

Exact Mass(mg)                298.99                 299.99                 300.98                 301.99                 302.99                 303.98                 304.98

 

 

Questions/Conclusion:

Analysis and Calculations:  (Show and label your calculations in the space provided.)

1.  Determine the percent, to the tenth, of each "mini M&M isotope" in your bag?

2.  What is the average atomic mass of the "mini M&M atom" in your bag?[Hint: use the equation in the introduction]

3.  Use a graph to represent the percent of each "mini M&M isotope" in your bag.