Bubble Gum Lab! Step 1 – Measure mass of empty cup. Record.

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Presentation transcript:

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.

Chapter 6, Section 6.1 Chemical Proportions and Percentage Composition

The Law of Definite Proportions The 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? Part / Whole x 100

How do you calculate the grade you got on your test? Number of points you got / total points x 100

Percentage composition Indicates the relative amount of each element present in a compound.

Calculating percentage composition Step 1 : Calculate molar mass

Calculating percentage composition Step 1 : Calculate molar mass Step 2 : Divide the subtotal for each element’s molar mass by the total molar mass.

Calculating percentage composition Step 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 1 Calculate 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 3 Find the percentage composition of hydrogen in sulfuric acid. (H2SO4)

Bite the Bubble: A Chemistry Mini-Lab Objective: 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? - Weighing spit, - artificial sweetner

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