DMHS Chemistry Name
Activity 9: Calculating the “Atomic Mass” of “Clippium”
Purpose:
To study “isotopes” of the element “Clippium” to understand how chemists calculate atomic mass (weight).
Materials needed:
Given samples of 3 different-sized paper clips
Balance scale
Pen/pencil
Procedure:
1. Obtain the sample of “Clippium.”
2. Separate the sample into three groups (“A”, “B”, and “C”) based on their different sizes. These represent the “isotopes.”
3. Measure the total mass of each group and record it in the table. Also count and record the number of “atoms” in each group.
4. Record the totals in each row as you complete measurements for Step 3.
A / B / C / TotalsTotal mass (g)
Number
Average mass (g)
Relative abundance
Percent abundance
Relative
mass
Analysis:
1. Calculate the average mass of each “isotope” by dividing the total mass by the number of “atoms” of that isotope, and record this in the data table.
2. Calculate the relative abundance of each isotope by dividing its number of “atoms” by the total number of atoms.
3. Calculate the percent abundance of each isotope by multiplying the relative abundance from Step 2 by 100%.
4. Calculate the relative mass of each isotope by multiplying the relative abundance by its average mass.
5. Calculate the weighted average mass of all Clippium particles by adding the relative masses. This is the atomic mass of Clippium.
DMHS Chemistry Name
Activity 9: Calculating the “Atomic Mass” of “Clippium” p. 2
Additional Questions
For questions 1 – 3, use Table 4.3 (in the “red” edition)[Table 5.3 in the “blue”].
1. Explain why the average atomic mass of H is closest to the mass of H-1.
2. Which isotope of O has the greatest mass?
3. Which of these elements have isotopes in a 3:1 ratio?
4. Complete the table below by filling in the number of protons, neutrons, and electrons for each isotope.
Isotope / # of protons / # of neutrons / # of electronsLi-6
N-14
S-33
Zn-67
5. Which isotope is often used by archeologists to determine how old an
artifact might be?