Average Atomic Mass of the Element, Candium
Name: ___________________________
Period: ____________
Purpose:
To analyze the isotopes of candium and to calculate its average atomic mass.
Materials:
a sample of Candium
Triple-beam balance
Weigh boat
Procedure:
1. Get a sample of Candium.
2. ISOTOPE: Separate the Candium into its isotopes. (Each type of candy is an isotope.)
3. NUMBER: Count the number of atoms for each isotope. Record your data. Add up the numbers to get the
total number of atoms of Candium. Record your total.
4. ISOTOPE MASS: Weigh each isotope to get the isotope’s mass. Record the isotopes’ masses. Add up the
masses to get the total mass of Candium. Record the total mass.
5. MASS OF 1 NUCLIDE: Calculate the mass for one nuclide of each isotope by dividing the isotope’s mass by
the number of atoms for that isotope. Record your results.
6. RELATIVE ABUNDANCE: Calculate each isotope’s relative abundance by dividing the number of atoms for
the isotope by the total number of atoms. Record the relative abundances. (This is in decimals.)
7. PERCENT ABUNDANCE: Multiply the relative abundance by 100%.
8. RELATIVE MASS: Calculate the relative mass for each isotope by multiplying its relative abundance by its
“1 nuclide” mass. Record.
9. Add all the relative masses together to get the average atomic mass of Candium.
DATA TABLE
ISOTOPE
NUMBER
TOTAL
ISOTOPE
MASS
MASS of 1
NUCLIDE
RELATIVE
PERCENT
ABUNDANCE ABUNDANCE
RELATIVE
MASS
1) Remember that averages should ALWAYS be between the maximum and minimum values of a measurement or
count. In this case, we are using a weighted average instead of a normal average. This means the average is
weighted to take into account how abundant (or rare) an isotope is. If one isotope is much more common than all
the others, then the average will be near the mass number of that most common isotope.
Is your value for average atomic mass between the minimum and maximum mass numbers? _____________
Does the average favor the most abundant isotope? ____________
2) Was your average atomic mass the same as any of the mass numbers?
3) What is the difference between percent abundance and relative abundance?
4) What should the sum be for all of the individual percent abundances? ________
Relative abundances? ______
5) Why can scientists not find the average atomic mass by simply adding up the mass numbers and dividing by the
number of isotopes?
6) Your neighbors performed the same lab as you, but with a different sample. For the sake of this question, let us
assume that everyone got the same mass number for each isotope. Explain, as concisely as possible, why your
neighbor’s average atomic mass was different than yours even though your mass numbers were the same.
Comparing data would be a good idea!
7) A gold miner collects a sample of gold from a mine in Alaska, which he sends to a laboratory for analysis (so he
knows how much it is worth, etc). A few days later, the miner receives the lab results for the gold sample. The
results included the average atomic mass for the sample, which was 196.89. On the periodic table, the average
atomic mass of gold is 196.97. Does the miner’s sample contain more or less of the most common/stable isotope
of gold?