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The Mole

The Mole. Chapter 6. The Mole. Remember it is a measurement for anything 1 mole means 6.022 x 10 23 of anything This is called Avogadro’s Number A sample of an element with a mass equal to that element’s average atomic mass expressed in grams contains 1 mol of atoms

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The Mole

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  1. The Mole Chapter 6

  2. The Mole • Remember it is a measurement for anything • 1 mole means 6.022 x 1023 of anything • This is called Avogadro’s Number • A sample of an element with a mass equal to that element’s average atomic mass expressed in grams contains 1 mol of atoms • 26.98 g of Aluminum has 6.022 x 1023 atoms = 1mol

  3. How can this help us? • If you know how many grams make 1 mole, you can figure out how many moles you have in a given mass • If you have 0.00568 g of Silicon how many atoms do you have? • Know that 1 mol Si is 28.09 g and 1 mole is 6.022 x 1023 atoms, these are your conversion factors • So 0.00568 g x 1 mol/28.09 g = 0.000202 mol Si • 0.000202 mol Si x 6.022 x 1023 atoms/ 1 mol = 1.22 x 1020 Si atoms

  4. Molar Mass • What is the mass of 1 mole of a compound? Simply add the mass of the elements moles to get the compounds molar mass • CH4 is made up of 1 mol of C and 4 mol of H • 1 mol C = 1 x 12.01 g = 12.01 g • 4 mol H = 4 x 1.008 g = 4.032 g • So 1 mol of CH4 = 12.01 g + 4.032 g = 16.04 g • Try to find molar mass of CaCO3 • Answer = • Now figure out how many grams of CaCO3 are in 4.86 mol • Answer =

  5. Practice Problem • How many moles and how many molecules of C7H14O2 is in a bee sting if 1 gram is released? • First find Molar Mass • Answer • Second find how many moles in 1 gram • Answer • Finally change moles to molecules • Answer

  6. Enough for 1 day, Watch the Video “The Mole”

  7. Percent composition of Compounds • Take mass of 1 element and divide it by the mass of entire compound and multiply by 100 • Example: C2H5OH (ethanol) What is the mass percent of Carbon in this compound? • What is mass of 1 mole of ethanol? • Answer • What is the mass percent of carbon in ethanol? • Answer • Now do Hydrogen and Oxygen • Answers

  8. 6.6 Formulas of Compounds • Empirical Formula – simplest formula and expresses the smallest whole-number ratio of the atoms present • C6H12O6 and C4H8O4 both have the same empirical formula CH2O • Molecular Formula – the actual formula of a compound that tells you the composition of the molecules that are present • C6H12O6 is the molecular formula for glucose

  9. 6.7 Calculation of Empirical Formulas • Important to learn the chemical formula of a new compound • First figure out relative masses • Second convert masses to number of moles • Divide by the smallest number of moles found • Multiply the numbers from 3rd step by smallest number that will make them all whole numbers, this is the empirical formula

  10. Example Problem • An oxide of aluminum is formed by the reaction of 4.151 g of aluminum with 3.692 g of oxygen. What is the empirical formula of the compound formed? • Relative Masses must be converted to moles • 4.151 g Al x 1 mol Al/ 26.98 g Al = 0.1539 mol of Al atoms • 3.692 g O x 1 mol O/ 16.oo g O= 0.2308 mol of O atoms • Divide by smallest number of moles • 0.1539 mol Al / 0.1539 = 1.000 mol Al • 0.2308 mol O / 0.1539 = 1.500 mol O • Multiply by smallest number to make them all whole • 1.500 O x 2 = 3 O atoms • 1.000 Al x 2 = 2 Al atoms • So formula is Al2O3

  11. Practice Problem • In a lab experiment it was observed that 0.6884 g of lead combines with 0.2356 g of chlorine to form a binary compound. What is the empirical formula of this compound? • Step 1 Relative Masses • Step 2 Convert to moles • Step 3 Divide by smallest number • Step 4 Multiply by smallest number that makes them all whole numbers • Rules apply no matter how many elements are in the compound

  12. Calculation of Molecular Formulas • Must know percent composition and the molar mass • It’s always a multiple of the empirical formula (Empirical Formula)n = molecular formula or Empirical Formula x n = molecular formula • Compare the empirical formula to molar mass

  13. Example • If Empirical formula is P2O5 and molar mass is 283.88 g, what is compound’s molecular formula? • Know we have 2 moles P and 5 moles O • 2 mol P = 2 x 30.97 g = 61.94 g • 5 mol O = 5 x 16.00 g = 80.00 g • 1 mol P2O5 = 141.94 g • Know empirical formula x n = molecular formula and that the molecular formula = molar mass • This tells us n = molar mass/ empirical formula • So 283.88 g / 141.94 = n = 2 • So (P2O5)2 means P4O10

  14. Practice Problem • What are the empirical and molecular formulas of a compound with these percent compositions 71.65% Cl, 24.27% C, 4.07% H and a molar mass of 98.96 g?

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