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Understanding the Mole: A Precise Unit of Measure for Atoms and Compounds

Learn about the concept of a mole, its importance in chemistry, and how to convert between moles and particles. Discover the molar mass of elements and compounds. Suitable for students and chemistry enthusiasts.

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Understanding the Mole: A Precise Unit of Measure for Atoms and Compounds

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  1. The Mole

  2. What is a mole? • It’s a precise number of things • Its similar to the concept of a dozen • A dozen eggs = 12 eggs • A mole = 6.02 X 1023 • Mole in latin = heap or pile

  3. Why do we use a mole? • Atoms are very small • You can’t see an atom • You cant see a dozen atoms not even a billion atoms • But if you had a mole of atoms now you can start to see them and weigh them

  4. How BIG is a Mole? • A mole of water is 18 ml • A mole of marbles would…?

  5. How BIG is a Mole? • A mole of water is 18 ml • A mole of marbles would cover the entire earth several miles deep

  6. How big is a mole? one mole of table tennis balls would cover the Earth to a depth of about 40 km.

  7. Counting atoms by weighing? • Atoms are too small to count individually • We count atoms by weighing them • A mole of carbon weighs 12.01 g

  8. Counting atoms by weighing? • Ex. imagine you work in a candy store and people wanted to buy 50 jelly beans or 300 or even 1000 jelly beans • instead of counting each jelly bean you could find out what 1 jelly bean weighs then multiply by the number you needed • ex. 1 jelly bean = 1 gram 500 JB = 500g

  9. Counting atoms by weighing? • 1 jelly bean = 1 gram • The customer wants 1000 jelly beans • 1000 beans x 1 grams = 1000 grams 1 jelly bean It’s a lot easier to weigh out 1000 g of jelly beans on a scale then count each one by hand

  10. The MOLE • Mole- SI unit for amount of matter • mol • 6.02 X 1023 representative particles • Avogadro’s number = 6.02 X 1023

  11. The MOLE • Mole- SI unit for amount of matter • mol • 6.02 X 1023 representative particles = Avogadro’s Number . Atom (Fe, C) • Molecule (molecular compounds; CH4) • Formula Units (salts, ionic compounds; NaCl) • Ions (Na+)

  12. 1 mole = 6.02 X 1023 particles : 6.02 X 1023 particles 1mol 0r 1mol . 6.02 X 1023 particles

  13. 1 mole = the atomic mass of an element in grams • Gram atomic mass is the atomic mass from the periodic table, expressed as “grams/mole” instead of “amu”

  14. 1 mole = the atomic mass of an element in grams • Gram atomic mass is the atomic mass from the periodic table, expressed as “grams/mole” instead of “amu” • Ex. 1 mole of Carbon has a mass of 12.01 g 1 mol Carbon12.01 g Carbon 12.01 g Carbon OR 1 mol Carbon

  15. Molar mass is the mass in grams of one mole of a substance. • It’s value comes from the periodic table. • Molar mass is related to Avogadro’s number like this: Molar mass (g) = 1mole = 6.02x1023 particles

  16. Elements For Zn, 1mol=65.39g For Al, 1mol=26.98g For Au, 1mol=196.97g Don’t forget the diatomics!! For O2, 1mol=32.00g Examples relating mass and moles

  17. Compounds For NaCl, 1 mol=(22.99+35.45)g For H2O, 1mol=((2x1.01)+16.00)g For C2H6, 1mol=((2x12.01)+(6x1.01))g Examples relating mass and moles

  18. Be able to convert from moles to particles: • How many molecules are in 0.360 mol of water?

  19. Be able to convert from moles to particles: • How many molecules are in 0.360 mol of water? 1st write given: 0.360 mol H2O x 1

  20. Be able to convert from moles to particles: • How many molecules are in 0.360 mol of water? 2nd write conversion factor: 0.360 mol H2O x 6.02 X 1023 molecules = 1 1mol H20

  21. Be able to convert from moles to particles: • How many molecules are in 0.360 mol of water? Next multiply everything on top divide by everything on the bottom: 0.360 mol H2O x 6.02 X 1023 particles = 1 1mol

  22. Be able to convert from moles to particles: • How many molecules are in 0.360 mol of water? Next multiply everything on top divide by everything on the bottom: 0.360 mol H2O x 6.02 X 1023 particles = 1 1mol Answer = 2.17 E23 molecules of water

  23. Be able to convert from particles to moles: • How many moles of Mg are in 1.25 X1023 atoms?

  24. Be able to convert from particles to moles: • How many moles of Mg are in 1.25 X1023 atoms? Write given then conversion factor 1.25 X1023 atoms Mg x 1 mol Mg = 1 6.02 X 1023 atoms

  25. Be able to convert from particles to moles: • How many moles of Mg are in 1.25 X1023 atoms? Write given then conversion factor 1.25 X1023 atoms Mg x 1 mol = 1 6.02 X 1023 atoms Answer = .208 moles of Mg

  26. Find the molar mass 1 mol C = 1 mol CH4 = 1 mol (NH4)2CO3 1 mol CaCl2 =

  27. Find the molar mass 1 mol C = 12.01 g/mol 1 mol CH4 = 16.05 g/mol 1 mol (NH4)2CO3 = 98.11 g/mol 1 mol CaCl2 = 110.98 g/mol

  28. 4.65 X 1024 molecules NO2 1 Ex. How many moles are in 4.65 X 1024 molecules of NO2?

