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NAME ____________________________
DATE _________
BLOCK #_______
AVERAGE ATOMIC MASS ACTIVITY
Lab Preview
1. What are isotopes? ___________________________________________________________
___________________________________________________________________________
2.
What is the mass number of an element? __________________________________________
___________________________________________________________________________
3.
What is the average atomic mass of an element? ____________________________________
___________________________________________________________________________
The extremely small size of atoms makes it impossible to count them individually or
directly determine their individual atomic masses. As we discussed in class, average
atomic masses depend on the number and masses of isotopes of an element.
In this activity, we will use colored candies to represent atoms in an average atomic mass
calculation. Plain candies will be assigned an imaginary mass number, and peanut
candies will be assigned a different imaginary mass number.
Purpose: To become proficient at calculating average atomic mass of mixtures of isotopes.
Materials:
 1 bag of red candy mixture (peanut and plain)

1 bag of blue candy mixture (peanut and plain)
 1 bag of yellow candy mixture (peanut and plain)

1 bag of orange candy mixture (peanut and plain)
 1 bag of green candy mixture (peanut and plain)

1 bag of brown candy mixture (peanut and plain)
 Calculator (optional)

This activity sheet
Set-up:
Six bags of candy will be placed on each lab bench. Each bag contains candy of a different color (see
materials list). Each bag will be a different “station.” Every bag is labeled with the “mass number” of the
peanut candy and the “mass number” of the plain candy.
SAFETY PRECAUTIONS: DO NOT EAT ANY CANDY USED IN THIS ACTIVITY. EVERY
GROUP IN MORE THAN ONE CLASS WILL USE IT, AND IT IS NOT SAFE TO EAT!
Procedure:
1. Find a partner (groups of 1 or 2, no groups of 3).
2. Each group must go to a different station at a bench. Once a group has chosen a bench, they must stay
at that bench (no examination of samples on the other bench).
3. Note the color of the candy in the bag at the starting station. CHECK TO MAKE SURE THAT
THERE ARE 20 PIECES OF CANDY IN THE BAG.
4. Record the “mass” of the peanut and plain candies that is marked on the bag in the appropriate space in
the data chart provided below.
5. Without opening the bag, count how many peanut candies are in the bag, and record that information
in the appropriate space in the data chart provided below.
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6.
Without opening the bag, count how many plain candies are in the bag, and record that information
in the appropriate space in the data chart provided below.
7. Move around the bench to the next station when instructed to do so.
8. Repeat steps 3 through 7 until the number and masses of each color of candy have been recorded in the
data table below.
Data Table:
Color 
Peanut Candy
“Mass Number”
Plain Candy
Number
“Mass Number”
Number
Blue
Red
Yellow
Orange
Green
Brown
9.
After all data has been recorded in the Data Table, use the information in the data to calculate the
product of number  mass for each type of candy. Record these calculations in the Calculations Table
below.
10. Calculate the average mass of each color of candy, and record these calculations in the Calculations
Table below.
11. Look at the average mass for each color of candy. Is the value closer to the value for peanut or plain?
Record this in the Calculations Table below.
Calculations Table:
Color 
Peanut Candy
Plain Candy
Average Mass
“Mass Number” 
Number of Candies
“Mass Number” 
Number of Candies
total _ mass
total _ candies
Is the average mass
closer to the peanut
or plain candy
mass?
Blue
Red
Yellow
Orange
Green
Brown
Data Analysis
1. Compare the results obtained for average mass with another group at a different bench. How did your
values of average mass for each color compare? ___________________________________________
__________________________________________________________________________________
2.
Does the number of each type of candy affect the value that you get for average mass? _____________
If yes, in what way? __________________________________________________________________
__________________________________________________________________________________