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Chapter 7 Lecture Basic Chemistry Fourth Edition Chapter 7 Chemical Quantities 7.2 Molar Mass Learning Goal Given the chemical formula of a substance, calculate its molar mass. © 2014 Pearson Education, Inc.

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Molar Mass © 2014 Pearson Education, Inc. The molar mass is the quantity in grams that equals the atomic mass of that element the mass of one mole of an element or compound the mass of 6.022 × 10 23 atoms of an element the mass of 6.022 × 10 23 molecules or formula units

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© 2014 Pearson Education, Inc. Molar Mass of Carbon

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To determine the molar mass of a compound, multiply the molar mass of each element by its subscript in the formula add the results and round to 0.01 gram Molar mass NH 3 1 mol NH 3 1 mol N =1(14.01 g N) = 14.01 g N 3 mol H =3(1.01 g H) = 3.03 g H Molar mass NH 3 = 17.04 g NH 3 © 2014 Pearson Education, Inc. Molar Mass of a Compound

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© 2014 Pearson Education, Inc. Guide to Calculating Molar Mass

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Calculate the molar mass of lithium carbonate, Li 2 CO 3, used to produce the red color in fireworks. © 2014 Pearson Education, Inc. Learning Check

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Calculate the molar mass of Li 2 CO 3. Step 1Obtain the molar mass of each element. From the periodic table: © 2014 Pearson Education, Inc. Solution

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© 2014 Pearson Education, Inc. Solution Calculate the molar mass of Li 2 CO 3. Step 2Multiply each molar mass by the moles (subscript) in the formula. 2 mol Li × = 13.88 g Li 1 mol C × = 12.01 g C 3 mol O × = 48.00 g O

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Calculate the molar mass of Li 2 CO 3. Step 3 Calculate the molar mass by adding the masses of the elements. 2 mol Li = 13.88 g Li 1 mol C = 12.01 g C 3 mol O = 48.00 g O Molar mass Li 2 CO 3 = 73.89 g Li 2 CO 3 © 2014 Pearson Education, Inc. Solution

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© 2014 Pearson Education, Inc. One-Mol Quantities One-mol samples: sulfur, S (32.07 g); iron, Fe (55.85 g); salt, NaCl (58.44 g); potassium dichromate, K 2 Cr 2 O 7 (294.2 g); and sucrose, C 12 H 22 O 11 (342.3 g).

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© 2014 Pearson Education, Inc. Molar Mass of Elements, Compounds

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Calculate the molar mass of potassium chloride, KCl. © 2014 Pearson Education, Inc. Learning Check

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Calculate the molar mass of potassium chloride, KCl. Step 1Obtain the molar mass of each element. © 2014 Pearson Education, Inc. Solution

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© 2014 Pearson Education, Inc. Solution Calculate the molar mass of potassium chloride, KCl. Step 2Multiply each molar mass by the moles (subscript) in the formula. 1 mol K x = 39.10 g K 1 mol Cl x = 35.45 g C

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Calculate the molar mass of potassium chloride, KCl. Step 3Calculate the molar mass by adding the masses of the elements. 1 mol K = 39.10 g K 1 mol Cl = 35.45 g Cl Molar mass KCl = 74.55 g KCl © 2014 Pearson Education, Inc. Solution

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