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Chapter-3-KW

# 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
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 10 u 1 g × ÷ ÷
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 × ÷ ÷ ÷
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
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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