Bubble Gum Lab!Step 1 – Measure mass of empty cup. Record.Step 2 – Unwrap a piece of gum for each

member of your group and place in the cup. Measure mass of cup again.

Step 3 - Subtract masses to get mass of gum alone. Record.

Step 4 – Chew one piece of gum each.

The Law of Definite ProportionsThe law states: “The elements in a chemical compound are

always in the same proportions by mass”

Eg. Humans use water in its many forms for recreation (swimming, ice skating, skiing) What is the chemical composition for water in all of these scenarios?

H2O

How do you calculate percent?

How do you calculate the grade you got on your test?

Percentage compositionIndicates the relative amount of each element

present in a compound.

Calculating percentage compositionStep 1 : Calculate molar mass

Calculating percentage compositionStep 1 : Calculate molar mass

Step 2 : Divide the subtotal for each element’s molar mass by the total molar mass.

Calculating percentage compositionStep 1 : Calculate molar mass

Step 2 : Divide the subtotal for each element’s molar mass by the total molar mass.

Step 3: Multiply by 100 to convert to a percentage.

Example 1

Calculate the percentage composition of water, H2O.

Example 1Calculate the percentage composition of water,

H2O.

1. Calculate the molar mass of H2O.

Step 1 – H- 2(1.01)= 2.02 O – 1(16.0)= 16.0 ________ 18.02 g/mol

2. Divide the subtotal for each element’s molar mass by the total molar mass.

2. Divide the subtotal for each element’s molar mass by the total molar mass.

Step 2 Hydrogen 2.02/18.02 X 100 = 11.21%

Oxygen 16.0 /18.02 X 100 = 88.79 %

2. Divide the subtotal for each element’s molar mass by the total molar mass.

Step 2 Hydrogen 2.02/18.02 X 100 = 11.21%

Oxygen 16.0 /18.02 X 100 = 88.79 %

Water is composed of 11.21 % hydrogen and 88.79 % oxygen.

Note: 11.21 + 88.79 = 100% **(total is always 100)**

Example 2

Calculate the percentage composition of sucrose , C12H22O11.

Example 3Find the percentage composition of hydrogen

in sulfuric acid. (H2SO4)

Bite the Bubble: A Chemistry Mini-LabObjective: To calculate the percentage of sugar in various types of

gum. (Assume chewing gum has 2 components; sugar and gum)

Step 5 - Collect the gum back in the cup and measure the mass of the chewed gum and the cup.

Step 6 - Subtract the mass of the cup to get the mass of the chewed gum. Record.

Step 7 - Subtract the mass of the chewed gum from the mass of the un-chewed gum to get the mass of the sugar that was removed.

Step 8 - Calculate the percentage of sugar in the gum. Show your calculations!

*All measurements should be made to the nearest tenth of a gram.

*One person from each group fill in chart on board.*

Questions:

1) Would a dentist recommend chewing this gum? Why or why not?

Sources of error?

2) Would changing the number of pieces of gum change the results of the lab? Explain.