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Stoichiometry: The Mole

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Stoichiometry The study of the quantitative aspects of chemical reactions.

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“The Mole” A counting unit 1 mole = 602 billion trillion: 602,000,000,000,000,000,000,000 6.02 X 10 23 (in scientific notation) 1 dozen eggs = 12 1 “mole” of eggs = 6.02 x 10 23 eggs 1 dozen cars = 12 cars 1 “mole” of cars = 6.02 x 10 23 cars Note that the NUMBER is always the same, but the MASS is very different! Mole is abbreviated “mol”

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= 6.02 x 10 23 C atoms = 6.02 x 10 23 H 2 O molecules A Mole of Particles A Mole of Particles Contains 6.02 x 10 23 particles 1 mole C 1 mole H 2 O Note that a particle could be an atom OR a molecule!

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6.02 x 10 23 particles 1 mole or 1 mole 6.02 x 10 23 particles Avogadro’s Number as a Conversion Factor

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1. Number of atoms in 0.500 mole of Al a) 500 Al atoms b) 6.02 x 10 23 Al atoms c) 3.01 x 10 23 Al atoms 2.Number of moles of S in 1.8 x 10 24 S atoms a) 1.0 mole S atoms b) 3.0 mole S atoms c) 1.1 x 10 48 mole S atoms Learning Check

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The Mass of 1 mole (in grams) Equal to the numerical value of the average atomic mass (get from periodic table) 1 mole of C atoms= 12.0 g 1 mole of Mg atoms =24.3 g 1 mole of Cu atoms =63.5 g Molar Mass

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Find the molar mass: (usually we round to the tenths place) Learning Check! A.1 mole of Br atoms B.1 mole of Sn atoms =79.9 g/mole = 118.7 g/mole

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Chemical Formulas of Compounds Formulas give the relative numbers of atoms or moles of each element in a formula unit - always a whole number ratio (the law of definite proportions).Formulas give the relative numbers of atoms or moles of each element in a formula unit - always a whole number ratio (the law of definite proportions). NO 2 2 atoms of O for every 1 atom of N NO 2 2 atoms of O for every 1 atom of N 1 mole of NO 2 : 2 moles of O atoms to every 1 mole of N atoms If we know or can determine the relative number of moles of each element in a compound, we can determine a formula for the compound.If we know or can determine the relative number of moles of each element in a compound, we can determine a formula for the compound.

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Mass in grams of 1 mole sum of the atomic masses 1 mole of CaCl 2 = 111.1 g/mol 1 mole Ca x 40.1 g/mol + 2 moles Cl x 35.5 g/mol = 111.1 g/mol CaCl 2 1 mole of N 2 O 4 = 92.0 g/mol Molar Mass of Molecules and Compounds

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A.Molar Mass of K 2 O = ? Grams/mole B. Molar Mass of antacid Al(OH) 3 = ? Grams/mole Learning Check!

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The artificial sweetener aspartame (Nutra-Sweet) formula C 14 H 18 N 2 O 5 is used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame? Learning Check!

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molar mass Avogadro’s number Grams Moles particles You can convert Grams to Particles, but you always must go through moles first. Calculations

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Flowchart Atoms or Molecules Moles Mass (grams) Divide by 6.02 X 10 23 Multiply by 6.02 X 10 23 Multiply by atomic/molar mass from periodic table Divide by atomic/molar mass from periodic table

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Atoms/Molecules and Grams How many atoms of Cu are present in 35.4 g of Cu? 35.4 g Cu 1 mol Cu 6.02 X 10 23 atoms Cu 63.5 g Cu 1 mol Cu = 3.4 X 10 23 atoms Cu

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Learning Check! How many atoms of K are present in 78.4 g of K?

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Learning Check! What is the mass (in grams) of 1.20 x 10 24 molecules of glucose (C 6 H 12 O 6 )?

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Using Equations Chemical equations also show mole ratios. In the equation: –2LiOH + CO 2 Li 2 CO 3 + H 2 O –For every 2 moles of LiOH and 1 mole of CO 2, 1 mole of Li 2 CO 3 and 1 mole of H 2 O are produced.

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Mole-Mass Conversions Most of the time in chemistry, the amounts are given in grams instead of moles We still go through moles and use the mole ratio, but now we also use molar mass to get to grams Example: How many grams of chlorine are required to react completely with 5.00 moles of sodium to produce sodium chloride? 2 Na + Cl 2 2 NaCl 5.00 moles Na 1 mol Cl 2 70.90g Cl 2 2 mol Na 1 mol Cl 2 = 177g Cl 2

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Learning Check For each of the following equations, calculate the moles of product that would be produced by reacting 4.0 moles of oxygen, O 2. Show your work. –4Fe + 3O 2 Fe 2 O 3 –2Mg + O 2 2MgO –2Cu + O 2 2CuO

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Learning Check Given the following reaction: –N 2 + O 2 2NO a)How many moles of NO can form when 40.0 g of N 2 react with excess oxygen? b)How many grams of NO can form, using the amounts in part A?

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