Chapter-3-KW - Chapter 3 The Mole: Relating the Microscopic...

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Chapter 3 The Mole: Relating the Microscopic World of Atoms to Laboratory Measurements
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2 Index 3.1 The mole conveniently links mass to number of atoms or molecules 3.2 Chemical formulas relate amounts of substances in a compound 3.3 Chemical formulas can be determined from experimental mass measurements 3.4 Chemical equations link amounts of substances in a reaction 3.5 The reactant in shortest supply limits the amount of product that can form 3.6 The predicted amount of product is not always obtained experimentally
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3.1 The mole conveniently links mass to number of atoms or molecules 3 Counting Atoms by Their Mass The mass of an atom is called its atomic mass . Atomic mass provides a means to count atoms by measuring the mass of a sample. The periodic table gives atomic masses of the elements in u per atom .
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3.1 The mole conveniently links mass to number of atoms or molecules 4 Relationships 1.66 × 10-27 kg = 1 u (from the inside back cover of the book) may also be written as: 6.0223 × 1023 u = 1 g (a form you will often use) We can use this as a conversion factor to convert between mass quantities in u, and those in g atomic mass units (u) grams (u) 23 1 g 6.0223 10 u ÷ × 23 6.0223 1 g × ÷ ÷
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3.1 The mole conveniently links mass to number of atoms or molecules 5 What Is a Mole? A mole is defined as the number of atoms in exactly 12 grams of 12C atoms. One mole of any substance contains the same number of units, called Avogadro’s number , N 1 mole formula unit = 6.0223 × 1023 formula units It is a large quantity of particles because the particles described are so small.
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3.1 The mole conveniently links mass to number of atoms or molecules 6 Why is Molar Mass the Same as Formula Mass? Suppose we start with 12.011 g of C. How many atoms of C are there? Given that the atomic mass of C is 12.011 u 12.011 g C = 6.0223 × 1023 atoms Thus for any substance, the formula mass (in g) corresponds to the same number of atoms, N 23 6.0223 10 u 1 atom 12.011 g C g 12.011 u × ÷ ÷ ÷
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3.1 The mole conveniently links mass to number of atoms or molecules 7 Molar Mass One mole contains the same number of particles as the number of atoms in exactly 12 g of carbon-12 ( Avogadro’s number , N) The molar mass of a substance has the same numeric value as the formula mass The value is different because the units are different § Thus if the formula mass of Ba3(PO4)2 is 601.93 u/fu, the molar mass of Ba3(PO4)2 is 601.93 g/mol
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3.1 The mole conveniently links mass to number of atoms or molecules 8 Relationships MM g = 1 mole Use this as a conversion factor to convert between these quantities Mass (g) mole 1 mole MM g    ÷   mole 1 g MM
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3.1 The mole conveniently links mass to number of atoms or molecules 9 Learning Check: Converting Between Mass And Moles Given that the molar mass of CO2 is 44.01 g/mol What mass of CO2 is found in 1.55 moles?
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This note was uploaded on 01/24/2012 for the course CHEMISTRY 211 taught by Professor Crowley during the Fall '08 term at Wichita State.

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Chapter-3-KW - Chapter 3 The Mole: Relating the Microscopic...

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