How much “POP” is in your ?

Introduction

Corn is a common , native to the Americas, which appears in many forms: , corn off the cob, , and popcorn. , which is also fed to livestock, is hung on doors at Halloween. Each variety of corn contains different amounts of water, sugars and . Popcorn is a favorite snack. Popping corn involves heating the corn until the pressure inside the kernel is greater than the standard pressure outside the kernel to cause it to burst, which turns the kernel inside out releasing the trapped moisture.

Purpose

To determine the percent water in the popcorn and use the ideal gas law to determine the pressure inside the kernel when it pops. Solve gas law problems.

Pre-Lab Questions: Read the procedures and then answer the following questions on a separate sheet of paper.

1. Explain how to measure volume using the water displacement method. 2. Explain why the popcorn kernels must be dried completely. 3. Why must you start over if you burn the popcorn? 4. Why must any condensation be heated until it disappears?

Safety

1. Wear safety goggles. 2. Heat flask evenly to prevent oil from spattering. 3. Heat with care, oil is flammable. 4. Don’t eat food in the lab.

Procedure

1. Mass 16 kernels of popcorn. 2. Use a graduated cylinder and water displacement to find the volume of the 16 kernels. Dry the kernels completely. 3. Add 1-2 mL of cooking oil and the 16 kernels to a 125 mL Erlenmeyer flask. Find mass. 4. Assemble a ringstand with ring and place wire gauze on top of the ring. 5. Use a utility clamp to fasten the flask to the stand so it sits on the wire gauze. Cover the flask with a piece of foil, poke a few small holes in the foil. 6. Light the Bunsen burner. Hold the burner and move it back and forth slowly until the popcorn begins to pop. Remove the heat when most of the kernels have popped. Don’t burn the popcorn. If you burn the popcorn you will have to start over. 7. If any water has condensed on the top of the flask heat that part until it disappears. 8. Let it cool, then remove cover and mass the flask and its contents. 9. Clean up.

Calculations: Do this on the separate sheet of paper you answered your pre- lab questions on.

1. Mass of unpopped kernels (g).

2. Volume of popcorn (mL).

3. Mass of flask, oil, and popcorn before popping (g).

4. Mass of flask, oil, and popcorn after popping (g).

5. Mass of water lost (g). Subtract Answer to #4 from answer to #3.

6. Calculate the % of water in popcorn. % = Mass of water Lost 푥 100 Mass of 16 Kernels

7. Estimate the pressure of the water vapor at the time of the “POP”.

Use PV = nRT

a) Rearrange to solve for P. b) Use the moles of water lost from #5. ( ) c) R = 0.0821 퐿 (푎푡푚) (푛)(퐾) d) Assume the popcorn pops at the boiling point of the cooking oil (225 °C). Convert to Kelvin. e) Pressure will be in atm.

Popcorn Lab Post-Lab Write-Up

1. Why should you be careful with aerosol cans around heat or flames?

2. Discuss why your ears “pop” when riding in a plane.

A technique has been developed to measure the gas pressure of the water vapor in corn kernels. The table below shows the pressure of water vapor of one as it is heated for 120 seconds. Pressure readings are recorded every 5 seconds:

Time Pressure Time Pressure (atm) (atm) 5 s 0.11 65 s 0.92 10 s 0.11 70 s 1.04 15 s 0.11 75 s 1.26 20 s 0.14 80 s 1.43 25 s 0.15 85 s 1.89 30 s 0.17 90 s 2.47 35 s 0.22 95 s 3.12 40 s 0.28 100 s 0.99 45 s 0.44 105 s 1.00 50 s 0.50 110 s 1.01 55 s 0.69 115 s 0.98 60 s 0.78 120 s 0.99

Choose only one of the prompts below to write up in your post lab.

Prompt A:

At what time did this popcorn kernel pop? Use the data in the table as evidence for your claim. Your reasoning should include an explanation of the motion of the water vapor molecules.

Prompt B:

Compare the temperature and volume of the water vapor at 10 s, 40 s, 70s, and 100s. Use the pressure data in the table to explain your answer. Post-Lab Prompt: A or B (circle the one you are writing about)