Lect 3 Stoichiometry Calculations

# Lect 3 Stoichiometry Calculations - Calculations with...

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Calculations with Chemical Formulas and Equations Stoichiometry Mass Relationships in Chemical Compounds and Chemical Reactions

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Operational Skills Calculating the formula weight from a chemical formula. Calculating the mass of an atom or molecule. Converting moles of substance to grams and grams to moles. Calculating the number of molecules in a given mass. Calculating the percentage composition from the chemical formula. Calculating the mass of an element in a given mass of compound. Determining the empirical formula from percentage composition. Determining the true molecular formula. Relating quantities of reactants and products in a chemical equation. Calculating products in reactions with a limiting reagent. Determining theoretical yield and percentage yield in a reaction Stoichiometry of Reactions in solution. Molarity, Dilution.
How do you relate the real microscopic masses of atoms and molecules to macroscopic gram quantities of atoms and molecules? What is a mole quantity? How do you convert mass % compositions to chemical formulas ? How do you convert chemical formulas to mass % compositions? How do you calculate the mass of reactants necessary for complete reaction How do you calculate the theoretical yield of products of a reaction? How do you treat reaction stoichiometery for reactants in solution?

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Molecular Weight and Formula Weight The molecular weight of a substance is the sum of the atomic weights of all the atoms in a molecule of the substance. H = 1.0 amu; O = 16.0 amu Molecular weight (MW) of H 2 O = 2 x 1.0 + 1 x 16.0 = 18.0 amu. The formula weight of a substance is the sum of the atomic weights of all the atoms in one formula unit of the compound. Na = 23.0 amu; Cl = 35.5 amu The formula weight (FW) of NaCl = 23.0 + 35.5 = 58.5 amu.

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Mass and Moles of a Substance A mole is the quantity of a given substance that contains as many molecules (or formula units) as the number of atoms in exactly 12 grams of carbon–12 (12C) The number of atoms in a 12 gram sample of carbon–12 is called The Avogadro’s number (N a ). The value of Avogadro’s number is 6.02 x 1023 The molar mass of a substance is the mass of one mole of a substance. The molar mass, in grams per mole, is numerically equal to the formula weight in atomic mass units. One mole of any element weighs its atomic mass in grams.
1 mole = 1 AW No. of atoms or = 1 MW (FW) molecules 12C 12.00 g 6.02 x 1023 C 12.01 g 6.02 x 1023 O 16.00 g 6.02 x 1023 CO 28.01 g 6.02 x 1023 CO 3 2- 60.01 g 6.02 x 1023 CaCO 3 100.09 g 6.02 x 1023 NaCl 58.44 g 6.02 x 1023

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Conversion factors Avagadro number (N) = 6.02 x 1023 /mol i.e. 6.02 x 1023 atoms or molecules mole mole Atomic weight = g/mol e.g. Ca 40.1 g/mole Ne 20.2 g/mole O = 16.0 g/mol CaO 56.1 g/mol
Mass and Moles of a Substance Mole calculations A of mass molecular) (or atomic A of mass A of = moles How many moles of aluminum (Al) are there in 100 g of aluminum? g/mol

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## This note was uploaded on 04/29/2009 for the course CHEM 211 taught by Professor Papanastasiou during the Spring '07 term at George Mason.

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Lect 3 Stoichiometry Calculations - Calculations with...

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