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The Mole

The Mole. "Not everything that counts can be counted, and not everything that can be counted counts." Albert Einstein. What is a mole?. The mole is a counting unit. Like . . . 1 dozen = 12 each 1 yard = 3 feet 1 cup = 8 ounce So then ... 1 mol = 6.022 x 10 23 particles

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The Mole

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  1. The Mole "Not everything that counts can be counted, and not everything that can be counted counts." Albert Einstein

  2. What is a mole? • The mole is a counting unit. • Like . . . • 1 dozen = 12 each • 1 yard = 3 feet • 1 cup = 8 ounce • So then ... • 1 mol = 6.022 x 1023 particles That’s Avogadro’s Number!

  3. Where did it come from? • Mole (n) is the SI unit for the number of particles • Amedo Avogadro determined the number of particles in a mole • The mole is the measure of the amount of a substance whose number of particles is the same as 12 grams of Carbon -12

  4. Calculations • Using dimensional analysis you can determine the number of particles in a mole • 1 mole = 6.022 x 1023 particles, molecules, etc. • 1 mole / 6.022 x 1023 particles • 6.022 x 1023 particles / 1 mole

  5. So, let’s count . . . • 1 mol of Ag = • 6.022 x 1023 atoms Ag • 1 mol of CO2 = • 6.022 x 1023 molecules of CO2 • 1 mol of pizza = • 6.022 x 1023 pizzas!

  6. Calculating # moles • 3.011 x 1023 atoms of Oxygen • 0.5 moles of Oxygen • 3.655 x 1012 molecules of CO • 6.070 x 10-10 moles of CO

  7. Classwork • Practice on these • pg. 228 #1-4 • pg. 229 #1-5

  8. Atomic Mass • The mass of an element at rest. • Relative Atomic Mass is the weighted average of all the atomic masses for all of the isotopes of an element. • Since the atomic mass is an average, it is not in whole number form.

  9. Atomic Mass Unit • Atomic mass is measured in atomic mass units (amu) as a standard • It equals the measure of 1/12 the mass of 12 grams of Carbon-12 • 1 a.m.u. = 1.6605 x 10-27kg

  10. For Example • The periodic chart list the atomic mass of Oxygen as 15.999 amu • Does Oxygen really weigh 15.999 g?

  11. Calculate the Mass of an Atom • Oxygen has an atomic mass of 15.999 amu • 1 amu = 1.6605 x 10-27 kg • So 1 atom of Oxygen really weighs, 15.999 a.m.u. x (1.6605 x 10-27kg a.m.u.) = 2.657 x 10-26 kg or 2.657 x 10-23 g

  12. Determine the Atomic Mass • What is the atomic mass in amu of Sodium? • Mass number = 22.989, so . . • Atomic mass = 22.989 amu • What is the atomic mass in amu of Uranium? • 238.03 amu

  13. Formula Mass • Chemical compounds are written as an empirical formula. • Ex. H2SO4 is Sulfuric Acid • To calculate atomic mass, add each atom. • H = 1.008 x 2 = 2.016 • S = 32.07 x 1 = 32.07 • O = 15.999 x 4 = 63.996 Total Atomic Mass = 2.016+32.07+63.996 = 98.08 amu

  14. Molar Mass • One mole of particles has a special mass associated with it. • Molar mass is grams per mole • g/mol • The number is represented by the mass number on the Periodic Chart

  15. So, then . . . • If the mass number on the periodic chart for Oxygen is 15.999, Then • Oxygen has a molar mass of . . . • 15.999 grams per mole

  16. What is the molar mass of ... • Oxygen? • Nitrogen? • Carbon?

  17. Molar Formula Mass • The subscripts in a chemical formula represent the number of moles of that element • each separate element contributes to the overall formula mass of a chemical compound • Example: H2O • H = 1.011 x 2 = 2.022 g/mol • O = 15.999 g/mol • H2O = 18.000 g/mol

  18. Classwork • Now try these in class • p. 231 # 1-4 • p. 233 # 6-13

  19. Periodic Mass Number • The mass number on the Periodic Chart can be the weight of a single atom in atomic mass units; (15.999 amu Oxygen) OR • The mass of one mole of the element (15.999 g/mol Oxygen)

  20. And . . . • If Oxygen is 15.999 g/mol; and, • 1 mol = 6.022 x 1023 atom, then . . . (15.999 g/mol) x (1 mol/6.022 x 1023 atom) = 2.657 x 10-23grams

  21. Wait a minute! • Have you seen that number before? • Let’s recap . . . 15.999 a.m.u. x (1.6605 x 10-27kg a.m.u.) = 2.657 x 10-26 kg or 2.657 x 10-23 g And (15.999 g/mol) x (1 mol/6.022 x 1023 atom) = 2.657 x 10-23grams

  22. Moles to Mass Conversions • Moles = mass (g) / Molar mass (g/mol) • n = m / M

  23. Let’s Calculate • Calculate the number of moles in 250 g of Copper • Molar mass of Cu = 63.55 g/mol • n = m / M • n = 250 g / 63.55 g/mol = 3.94 mol Cu

  24. And another . . . • Calculate the mass of 3.50 mol of Cu • Molar mass of Cu is 63.55 g/mol • n = m / M and m = n * M • m = 3.50 mol * 63.55 g/mol = 222 g Cu

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