Bell Ringer With your lab partner, work on the following question in pairs: When copper (II) reacts with silver nitrate, the number of grams of copper required to produce 432 grams of silver is: A 31.5 g B 127 g C 216 g D 252 g Cu + 2 AgNO3 2 Ag + Cu(NO ? 3)2 432 g Ag x 1 mol Ag x 1 mol Cu x 63.55 g Cu 107.87 g Ag 2 mol Ag 1 mol Cu = 127.25 g Cu 2002 VA Chemistry SOL Mass-Mass Quiz Good job on: - Calculating molar mass - Balancing reactions with coefficients We need to fix: - remembering decomposition reactions - making units cancel in stoichiometry work - using the mole ratio Decomposition of Carbonates Common mistake: CO2 BaCO3 BaO + C How to balance? What are we missing? To remember: think of a soda why do we call them “carbonated” ? H2CO3 CO2 + H2O The Wisdom of Gallagher Why are there Interstate Highways in Hawaii? Why are there floatation devices under plane seats instead of parachutes? Why do we drive on parkways and park on driveways? Why do hot dogs come ten to a package and hot dog buns only eight? Limiting Factors and Percent Yield Hot Dogs in the News Takeru Kobayashi of Japan downed 44½ hot dogs in 12 minutes. One hot dog = one hot dog + one bun. WHAT IF… Mr. Kobayashi didn’t do his math correctly. He bought 5 packs of hot dogs (10 per package) and 5 packs of hot dog buns (8 per package). How many hot dogs (according to the official formula) could he have eaten? Source: CNN.com Hot Dogs in the News One hot dog = one hot dog + one bun. WHAT IF… Mr. Kobayashi didn’t do his math correctly. He bought 5 packs of hot dogs (10 per package) and 5 packs of hot dog buns (8 per package). How many hot dogs (according to the official formula) could he have eaten? 5 hot dog packs x 5 bun packs x 10 hot dogs 1 hot dog pack 8 buns 1 bun pack = 50 hot dogs = 40 buns 40 possible hot dogs Source: CNN.com Let’s Revisit the Cookies (again)… For 1 batch: • • • • • • • • • • 2.25 cups flour 8 Tbsp butter 0.5 cups shortening 0.75 cups sugar 0.75 cups brown sugar 1 tsp salt 1 tsp baking soda 1 tsp vanilla 0.5 cups Egg Beaters 12 oz. Chocolate chips In my pantry, I have: • 5 cups of flour • 16 Tbsp of butter • lots of everything else How many batches of cookies can I make? Let’s Revisit the Cookies (again)… For 1 batch: • • • • • • • • • • 2.25 cups flour 8 Tbsp butter 0.5 cups shortening 0.75 cups sugar 0.75 cups brown sugar 1 tsp salt 1 tsp baking soda 1 tsp vanilla 0.5 cups Egg Beaters 12 oz. Chocolate chips How many batches of cookies can I make? EXCESS 5.5 c flour x 1 batch cookies = 2.25 c flour 2.4 batches LIMITING 16 Tbsp butter x 1 batch cookies = 8 Tbsp butter 2.0 batches Now I Want to Bake a Cake! But do I have all the ingredients I need? How much flour do I have left after baking all those cookies? 5.5 c flour x 1 batch cookies = 2.4 batches 2.25 c flour of cookies GONE! 16 Tbsp butter x SOME FLOUR LEFT OVER… 1 batch = 2.0 batches 8 Tbsp butter of cookies 2.0 batches x 2.25 cups flour 1 batch cookies = 4.5 cups flour used 5.5 cups – 4.5 cups = 1.0 cups left Limiting Reactants in Chemistry 5.0 moles of chlorine gas react with 5.0 moles of sodium to produce sodium chloride. Which reagent is the limiting factor? How much of the excess reactant is left over? Cl2 (g) + 2 Na 2 NaCl EXCESS givens equations! mol NaCl ==2 10. 5.0 mol Cl2 x 2 2 mol NaCl 1 mol Cl2 LIMITING 5.0 mol Na x 2 mol NaCl = 5.0 mol NaCl 5.0 mol Cl2 given 2 mol Na 5.0 mol Na x 1 mol Cl2 = 2.5 mol Cl2 2 mol Na 2.5 mol Cl2 used 2.5 mol Cl2 left Practice Problems 1. 3 CuSO4 20.0 g CuSO4 x 20.0 g Al x + 2 Al Al2(SO4)3 + 3 Cu 1 mol CuSO4 x 3 mol Cu = 0125 mol Cu 159.61 g CuSO4 3 mol CuSO4 1 mol Al x 26.98 g Al 3 mol Cu = 1.11 mol Cu 2 mol Al 20.0 g CuSO4 x 1 mol CuSO4 x 2 mol Al x 159.61 g CuSO4 3 mol CuSO4 20.0 g Al – 2.25 g Al = 17.8 g Al EXCESS 26.98 g Al = 1 mol Al 2.25 g Al USED Practice Problems 2. 2 H2 (g) + O2 (g) 5.0 g H2 x 1 mol H2 2.02 g H2 5.0 g O2 x 1 mol O2 32.00 g O2 2 H2O 2 mol H2O 2 mol H2 x x 2 mol H2O 1 mol O2 5.0 g O2 x 1 mol O2 x 2 mol H2 x 32.00 g O2 1 mol O2 5.0 g H2 – 0.63 g H2 = = 2.5 mol H2O = 0.31 mol H2O 2.02 g H2 = 0.63 g H2 1 mol H2 USED 4.37 g H2 EXCESS On Perfection “Perfection never exists in reality, but only in our dreams.” - Dr. Rudolf Dreikurs “Perfection is our goal, excellence will be tolerated.” - J. Yahl Get Real! Johnny took a quiz yesterday. He missed 4 questions and earned 63 points out of 70. -Was he perfect? -What was his possible score? -What was his actual percent score? Get Real! Mrs. Howell ran a reaction in her lab yesterday. She predicted that 183 grams of product would be formed. The reaction only yielded 162 grams of product. But she looked really cool in her lab coat. -Was her reaction perfect? -What was the percent yield? 162 grams 183 grams x 100 = 88.5 % Example: What volume of ammonia can be obtained by reacting 100 L of nitrogen gas with an excess of hydrogen, if the yield is 90%? N2 + 3 H2 100 L N2 x 1 mol N2 22.4 L N2 2 NH3 x 2 mol NH3 x 1 mol N2 22.4 L NH3 = 1 mol NH3 200 L NH3 THEORETICAL YIELD 200 L NH3 x 90 % = 180 L NH3 ACTUAL YIELD

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