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Here’s a lesson you can sink your teeth into – calculating the percent composition of gum
9, 10, 11, 12
Title – Percent Composition of Gum
By – Jennifer Thomas
Primary Subject – Science
Grade Level – 9-12
Concept / Topic To Teach:
Percent Composition of Compounds
Standards Addressed: NC Standard Course of Study for Chemistry 2.02
General Goal(s): Students will understand the concept of percent composition of compounds and be able to perform the associated calculations. A lab will be used to reinforce the concept.
Specific Objectives: Students will be able to define percent composition. Students will be able to calculate the percent composition of a compound.
Required Materials: Calculator, Balances, Chewing Gum, Paper Cups
Anticipatory Set (Lead-In):
How do you calculate percent? (Part/Whole x 100)
How do you calculate the grade on your test?
(Number of points you got/Total Points x 100)
We’re going to do the same thing for elements in compounds
Define percent composition – gives the percent of mass each element contributes to the compound
Give formula: Mass element / Total Mass Compound x 100
NaCl 1(22.99 g/mol) + 1(35.45 g/mol) = 58.44 g/mol
% Na = 1(22.99) / 58.44 x 100 = 39.3%
CaF2 1(40.08 g/mol) + 2(19.00 g/mol) = 78.08 g/mol
% Ca = 1(40.08) / 78.08 x 100 = 51.3 %
% F = 2 (19.00) / 78.08 X 100 = 48.7 %
Plan For Independent Practice: Give students 2 practice compounds that include subscripts and polyatomic ions
Lab Activity: Calculate Percent Composition of Chewing Gum
We’re assuming chewing gum has 2 components – gum and sugar. The sugar will dissolve when you chew it, leaving behind only the gum. Thus we can calculate the percent of sugar in the gum.
This works best with 4-5 students in a group. Each student gets a piece of gum.
Get the mass of a paper cup. Unwrap the gum and put all sticks in the cup. Get the mass of the gum + cup. Calculate the mass of the gum. (This is “total” gum – includes gum and sugar).
Each person chews their piece of gum for 5 minutes. Then everyone puts chewed gum in the cup. Get mass of chewed gum + cup. Calculate mass of chewed gum. (This is just the gum, no sugar.)
Calculate the mass of sugar in the gum. (Total gum – chewed gum)
Calculate the percent sugar in the gum. (mass sugar/total gum x 100)
1) Would a dentist recommend chewing this gum? Why or why not?
2) Would changing the number of pieces of gum change the results of the lab? Explain.
Assign Homework – calculate the percent composition of 3 compounds.
Possible Connections To Other Subjects: Math
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