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LAB in Half Lives, Graphing, Unlocked Resources, Kitchen Chemistry. Last updated October 14, 2019.

Summary

In this lab, students will use licorice to better understand the concept of half-life.

Grade Level

High school

Objectives

By the end of this lesson, students should be able to

  • Understand what a half-life is.

Chemistry Topics

This lesson supports students’ understanding of

  • Half-life
  • Radioactive decay

Time

Teacher Preparation: 30 minutes

Lesson: 50 minutes

Materials

  • 2 pieces of licorice

Safety

  • 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.

Teacher Notes

  • Students could work individually or together.

For the Student

Lesson

In this activity, you will develop your understanding of half-life using licorice.

Procedure

  1. 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.
  2. Place one piece of licorice on the y-axis. This is the original amount of radioisotope.
  3. Break the second licorice in half. Place one half on your graph at 1 on the x-axis.
  4. Break the remaining half in half again. Place one piece at 2 on the x-axis.
  5. Continue this process until the remaining piece is too small to break in half.
  6. On your graph, make a small pencil mark at the top of each piece of licorice.
  7. Remove the licorice and draw a smooth line through your marks.

Analysis

  1. What is the shape of the line on your graph?
  2. How would you describe what happens to the amount of licorice after each step?
  3. Suppose the units on the x-axis are seconds. What is the half-life of your licorice?
  4. 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.
  5. 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?
  6. 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?