Lab 8
The Atomic Mass of “Boltium”
Date:
Objective
Calculate the atomic mass of “Boltium”
Background
The atomic mass of any element is the average of the masses
of all the naturally occurring isotopes of an element,
weighted according to the abundance of each isotope.
Take copper for example…
Take any sample of pure copper and run it
through a mass spectrometer…
No matter where the copper came from, it
will separate into the following isotopes:
69.17%: Copper-63, 62.939598 amu
30.83%: Copper-65, 64.927793 amu
The atomic mass is calculated as a weighted average…
62.939598 x 0.6917 + 64.927793 x 0.3083
= 63.55 (rounded)
Experiment
Boltium sample: 50 atoms, separate into 4 different
isotopes (types of bolts)
Calculate in Analysis section
Isotope Isotope Count Total Mass (g) Average Mass (g) % Abundance
(type of
bolt)
(number of bolts of
each type)
(mass of pile)
(Analysis #1)
(Analysis #2)
Analysis
1. Calculate the average mass of each isotope, record
this in the data table.
2. Calculate the percent abundance of each isotope,
record this in the data table.
3. Calculate the atomic mass of “Boltium.” This is a
weighted average that factors in the abundance
and mass of each isotopes of the element.
Results
Questions
1. Explain why the atomic mass of an atom should be a
weighted average.
2. The atomic mass of carbon is 12.011 amu, although no
atom of carbon actually weighs this amount. Explain why
this is so.
3. What did each bolt in this lab represent?
4. This activity was a simulation of how isotopes affect the
average atomic masses calculation. Describe 2 flaws of
this simulation.