Chem proj help 7

Experiment 7 ANALYSIS FOR PERCENT WATER IN

POPCORN

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Purpose: To investigate the percentage by mass of water in commercial popcorn and see if the popping ability is affected by the percentage of water in the kernels before popping. Introduction A kernel of popcorn has three main regions as shown in Figure 7.1: the germ (which is the reproductive part), the pericarp, and the endosperm. The pericarp is a tough shell that can withstand pressures of up to 9 atmospheres. The endosperm is made up of two kinds of starch: hard or translucent starch and soft or opaque starch. Commercial popcorn kernels contain about 13-15% by mass of water for optimum popping ability. When popcorn is heated sufficiently, the water within the kernels is converted to water vapor, which expands with increasing temperature until it bursts out of the pericarp. In the process, the hard or translucent starchy material of the corn fluffs up and becomes “popped” corn. Figure 7.1

Sometimes there is a crack in the pericarp of the kernels allowing the water vapor to slowly leak out. In such a case, no pressure will build up to “pop” the shell, and we have a “dud.” A stale kernel that has lost its water will also not be able to pop and end up as a “dud” as well.

In this experiment you will determine the percentage of water in two brands of popcorn by weighing them before and after they have been popped and the percent duds in each sample. The percent by mass of water is determined as follows:

% water = !"## !" !"#$% !"#$ !"#$ !"#$"%&

!"## !" !"#$"%& !"#$%" !"!!#$ x 100

The percent duds can be determined as follows:

% duds = !"#$%& !" !"#$##%& !"#$"%& (!"!#)

!"#$%& !" !"#$"%& !"#$ x 100

Equipment/Materials Electronic balance, ceramic heat pad, crucible tongs, iron ring, ring stand, wire gauze, lab burner, evaporating dish, 250-mL beaker, 100-mL beakers (2), watch glass, aluminum foil, Orville Redenbacher popcorn (unpopped), unknown Brand X popcorn (unpopped). Warning: Materials provided in the lab are for experiments only. Never consume any of the materials provided for experiments.

Experiment 7: ANALYSIS FOR PERCENT WATER IN POPCORN

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Procedure (Using a pen or pencil, record by hand all of your data and results on the Data Collection and Results Pages.)

1. Obtain a ceramic heat pad and a pair of crucible tongs. Attach an iron ring onto a ring stand, place a wire gauze on top, and place a lab burner below the ring. Position the iron ring at a height such that the tip of the blue cone of the flame would be touching the wire gauze. Adjust as necessary.

2. Heat the wire gauze (without the beaker) for 5 minutes to drive off any moisture that may have collected on it. Turn off the burner after 5 minutes.

3. Weigh and record the mass of a clean and dry evaporating dish. Place exactly 10

kernels of Orville Redenbacher popcorn in the evaporating dish and record the total mass of the dish and kernels. (From the two masses the mass of the kernels can be calculated. This is called weighing by difference. In other words, you are not measuring the mass of the kernels directly, but determining the mass by weighing the dish before and after the kernels have been added.)

4. Obtain a 250-mL beaker and remove any labels that may have been left on it. (They

will char and burn if you don’t!) Wrap the sides (not the bottom) of the 250-mL beaker with aluminum foil to provide insulation (see demonstration setup). Place the evaporating dish on top of the beaker, cover it with a watch glass, and set everything on top of the wire gauze as shown in Figure 7.2.

Ring Stand

Inner blue cone of flame touching wire gauze

Watch Glass Evaporating Dish 250-mL Beaker (wrapped with Al foil)

Wire Gauze Iron Ring

Ceramic Heat Pad

Bunsen burner Crucible Tongs

Figure 7.2

5. Heat the kernels until they pop (roughly 10 minutes). Do not allow the popcorn to burn. After they appear to have stopped popping, continue heating for another 10 seconds. If it starts to smoke, remove the lab burner immediately, and with your crucible tongs, remove the watch glass and place the evaporating dish on the ceramic heat pad. You may have to repeat the experiment if it smoked badly because you would have lost more than water as the popcorn burns!

Experiment 7: ANALYSIS FOR PERCENT WATER IN POPCORN

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6. After the popping is finished, turn off the gas and allow the evaporating dish to cool down. Do not attempt to move it while it is still hot.

7. When the evaporating dish and its contents are at room temperature, weigh

and record the mass. (Objects that you weigh must always be at room temperature or it would give a false mass. Warm objects will heat up the air around it and create a convection current. If it is placed on the balance pan while still warm, the air current will lift up the pan and the mass would appear to be lighter than it actually is. If the mass displayed on the balance keeps increasing, it is a sign that the object is still warmer than room temperature.)

8. Pour the popped corn from the evaporating dish into a clean and dry 100-mL

beaker. Label the beaker “Orville Redenbacher” and set it aside. Use a piece of paper towel to wipe out the evaporating dish. Do not wash your evaporating dish with water.

9. Using the same apparatus and set-up, repeat Steps 3 through 7 with the

unknown brand X of popcorn. After completing Step 7, pour the popped corn into a clean and dry 100-mL beaker and label it Brand X.

10. Count the number of duds in each of the two brands of popcorn.

11. Calculate percentage of water in each brand of popcorn.

Clean-up 1. Discard the popped popcorn in the trash can. 2. Scrub out the evaporating dish with detergent and hot water. 3. Remove the iron ring from the ring stand and return all equipment to the proper

locations. 4. Wipe up your work area. 5. Wipe off and return the safety goggles to the cabinet (or place it in your drawer if

it belongs to you). Note that once you put away your safety goggles, you must leave the lab. Remember to wash your hands before leaving.