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Stoichiometry: The Mole

Stoichiometry: The Mole. Stoichiometry. The study of the quantitative aspects of chemical reactions. “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

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Stoichiometry: The Mole

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  1. Stoichiometry: The Mole

  2. Stoichiometry The study of the quantitative aspects of chemical reactions.

  3. “The Mole” • A counting unit • 1 mole = 602 billion trillion: 602,000,000,000,000,000,000,000 • 6.02 X 1023 (in scientific notation) • 1 dozen eggs = 12 • 1 “mole” of eggs = 6.02 x 1023 eggs • 1 dozen cars = 12 cars • 1 “mole” of cars = 6.02 x 1023 cars Note that the NUMBER is always the same, but the MASS is very different! Mole is abbreviated “mol”

  4. A Mole of ParticlesContains 6.02 x 1023 particles = 6.02 x 1023 C atoms = 6.02 x 1023H2O molecules 1 mole C 1 mole H2O Note that a particle could be an atom OR a molecule!

  5. Avogadro’s Number as a Conversion Factor 6.02 x 1023 particles 1 mole or 1 mole 6.02 x 1023 particles

  6. Learning Check 1. Number of atoms in 0.500 mole of Al a) 500 Al atoms b) 6.02 x 1023 Al atoms c) 3.01 x 1023 Alatoms 2.Number of moles of S in 1.8 x 1024 S atoms a) 1.0 mole S atoms b) 3.0 mole S atoms c) 1.1 x 1048 mole S atoms

  7. Molar Mass • 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

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

  9. 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). • NO2 2 atoms of O for every 1 atom of N • 1 mole of NO2 : 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.

  10. Molar Mass of Molecules and Compounds Mass in grams of 1 mole sum of the atomic masses 1 mole of CaCl2 = 111.1 g/mol 1 mole Ca x 40.1 g/mol + 2 moles Cl x 35.5 g/mol = 111.1 g/mol CaCl2 1 mole of N2O4 = 92.0 g/mol

  11. Learning Check! • Molar Mass of K2O = ? Grams/mole • B. MolarMass of antacid Al(OH)3 = ? Grams/mole

  12. Learning Check! The artificial sweetener aspartame (Nutra-Sweet) formula C14H18N2O5 is used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame?

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

  14. Flowchart Atoms or Molecules Divide by 6.02 X 1023 Multiply by 6.02 X 1023 Moles Multiply by atomic/molar mass from periodic table Divide by atomic/molar mass from periodic table Mass (grams)

  15. 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 1023 atoms Cu 63.5 g Cu 1 mol Cu = 3.4 X 1023 atoms Cu

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

  17. Learning Check! What is the mass (in grams) of 1.20 x 1024 molecules of glucose (C6H12O6)?

  18. Using Equations • Chemical equations also show mole ratios. • In the equation: • 2LiOH + CO2 Li2CO3 + H2O • For every 2 moles of LiOH and 1 mole of CO2, 1 mole of Li2CO3 and 1 mole of H2O are produced.

  19. 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 + Cl2 2 NaCl 5.00 moles Na 1 mol Cl2 70.90g Cl2 2 mol Na 1 mol Cl2 = 177g Cl2

  20. Learning Check • For each of the following equations, calculate the moles of product that would be produced by reacting 4.0 moles of oxygen, O2. Show your work. • 4Fe + 3O2 Fe2O3 • 2Mg + O2  2MgO • 2Cu + O2  2CuO

  21. Learning Check • Given the following reaction: • N2 + O2 2NO • How many moles of NO can form when 40.0 g of N2 react with excess oxygen? • How many grams of NO can form, using the amounts in part A?

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