 # The Mole: A Shortcut for Chemists S-C-8-1_The Mole Presentation Source:

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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)

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.

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.

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

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

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

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

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

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

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 ?

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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