• students will be able to describe why a control is important in a scientific experiment
• students will be able to distinguish between variables and controls in a scientific experiment
• students will be able to describe an experiment to determine whether sugarless gum loses as much mass after chewing as regular gum does

A quick read of the nutrition label on a typical pack of bubble gum will show that one piece has a mass of about 8 grams, and of that mass, about 6 grams is sugar. Sugar dissolves readily in water, and about equally well in saliva. Most of the flavor in gum is due to the sugar, which dissolves in saliva and is swallowed, never to be tasted again. Also, the size of a wad of gum decreases considerably in the first 10 or 15 minutes of chewing. This change in volume is due to that same loss of sugar. In the case of sugarless gum, the sweetener used is typically a synthetic compound known as sorbitol, which may be listed as "sugar alcohol" on the nutrition label. It occurs in about the same proportion as does sugar in regular gum, and it also dissolves in saliva, reducing both volume and flavor, just as the sugar in regular gum does.

After students have completed their experiments, have them analyze their data by determining the amounts of mass lost from their gum and determining the percent of mass lost. Help them understand the percent of mass lost is the more important number, since the initial weights of the gum may not have been identical. Thus, if a larger piece of gum lost more mass than a smaller one, both may have had the same proportion of sugar all along. Only by calculating the percent of mass lost can we determine the relative proportions of sugar in different types of gum.

Next, have students prepare graphs of their results. Weights of gum before and after chewing can be shown in a bar graph, and the percentages of sugar in different types of gum can also be compared in bar graphs. If students conducted an experiment to see how the mass changes depending on how long the gum is chewed, they can show their results in an x-y scatter plot, with mass (the dependent variable, since it depends on how long the gum was chewed) on the y-axis and time (the independent variable) on the x-axis.

Then have each group share its finding with the rest of the class. A good way to do this is for each group to prepare a poster. Scientists frequently use posters as an efficient and timely means of communicating with each other when they get together at meetings devoted to a particular topic area. Their posters contain the same type of information a formal paper published in a scientific journal would:

• a descriptive title
• a description of the methods used to conduct the experiment, including diagrams if appropriate
• the results of the experiment, shown in tables and graphs, and summarized in words
• the conclusions drawn from the data

Allow students a day or two of class time to prepare a "semi-formal" poster to display in the classroom. The poster should be formal in the sense that it must give a succinct and objective reporting of the experiment, be neat, and use good grammar and correct spelling. However, students can still be allowed to exercise their creativity in the way they lay out and embellish their posters with color, illustrations, etc.

Because there are several components of the poster's preparation, all students will have opportunities to contribute in ways that highlight their own particular strengths. When their posters are done, each group should present its poster to the rest of the class with a brief summary of the results and conclusions. Other students should be encouraged to ask questions and give feedback to the presenting group.

• Students can conduct Internet or library research to discover some interesting history and facts about chewing gum, including how it is made. Did you know that it is impossible to make chocolate gum?
• This lesson can be used as part of a unit on chemistry, and makes a good way to introduce the biochemically important sugars.