Percentage of water in popcorn



Percentage of water in popcorn

Introduction

Popcorn, a cereal grain like wheat or oats, is about 75% carbohydrate (starch) with smaller amounts of protein, fat, minerals, and water. The water plays a critical role in the popping process. When heated, the moisture inside the kernel turns into steam. The hard outer covering of the kernel acts like a seal, causing a build up of pressure inside the kernel. When the pressure gets high enough, the kernel explodes and the starch rapidly expands to create the fluffy “flower” or popcorn. To ensure maximum popping expansion, the corn is carefully cured (dried) until it reaches a certain percentage of water. In this lab you will determine the percentage of water in popcorn and the average number of moles of water in a kernel of popcorn.

Materials & Safety

Open flame: goggles; tie long hair back; beware of hot glass and hot oil

Ring stand, iron ring, two wire screens, Bunsen burner, vegetable oil, beaker tongs

Procedure

1. Add a small amount of vegetable oil (1-2 droppers) to a 400 mL beaker. Measure and record the mass of the beaker and oil.

2. Add 35-40 kernels of popcorn and measure and record the mass of the beaker, oil, and corn.

3. Assemble a ring stand, iron ring, and wire screen as a support for the beaker. You will heat the beaker using a Bunsen burner.

4. Place another wire screen or aluminum foil (perforated) on top of the beaker and pop the popcorn until all or nearly all kernels have popped. Use the beaker tongs to keep the beaker moving to avoid scorching.

5. Let the beaker cool. If any moisture accumulates on the wall of the beaker, evaporate it by “flaming” the beaker. If the liquid does not evaporate from the walls of the beaker, it is oil. Use beaker tongs to handle warm beakers.

6. Place a hot pad on the scale to protect it from high temperatures. Measure and record the mass of popper, oil, and popped corn.

7. Dispose of the popcorn in the trash. Do not eat the popcorn!

8. If time allows, repeat the procedure for trial 2.

9. Clean the beaker and save it for the next class.

Data

Record your measurements and the answers to the analysis calculations in the data table. If time permits, perform two trials.

| |trial 1 |trial 2 |

|Mass of beaker + oil (g) | | |

|Number of kernels of popcorn | | |

|Mass of beaker, oil, unpopped popcorn (g) | | |

|Mass of popcorn before popping (g) | | |

|Mass of beaker, oil, popped popcorn (g) | | |

|Mass of popcorn after popping (g) | | |

|Mass of water in popcorn (g) | | |

|Percent water in popcorn | | |

|Moles of water in popcorn | | |

|Moles of water per kernel of popcorn | | |

Analysis: In all cases, show your calculations.

1. For each trial, calculate the mass of the unpopped corn.

2. For each trial, calculate the mass of water in the unpopped corn.

3. For each trial, calculate the percentage of water in popcorn.

4. For each trial, calculate the number of moles of water contained in the popcorn kernels.

5. For each trial, calculate the number of moles of water per kernel.

6. If two trials were performed, calculate the average for percentage of water in popcorn and the average moles of water per kernel.

7. For each trial, did you have any unpopped kernels? If so, how many?

8. Compile classroom data to determine the classroom average in the table below

| |% water in popcorn |Moles water per kernel |

|Group 1 | | |

|Group 2 | | |

|Group 3 | | |

|Group 4 | | |

|Group 5 | | |

|Group 6 | | |

|Class Average | | |

Conclusions

1. Explain what makes popcorn pop in your own words (i.e., not the words of your lab partner).

2. Explain in your own words how you determined the mass of water in the popcorn.

3. Explain in your own words how you determined the percentage of water in the popcorn.

4. Explain in your own words how you determined the number of moles of water present in the popcorn.

5. State whether the following errors would make the calculated percentage of water higher or lower. Explain your reasoning.

• Unpopped kernels

• Too much oil – some burns off as smoke

• Eating some popped corn before the final weighing, even though you weren’t supposed to.

6. If you had unpopped kernels, how would this affect your results? How did or would you correct for unpopped kernels?

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