#### Transcript of Percent Composition

**% of one out of a whole!!**

**Percent Composition**

Percent Composition

The percentage by mass of each element in a compound

Steps for Solving

Find the % composition of each element in Cu2S

Example Problem

What is the mass percentage of water in calcium chloride dihydrate: CaCl2*2H2O

Percent Composition (%) = mass of element x 100

Total Mass

Step 1: Determine the Molar Masses of each element in the compound.

Step 2: Determine the Formula Mass of the compound

Step 3: Divide the molar mass of each element by the formula mass of the compound then multiply by 100

Find the percentage composition of a compound that is 28g Fe and 8.0 g oxygen.

Example Problem

Example Problem

How many grams of copper are in a 38.0g sample of Cu2S?

Table of Contents

Date Lecture/Activity Pg#

12/16/15 Percent Composition

Objective:

Today I will record the steps used to calculate percent composition so that I can calculate the % of water in a hydrate.

Agenda:

% Composition - Lecture

Analyzing Chewing Gum

Chemcatalyst:

How many atoms of calcium nitrate are in 12.5 g of calcium nitrate?

Analyze Chewing Gum

Procedure:

1. Unwrap two pieces of chewing gum. Place each piece on a weighing boat. Measure and record each mass using a balance.

2. Add 150 mL of cold tap water to a 250-mL beaker. Place one piece of chewing gum in the water and stir with a stirring rod for 2 mins.

3. Pat the gum dry using paper towels. Measure and record the mass of the dried gum.

4. Use scissors to cut the second piece of gum into small pieces. Repeat step 3 using fresh water. Keep the pieces from clumping together.

5. Use a 10 cm x 10 cm piece of window screen to strain the water from the gum. Pat the gum dry using paper towels. Measure and record the mass of the dry gum.

Analyze Chewing Gum

Analysis:

1.

Calculate

: For the uncut piece of gum, calculate the mass of sweeteners and flavoring that dissolved in the water. The mass of sweeteners and flavorings is the difference between the original mass of the gum and the mass of the dried gum.

2.

Calculate

: for the gum cut into small pieces, calculate the mass of dissolved sweeteners and flavorings.

3.

Apply

: For each piece of gum, determine the percent of the original mass from the soluble sweeteners and flavorings.

4.

Infer

: What can you infer from the two percentages? Is the gum sugar-coated or are the sweeteners and flavorings mixed throughout?

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