Creating a New Unit: PCU Lab

Creating a New Unit: PCU

Objective:

To devise a new counting unit, use it in calculations, and compare it to the use of a mole.

Part 1:

Procedure:

1. Weigh out 5.0 grams of popcorn kernels on the scale. (Remember to zero out the cup you are measuring them in!).  Count the number of kernels there are in 5.0 grams. This number will be called “1 PCU” (1 popcorn counting unit)

Data:

1. Complete the following equation in your data record:

 1 PCU = ____kernels = 5.0 g of kernels

2. Show how you would calculate the number of kernels in 3 PCUs:  (Remember to follow your steps, what you know, looking, rid of and the data above)

3. Show how you would calculate the number of kernels in 20.0 grams of popcorn:

4. Show how you would calculate the mass, in grams, of 100 popcorn kernels:

5. Complete the table:

Number of popcorn kernels	Number of PCUs	Mass of popcorn kernels (g)
	10
	500
		10.0
		650.0
498
7,000

Part 2:

Procedure:

1. Use the balance to find the mass, in grams, of the container of popcorn kernels.

Data:

1. What is the mass of the popcorn kernels in the container?

2. Use the mass of the popcorn bag and your PCU to determine how many kernels are in the bag. Show your work here, and record your answer on the class data table at the front of the room.  Label with your group number.

3. Based on the class data table, what is the average number of kernels in the popcorn bag?

4. How close to the class average number is the number you found?

5. Explain what could account for the different numbers of kernels calculated by each student.

Part 3:

Pre-Questions:

1. How many popcorn kernels have you determined to be equal to 1 PCU? If you were counting out 1 PCU of marbles, how many marbles would you count out? If you were counting out 1 PCU of each type of bean, how many of each would you count out?

Procedure:

1. Count out 1 PCU of pinto beans. This will be the number of pinto beans equal to the number of kernels in one PCU. Use a balance to determine the mass of 1 PCU of pinto beans and record in the table below.

2. Count out a PCU for yellow lentils, black beans, kidney beans, and peas. Record the data in the table below.

Data:

Type of particle	Number of particles in PCU	Mass of 1 PCU (g)
Pinto bean
Yellow lentil
Black bean
Kidney beans
Peas

1. Is the number of kidney beans in 1 PCU more than, less than, or equal to the number of black beans in 1 PCU?

2. How does the mass of 1 PCU of kidney beans compare to the mass of 1 PCU of black beans? Why is the mass different between the PCU of kidney and black beans?

3. Would 5.0 grams of kidney beans be more than, less than, or equal to the mass of 1 PCU of kidney beans? Would 10.5 grams of peas be more than, less than, or equal to the mass of 1 PCU of peas?

4. Why is a mole a better unit than a PCU for counting atoms?

5. How many particles are in a mole?