The Atomic Mass of Candium

Laboratory Recordsheet

Purpose

To analyze the isotopes of “candium” and to calculate its atomic mass.

Materials

• sample of candium

• pencil

• balance

• paper

Procedure

Obtain a sample of “candium” that contains three different brands of round, coated candy. Treat each brand of candy as an isotope of candium. Separate the three isotopes into groups labeled A, B, and C, and measure the mass of each isotope. Count the number of atoms in each sample. Make a table similar to the one below to record your measured and calculated data.

Table

Analyze

Using the experimental data, record the answers to the following questions below your data table.

1. Calculate the average mass of each isotope by dividing its total mass by the number of particles of that isotope.

2. Calculate the relative abundance of each isotope by dividing its number of particles by the total number of particles.

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 its relative abundance from Step 2 by its average mass.

5. Calculate the weighted average mass of all candium particles by adding the relative masses. This weighted average mass is the atomic mass of candium.

6. Explain the difference between percent abundance and relative abundance. What is the result when you total the individual relative abundances? The individual percent abundances?

7. The percent abundance of each kind of candy tells you how many of each kind of candy there are in every 100 particles. What does relative abundance tell you?

8. Compare the total values for rows 3 and 6 in the table. Explain why the totals differ and why the value in row 6 best represents atomic mass.

9. Explain any differences between the atomic mass of your candium sample and that of your neighbor. Explain why the difference would be smaller if larger samples were used.

You’re the Chemist

The following small-scale activities allow you to develop your own procedures and analyze the results.

1. Analyze It! Determine the atomic mass of a second sample of candium. How does it compare with the first? Suggest reasons for any differences between the samples.

2. Design It! Design and test methods to produce identical samples of candium. Try measuring mass or volume as a means of counting. Test these methods by counting each kind of candy in each sample you produce. Which method of sampling gives the most consistent results?