CHM1311 - Lecture(4)

CHM1311 - Lecture(4) - Mass Relationships and Mass Chemical...

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1 Mass Relationships and Mass Relationships and Chemical Compounds Chemical Compounds Petrucci Ch. 2-7, 2-8, Ch. 3 Petrucci Ch. 2-7, 2-8, Ch. 3

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2 Avogadro’s Number (The mole) Avogadro’s Number (The mole) In real life, we deal with macroscopic samples containing large numbers of atoms. We need a unit to define a very large numbers of atoms. 12 1 dozen 144 1 gross 6.022 x 10 23 1 mole 12 atoms = 1 dozen atoms 144 atoms = 1 gross of atoms 6.022 x 10 23 atoms = 1 mol of atoms (Petrucci, Ch. 2-7) number unit Definition: 1 mole is defined as the number of 12 C atoms found in exactly 12 g of 12 C (6.022 x 10 23 ).
3 Molar Mass: mass in grams of 1 mole (6.022 x 10 23 atoms or molecules) of a substance Molar Mass ( Molar Mass ( Molecular Weight Molecular Weight ) ) molar mass of 12 C = 12.0000 g 1 mole of O = 15.9994 g 1 mole of H = 1.0079 g 1 mole of C = 12.011 g In nature, elements occur as a mixture of their isotopes. The molar mass of an element is the mass of 1 mole of the naturally occurring mixture of isotopes . Mass Number for the Element (as shown on the periodic table) Molar mass of an element (including all naturally occurring isotopes) =

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4 Conversion Between Mass, Moles, and Atoms Conversion Between Mass, Moles, and Atoms How many moles of Al are in a 10.0 g sample? (Petrucci, Ch. 2-8)
5 Molecular Mass: the average mass (in amu) of one molecule. Molecular Mass Molecular Mass Determine the molecular mass of H 2 O: (Petrucci, Ch. 3-2) molecular mass = sum of atomic mass of each atom in the molecule (in amu) 1 molecule H 2 O = 2.016 amu + 15.999 amu = 18.015 amu 2 atoms H x 1.008 amu 1 H atom = 2.016 amu 1 atom O x 15.999 amu 1 O atom = 15.999 amu molecular mass

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6 Composition of Chemical Compounds Composition of Chemical Compounds
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CHM1311 - Lecture(4) - Mass Relationships and Mass Chemical...

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