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ACTIVITY in Mole Concept, Kitchen Chemistry. Last updated April 13, 2020.


In this activity, students develop a new method of counting objects, called the PCU, and compare this method to the concept of the mole.

Grade Level

High school


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

  • explain how a mole is used to count atoms.
  • explain why one mole of different elements have different masses.
  • accurately state the number of atoms in one mole of an element.

Chemistry Topics

This lesson supports students’ understanding of

  • Mole concept


Teacher Preparation: 15 minutes

Lesson: 30-45 minutes


For each group:

  • Student worksheet
  • Popcorn kernels
  • Lentils
  • Lima beans
  • Kidney beans
  • Electronic balance


There are no special safety considerations for this activity.

Teacher Notes

  • It may be helpful to have the beans and kernels in small plastic cups to prevent scattering.
  • At the end of the activity, have students present their individual counting units and see if other students can properly use these new units.

For the Student



To explore and utilize a new unit for counting objects (PCU) and to compare this with the concept of a mole.


  • Popcorn kernels
  • Kidney beans
  • Lentils
  • Lima beans
  • Electronic balance


  1. Weigh out 5.0 grams of popcorn kernels on the balance.
  2. How many popcorn kernels are there in 5.0 grams of popcorn kernels? This number is 1 PCU (popcorn counting unit).
  3. 1 PCU = ___________ particles = 5.0 grams of popcorn kernels.
  4. Complete the following table.
Type of particle Number of particles in 1 PCU Mass of 1 PCU
Kidney beans
Lima beans
  1. Count out 1 PCU of kidney beans. Use the electronic balance to determine the mass of 1 PCU of kidney beans. Record this value in the table above.
  2. Count out 1 PCU of lentils and 1 PCU of lima beans, mass them on the balance and record their mass in the table above.
  3. How does the number of kidney beans in 1 PCU compare to the number of lentils in 1 PCU?
  4. How does the mass of 1 PCU of kidney beans compare to the mass of lentils?
  5. How can you account for any differences in mass that you observed?
  6. Name three other substances whose particles you could easily count using PCU’s.
  7. Why is mole a better unit than a PCU for counting atoms? How many particles are in a mole?
  8. How would the mass of one mole of iron atoms compare to the mass of one mole of aluminum? Explain.


  1. Devise a counting unit of your own and use it to count at least five different kinds of particles. Name your unit, describe the standard you use for setting your unit (for example, the standard for PCU is the number of particles in 5.0 grams of popcorn kernels).
  2. What standard is presently used for the mole?