Analyzing the “Pop” in Popcorn

Introduction

In this experiment you will use the ideal gas law (PV = nRT) to determine the pressure inside the kernel

when it pops. Corn is a common foodstuff, native to Americans, which appears in many forms: corn on the cob,

corn off the cob, creamed corn, and popcorn. Field corn, which is also fed to livestock, is hung on our doors at

Halloween. Each variety of corn contains different amounts of water, sugars, and starches.

Popcorn is a favorite movie snack. Popping popcorn involves heating the corn until the pressure inside

the kernel is great enough to cause it to burst, turning the kernel inside out and releasing the trapped moisture.

Cooking oil surrounds and softens the kernel shell and provides a medium through which heat can be

transferred from the glass flask to the popcorn.

Procedure

1. Record the atmospheric pressure in the classroom.

2. Using a 10-mL graduated cylinder and the water displacement method, find the volume of the 16

kernels. Record. Dry the kernels.

3. Obtain a special popcorn flask from the tray. Use the special popcorn flasks that are labeled "Popcorn

Lab". Add 2 medicine droppers-full (not just 2 drops!!!) of cooking oil to the 125 mL Erlenmeyer

flask.

4. Record the mass of flask and oil.

5. Add the 16 kernels of corn to the flask (with the oil in it) and measure the mass with flask, oil, and corn.

6. Place a piece of aluminum foil on top of the flask opening. Bend the sides of the aluminum foil around

the flask's mouth and poke some holes in the top. You want to prevent popcorn from flying out of the

flask while allowing heat to escape.

7. Assemble a ring stand with ring, placing wire gauze on top of the ring.

8. Using a utility clamp, fasten the flask to the stand so it sits on the wire gauze.

9. Light a Bunsen burner.

10. Hold the burner, moving it back and forth slowly until the popcorn just begins to pop. Remove the heat

when most of the kernels have popped. Do not burn the popcorn.

11. If you see water condensed on the upper part of the flask, heat that part very gently with the burner until

it disappears. Do not heat the rubber/plastic part of the utility clamp.

12. Let the flask cool completely. Then, carefully remove the flask. Remove the piece of aluminum foil.

Determine and record the mass of the flask and its contents.

13. Dispose of the flask’s contents in the trash. Wash the flask with soap, water, and a test tube brush. Dry

with a paper towel and then set it on the drying rack above the sink. Wash your hands before leaving the

lab.

Safety Precautions

• Vegetable oil is flammable. Heat the flask with care.

• The ring must be fastened onto the rind stand securely. The flask must also be securely fastened to the

ringstand with a utility clamp.

• Do NOT eat the popcorn from the flask. You will be consuming chemicals that have been placed in the

flask during other experiments.

Analyzing the Pop in Popcorn Pre-Lab Name ___________________

The Pre-Lab (Purpose, Pre-Lab Questions, Hypothesis, Data Table set-up) is due before you plan to conduct

the experiment.

Purpose Statement: What is the purpose of this lab?

Pre-Lab Questions: 1. How is popcorn different from field corn?

2. Discuss the process of popping popcorn:

a. When you heat popcorn, what happens to the water inside the popcorn kernels?

b. Why don’t some popcorn kernels pop?

3. What is the purpose of the cooking oil in this lab?

4. What is the pressure of 0.010 mol of water vapor at 200oC if it occupies a volume of 0.0020 L?

5. Calculate the pressure of the 0.010 mol of water vapor at 150oC if its volume is held constant at

0.0020L.

6. What is the relationship between pressure and temperature?

Hypothesis: Will the pressure inside the kernel be greater than or less than the atmospheric pressure in the classroom?

Explain your prediction.

Data Table: Create a data table to record all of the measurements you will make in the lab. Read the procedure and

calculations section to know what data you need to record. If it says to “record” a value include this in your

table.

Data Analysis and Conclusions

1. Complete the required Calculations. Show your work and label your final answer with proper units.

Calculation Work Final Answer

Volume of 16 kernels of

popcorn in liters (aka:

volume of water vapor)

Mass of water lost (in

grams)

Moles of water lost

2. Use the ideal gas law to determine the pressure of steam (water vapor) inside the kernel at the time of

“pop.” Assume that the popcorn pops at the boiling point of cooking oil (200oC). Use the data you

recorded in your data table from the prelab. (PV=nRT) Show your work and label your answer in atm.

3. Find your answer to #2 in pounds per square inch, psi.

4. We made two assumptions that might cause errors in our calculation of the popcorn pressure. Examine

the numbers you used to calculate the pressure in #2. List the two measurements that you did not

measure directly, but instead measured indirectly or assumed.

5. Compare the pressure required to “pop” corn with atmospheric pressure. Explain how this difference

allows popcorn to “pop.”

6. Explain how this lab relates to the concepts of this unit.