Purpose: To determine the relative abundances of two common isotopes of an
imaginary element, candium.
Materials: Your brain, stapled bag containing a representative sample of candium, any
other supplies you need
Background Information: All elements in the universe have various isotopes, or atoms
of the same element with differing masses or number of neutrons. The percentage of
each of these isotopes in the universe is constant; for example, Cl-35 comprises 76% of
all known chlorine atoms in the universe, while Cl-37 comprises 24% of all known
chlorine atoms in the universe. It is possible to determine these abundances through mass
analysis – Using a mass spectrometer, if the average mass of chlorine can be determined,
and the individual masses of all representative samples can be determined, mathematics
can allow us to calculate the relative abundances.
Procedure: Follow whatever procedure your group deems necessary to figure out the
relative abundances of the isotopes of candium. YOU CANNOT OPEN THE BAG
Calculations: Show any and all calculations, complete with units, keeping mind of
significant figures.
Data: Construct a data table that displays all measured data, as well as the calculated
relative abundances of each isotope.
1. What were the relative abundances of each isotope of candium?
2. Calculate the % error for each isotope given the actual relative abundances. Use
the unrounded numbers or abundances to calculate % error.
3. What is the single greatest source of error in this experiment?
4. Why are the atomic masses on the periodic table not whole numbers?
5. If the isotopes of candium were truly isotopes of elements, and not candy, what
characteristic would they have in common?
6. Copper has two isotopes: Cu-63, and Cu-65. The relative abundance of Cu-63 is
69.1%. What is the average atomic mass of copper? Assume the masses listed
are 63.000 and 65.000.
7. Only two isotopes of boron exist in nature. One isotope is well known: B-11
with a relative abundance of 80.39%. If the average atomic mass of boron is
10.811 amu, what is the mass of one atom of the other isotope of boron?