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Summary
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
Objectives
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
Time
Teacher Preparation: 15 minutes
Lesson: 30-45 minutes
Materials
For each group:
- Student worksheet
- Popcorn kernels
- Lentils
- Lima beans
- Kidney beans
- Electronic balance
Safety
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
Lesson
Purpose
To explore and utilize a new unit for counting objects (PCU) and to compare this with the concept of a mole.
Materials
- Popcorn kernels
- Kidney beans
- Lentils
- Lima beans
- Electronic balance
Procedure
- Weigh out 5.0 grams of popcorn kernels on the balance.
- How many popcorn kernels are there in 5.0 grams of popcorn kernels? This number is 1 PCU (popcorn counting unit).
- 1 PCU = ___________ particles = 5.0 grams of popcorn kernels.
- Complete the following table.
Type of particle | Number of particles in 1 PCU | Mass of 1 PCU |
---|---|---|
Kidney beans | ||
Lentils | ||
Lima beans |
- 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.
- 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.
- How does the number of kidney beans in 1 PCU compare to the number of lentils in 1 PCU?
- How does the mass of 1 PCU of kidney beans compare to the mass of lentils?
- How can you account for any differences in mass that you observed?
- Name three other substances whose particles you could easily count using PCU’s.
- Why is mole a better unit than a PCU for counting atoms? How many particles are in a mole?
- How would the mass of one mole of iron atoms compare to the mass of one mole of aluminum? Explain.
Analysis
- 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).
- What standard is presently used for the mole?