Title: % Composition Learning Target: Calculate empirical and molecular formulas. 1.4b DOL: Given 3 problems, calculate the percent composition of 3/3 correctly. Why? We need to be able to calculate % comp in order to calculate emp and mole formulas.

% Composition Guided Inquiry Calculating Mass Percent Check out examples 1 and 2, then together answer the questions. 1. In Example 1, where on the periodic table does the number 22.99 come from? 2. Comparing both examples, why is 102.89 used in both problems? What does that number represent? 3. Looking at the two answers to the examples above, what do they add up to? Does this make sense? Explain. 4. Calculate the mass percent of copper in CuOH. Show your work.

Model 2: Calculating mass % using subscripts Using examples 1 and 2, answer the questions together. 1. Looking at Example 1, why is the 35.45 multiplied by 2? Where did the two come from?   2. Why don’t the answers in the examples add up to 100% this time? 3. Calculate the percent of fluorine in chlorofluorocarbon. Show your work. Do all of the answers add up to 100%?

Making Sense of it All 1. TOGETHER: Write three to four steps for solving mass percent calculations. Include ways to check your answers. 2. Calculate the mass percent of chlorine in Freon-112, C2Cl4F2, a refrigerant commonly used in air conditioners in cars and refrigerators. 3. Acetic acid, C2H4O2, is the active ingredient in vinegar. Calculate the mass percent composition of oxygen in acetic acid.

Conversion Factors The mass percent of an element in a compound can be used as a conversion factor when converting from an element and the mass of a compound. In Model 2, you saw that chlorine makes up 58.64% of CCl2F2. Since % means per hundred, there are 58.64 g Cl per hundred grams of CCl2F2.

Model 3: Mass % as Conversion Factor Use Examples 1 and 2 to answer questions 1-3. 1. Just like in the mole conversion problems, the charts help us see how our units cancel and what the units of the final answer will be. In both examples, cancel the units and circle the units for the final answer. 2. Why is the conversion factor flipped in example 2 compared to example 1? 3. Write a rule explaining how to determine which direction the conversion factor will be written.

Making Sense of it All 1. TOGETHER: Write two or three ways you are going to know what type of problem you are working. Either calculating mass percent or using mass percent as a conversion factor. 2. What mass of iron (III) oxide contains 58.7 grams of iron? Iron (III) oxide is 69.94% iron by mass. 3. What is the percent of carbon and fluorine in carbon tetrafluoride. 4. How many grams of sulfur are in a 125 gram sample of sulfur dioxide? SO2 is 50% sulfur by mass.

Title: % Comp Sugar in Gum Learning Target: Calculate empirical and molecular formulas. 1.4b DOL: Calculate the % composition sugar in bubble gum using lab data. Why? Which bubble gum is the healthiest or the easiest on your teeth?

What % of the mass of bubble gum is sugar? Follow your lab procedure. During the 15 min of “chew time” you will complete a practice worksheet (moles, conversions and % comp problems) This worksheet is due WITH YOUR LAB at end of period.

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