In this lab, students will be introduced to the concept of percent composition. Students will determine the amount of sweetener in various brands of gum by determining the mass difference of the gum before and after it is chewed.
By the end of this lesson, students should be able to
- define percent composition.
- calculate percent composition.
- Quantitative Chemistry
- Percent Composition
Teacher Preparation: 30 minutes
Lesson: 45 minutes
- Sugarless gum (one piece per student)
- Regular gum (one piece per student)
- wax paper/gum wrapper
- lab handout
- Food should never be consumed in a lab setting, make sure the activitiy is not carried out in a lab setting.
- Chapter 10.3 in the Prentice Hall Chemistry book will assist the student and teacher in learning about percent composition.
- It would be helpful for the teacher to discuss exactly what percent composition is and how to solve for it before he/she begins the lab.
- Students should not mix gums; measure and chew one piece at a time.
- For an advanced chemistry setting, the teacher may require the students to chew each piece 25 times then weigh the gum, chew for another 25 times then weigh the gum, etc. until 625 chews are reached.
- For a lower level chemistry setting, the teacher may have more information already listed on the lab sheet to help guide the students through the lab more thoroughly.
For the Student
Percent composition is a common laboratory procedure that is used to identify a substance. In this lab we will assume that bubble gum has two components, “sugar” and “everything else.” “Everything else” is insoluble and is what will be left behind once you chew the gum and dissolve the sugar. So you will be able to calculate the percent of sugar in the gum, as well as the number of moles of sugar in the gum.
- 2 sticks of gum (regular & sugarless)
- piece of wax paper OR gum wrapper
- lab sheet
- Food should never be consumed in a lab setting; this activity should not be carried out not in a lab setting.
- Collect two sticks of gum (one regular and one sugarless) and a balance.
- Set your balance to zero.
- Unwrap your regular piece of gum but DO NOT CHEW IT YET! Place the gum wrapper on the scale and make sure that it does not show a mass (zero the balance).
- Now place your unchewed piece of gum on the balance and record the mass in the data table below.
- Next, place the piece of gum into your mouth and chew it for five minutes (set your timer!).
- After five minutes, take the gum out of your mouth and place it back on the gum wrapper on the balance, weigh it and record the mass in the data table.
- Now take the sugarless gum and complete steps 3-6 again.
- Complete the data table below. Use the percent composition equation for guidance.
|Mass of Unchewed
|Mass of Chewed
|Mass of Sugar in
|Percent Composition of
Sugar in Gum (g)
To calculate percent composition you will use the following equation
|Percent Composition =||Mass of the Sugar
Total mass of the gum
- How did the percent composition of your two (regular and sugarless) gum samples compare to each other?
- Sugar’s chemical formula is C12H22O11. What is the mass of one mole of sugar? In other words, find the molar mass of the sugar.
- How many moles of sugar were present in your group’s regular gum?
|Mass of sugar in regular gum
|Molar mass of sugar