In this lab, students will use licorice to better understand the concept of half-life.
By the end of this lesson, students should be able to
- Understand what a half-life is.
This lesson supports students’ understanding of
- Radioactive decay
Teacher Preparation: 30 minutes
Lesson: 50 minutes
- 2 pieces of licorice
- Food in a lab should be treated as a chemical and not consumed.
- If you allow students to consume the licorice after the activity, make sure to complete the activity away from a lab setting, chemicals, or other harmful materials. Have students handle their own licorice.
- Students could work individually or together.
For the Student
In this activity, you will develop your understanding of half-life using licorice.
- On the graph paper provided (see page 2), label the y-axis as “Amount” and the x-axis as “Half-Life.” Number the x-axis from 1 to 10.
- Place one piece of licorice on the y-axis. This is the original amount of radioisotope.
- Break the second licorice in half. Place one half on your graph at 1 on the x-axis.
- Break the remaining half in half again. Place one piece at 2 on the x-axis.
- Continue this process until the remaining piece is too small to break in half.
- On your graph, make a small pencil mark at the top of each piece of licorice.
- Remove the licorice and draw a smooth line through your marks.
- What is the shape of the line on your graph?
- How would you describe what happens to the amount of licorice after each step?
- Suppose the units on the x-axis are seconds. What is the half-life of your licorice?
- Using your graph, determine whether this statement is true or false. Explain your answer. Half-life means that half of a sample decays after one half-life and the rest of the sample decays after the next half-life.
- One reason it is important to know the half-life of a sample is to safely dispose of radioactive waste, which is usually stored for 10 half-lives. If you have 250 g of radioactive waste, how much of the sample would be left after 10 half-lives?
- Radioisotope A has a half-life of 2 minutes. Radioisotope B has a half-life of 2 hours. Which one would have a larger amount left after 5 hours has elapsed?