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Chemical Composition

Chemical Composition. Chapter 10. Chemical Packages - Moles. We use a package for atoms and molecules called a mole A mole is the number of particles equal to the number of Carbon atoms in 12 g of C-12 One mole = 6.022 x 10 23 units

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Chemical Composition

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  1. Chemical Composition Chapter 10

  2. Chemical Packages - Moles • We use a package for atoms and molecules called a mole • A mole is the number of particles equal to the number of Carbon atoms in 12 g of C-12 • One mole = 6.022 x 1023 units • The number of particles in 1 mole is called Avogadro’s Number • This is the magic number that allows us to turn atomic masses (amu) into grams

  3. Atomic Masses • Unit is the amu. • atomic mass unit • 1 amu = 1.66 x 10-24g • We define the masses of atoms, molecules, and formula units in terms of atomic mass units. • 1 Carbon atom = 12.01 amu • 1 O2 molecule = 2(16.00 amu) = 32.00 amu • 1 MgCl2 F.U. = 24.31 + 2(35.45) = 95.21 amu • Atomic mass, molecular mass, and formula mass are ALL measured in amu.

  4. Molar Mass • The molar mass is the mass in grams of one mole of a compound • The molecular mass can be calculated from atomic masses: water = H2O = 2(1.01 amu) + 16.00 amu = 18.02 amu • 1 mole of H2O will weigh 18.02 g, therefore the molar mass of H2O is 18.02 g • C = 12.01 amu = 12.01 g • O2 = 32.00 amu = 32.00 g • MgCl2 = 95.21 amu = 95.21 g

  5. Example #1 Compute the number of moles and number of atoms in 10.0 g of Al • Use the Periodic Table to determine the mass of 1 mole of Al 1 mole Al = 26.98 g • Use this as a conversion factor for grams-to-moles

  6. Example #1 Compute the number of moles and number of atoms in 10.0 g of Al • Use Avogadro’s Number to determine the number of atoms in 1 mole 1 mole Al = 6.022 x 1023 atoms • Use this as a conversion factor for moles-to-atoms

  7. Mole Conversions – mol to g A .267 mol sample of magnesium nitride equals how many grams? Formula = ??? Mg+2 N-3 Mg3N2 Molar Mass = ??? Mg = 3(24.31) = 72.93 g N = 2(14.01) = 28.02 g Molar Mass = 100.95 g 100.95 g Mg3N2 = 1 mol Mg3N2 .267 mol Mg3N2 x 27.0 g Mg3N2

  8. Mole Conversions – g to mol A 56.51 g sample of potassium oxide contains how many moles? Formula = ??? K+1 O-2  K2O Molar Mass = ??? K = 2(39.10) = 78.20 g O = 1(16.00) = 16.00 g Molar Mass = 94.20 g 56.51 g K2O 1 mol K2O 94.20 g K2O x = .5999 mol K2O

  9. Mole Conversions – g to molecules If you have a 24.31 g sample of propanol, C3H8O, how many molecules are produced? Molar Mass = ??? C = 3(12.01) = 36.03 g H = 8(1.01) = 8.08 g O = 1(16.00) = 16.00 g Molar Mass = 60.11 g 1 mol C3H8O 60.11 g C3H8O 6.022 x 1023 molecules 1 mol C3H8O 24.31 g C3H8O x x = 2.435 x 1023 molecules

  10. Mole Conversions – g to atoms A 6.93 g sample of sodium oxalate contains how many carbon atoms? Formula = ??? Na+1 C2O4-2 Na2C2O4 Molar Mass = ??? Na = 2(22.99) = 45.98 g C = 2(12.01) = 24.02 g O = 4(16.00) = 64.00 g Molar Mass = 134.00 g 6.93 g Na2C2O4 1 mol Na2C2O4 134.00 g Na2C2O4 6.022 x 1023 F.U. 1 mol Na2C2O4 x x x 2 carbon atoms 1 F.U. = 6.23 x 1022 carbon atoms

  11. Molar Volume of a Gas at STP Standard Temperature = 0 0 C Standard Pressure = 1 atm (101.3 kPa) These 2 conditions together are known as STP At STP 1 mol of ANY gas has a volume of 22.4 L Ex: what is the volume of 3.00 mol of hydrogen gas at STP?

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