1. Percentage Composition Lesson 28

2. Warm up Submit Mole Conversion packages in basket, and copy the following upon arrival Write-Pair-Share What is the percent of the total composition of each ingredient in the following recipe (masses are fictitious): – 2 bananas (100 g) – 1 cup of flour (100 g) – 1 cup of sugar (150 g)

3. Results? Reflection Question: Why may results have varied during your warm up?

5. Learning Objectives 1.I know the meaning of “Percent Composition” 2.I can calculate the percent composition of a particular chemical 3.I can determine empirical formulas using percent composition

6. Percent Composition Let’s look at some examples and create our own definition

7. Percent Composition This class is: _____% Male and ______% Female

8. Write-Pair-Share Definition and calculation for percent composition…

9. Determining the Percent Composition by Mass of Chemicals Example: Determine the percent composition by mass of each atom in the chemical, CO 2 How could we determine the percent composition if we do not know the mass of an individual Carbon and Oxygen atom?

10. Determining the Percent Composition by Mass of Chemicals ASSUME THAT WE ARE DEALING WITH 1 MOLE OF THE SUBSTANCE!

11. Step-by-Step Step 1: Find the molar mass of the individual atoms.

12. Step-by-Step Step 2: Find the number of grams of each component, multiplying the molar mass by number of moles of each atom

13. Step-by-Step Step 3: Find the total mass of the compound

14. Step-by-Step Step 4: Divide the mass of each component (step 2) by the total mass of the compound (step 3), and multiply by 100

15. You Practice! Complete page 9 of Mole Conversion workbook

16. Determining Formula using Percent Composition Refresher… Empirical Formula: the simplest whole number ratio of one element to another in a compound Example: Octane is C 8 H 18. But that is not the simplest ratio. The simplest ratio is C 4 H 9, so this is its empirical formula

17. % Composition  Formula Example problem: What is the empirical formula of a compound that is 79.8% carbon and 20.2% H? If we assume that we have 100.g of compound, the percentages convert to grams.

18. Step 1: Convert % to grams  79.8% C becomes 79.8g C and 20.2% H becomes 20.2g H.

19. Step 2: Convert grams to moles

20. Step 3: Convert Ratio to Whole Number Since all compounds have simple whole number ratios of one element to another, we must convert the ratio 6.64:20 to a whole number one. The easiest way is to divide through by the smallest number, so… [show calc]

21. Step 4: Write the Empirical Formula The ratio is 1:3, resulting in an empirical formula of CH 3. You may encounter examples where the ratio works out to something like 1:2.5 or 1:3.5. If that is the case, the ratio actually becomes 2:5 or 2:7.

22. You Practice! Complete Page 12 to practice

23. Learning Objectives 1.I know the meaning of “Percent Composition” 2.I can calculate the percent composition of a particular chemical 3.I can determine empirical formulas using percent composition

24. Post-Assessment 1.Determine the percent composition of each atom in water 2.Determine the empirical formula of a substance with 70.0% iron and 30.0% oxygen.