chap03.slides.calculations

chap03.slides.calculations - Chapter 3 Calculations with...

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Chapter 3 Calculations with  Chemical Formulas and Equations Chapter 4 Sections 4.7 – 4.10
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Molar Mass, Molecular Weight and Formula Weight Molar Mass  – or molecular mass or molecular weight is the sum  of the atomic masses of the individual atoms in the molecule. Formula Weight  – or formula mass is the sum of the atomic  masses of the individual atoms in a formula unit of a compound. Molar Mass is symbolized as MM. The unit of molar mass is  g/mol or amu. Sample Problem 1: Calculate the molar mass calcium hydroxide.
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Mole Concept  A Mole  – the quantity of a given substance than contains as many  atoms, molecules or formula units as the number of atoms  in exactly 12 g of  12 C. - the symbol is mol - The amount of substance containing Avogadro’s number     of atoms, molecules or formula units.   Avogadro’s Number is 6.02  x 10 23 1 mol of CO 2  contains  6.02 x 10 23  CO molecules. 6.02 x 10 23  atoms of C x  6.02 x 10 23   = 1.20 x 10 24  atoms of O 1 mol of KBr contains  6.02 x 10 23  formula units of KBr. 6.02 x 10 23  K +  ions   6.02 x 10 23  Br -  ions
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Number of moles  =   Mass in g   Molar Mass in g/mol Mole Calculations Mass of  substance Moles of  substance Number of  molecules Molar Mass   (g/mol) Avogadro’s Number 6.02 x 10 23 Mass of  element Moles of  element Number of  atoms  Atomic   Mass   (g/mol) Avogadro’s Number 6.02 x 10 23
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Sample Problem 2: What is the mass of the nitric acid molecule, HNO 3 ? Sample Problem 3: A sample of nitric acid contains 0.253 mol HNO 3 .   How many grams is this? Sample Problem 4: Calcite is a mineral composed of calcium carbonate, CaCO 3 .   A sample of calcite composed of pure calcium carbonate  weighs 23.6 g.  How many moles of calcium carbonate is this?
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Sample Problem 5: The average daily requirement of the essential amino acid  leucine, C 6 H 14 O 2 N, is 2.2 g for an adult.  How many moles of  leucine are required daily? Sample Problem 6: The daily requirement of chromium in the human diet is  1.0 x 10 -6  g.  How many atoms of chromium does this  represent?
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  Percentage Composition Percent composition  - mass percentages of each element in the              compound. x 100 % mass  A =  Mass of A in the whole Mass of the whole Percent composition of NaCl (MM =  58.45 g/mol) % Na =  23.00 g/mol 58.45 g/mol x 100 = 39.35 % % Cl =   35.45 g/mol 58.45 g/mol x 100 = 60.65 %
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Sample Problem 7: Lead (II) chromate, PbCrO 4 , is used as a paint pigment  (chrome yellow).  What is the percentage composition of 
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