Chapter3 - 1 Chapter Three Stoichiometry: Chemical...

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1 Stoichiometry: Chemical Calculations Chapter Three Chapter Three Two parts: stiochiometry of chemical compounds stiochiometry of chemical reactions
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2 Part 1: Stiochiometry of Chemical Compounds
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3 Molecular mass : sum of the masses of the atoms represented in a molecular formula. Molecular mass is specifically for molecules. Formula mass : sum of the masses of the atoms or ions present in a formula unit . Formula mass is specifically for ionic compounds. Molecular Masses and Formula Masses
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4 Example Calculate the molecular mass of sucrose, C 12 H 22 O 11 . Example Calculate the formula mass of Cu(NO 3 ) 2 .
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5 Mole (mol): amount of substance that contains as many elementary entities as there are atoms in exactly 12 g of the carbon-12 isotope. Atoms are small, so this is a BIG number … • Avogadro’s number ( N A ) = 6.022 × 10 23 mol –1 1 mol = 6.022 × 10 23 “things” (atoms, molecules, ions, formula units, oranges, etc.) A mole of oranges would weigh about as much as the earth! The Mole & Avogadro’s Number
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6
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7 One Mole of Four Elements One mole each of helium, sulfur, copper, and mercury. How many atoms of helium are present? Of sulfur? Of copper? Of mercury?
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8 Molar mass is the mass of one mole of a substance. Molar mass is numerically equal to atomic mass, molecular mass, or formula mass but expressed in unit grams per mole (g/mol). Examples: 1 atom Na = 22.99 u 1 mol Na = 22.99 g MM Na = 22.99 g/mol 1 molecule CO 2 = 44.01 u 1 mol CO 2 = 44.01 g MM CO 2 = 44.01 g/mol 1 formula unit KCl = 74.56 u 1 mol KCl = 74.56 g MM KCl = 74.56 g/mol The Mole and Molar Mass
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9 We can use these equalities to construct conversion factors, such as: 1 mol Na ––––––––– 22.99 g Na Conversions involving Mass, Moles, and Number of Atoms/Molecules 22.99 g Na ––––––––– 1 mol Na 1 mol Na –––––––––––––––––– 6.022 × 10 23 Na atoms Conversions: mass moles use molar mass number of
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10 Example 3.3 Determine (a) the mass of a 0.0750-mol sample of Na, (b) the number of moles of Na in a 62.5-g sample, (c) the mass of a sample of Na containing 1.00 × 10 25 Na atoms, and (d) the mass of a single Na atom.
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11 We can read formulas in terms of moles of atoms or ions.
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12 Example Calculate the mass, in grams, of 0.050 mol sample of CO 2 . Example Calculate numbers of moles of MgCl 2 , Mg 2+ ions and Cl - ions, and number of MgCl 2 in a 1.38 g sample of MgCl 2 . Example Calculate number of moles of Br 2 in 125 mL of liquid bromine ( d = 3.21 g/mL).
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13 The mass percent composition of a compound refers to the proportion of the constituent elements, expressed as the number of grams of each element per 100 grams of the compound. In other words … Mass Percent Composition from Chemical Formulas X g element X % element = –––––––––––––– OR … 100 g compound g element % element = ––––––––––– × 100 g compound
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14 Percentage Composition of Butane
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Chapter3 - 1 Chapter Three Stoichiometry: Chemical...

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