Download candium lab

*CANDIUM LAB___________________________________
ISOTOPES
BACKGROUND:
The extremely small size of atoms makes it impossible to count them or determine their individual masses
directly. An instrument called a mass spectrometer is used to determine the masses and relative
abundance of atoms of the elements. Because we do not have a mass spectrometer and because knowing
how to do a weighted average is a skill to acquire, today you are going to be the mass spectrometers.
During this lab you will carefully measure and record data which will enable you to perform the
calculations to determine the atomic mass of the fictitious element Candium.
The average atomic mass for an element depends on the relative abundances and masses of all the
isotopes that exist for that element. Isotopes are atoms with the same atomic number having different
masses due to different numbers of neutrons. The atomic mass of an element, as reported on the periodic
table, is the weighted average of the masses of the isotopes of that element. The weighted average takes
into account both the mass and relative abundance of each isotope as it occurs in nature.
In this lab you will carry out experiments and perform the necessary calculations to determine the average
atomic mass of the fictitious element Candium, for which there are three different isotopes. The three
isotopes of Candium are Skittlitium, M&M Peanutium, and M&M Regularium. In this lab each piece of
candy represents an atom. Your job will be to obtained a sample of Candium and determine the relative
abundance of each isotope and the mass of each type of particle. From the data you will calculate the
weighted average mass, or atomic mass, of Candium. Unlike real isotopes, the individual isotopic
particles of Candium differ slightly in mass, so you will determine a representative mass for each type of
isotope. Then, you can calculate the weighted average mass, or “atomic mass”, of Candium.
SAFETY:
DO NOT EAT THE CANDY (until the end of the experiment)
Place the candy on clean paper towels or in clean containers.
FORMULAS FOR CALCULATIONS:
Average mass (g) =
total mass
number of pieces of candy
Relative abundance (decimal form) =
number of pieces of one type of candium
total number of pieces of candy
Relative Mass = relative abundance × average mass
Percent Abundance = relative abundance × 100
PROCEDURE:
1. Obtain a sample of Candium from your teacher.
2. Separate the samples of Skittlitium, M&M Peanutium, and M&M Regularium “isotopes” of
Candium.
3. Place a clean weigh boat on your scale and “zero” out the mass.
4. Take three “atoms” of Skittlium that you feel are representative particles of this isotope and place
them in the clean weigh boat. Divide the mass by three and record this in the table as the “mass of
an atom” for Skittlium.
5. Repeat step 4 for both M&M Peanutium and M&M Regularium.
6. Count the number of particles for each “isotope” in your candium sample and record this in the
data table. Calculate the total.
7. Calculate the percent abundance of each isotope (one type of isotope divided by the total number
x 100). Compute the total for that row.
8. Calculate the relative abundance of each isotope. (Divide the percent abundance by 100).
Compute the total for that row.
9. Calculate the relative mass of each isotope. (Multiply the relative abundance by the respective
mass of each isotope)
10. Add the relative masses to get the weighted average for the Candium element. AHA! YOU
FOUND THE AVERAGE ATOMIC MASS OF CANDIUM!