Ch9 - Chapter 9 Chemical Calculations: The Mole and...

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1 Chapter 9 Chemical Calculations: The Mole and Chemical Formula
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2 Determination of Percent Composition Chapter 9 § Law of Definite Proportions (Dalton) A given compound always contains the same proportion, by mass, of the elements. Decompose samples of a pure compound to give the constituent elements: NO 2 Sample Mass decompose Mass of nitrogen Mass of oxygen A 5.362 g 1.632 g 3.730 g B 10.613 g 3.230 g 7.383 g
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3 Percent Composition Sample A Sample B oxygen % 69.57 = % 100 x g 613 . 10 g 7.383 nitrogen % 30.43 = % 100 x 613 . 10 g 3.230 oxygen % 69.56 = % 100 x g 5.362 g 3.730 nitrogen % 30.44 = % 100 x g 362 . 5 g 632 . 1 g
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4 Formula Unit and Formula Mass § Formula Unit § gives proportions of elements in a pure compound NO 2 CaCl 2 molecular ionic § Formula Mass § sum of atomic masses of atoms in one formula unit eg: NO 2 atomic mass of N 14.01amu atomic mass of O 16.00 amu formula mass of NO 2 : 14.01 + 2(16.00) amu = 46.01 amu
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5 Percent Composition from Formula § NO 2 formula mass 46.01 amu total mass from each element x 100 % formula mass % N 14.01amu / 46.01 amu x 100% = 30.45 % % O 2(16.00) amu / 46.01 amu x 100% = 69.55 %
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6 Percent Composition Sample A Sample B oxygen % 69.57 = % 100 x g 613 . 10 g 7.383 nitrogen % 30.43 = % 100 x 613 . 10 g 3.230 oxygen % 69.56 = % 100 x g 5.362 g 3.730 nitrogen % 30.44 = % 100 x g 362 . 5 g 632 . 1 g 30.45 % 69.55 %
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7 Counting Atoms, Ions and Molecules Consider a reaction to form CO where: 1 atom of C combines with 1 atom of O to give CO, 1 molecule of carbon monoxide 1 pair of C atoms + 1 pair of O atoms gives 1 pair of CO molecules 1 dozen C atoms + 1 dozen O atoms gives 1 dozen CO molecules 1 gross of C atoms + 1 gross of O atoms gives 1 gross CO molecules 1 mole of C atoms + 1 mole of O atoms gives 1 mole of CO molecules 1 mole = 6.022137 x 10 23 objects Avogadro’s number
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8 One Mole § 6.02 x 10 23 copies of the Chem 110/111 course text book, piled on top of each other would reach to the moon and back 13 billion times § It would take 6 trillion galaxies the size of the Milky Way to provide 6.02 x 10 23 stars
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9 What is the formula mass of H 2 O? § sum of the atomic masses of the total number of atoms represented by the formula § 2 x H = 2 (1.0079) = 2.0158 amu 1 x O = 1 x 15.994 = 15.994 amu formula mass 18.0098 amu = 18.010 amu
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10 The Mole § One mole is the amount of a substance that contains as many elementary units as there are 12 6 C atoms in exactly 12.00000… g of 12 6 C i.e. In 12.000000… g of 12 6 C there are 6.022137 x 10 23 atoms of 12 6 C
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11 Converting between Moles and number of particles How many atoms are in 1.50 moles of Carbon?
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Ch9 - Chapter 9 Chemical Calculations: The Mole and...

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