Background

Popcorn is one of our favorite snacks! Who can sit through a movie without a big tub of buttered corn? And what would Halloween be like without popcorn balls or Christmas without popcorn strings on the tree and the big cans of caramel and cheese popcorn? Have you ever wondered what makes hard corn kernels “pop”? There are many different varieties of corn and each contains different amounts a starch, water and sugar. When popcorn kernels are heated in hot oil on the stove or in the microwave, the water trapped inside the hard shell begins to boil and vaporize. Eventually, the pressure inside the kernel causes it to pop open and fluff up. When that happens, the water in the kernel escapes as a gas, leaving only the corn behind.

Objective

What is the pressure inside a kernel of popcorn? What is the percent water present in the average kernel when it pops? You will take lab measurements before and after popping the corn to help you answer these questions.

Equipment

Safety

• Always wear safety goggles when performing experiments in the lab.
• Exercise caution when using a heat source. Hot plates should be turned off and unplugged as soon as they are no longer needed.
• Heat flask/beaker evenly to prevent the oil from spattering. Boiling oil is hotter than boiling water.
• Food in the lab should be considered a chemical not for consumption.
• Wash flask/beaker in soapy water, rinse, and dry.
• Wash your hands thoroughly before leaving the lab.

Procedure

Part 1: Collecting Data

1. Assume that the temperature inside each popcorn kernel is the same as the boiling point of the oil that is used. The table shows boiling point data from the Department of Physics at the University of Illinois at Urbana-Champagne.
2. Use a weighing boat and scale determine the mass of 25 popcorn kernels. Record the mass in the data table below.
3. Assume that the volume used in the Ideal Gas Law is equal to the volume of one kernel. Add about 5 mL of water to a 10-mL graduated cylinder. Record exact volume in the data table below. Then, add the 25 kernels of popcorn and record the volume.
4. Discard the 25 kernels of popcorn and wash out the graduated cylinder.

Part 2: Popping Corn

1. Get 25 fresh popcorn kernels.
2. Cover the bottom of a dry Erlenmeyer flask/beaker with cooking oil using a pipette.
3. Add the popcorn.
4. Record the mass of the flask/beaker, popcorn, and oil.
5. Cover the top of the flask/beaker with aluminum foil and poke several holes so that the water vapor can escape.
6. Use a hotplate set on medium heat to pop the corn, slowly swirling the flask/beaker around with tongs to avoid burning it.
7. IF THE POPCORN BURNS YOU MUST START OVER!
8. Remove the flask/beaker from heat when the kernels have popped. 
9. Carefully remove the foil and use a paper towel to dry any water from the top of the flask/beaker.
10. Be careful when using the hotplate and turn it off and unplug it when you are finished using it.
11. Let the flask/beaker cool.
12. Pour popcorn onto a clean paper towel and count the number of unpopped kernels. Since they did not pop, the water inside them was not released and will not be considered in your calculation of the mass and moles of water in the kernels.

Data

(Don’t forget your units)

Calculations

(show your work for each section in the space provided)

Background

Popcorn is one of our favorite snacks! Who can sit through a movie without a big tub of buttered corn? And what would Halloween be like without popcorn balls or Christmas without popcorn strings on the tree and the big cans of caramel and cheese popcorn? Have you ever wondered what makes hard corn kernels “pop”? There are many different varieties of corn and each contains different amounts a starch, water and sugar. When popcorn kernels are heated in hot oil on the stove or in the microwave, the water trapped inside the hard shell begins to boil and vaporize. Eventually, the pressure inside the kernel causes it to pop open and fluff up. When that happens, the water in the kernel escapes as a gas, leaving only the corn behind.

Objective

What is the pressure inside a kernel of popcorn? What is the percent water present in the average kernel when it pops? You will take lab measurements before and after popping the corn to help you answer these questions.

Available Equipment

Safety

• Always wear safety goggles when performing experiments in the lab.
• Exercise caution when using a heat source. Hot plates should be turned off and unplugged as soon as they are no longer needed.
• Heat flask/beaker evenly to prevent the oil from spattering. Boiling oil is hotter than boiling water.
• Food in the lab should be considered a chemical not for consumption.
• Wash flask/beaker in soapy water, rinse, and dry.
• Wash your hands thoroughly before leaving the lab.

Prelab Questions

You will collect data to determine the pressure inside the kernel when it pops using the Ideal Gas Law (PV = nRT) and calculate the percent of water present in the average popcorn kernel. Read through the lab and determine what measurements to take to collect data that will allow you to make these two calculations.

1. You can assume that the temperature inside each popcorn kernel is the same as the boiling point of the oil that is used. The table shows boiling point data from the Department of Physics at the University of Illinois at Urbana-Champagne. What cooking oil is your group using and what temperature is the kernel as it pops? Convert the temperature to Kelvin to use with the Ideal Gas Law.
2. You can also assume that the moles of water used in the Ideal Gas Laws equation is equal to the moles of water in each kernel. Get the mass of 25 popcorn kernels to calculate the average mass of one kernel. But that’s the total mass of a kernel, how will you figure out the mass of the water? Describe the measurements you will take to determine the mass of the water in one kernel.
3. What equipment will you use to take your mass data?
4. Unfortunately, you can’t use mass in the ideal gas law. What conversion do you need to use to make your data usable?
5. How will you calculate the percentage of water in a kernel of popcorn?
6. Assume that the volume used in the Ideal Gas Law is equal to the volume of one kernel. Describe how you can determine that value using a 10-mL graduated cylinder and water.
7. What equipment will you use to collect the volume data?
8. You can’t use milliliters in the Ideal Gas Law. What conversion do you need to make your data usable?

Procedure for Popping Corn

After collecting mass and volume data following the procedures you outlined in the prelab, it’s time to pop some corn! Follow these steps, keeping in mind that if the popcorn burns, you will need to start over.

1. Get the same number of popcorn kernels to pop as you used to collect your data.
2. Cover the bottom of a dry Erlenmeyer flask/beaker with cooking oil and add the popcorn.
3. Cover the top of the flask/beaker with aluminum foil and poke several holes so that the water vapor can escape.
4. Use a hotplate to pop the corn, slowly swirling the flask/beaker around with tongs to avoid burning it. 
5. Remove the flask/beaker from heat when the kernels have popped. 
6. Carefully remove the foil and use a paper towel to dry any water from the top of the flask/beaker.
7. Be careful when using the hotplate and turn it off and unplug is when you are finished using it.
8. Let the flask/beaker cool.
9. Pour popcorn onto clean paper towel and count the number of unpopped kernels. You will want to make sure to consider these in your final calculations.

Data Collection and Calculations

Use the procedures you outlined in the prelab questions to collect date to calculate the following values. Indicate the data collected and calculations used for each variable.