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Chpter 3 (Lecture 5-6)

# Chpter 3 (Lecture 5-6) - Chapter 3 Calculations with...

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Chapter 3 Calculations with Chemical Formulas & Equations Calculation from chemical formula Mole concept and Avogadro’s number Conversions between mass (grams) and moles Calculate No. of particles Molecules, atoms, ions, formula units Calculate mass & mass % (elemental analysis) Determine chemical formula and % composition

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3.1 Molecular and Formula Weights 3.1.1 Molecular weight ( MW ) of a substance Sum of atomic weights (AW) of all the atoms in a molecule of molecular substance 3.1.2 Formula weight (FW) of a compound The sum of atomic weights (AW) of all the atoms in a formula unit of the compound For ionic or molecular compounds Both expressed in amu (atomic mass unit)
Example: 1. Calculate MW of glucose (C 6 H 12 O 6 ) to 3 s.f. Given: AW of C = 12.01 amu; AW of H = 1.01 amu; AW of O = 16.00 amu 2. Calculate the FW of Fe 2 (SO 4 ) 3 to 3 s.f. Given: AW of Fe = 55.80 amu; AW of S = 32.10 amu; AW of O = 16.00 amu)

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3.2 The Mole Concept 3.2.1 Mole : The amount of substance that contains as many elementary particles (atoms/molecules/ions) as there are atoms in exactly 12.000 g of carbon-12. One mole of carbon-12 atoms has a mass of exactly 12.000 grams and contains 6.023x10 23 atoms. 1 mole of atoms of an element = the atomic mass of the element in grams = AW grams = 6.023x10 23 elementary particles/entities ( Avogadro’s number : the number of atoms in a 12-g sample of carbon-12, which is about 6.022 ×10 23 )
3.2.1 Molar Mass Molar mass of a substance (in grams per mole ) - The mass of one mole of the substance - Numerically equal to formula weight in amu

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Molar mass is the mass of 1 mole of in grams eggs shoes marbles atoms 1 mole 12 C atoms = 6.022 x 10 23 atoms = 12.00 g 1 12 C atom = 12.00 amu 1 mole 12 C atoms = 12.00 g 12 C 1 mole lithium atoms = 6.941 g of Li For any element atomic mass (amu) = molar mass (grams)
1 amu = 1.66 x 10 -24 g 1 12 C atom 12.00 amu x 12.00 g 6.022 x 10 23 12 C atoms = 1.66 x 10 -24 g 1 amu 1.2 M = molar mass in g/mol N A = Avogadro’s number

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Do You Understand Molar Mass? How many atoms are in 0.551 g of potassium (K) ? 1 mol K = 39.10 g K 1 mol K = 6.022 x 10 23 atoms K 0.551 g K 1 mol K 39.10 g K x x 6.022 x 10 23 atoms K 1 mol K = 8.49 x 10 21 atoms K
Molecular mass (or molecular weight) is the sum of the atomic masses (in amu) in a molecule. SO 2 1S 32.07 amu 2O + 2 x 16.00 amu SO 2 64.07 amu For any molecule molecular mass (amu) = molar mass (grams) 1 molecule SO 2 = 64.07 amu 1 mole SO 2 = 64.07 g SO 2

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Do You Understand Molecular Mass? How many H atoms are in 72.5 g of
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Chpter 3 (Lecture 5-6) - Chapter 3 Calculations with...

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