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Stoichiometry Chapter 12 Notes Chapter 12 Notes

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Review - The Mole A counting unit A counting unit Similar to a dozen, except instead of 12, its 602,000,000,000,000,000,000,000 Similar to a dozen, except instead of 12, its 602,000,000,000,000,000,000, X (in scientific notation) 6.02 X (in scientific notation) This number is named in honor of Amedeo Avogadro (1776 – 1856) This number is named in honor of Amedeo Avogadro (1776 – 1856)

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The Mass of 1 mole of substance (in grams) Equal to the numerical value of the average atomic mass (get from periodic table), or add the atoms together for a molecule 1 mole of C atoms= g 1 mole of Mg atoms =24.31 g 1 mole of O 2 molecules =32.00 g 1 mole of BCl 3 molecules = g Review - Molar Mass

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Molar Mass of Compounds The molar mass (MM) of a compound is determined the same way, except now you add up all the atomic masses for the compound The molar mass (MM) of a compound is determined the same way, except now you add up all the atomic masses for the compound Ex. Molar mass of CaCl 2 Ex. Molar mass of CaCl 2 Avg. Atomic mass of Calcium = 40.08g Avg. Atomic mass of Calcium = 40.08g Avg. Atomic mass of Chlorine = 35.45g Avg. Atomic mass of Chlorine = 35.45g Molar Mass of calcium chloride = g/mol Ca + (2 x 35.45) g/mol Cl Molar Mass of calcium chloride = g/mol Ca + (2 x 35.45) g/mol Cl g/mol CaCl g/mol CaCl 2 20 Ca 40.08a 17 Cl Cl

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Flowchart Atoms or Molecules Moles Mass (grams) Divide by 6.02 X Multiply by 6.02 X Multiply by atomic/molar mass from periodic table Divide by atomic/molar mass from periodic table

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Practice Calculate the Molar Mass of calcium phosphate Calculate the Molar Mass of calcium phosphate Formula = Formula = Masses elements: Masses elements: Ca: 3 Cas X = Ca: 3 Cas X = P: 2 Ps X = P: 2 Ps X = O: 8 Os X = O: 8 Os X = Molar Mass = Molar Mass = Ca 3 (PO 4 ) g g g g g g g/mol

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molar mass Avogadros number Grams Moles particles molar mass Avogadros number Grams Moles particles Everything must go through Moles!!! Calculations

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Atoms/Molecules and Grams How many atoms of Cu are present in 35.4 g of Cu? 35.4 g Cu 1 mol Cu 6.02 X atoms Cu 63.5 g Cu 1 mol Cu = 3.36 X atoms Cu

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Learning Check! What is the mass (in grams) of 1.20 X molecules of glucose (C 6 H 12 O 6 )?

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Chocolate Chip Cookies!! 1 cup butter 1/2 cup white sugar 1 cup packed brown sugar 1 teaspoon vanilla extract 2 eggs 2 1/2 cups all-purpose flour 1 teaspoon baking soda 1 teaspoon salt 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 many eggs would we need to make 9 dozen cookies? How much brown sugar would I need if I had 1 ½ cups white sugar?

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Cookies and Chemistry…Huh!?!? Just like chocolate chip cookies have recipes, chemists have recipes as well Just like chocolate chip cookies have recipes, chemists have recipes as well Instead of calling them recipes, we call them reaction equations Instead of calling them recipes, we call them reaction equations Furthermore, instead of using cups and teaspoons, we use moles Furthermore, instead of using cups and teaspoons, we use moles Lastly, instead of eggs, butter, sugar, etc. we use chemical compounds as ingredients Lastly, instead of eggs, butter, sugar, etc. we use chemical compounds as ingredients

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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) 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) The study of the quantative relationships among the amounts of reactants used and the amounts of products formed by a chemical reaction is called The study of the quantative relationships among the amounts of reactants used and the amounts of products formed by a chemical reaction is calledSTOICHIOMETRY

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Chemistry Recipes Be sure you have a balanced reaction before you start! Be sure you have a balanced reaction before you start! Example: 2 Na + Cl 2 2 NaCl Example: 2 Na + Cl 2 2 NaCl This reaction tells us that by mixing 2 moles of sodium with 1 mole of chlorine we will get 2 moles of sodium chloride This reaction tells us that by mixing 2 moles of sodium with 1 mole of chlorine we will get 2 moles of sodium chloride What if we wanted 4 moles of NaCl? 10 moles? 50 moles? What if we wanted 4 moles of NaCl? 10 moles? 50 moles?

