chapter 3

chapter 3 - CHAPTER THREE CHEMICAL EQUATIONS REACTION...

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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

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4 The Mole z Example 1: Calculate the mass of a single Mg atom, in grams, to 3 significant figures. Mg g 10 4.04 atoms Mg mol 1 Mg g 24.30 atoms Mg 10 6.022 atoms Mg mol 1 atom Mg 1 Mg g ? 23 23 × = × × = 5 The Mole z Example 2: Calculate the number of atoms in one- millionth of a gram of Mg to 3 significant figures. atoms Mg 10 2.48 atoms Mg mol 1 atoms Mg 10 6.022 Mg g 24.30 Mg mol 1 Mg g 10 1.00 atoms Mg ? 16 23 6 × = × × = 6 The Mole z Example 3. How many atoms are contained in 1.67 moles of Mg? atoms Mg 10 1.00 Mg mol 1 atoms Mg 10 6.022 Mg mol 1.67 atoms Mg ? 24 23 × = × =
7 The Mole z Example 4: How many moles of Mg atoms are present in 73.4 g of Mg? Mg mol 02 . 3 Mg g 24.30 atoms Mg mol 1 Mg g 4 . 73 Mg mol ? = = IT IS IMPERATIVE THAT YOU KNOW HOW TO DO THESE PROBLEMS 8 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: amu 44.11 mass Molar amu 8.08 amu 1.01 8 H 8 amu 36.03 amu 12.01 3 C 3 = = × = × = × = × 9 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

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10 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? 11 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 ? 12 Formula Weights, Molecular Weights, and Moles z Law of Definite Proportions: A given compound always contains exactly the same proportion of elements by mass.
13 Formula Weights, Molecular Weights, and Moles z Example: The molecular formula for a compound is CX 4 . If 2.819g of this compound contains 0.102 g of carbon, what is the atomic weight of X?

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chapter 3 - CHAPTER THREE CHEMICAL EQUATIONS REACTION...

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