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The Mole

The Mole. What is a mole?. Mole (mol) – a counting unit. Similar to a dozen. 1 dozen is always 12. Chemists use moles to count very small objects, like atoms and molecules. 1 mole = 6.022x10 23 particles. 6.022x10 23 = 602.2 billion trillion Avogadro’s Number (N).

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The Mole

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  1. The Mole

  2. What is a mole? • Mole (mol) – a counting unit. • Similar to a dozen. • 1 dozen is always 12. • Chemists use moles to count very small objects, like atoms and molecules. • 1 mole = 6.022x1023 particles. • 6.022x1023 = 602.2 billion trillion • Avogadro’s Number (N)

  3. Amadeo Avogadro (1776-1856)

  4. How Big Is Avogadro’s Number? • If you had Avogadro’s number of dollars: • you’d be 12.8 trillion times richer than Bill Gates. • you could match the entire world’s gross domestic product 11 billion times. • you could pay every person on Earth almost 90 trillion dollars (as of September 2008).

  5. Counting by Weighing – A Marble Analogy • Imagine being asked to count a small handful of green marbles. Easy, right?

  6. Counting by Weighing – A Marble Analogy • Now imagine being asked to count the marbles in a large paper bag. • You could count the marbles individually (tedious!) or... • You could find the mass of one marble, then weigh the bag of marbles and get a good estimate of how many marbles the bag contains.

  7. Counting by Weighing – A Marble Analogy • Could you count the marbles in the back of a dump truck? • You’d have to count them exclusively by weighing. • (Don’t forget to subtract the mass of the truck!)

  8. Counting by Weighing • Like the marbles in the dump truck, atoms are too numerous to count individually. • But we can estimate their numbers by weighing.

  9. Molar Mass • Molar mass (MM) – the mass of one mole of a substance in grams. • For elements, the MM is equal in number to the atomic mass.

  10. 6 1 carbon atom = 12.01 daltons (average) C 1 mol C = 12.01 grams 12.01 Molar Mass

  11. Molar Mass • What is the mass (in grams) of 4.60 mol C? 4.60 mol C 12.01 g C = 55.2 g C 1 mol C

  12. Molar Mass • How many atoms are in 4.60 mol C? 4.60 mol C 6.022x1023 atoms = 2.77x1024 atoms 1 mol C

  13. Molar Mass • Are 4.60 moles of carbon, 55.2 grams of carbon, and 2.77x1024 atoms of carbon all the same amount? • Yes!

  14. Molar Mass • How many moles are in 16.00 g He? 16.00 g He 1 mol He = 4.00 mol He 4.00 g He

  15. Molar Mass of Compounds • To find the MM of a compound: • Add the MMs of its elements. • EXAMPLE: The MM of H2O is: • 2 x H = 2 x 1.01 g/mol = 2.02 g/mol • 1 x O = 1 x 16.00 g/mol = 16.00 g/mol • TOTAL = 18.02 g/mol • 1 mol of H2O masses 18.02 g.

  16. Molar Mass of Compounds • The MM of Na2SO4 is: • 2 x Na = 2 x 22.99 g/mol = 45.98 g/mol • 1 x S = 1 x 32.07 g/mol = 32.07 g/mol • 4 x O = 4 x 16.00 g/mol = 64.00 g/mol • TOTAL = 142.05 g/mol • 1 mol of Na2SO4 masses 142.05 g.

  17. Molar Mass of Compounds • The MM of Ca(NO3)2 is: • 1 x Ca = 1 x 40.08 g/mol = 40.08 g/mol • 2 x N = 2 x 14.01 g/mol = 28.02 g/mol • 6 x O = 6 x 16.00 g/mol = 96.00 g/mol • TOTAL = 164.10 g/mol • 1 mol of Ca(NO3)2 masses 164.10 g.

  18. Molar Mass of Compounds • How many moles of CO2 are in 22.0 grams of CO2? MM of CO2 = 22.0 g CO2 1 mol CO2 1 x 12.01 g/mol = 12.01 g/mol 2 x 16.00 g/mol = 32.00 g/mol 44.01 g CO2 TOTAL = 44.01 g/mol = 0.500 mol CO2

  19. Molar Mass of Compounds • What is the mass (in grams) of 10.5 moles of SO2? MM of SO2 = 10.5 mol SO2 64.07 g SO2 1 x 32.07 g/mol = 32.07 g/mol 2 x 16.00 g/mol = 32.00 g/mol 1 mol SO2 TOTAL = 64.07 g/mol = 673 g SO2

  20. Molar Mass of Hydrates • Hydrate – an ionic cmpd that has water molecules in it. • EXAMPLES: • CuSO4•5H2O • Fe(NO3)3•9H2O • Ba(C2H3O2)2•2H2O

  21. Molar Mass of Hydrates • The MM of CuSO4•5H2O is: • 1 x Cu = 1 x 63.55 g/mol = 63.55 g/mol • 1 x S = 1 x 32.07 g/mol = 32.07 g/mol • 4 x O = 4 x 16.00 g/mol = 64.00 g/mol • 5 x H2O = 5 x 18.02 g/mol = 90.10 g/mol • TOTAL = 249.72 g/mol • 1 mol of CuSO4•5H2O masses 249.72 g.

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