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Unformatted text preview: Chapter 3 Chapter 3 Stoichiometry Stoichiometry The mole The mole A A mole mole of a substance is defined as of a substance is defined as the amount of the substance that the amount of the substance that contains as many elementary entities contains as many elementary entities as there are atoms in 12.000 g of as there are atoms in 12.000 g of 12 12 C. C. A A mole mole is Avogadro’s number (N is Avogadro’s number (N A ) of ) of things; N things; N A = = 6.022 x 10 6.022 x 10 23 23 units/mol. units/mol. A A mole mole of water contains of water contains 6.022 x 10 6.022 x 10 23 23 water molecules water molecules Molar masses Molar masses Definition: 1 mole of Definition: 1 mole of 12 12 C weighs exactly 12 g, C weighs exactly 12 g, which equals 6.022 x 10 which equals 6.022 x 10 23 23 atoms atoms 12 12 C. C. Atomic mass of Atomic mass of 12 12 C is defined as 12 atomic C is defined as 12 atomic mass units (amu). All other atomic masses mass units (amu). All other atomic masses are relative to this. are relative to this. Natural carbon = Natural carbon = 98.89% 98.89% C C and and 1.11% 1.11% 13 13 C C Molar Mass of Molar Mass of Compounds Compounds (Review) (Review) Recall the molar mass of a compound is Recall the molar mass of a compound is calculated by adding the atomic masses calculated by adding the atomic masses of all of the atoms in its formula. of all of the atoms in its formula. 2 C = 2(12.01 g/mol) = 24.02 g/mol 6 H = 6(1.01 g/mol) = 6.06 g/mol 1 O = 1(16.00 g/mol) = 16.00 g/mol 46.08 g/mol Calculate the molar mass of C 2 H 6 O, Ethanol. Percent Percent Composition Composition of Compounds of Compounds Percent composition of a compound is the mass percent of each element in the compound. 11.21% H by mass 88.79% O by mass total mass of the element x 100 = percent of the element molar mass • Total mass of H in H 2 O = 2.02g/mol. • Total mass of O in H 2 O = 16.00g/mol. • Total molar mass of H 2 O = 18.02g/mol. Therefore: (2.02g mol1 /18.02g mol1 ) x 100 = 11.21 % H (16.00g mol1 /18.02g mol1 ) x 100 = 88.79 % O total mass of the element x 100 = percent of the element molar mass Empirical and Molecular Empirical and Molecular Formulas Formulas • The empirical formula, or simplest formula, gives the smallest wholenumber ratio of the atoms present in a compound. • The molecular...
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 Spring '10
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