Do Now – April 7(3), 20091. What is the molar mass of cobalt?2. What is the mass of one mole of silicon?3. Calculate the molecular weight of oxygen gas, O2.

Agenda• Do Now/Announcements• Review Molecular Weight• Percent Composition• Bubble Gum Investigation• Exit TicketTOMORROW IS EARTH DAY!

Objectives• SWBAT calculate the percent composition of given compounds.• SWBAT perform an investigation to calculate the percent composition of bubble gum.

PercentYou already know this stuff!How do you calculate percent?(Part/Whole) x 100ExampleThere are 46 girls and 54 boys at the movie theater. What percent is boys?(54/100) x 100 = 54%

PercentYou already know this stuff!How do you calculate the grade on your test?(Points Correct/Total Points) x 100ExampleYou got 56 points correct out of 70 possible points. What percent of the test did you get correct?(56/70) x 100 = 80%(MASTERY LEVEL)

Percent Composition is the same thing!...Except you use chemical formulas• A chemical formula is a combination of chemical symbols and subscript numbers used to represent a compoundH2O CO2

Why is percent composition so important?• Chemists often develop new compounds for industrial, pharmaceutical, and home uses• After a synthetic chemist produces a new compounds, an analytical chemist analyzes the compound to provide experimental proof of its composition and its chemical formula

Percent Composition• It is the analytical chemist’s job to identify the elements a compound contains and determine their percent by massHi, I’m Carrie. I am analyzing a new compound that my buddy Germaine just created. A 100-g sample contains 35 g of element X and 65 grams of element Y. I can calculate the percent composition using a handy formula!

Percent CompositionHere it is!

mass element x 100 = percent

mass compound

So…

35 g element X x 100 = 35% X

100 g compound

65 g element Y x 100 = 65% Y

100 g compound

Percent CompositionYou see…

Percent composition is just the percent by mass of each element in a

compound.

Your teacher told me to tell you to add this to your Vocabulary Log?

Percent Composition of that beloved substance….WATER!We already know the chemical formula – H2O mass element x 100 = % element mass compound mass hydrogen x 100 = % hydrogen mass water mass oxygen x 100 = % oxygen mass water

Percent Composition of that beloved substance….WATER!We already know the chemical formula – H2O mass element x 100 = % element mass compound 2(1.0 g) H x 100 = 11% H 18.0 g H2O 1(16.0 g) O x 100 = 89% O 18.0 g H2O

Percent CompositionCalculating percent composition is just one more step in describing compounds.Imagine you find two intriguing substances during your Australian study abroad trip in college. Natives tell you that both substances contain iron and oxygen - one is iron(II) oxide, FeO, and the other is iron (III) oxide, Fe2O3. They also tell you that the substance with more iron is worth a lot of money. They ask you to help them figure out which substance has more iron. PERCENT COMPOSITION IS THE WAY!

Steps for Calculating Percent Composition1. Molecular weight (total mass of compound)2. Mass contributed by each element3. Calculate the percentage of each element4. Check! Add up all percents to make sure they add up to 100%

Percent Composition of the Australian Iron-Oxygen Substancesiron(II) oxide, FeOiron (III) oxide, Fe2O3Which is worth more GREEN?

Percent Composition with Polyatomic IonsCalculate the percent composition of barium nitrate

Percent Composition Practice• Complete Practice Problems 42 – 45 on page 331 in your book.• Use the examples we have worked through as well as Example Problem 11-10 on page 330 if you need help.

Percent CompositionBubble Gum InvestigationYour task is to calculate the percent composition of bubble gum. We are assuming that bubble gum is composed of 2 things – gum and sugar. You should be able to calculate the percent gum and percent sugar after completing your investigation.

Exit Ticket1. What is the formula for calculating percent composition?2. Calculate the percent composition of sulfur trioxide.

S’more Lab • What makes up the delicious goodness of a s’more?• Well, as a chemistry student, you can find out just what makes a s’more taste so good!• It’s all about the ingredients – the parts of the whole!• Your mission: calculate the percent composition of a s’more?