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Practice Write the balanced reaction for hydrogen gas reacting with oxygen gas. Write the balanced reaction for hydrogen gas reacting with oxygen gas. 2 H 2 + O 2 2 H 2 O 2 H 2 + O 2 2 H 2 O How many moles of reactants are needed? How many moles of reactants are needed? What if we wanted 4 moles of water? 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 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 produced? What if we had 50 moles of hydrogen, how much oxygen would we need and how much water produced? 2 mol H 2 1 mol O 2 4 mol H 2 2 mol O 2 6 mol H 2, 6 mol H 2 O 25 mol O 2, 50 mol H 2 O

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Mole Ratios These mole ratios can be used to calculate the moles of one chemical from the given amount of a different chemical 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 sodium (without any sodium left over)? Example: How many moles of chlorine are needed to react with 5 moles of sodium (without any sodium left over)? 2 Na + Cl 2 2 NaCl 5 moles Na 1 mol Cl 2 2 mol Na = 2.5 moles Cl 2

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Mole-Mole Conversions How many moles of sodium chloride will be produced if you react 2.6 moles of chlorine gas with an excess (more than you need) of sodium metal? How many moles of sodium chloride will be produced if you react 2.6 moles of chlorine gas with an excess (more than you need) of sodium metal? 2 Na + Cl 2 2 NaCl

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Mole-Mass Conversions Most of the time in chemistry, the amounts are given in grams instead of moles We still go through moles and use the mole ratio, but now we also use molar mass to get to grams Example: How many grams of chlorine are required to react completely with 5.00 moles of sodium to produce sodium chloride? 2 Na + Cl 2 2 NaCl 5.00 moles Na 1 mol Cl g Cl 2 2 mol Na 1 mol Cl 2 = 177g Cl 2

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Practice Calculate the mass in grams of Iodine required to react completely with 0.50 moles of aluminum. Calculate the mass in grams of Iodine required to react completely with 0.50 moles of aluminum. 2 Al + 3 I 2 2 AlI 3

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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 ethane (C 2 H 6 ) needed to produce 10.0 g of water 2 C 2 H O 2 4 CO H g H 2 O 1 mol H 2 O 2 mol C 2 H g H 2 O 6 mol H 2 0 = mol C 2 H 6

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Practice Calculate how many moles of oxygen are required to make 10.0 g of aluminum oxide Calculate how many moles of oxygen are required to make 10.0 g of aluminum oxide 4 Al + 3 O 2 2 Al 2 O 3 4 Al + 3 O 2 2 Al 2 O 3

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Mass-Mass Conversions Most often we are given a starting mass and want to find out the mass of a product Most often we are given a starting mass and want to find out the mass of a product This is called the theoretical yield… or how much of another reactant we need to completely react (with no leftover ingredients!) This is called the theoretical yield… or how much of another reactant we need to completely react (with no leftover ingredients!) Now we must go from grams to moles, to the mole ratio, and back to grams of the compound we are interested in Now we must go from grams to moles, to the mole ratio, and back to grams of the compound we are interested in

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Mass-Mass Conversion Ex. Calculate how many grams of ammonia are produced when you react 2.00g of nitrogen with excess hydrogen. Ex. Calculate how many grams of ammonia are produced when you react 2.00g of nitrogen with excess hydrogen. N H 2 2 NH 3 N H 2 2 NH 3

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Practice How many grams of calcium nitride are produced when 2.00 g of calcium reacts with an excess of nitrogen? 3 Ca + N 2 Ca 3 N 2

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