Title:
Mass Spectrometry
Name _________________________ Hr ___
Purpose:
To use a mass spectrometer to determine each isotope’s mass and percent abundance.
Theory:
Isotopes are atoms of the same element that behave the same chemically but have
different masses. Therefore, the mass of an element stated on the Periodic Table is not a whole
number, but rather the “weighted” average of all the isotopes that naturally occur. “Weighted”
average means that the percent (or fraction) of the naturally occurring isotope must be used to
calculate the atomic mass stated on the Periodic Table. This experiment will serve as a model for
the determination of average atomic masses using a mass spectrometer. A mass spectrometer
uses a large magnet to separate isotopes of a pure element. A sample of the pure element is
vaporized and charged, then shot past a strong magnet. Less massive isotopes are pulled closer
to the magnet as they pass by it. The separated isotopes then run into a wall that records the
relative position and counts the number of all isotopes
All masses are in
atomic mass units,
amu or u
What data is missing from the results of the mass spectrometer above?
What element do you think is represented by the mass spectrometer above?
How to use the data from a mass spectrometer
The following information was collected using the mass spectrometer above.
Lithium-6 has an atom percent abundance of 7.5% and an atomic mass of 6.0151 u.
Lithium-7 has an atomic abundance of 92.5% and an atomic mass of 7.016003 u.
Determine the AVERAGE ATOMIC MASS.
Procedures:
1.
2.
Each of the following elements were purified and analyzed using a mass spectrometer.
For each of the following elements determine the average atomic mass. SHOW YOUR
WORK.
Data:
Potassium
Nuclide
K-39
K-40
K-41
Boron
Nuclide
B-10
B-11
Abundance
93.22%
0.118%
6.77%
Abundance
19.7%
80.3%
Mass
39.0
40.0
41.0
Mass
10.01
11.01
Magnesium
Nuclide
Mg-26
Mg-24
Mg-25
Abundance
11.17%
78.7%
10.13%
Mass
26.0
24.0
25.0
Copper
Nuclide
Cu-63
Cu-65
Abundance
69.09%
30.91%
Mass
62.9
64.9
Which isotope is most abundant?
There are three isotopes of Hydrogen, H-1, H-2, and H-3. The average atomic mass of Hydrogen is
1.01 u.
There are two isotopes of Chlorine, Cl-35 and Cl-37. The average atomic mass of chlorine is 35.45u.
There are five isotopes of Nickel, Ni-58, Ni-60, Ni-61, Ni-62, Ni-64. The average atomic mass of
Nickel is 58.71 u.