Names:_______________________
Average Atomic Mass of “Beanium” Lab
Introduction
On the periodic table, values for atomic number and atomic mass are
given for each element. The atomic number is a whole number that
represents the number of protons in the atom. The atomic mass is a
decimal number because it represents a weighted average of the
masses of the isotopes of each element based on how often each
isotope is found in nature.
Nuclear chemists have discovered what is believed to be element
number 119. The researchers have named this element “Beanium”. There are four naturally occurring
isotopes of beanium: beanium-white, beanium spotted, beanium-brown, and beanium-green. Your job
is to determine the atomic mass of each individual isotope, the percentage abundance of each isotope,
and ultimately the average atomic mass of beanium. One unique property of beanium that should
make this determination particularly easy is that beanium atoms are very large, so sorting the isotopes
of this element should be accomplished with little difficulty.
Purpose
To determine the average atomic mass for the fictitious element “beanium”.
Pre-Lab Questions &amp; Prediction
1.
Chlorine has two isotopes:
mass #
35
37
exact mass
34.968852
36.965903
% abundance
75.77
24.23
Using this information, calculate the atomic mass of chlorine. (Show your work!)
2.
Prediction: In this lab, you will determine the average mass of all the beans together, and also the
average mass of each type of bean based in their abundance. How close do you think these
values will be to each other?
Equipment
balance
beaker (100 mL)
Materials
beans, various types
Safety Considerations
 None for this lab beyond standard lab safety procedures.
Names:_______________________
Procedure
1.
2.
3.
4.
5.
6.
Obtain a sample of beanium isotopes by scooping up a beaker full of beans from the bean
container.
Separate the beans by isotope and count them. Record the total number of each type of bean.
For each isotope sample of beanium, determine and record its total mass.
Determine and record the total mass of your entire sample of beanium.
For each isotope, calculate its average mass and percent abundance
Calculate the average mass for the total sample using the method from Ch. 5
Data and Calculations
White
Spotted
Brown
Green
Total
Mass of each isotope
Number of each isotope
Average mass of each
Percent abundance of each
Clean-up and Disposal
1.
Return your beanium sample to the bean container. DO NOT LEAVE ANY BEANS IN THE SINK
2.
Wash your hands before leaving the lab.
Questions
1.
For all the rows except average mass the “total” column could be found by adding the numbers
across the row. It is an exception because it doesn’t take into account the different abundances of
the different isotopes. Compare the average you found correctly in step 6 to an average mass
found by dividing the total mass by the total number.
2.
Compare your average mass of beanium with that of two other groups. How does your average
mass compare to theirs? Why do you think this happened?
3.
If you were to do this lab over again, what would be more helpful – a more precise scale (i.e.,
0.001 precision instead of the 0.01 we used) or a larger sample of beans? Why?
4.
Neon-20 has a mass of 19.9924 amu, neon-21 has a mass of 20.9940 amu, and neon-22 has a
mass of 21.9914 amu. The relative abundance of Ne-20 is 90.92%, while Ne-21 is 0.257% and
Ne-22 is 8.82%. Using the same techniques that you used in this lab, calculate the average
atomic mass for neon. How does this compare to the value for neon found on the periodic table?