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Thursday, April 7 th : A Day Friday, April 8 th : A Day Agenda Finish Section 7.1: Avogadros Number & Molar Conversions In-Class: Practice pg. 231: #1-4 Practice pg. 232: #1-3 Concept Review: Avogadros Number & Molar Conversions: #6-10 Section 7.1 quiz next time…

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Finish 7.1: Avogadros Number and Molar Conversions X atoms 1 mole

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Molar Mass Relates Moles to Grams Molar mass: the mass in grams of one mole of an element or compound. Molar mass is numerically equal to the atomic mass of elements (Fe, Al, etc.) and the formula mass of compounds (H 2 O, CH 4, etc. ) and diatomic elements. (O 2, F 2, etc.) The units for molar mass are grams mole

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Molar Mass Example #1 What is the molar mass of water, H 2 O? To determine the molar mass, look up the atomic mass of each element present in the compound and add them up. This is the molar mass. H = 1.01 g/mol O = 16.0 g/mol Molar mass of water = g H 2 O 1 mole

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Molar Mass Example #2 What is the molar mass of sulfuric acid, H 2 SO 4 ? H = 1.01 g/mol S = g/mol O = 16.0 g/mol Molar mass of sulfuric acid = g H 2 SO 4 1 mole

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So, why do we need to know the molar mass… Molar mass can be used as a conversion factor in problems converting between mass and amount!!!

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Converting Number of Particles to Mass To convert from number of particles to mass, you must use a two-step process: First, convert number of particles to amount in moles using Avogadros number. Second, convert amount in moles to mass in grams using the molar mass. Two different conversion factors must be used!

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Converting Between Mass, Amount, and Number of Particles

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Sample Problem C, pg. 231 Converting Number of Particles to Mass Find the mass in grams of 2.44 X atoms of carbon, whose molar mass is g/mol. Known: 2.44 X atoms of carbon Unknown: Mass in grams of carbon Two conversion factors: 1 mole C AND g C X atoms C 1 mole C

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Sample Problem C, continued Converting Number of Particles to Mass Step 1: Convert # of particles amount in moles: 2.44 X C atoms X 1 mole C X atoms C = 4.05 moles C Step 2: Convert amount in moles mass (in grams) 4.05 moles C X g C 1 mole C = 48.6 g C

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Additional Practice Find the mass in grams of 6.12 X formula units of rhenium dioxide, ReO 2, g/mol. Known: 6.12 X formula units ReO 2 Unknown: Mass in grams of ReO 2 Two conversion Factors: 1 mole ReO 2 AND g ReO X form unit ReO 2 1 mole ReO 2

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Additional Practice Step 1: Convert # of particles amount in moles: 6.12 X form. unit X _1 mol_ReO 2 __ X form. unit ReO 2 = 1.02 X mole ReO 2 Step 2: Convert amount in moles mass (in grams) 1.02 X mole ReO 2 X g ReO 2 1 mole ReO 2 = 2.23 X g ReO 2

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Converting Mass to Number of Particles Converting from mass to number of particles is simply the opposite of the previous problems. To convert from mass to number of particles, you must use a two-step process: 1.First, convert mass in grams to amount in moles using molar mass. 2.Second, convert amount in moles to number of particles using Avogadros number. Two different conversion factors must be used!

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Sample Problem D, pg. 232 Converting Mass to Number of Particles Find the number of molecules present in 47.5 g of glycerol, C 3 H 8 O 3. The molar mass of glycerol is g/mol. Known: 47.5 g glycerol, C 3 H 8 O 3 Unknown: # of molecules present Two conversion factors: 1 mole C 3 H 8 O 3 AND X molecules C 3 H 8 O g C 3 H 8 O 3 1 mole C 3 H 8 O 3

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Sample Problem D, cont. Converting Mass to Number of Particles Step 1: Convert mass (in grams) amount in moles: 47.5 g C 3 H 8 O 3 X 1 mole C 3 H 8 O 3 = mol C 3 H 8 O g C 3 H 8 O 3 Step 2: Convert amount in moles # of molecules: mol C 3 H 8 O 3 X X molecules C 3 H 8 O 3 1 mole C 3 H 8 O 3 = 3.11 X molecules C 3 H 8 O 3

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Additional Practice Determine the number of atoms present in 54.3 grams of cobalt, Co. Known: 54.3 g of cobalt, Co. Unknown: # of atoms Two conversion Factors: 1 mole Co AND X atoms Co g Co 1 mole Co

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Additional Practice Step 1: Convert mass (in grams) amount in moles: 54.3 g Co X 1 mol Co = mol Co g Co Step 2: Convert amount in moles # of atoms: moles Co X X atoms Co 1 mole Co = 5.55 X atoms Co

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In-Class Assignments/Homework You Must SHOW WORK! Practice pg. 231: #1-4 Practice pg. 232: #1-3 Concept Review: Avogadros Number & Molar Conversions: #6-10 Section 7.1 quiz next time…

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