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Zumdahl%20Chapter%203%20equations%20and%20rxn%20lecture%20slides%20sp09

Zumdahl%20Chapter%203%20equations%20and%20rxn%20lecture%20slides%20sp09

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1 CHAPTER THREE z CHEMICAL EQUATIONS & REACTION STOICHIOMETRY 2 The Mole z A number of atoms, ions, or molecules that is large enough to see and handle. z A mole = number of things Just like a dozen = 12 things One mole = 6.022 x 10 23 things z Avogadro’s number = 6.022 x 10 23 Symbol for Avogadro’s number is N A . 3 The Mole z How do we know when we have a mole? count it out weigh it out z Molar mass - mass in grams numerically equal to the atomic weight of the element in grams. z H has an atomic weight of 1.00794 g 1.00794 g of H atoms = 6.022 x 10 23 H atoms z Mg has an atomic weight of 24.3050 g 24.3050 g of Mg atoms = 6.022 x 10 23 Mg atoms 4 The Mole Example 1: Calculate the mass of a single Mg atom, in grams, to 3 significant figures. Example 2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures. 23 23 1 mol Mg atoms 24.30 g Mg 1 Mg atom = 4.04×10 g Mg 6.022×10 Mg atoms 1 mol Mg atoms  23 -6 16 1mol Mg 6.022×10 Mg atoms 1.00×10 g Mg =2.48×10 Mg atoms 24.30 g Mg 1mol Mg  5 The Mole Example 3. How many atoms are contained in 1.67 moles of Mg? Example 4: How many moles of Mg atoms are present in 73.4 g of Mg? 23 24 6.022 10 Mg atoms 1.67 mol Mg 1.00 10 Mg atoms 1mol Mg × = × 1 mol Mg atoms 73.4 g Mg 3.02 mol Mg 24.30 g Mg = 6 Formula Weights, Molecular Weights, and Moles z How do we calculate the molar mass of a compound? add atomic weights of each atom z The molar mass of propane, C 3 H 8 , is: 3 × C = 3 × 12.01 amu = 36.03 amu 8 × H = 8 × 1.01 amu = 8.08 amu Molar mass = 44.11 amu

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7 Formula Weights, Molecular Weights, and Moles z One Mole of Contains Cl 2 or 70.90g 6.022 x 10 23 Cl 2 molecules 2(6.022 x 10 23 ) Cl atoms C 3 H 8 or 44.11 g 6.022 x 10 23 C 3 H 8 molecules 3 (6.022 x 10 23 ) C atoms 8 (6.022 x 10 23 ) H atoms 8 Formula Weights, Molecular Weights, and Moles A mole of H 2 O has a molar mass of 18.0 g 2 H = 2 (1.0 g) = 2.0 g 1 O = 1(16.0) g = 16.0g 18.0 g 1. If you have 5.00 x 10 25 molecules of water, what is the mass of the water? 2. If you have 52.5 g of H 2 O, how many hydrogen atoms do you have? 9 1. If you have 5.00 x 10 25 molecules of water, what is the mass of the water? 2. If you have 52.5 g of H 2 O, how many hydrogen atoms do you have? ( ) O H g 10 50 . 1 O H mol 0 . 1 O H g 0 . 18 molecules O H 10 02 . 6 O H mol 0 . 1 molecules O H 10 00 . 5 2 3 2 2 2 23 2 2 25 × = = × × ( ) atoms H 10 51 . 3 atoms H mol 0 . 1 atoms H 10 02 . 6 O H mol 0 . 1 atoms H mol 0 . 2 O H g 0 . 18 O H mol 0 . 1 O H g 5 . 52 24 23 2 2 2 2 × = = × 10 Formula Weights, Molecular Weights, and Moles 3. What mass of FeCl 3 would contain the same total number of ions as 16.8 g of Al 2 (SO 4 ) 3 ? ( ) 2 4 3 3 3 2 2 4 3 4 3 3 ( ) 2 4 3 2 4 3 2 4 3 2 4 3 1 ( ) 2 3 5 1 3 4 330.22 / 162.20 / 1.0 ( ) 1.0 5 16.8 ( ) 330.22 ( ) 1.0 ( ) Al SO FeCl mol Al SO mol Al mol SO mol ions mol FeCl mol Fe mol Cl mol ions MM g mol MM g mol mol Al SO mol ions g Al SO g Al SO mol Al SO + + + = + = = =    3 3 3 162.20 4 1.0 10.3 g mol FeCl g FeCl mol ions mol FeCl g FeCl
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