Name_______________________________Hr. __________ Date_______________________
The Atomic Mass of Candium Activity
Isotopes are atoms of the same element with the same atomic number (number of
protons) but different masses due to different numbers of neutrons in the nuclei. The
atomic mass of an element is the weighted average of the masses of the different
isotopes. The weighted average takes into account both the masses of the isotopes and
their relative (percent) abundance of each isotope as it occurs in nature; therefore the
most abundant isotope contributes the most to the overall atomic mass of the element.
In the laboratory, An instrument called a mass spectrometer can measure the mass of
each isotope and can determine the relative abundance of each isotope in a sample of
an element.
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 performer the calculations to determine the atomic mass of the fictitious
element Candium.
There are 3 isotopes of Candium – Skittlituim, M&M peanutium and Candy Cornium. In
this model each piece of candy represents an atom. You will obtain a sample of
Candium in pre-prepared beaker and determine the relative abundance and mass of
each isotope in your sample. As in real elements, these isotopes each have different
masses. Unlike real elements each atom of a given isotopes does not have the same
mass as other atoms of the same isotope. Therefore you have to determine the average
mass of one atom of each isotope of Candium.
Note= do not eat or dispose of your Candium atoms- they will be used next hour .
Problem: Given the masses and abundances, how is the Average Atomic Mass determined?
Purpose: To determine the Average Atomic Mass of Candium
Materials:
Sketch:
Procedure:
1. Obtain a sample of Candium in a labeled beaker.
2. Separate the three isotopes (m & m’s, Skittles, and Candy corn) and measure the mass
of each isotope. Record in Data Table 1-1.
3. Count the number of peanut M&Ms, Skittles, and Candy corn. Record in Data Table 1-1.
Write your Beaker #/ letter here__________________
Data Table 1-1: Average mass, Percent Abundance, Relative Abundance, and
Relative mass of Candium
Skittles
Peanut
M&Ms
Candy
Corn
Totals
Total Isotope
Mass
Number of
pieces
Average
Isotope mass
Percent
Abundance
Relative
Abundance
Relative
Mass
Average Candium
Weighted Atomic
Mass (amu)
Data Analysis: (Show all work on a bottom of paper)
1. Calculate the average mass of each isotope.
average mass = Total mass of isotope
Number of particles of isotope
2. Calculate the percent abundance of each isotope.
% abundance = number of particles of isotope x 100
total number of particles
3. Calculate the relative abundance of each isotope.
relative abundance = percent abundance of each isotope
100
4. Calculate the relative mass of each isotope.
relative mass = relative abundance of isotope x average mass of isotope
5. Calculate the average atomic mass of all Candium particles.
average atomic mass of Candium = relative mass + relative mass + relative mass