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The Mole: A Shortcut for Chemists S-C-8-1_The Mole Presentation Source: http://en.wikipedia.org/wiki/Mole_(animal)

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The Mole The mole is a counting unit for chemists, the same way a baker uses a dozen. 1 dozen = 12 objects 1 mole = 6.02 × 10 23 objects = 602,000,000,000,000,000,000,000 objects That’s almost a trillion trillion! 6.02 × 10 23 is called Avogadro’s number. “Mole” in writing; “mol” in calculations.

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Representative Particles Moles can be used to count “representative particles:” atoms, molecules, ions, and formula units. The representative particle of an ionic compound is the formula unit. The representative particle of a covalent compound is the molecule. The representative particle of an element is the atom.

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Atomic Masses What do the atomic masses on the periodic table represent? Carbon has an atomic mass of 12; this means a carbon atom weighs 12 atomic mass units (amu). The actual mass of an atom of carbon is only 2 x 10 -23 grams. Practice: What is the atomic mass of one molecule of CO 2 ? 12.01 + 16.00 + 16.00 = 44.01

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Formula Weight Formula weight: The weight of a molecule or an ionic compound. Molecule: CO 2 12.01 + 16.00 + 16.00 = 44.01 amu For molecules, formula weight is also called the “molecular weight.” Ionic compound: NaCl 22.99 + 35.45 = 58.44 amu

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Molar Mass Molar mass = the mass of one mole. For atoms, molar mass is the same as atomic mass. The molar mass of a compound allows you to convert between the amount of the element (moles) and its mass (grams). If you want to convert from amount (moles) to mass (grams): If you want to convert from mass (grams) to amount (moles): # of moles × Formula weight = Mass (in grams) 1 mol mass (grams) × 1 mol = # of moles formula weight

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Molar Mass Examples 1 mol N = 14.01 g N Written as 14.01 g/mol Calculate the following molar masses: Br CaF 2 NO 2 NaCl

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Molar Mass Examples: Solutions Calculate the following molar masses: Br 79.90 CaF 2 40.08 + 19.00(2) = 78.08 g/mol NO 2 14.01 + 16.00(2) = 46.01 g/mol NaCl 22.99 + 35.45 = 58.44 g/mol

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Conversion Factors: Mole-Mass Problems The red portions in the examples above are the conversion factors. Conversion factor: A ratio equal to one that expresses the same quality in two different ways. Another example: To find the number of eggs in 3 dozen: 3 dozen x 12 eggs/dozen = # of eggs

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Mole-Mass Problems 1. What is the mass of 0.50 mol HCl? 2. What is the mass of 2 mol Zn? 3. How many moles are in 1.5 g of Cu? 4. How many moles are in 50 g H 2 SO 4 ?

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Mole-Mass Answers 1. What is the mass of 0.50 mol HCl? 0.50 mol × 36.46 g/mol = 18.23 g HCl 2. What is the mass of 2 mol Zn? 2 mol × 65.41 g/mol = 130.82 g 3. How many moles are in 1.5 g of Cu? 1.5 g × 1 mol/63.55 g = 0.02 mol 4. How many moles are in 50 g H 2 SO 4 ? 50 g × 1 mol/98.09 g = 0.51 mol

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