1. Bell Ringer (5 minutes)  The chemical analysis of aspirin indicates that the molecule is 60.00% carbon, 4.44% hydrogen and 35.56% oxygen. Determine the empirical formula for aspirin.

2. Ms. Miranda Mack Chemistry I May 4-8, 2009

3. Why It’s Important The cost of the things that you buy is lower because chemists use stoichiometric calculations to increase efficiency in laboratories, decrease waste in manufacturing and produce products more quickly.

4. What You’ll Learn  Write mole ratios from balanced chemical equations  Calculate the number of moles and the mass of a reactant of product when given the number of moles or the mass of another reactant or product.  To identify the limiting reactant or product  Determine the percent yield of a chemical reaction.

5. Things to Remember  Scientific notation  Significant Figures  Dimensional Analysis  Average atomic mass  Mole Conversions

6. Stoichiometry  Let’s pronounce it together! STOY-KEE-AHM-EH-TREE!  YOU DID IT!  So, what does stoichiometry mean?  Derived from the combination of two Greek words, which when used together mean, “To measure the elements.”

7. Let’s think about it!  Take a look at this candle, pg. 352  What determines how long the candle will burn? Think about what is involved What is needed for burning (combustion) to take place

8. What is Cinco de Mayo!  The holiday Cinco de Mayo commemorates the victory of the Mexican militia over the French army at the Battle of Puebla in 1862. It is mostly a regional holiday celebrated in the capital city of Puebla, Mexico and some recognition in other parts of Mexico and especially in U.S. cities with significant Mexican populations. It is different from Mexico’s Independence Day celebrated on September 16.

9. Stoichiometry Is…  All about AMOUNTS  Reactions happen as long as the reactants are available  All reactions depend on how much “stuff” you have!  Based on the law of conservation of mass. Does anyone know what it says?

10. Mexican Flag Cake Recipe!  1-1/2 cups boiling water  2 pkg. (3 oz. each) JELL-O Strawberry Flavor Gelatin  ice cubes  1 cup cold water  1 pkg. (10.75 oz.) pound cake, cut into 10 slices  2 pkg. (8 oz. each) PHILADELPHIA Cream Cheese, softened  1/4 cup sugar  1 tub (8 oz.) COOL WHIP Whipped Topping, thawed  4 kiwi, peeled, sliced  10 fresh strawberries, cut in half

11. Stoichiometry and the Law of Conservation of Mass…  In chemical reactions, bonds in reactants break and new bonds are formed.  The amount of matter present at the end of the reaction is the same as the amount of matter at the beginning!  See pg. 355- “Interpreting Chemical Reactions”

12. What do you know about this reaction? N 2 (g) + 3H 2 (g) 2NH 3 (g)

13. What’s in a reaction? coefficients? What are coefficients?  Mole ratios  Mole ratios are ratios between the numbers of any two substances in a balanced chemical equation. Example: 4 Al(s) + 3O 2 (g)2 Al 2 O 3 (s) See board for solutions

14. Writing Mole Ratios  Who cares about mole ratios?  Mole ratios are the KEY to calculations based upon a chemical equation.  With a given quantity of reactants, mole ratios can be use

15. Check for Understanding  What is stoichiometry?  How does the law of conservation of matter relate to a chemical reaction?  What is a mole ratio?

16. Pg. 357 # 4-7 (5/5/09)

17. Three Types of Stoichiometric Calculations-Use MOLE ratios!  Mole-to-Mole: find out how many moles of reactant or product  Mole-to-Mass: allows you to calculate the mass of a product or reactant in a chemical reaction given the number of moles of a reactant or product.  Mass-to-Mass: We need to know how much of each reactant to use in order to produce a certain mass of product!