• Students should be able to use a balance to find the mass of an object to at least the nearest 0.1 gram.
• It is helpful, but not essential, for students to be able to do calculations involving percents, e.g., 4.2 is what percent of 14?

• a few sheets of aluminum foil (or small plastic weighing boats, if available)
• a few permanent markers
• one piece of gum per student; packaged bubble gum (e.g., Bubble Yum or Bubblicious brands) containing sugar works best for the initial experiment; use only one brand and flavor of gum for the whole class
• several triple-beam balances accurate to 0.1 g (or electronic balances)
• additional gum will be needed for the second set of student-devised experiments; amounts and types depend on what students choose to investigate

1. Procedure for Initial Experiment

• Have each student make a small weighing boat out of a few square inches of foil. This can be made by folding two or three layers of aluminum foil into a 1-2 inch square, and then turning the edges up to make sides about ¼-½ inch high. Students should use permanent markers to label their boats with their names or initials, and the date.
• Have each student find the mass of an unwrapped but unchewed piece of gum, using the weighing boat. Have them measure to the nearest 0.1 g, and tell them not to discard the weighing boats.
• Have students chew their gum for exactly 15 minutes. By this time it should have little or no flavor left.
• Have students put the gum back on the weighing boat. Collect all the chewed gum pieces in their boats on a cafeteria tray and leave them in a dry place for at least 2 full days, and preferably 3 or 4 days.
• Have students find the mass of the dried, chewed gum.
• Have students determine the amount of mass lost due to chewing, and calculate the percent of mass lost.

2. Discussion of Initial Experiment

Let students compare their results with those of other students. Then show students the original gum package, which lists the ingredients and gives nutritional information. Have the students calculate the percent of sugar in the gum based on the package information. Compare this "theoretical" percentage to the "experimental" percentages. The two will be fairly close for most students.

Discuss sources of error for the experiment. Then ask if there was a control for the experiment. The answer is no, and this is an important point to make. How do we know that an unchewed piece of gum wouldn't lose just as much mass by sitting and drying for the same amount of time in the same place that a chewed piece did? (We don't.) What should the control have been? Give students time to think about this. Some will be able to answer that they should have removed a piece of gum from its wrapper and found its mass, but then, instead of chewing it, simply left it on the tray along with the chewed pieces of gum. Then, at the end of the experiment, it would have been re-weighed to find out if its mass changed.

Ask also which variables were controlled and which were not. Everyone chewed for the same amount of time, but did everyone chew at the same rate or with the same vigor? Did some students chew less because they spent a lot of time blowing bubbles? Did everyone chew the same type of gum? Might some people have more or "stronger" saliva than others?

3. Designing the Next Experiment

Questions that can be answered through experimentation should arise naturally from the discussion of the first experiment, and students should also welcome the opportunity to chew gum in class again. Have students work in groups of four to make a written proposal. The proposal should answer these questions:

• What is the question you are asking?
• How will you try to answer it?
• How many trials will you do?
• How will you report your results quantitatively?
• What will be your control(s)?
• What is your hypothesis?

Model answering these questions by applying them to the initial gum experiment. Ask students for the answers to each of the questions as they apply to the first experiment. They may need time to think about some of the questions, but they should be able to respond:

• The question we were trying to answer was, "Can we find out how much sugar is in bubble gum?"
• We tried to answer it by weighing gum, then chewing it until it lost its flavor, then letting it dry, and then weighing it again to see how much weight it lost. (Ideally, students will also realize that it is an assumption that the sugar is was what was actually lost, since in the experiment, there isn't any way to know for sure. The loss of sweet flavor makes the assumption a reasonable one, however.)
• The number of trials is equal to the number of students who chewed gum for the experiment.
• The results were reported as the differences in weight of the gum before and after chewing, and as the percent of sugar calculated from the weight loss. The weight changes could also have been reported in the form of a bar graph, with one bar depicting the unchewed weight, and another bar depicting the chewed weight.
• In the initial experiment, there wasn't a control, but there should have been at least one unchewed piece of gum that was otherwise treated the same way as the rest of the gum.
• The hypothesis was, "It is sugar that gives gum its flavor, and during chewing, the sugar is lost (swallowed), which makes the gum get smaller as it loses flavor."

Make sure students understand the questions, and the answers that apply for the first experiment. Then give students time (20 minutes or so) to agree on questions within their groups and write down their answers to the questions as they apply to their proposed experiment. Each group should come up with its own question and experiment, although some groups may independently generate the same ones.

The following are some examples of student questions and their corresponding hypotheses that turned into successful experiments in the past:

• How will the weight losses compare in sugared gum versus sugarless gum? Hypothesis: Since sugarless gum is supposed to be better for people, it won't contain as much sweetener, so the sugarless gum will lose less mass than sugared gum.
• Would gum chewed in saliva lose more mass than gum chewed in water? Hypothesis: Saliva will cause more sugar, and thus more mass, to be lost than water. Note: After a discussion of controls and variables, this group wisely changed its question to, "Will gum mashed in water in a small beaker lose as much mass as gum mashed in an equal volume of saliva in a beaker?"
• Do different flavors of the same brand of gum contain different amounts of sugar? Hypothesis: Fruit flavored gum tastes sweeter than cinnamon or mint flavored gum, so the fruit flavors will lose more mass.
• Does the amount of mass lost depend on how long you chew the gum? Hypothesis: The longer you chew, the more sugar will dissolve and the more mass will be lost. Note: These students quickly realized that there was a time limit - the length of a class period - for the maximum amount of time they could test. They decided to chew gum for various lengths of time: 5 minutes, 10 minutes, 20 minutes, and 40 minutes, to test their hypothesis. In order to get an adequate sample size, each student in the group needed to chew a fresh piece of gum for each of the time lengths. Fortunately, they were able to obtain permission from a few other sympathetic teachers to chew gum during their classes, so that all the gum could be chewed on the same day.
• Do some brands have more sugar than others? Hypothesis: Sweeter gum tastes better, so the most popular brands will lose more mass.

After the teams get your approval, have them submit their shopping lists, including brand names and number of pieces required. Obtain the gum (students could be asked to provide it if necessary) and let them conduct their experiments.

• Some students may want to compare chewing gum to bubble gum, or compare different types of bubble gum. Since chewing gum and some types of bubblegum come in smaller sizes than the bubble gum used in the initial experiment, students may need to chew more than one piece in order to accurately determine the amount of mass lost during chewing. Advise students to start with quantities of gum that weigh at least 6 grams. Avoid very large wads of gum, however. See Activity Safety Issues above.
• There will be lots of unstructured time while students chew gum for 15 minutes. It would be best to have a reading assignment or some other short activity students can work on while they are chewing.

• In a written assignment, ask students to explain why a control should have been used in the initial gum experiment.
• In a written assignment, ask students to describe an experiment to determine whether sugarless gum loses as much mass after chewing as regular gum does.

Acknowledgements: