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It’s time to learn about . . . What's The Difference Between Roast Beef And Pea Soup? Anyone Can Roast Beef. Stoichiometry Stoichiometry : Mole Ratios to Determining Grams of Product At the conclusion of our time together, you should be able to: 1. Review the conversion of particles or grams to moles 2. Determine mole ratios from a balanced chemical equation 3. Determine the amount of product produced when given the amount of reactants Review the Molar Mass of Compounds The molar mass (MM) of a compound is determined by adding up all the atomic masses for the molecule (or compound) 20 Ca ◦ Ex. Molar mass of CaCl2 40.08 ◦ Avg. Atomic mass of Calcium = 40.08g ◦ Avg. Atomic mass of Chlorine = 35.45g ◦ Molar Mass of calcium chloride = 40.08 g/mol Ca + (2 X 35.45) g/mol Cl 17 110.98 g/mol CaCl2 Cl 35.45 Practice Calculate the Molar Mass of calcium phosphate ◦ Formula = Ca3(PO4)2 ◦ Masses elements: ◦ Molar Mass = 310.18 g My new book on GOLF will give the reader valuable playing tips and insider information I've gained through my years of lessons, struggles and experiments. Here are just a few of the chapter titles: Chapter 5 - When to Give the Ranger the Middle Digit. Chapter 14 – The Best Time to Let a Foursome Play through Your Twosome. Calculations molar mass Avogadro’s number Grams Moles Particles Everything must go through Moles!!! Atoms or Flowchart Molecules Divide by 6.02 X 1023 Multiply by 6.02 X 1023 Multiply by Moles atomic/molar mass from periodic Divide by table atomic/molar mass from periodic table Mass (grams) Chocolate Chip Cookies!! 1 cup butter 2 eggs 1/2 cup white sugar 1 teaspoon salt 1 cup packed brown sugar 1 teaspoon vanilla extract 2 1/2 cups all-purpose flour 1 teaspoon baking soda 2 cups semisweet chocolate chips Makes 3 dozen How many eggs are needed to make 3 dozen cookies? How much butter is needed for the amount of chocolate chips used? How much brown sugar would I need if I had 1½ cups white sugar? Cookies and Chemistry…Huh!?!? Just like chocolate chip cookies have recipes, chemists have recipes as well Instead of calling them recipes, we call them chemical equations Furthermore, instead of using cups and teaspoons, we use moles Lastly, instead of eggs, butter, sugar, etc. we use chemical compounds as ingredients Chemistry Recipes Looking at a reaction tells us how much of something you need to react with something else to get a product (like the cookie recipe) Be sure you have a balanced reaction before you start! Balance #1 on your worksheet!! Example: 2 Ag+ Cl2 2 AgCl This reaction tells us that by mixing 2 moles of silver with 1 mole of chlorine we will get 2 moles of silver chloride What if we wanted 4 moles of AgCl? 10 moles? 50 moles? Let’s sit down and figure this out!! Practice Write the balanced reaction for hydrogen gas reacting with oxygen gas. 2 H2 + O2 2 H2O ◦ How many moles of reactants are needed? ◦ What if we wanted 4 moles of water? ◦ What if we had 3 moles of oxygen, how much hydrogen would we need to react, and how much water would we get? ◦ What if we had 50 moles of hydrogen, how much oxygen would we need, and how much water would be produced? Mole Ratios These mole ratios can be used to calculate the moles of one chemical from the given amount of a different chemical Example: How many moles of chlorine are needed to react with 5 moles of silver (without any silver left over)? 2 Ag + Cl2 2 AgCl 5 Ag + 2.5 Cl2 5 AgCl Question Answer 2 Ag+ Cl2 2 AgCl # moles of Cl2 = 5 mol Ag x 1 mol Cl2 2 mol Ag = 2.5 mol Cl2 Mole-Mole Conversions How many moles of silver chloride will be produced if you react 2.6 moles of chlorine gas with an excess (more than you need) of silver metal? 2 Ag + Cl2 2 AgCl # moles of AgCl = 2.6 mol Cl2 x 2 mol AgCl 1 mol Cl2 = 5.2 mol AgCl Mass-Mole We can also start with mass and convert to moles of product or another reactant We use molar mass and the mole ratio to get to moles of the compound of interest ◦ Calculate the number of moles of the combustion of ethane (C2H6) needed to produce 10.0 g of water ◦ 2 C2H6 + 7 O2 4 CO2 + 6 H20 Mass-Mole 2 C2H6 + 7 O2 4 CO2 + 6 H20 10.0 g H2O x 1 mol H2O x 2 mol C2H6 18.02 g H2O 6 mol H2O = 0.185 mol C2H6 A Comparison of the Arousal of the Sexes Start your HomeLearning NOW!! Stoichiometry Continued: Stoichiometry : Mole Ratios to Determining Grams of Product At the conclusion of our time together, you should be able to: 1. Review the conversion of particles or grams to moles 2. Determine mole ratios from a balanced chemical equation 3. Determine the amount of product produced when given the amount of reactants Mass-Mass Conversions Most often we are given a starting mass and want to find out the mass of a product we will get (called theoretical yield) or how much of another reactant we need to completely react with it (no leftover ingredients!) Now we must go from grams to moles, to mole ratios, and back to grams of the compound we are interested in. Mass-Mass Conversion Ex. Calculate how many grams of ammonia are produced when you react 2.00 g of nitrogen with excess hydrogen. N2 + 3 H2 2 NH3 2.00 g N2 1 mol N2 2 mol NH3 17.06 g NH3 28.02 g N2 1 mol N2 1 mol NH3 = 2.4 g NH3 Practice Mass-Mole-Mass How many grams of calcium nitride are produced when 2.00 g of calcium reacts with an excess of nitrogen? Ca + N2 Ca3N2 3 Ca + N2 Ca3N2 Mass-Mole-Mass 3 Ca + N2 Ca3N2 2.00 g Ca x 1 mol Ca x 1 mol Ca3N2 40.08 g Ca 3 mol Ca x 148.26 g Ca3N2 = 2.47 g Ca3N2 1 mol Ca3N2 Some Things Just Take a Lot of Work!!! Stoichiometry : Mole Ratios to Determining Grams of Product Let’s see if you can: 1. Review the conversion of particles or grams to moles 2. Determine mole ratios from a balanced chemical equation 3. Determine the amount of product produced when given the amount of reactants Mass-Mole-Mass NaN3 Na + N2 Synthesis 2 NaN3 2 Na + 3 N2 65.02 g 22.99 g 28.02 g 94.5 g NaN3 x 1 mol NaN3 x 3 mol N2 40.08 g NaN3 2 mol NaN3 x 28.02 g N2 = 99.1 g N2 1 mol N2 Don’t you just love these types of problems??? Review Mass-Mole-Molecules: Determine the number of molecules in 73 g of water # H2O molecules = 73 g H2O x 1 mol H2O x 6.02x1023 molecules 18.02 g H2O 1 mol H2O = 2.4 x 1024 molecules H2O Try this one: Calculate the mass in grams of iodine required to react completely with 0.50 moles of aluminum. Al + I2 AlI3 2 Al + 3 I2 2 AlI3 0.50 mol Al x 3 mol I2 2 mol Al x 253.80 g I2 1 mol I2 = 190 g I2 Try this one: Calculate the mass in grams of iodine required to react completely with 0.50 g of aluminum. Al + I2 AlI3 2 Al + 3 I2 2 AlI3 0.50 g Al x 1 mol Al x 3 mol I2 26.98 g Al 2 mol Al x 253.80 g I2 = 7.1 g I2 1 mol I2

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posted: | 4/8/2013 |

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