  29. 4.65 X 1024 molecules NO2 x 1 mole NO2 = 1 6.02x1023 molecules Ex. How many moles are in 4.65 X 1024 molecules of NO2?

  30. 4.65 X 1024 molecules NO2 x 1 mole NO2 = 1 6.02x1023 molecules Answer = 7.72 moles NO2 Ex. How many moles are in 4.65 X 1024 molecules of NO2?

  31. Molar Mass- mass of 1 mol in g, • use periodic table & add up the masses, • round to 2 spaces past the decimal

  32. Molar Mass- mass of 1 mol in g, • use periodic table & add up the masses, • round to 2 spaces past the decimal Find Molar Mass of: Ne Cl2 NH3

  33. Molar Mass- mass of 1 mol in g, • use periodic table & add up the masses, • round to 2 spaces past the decimal Find Molar Mass of: Ne = 20.18 g Cl2 = 35.45 x 2 = 70.90 g NH3 = 14.01 + 3(1.01) = 14.01 + 3.03 = 17.04g

  34. Be able to convert moles to mass: • Use the following conversion factor: Molar mass (g) 1 mol

  35. Be able to convert moles to mass: • Use the following conversion factor: Molar mass (g) 1 mol • How many g are in 9.45 mol N2O3? First find Molar Mass N2O3 2(14.01) + 3(16.00) = 28.02 +48.00 =76.02 g

  36. Be able to convert moles to mass: • Use the following conversion factor: Molar mass (g) 1 mol • How many g are in 9.45 mol N2O3? 9.45 mol N2O3 x 76.02 g N2O3 = ??? 1 mol N2O3

  37. Be able to convert moles to mass: • Use the following conversion factor: Molar mass (g) 1 mol • How many g are in 9.45 mol N2O3? 9.45 mol N2O3 x 76.02 g N2O3 = 718.39 g 1 mol N2O3

  38. Be able to convert mass to moles: • Multiply by: 1 mol Molar mass (g)

  39. Be able to convert mass to moles: • Multiply by: 1 mol Molar mass (g) How many moles are in 92.2 g Fe2O3?

  40. Be able to convert mass to moles: • Multiply by: 1 mol Molar mass (g) How many moles are in 92.2 g Fe2O3? 92.2 g Fe2O3 X 1 MoleFe2O3 = g Fe2O3

  41. Be able to convert mass to moles: • Multiply by: 1 mol Molar mass (g) How many moles are in 92.2 g Fe2O3? Molar Mass Fe2O3 = 2(55.85g) + 3(16.00g)= 111.70 + 48.00 =159.7

  42. Be able to convert mass to moles: • Multiply by: 1 mol Molar mass (g) How many moles are in 92.2 g Fe2O3? 92.2 g Fe2O3 X 1 MoleFe2O3 = 159.7 g Fe2O3

  43. Be able to convert mass to moles: • Multiply by: 1 mol Molar mass (g) How many moles are in 92.2 g Fe2O3? 92.2 g Fe2O3 X 1 MoleFe2O3 = 159.7 g Fe2O3 Answer = 0.577 moles Fe2O3

  44. Multi-step problems- convert to moles then to desired unit • Calculate number of molecules in 60.0g NO2. 60.0g NO2 x 1 mole NO2 46.01 g NO2

  45. Multi-step problems- convert to moles then to desired unit • Calculate number of molecules in 60.0g NO2. 60.0g NO2 x 1 mole NO2 x 6.02x1023 molecules 46.01 g NO2 1 mole NO2

  46. Multi-step problems- convert to moles then to desired unit • Calculate number of molecules in 60.0g NO2. 60.0g NO2 x 1 mole NO2 x 6.02x1023 molecules 46.01 g NO2 1 mole NO2 Answer = 7.85 x 1023 molecules of NO2

  47. Lab Counting by weighing

  48. For all substances: • 1 mol=molar mass=6.02 X 1023 particles • FOR GASES ONLY: • 1 mol=molar mass=6.02 X 1023 particles • AND at STP (standard temperature & pressure) OC &101.3kpa or 1 atm 1mol= 22.4L • Molar volume- 1 mol of gas at STP has 22.4 L

  49. Convert mol volume • Multiply by: 22.4L 1 mol • Determine the volume of 0.60 mol SO2 at STP. • To convert from volumemol invert the conversion factor • Determine the number of moles in 2 L of CO2 gas at STP.

  50. Can also use density to solve problems • D=mass/volume= m/v=g/L • D of a gas containing C & O is 1.964 g/L at STP. Determine that molar mass. • What is the density of krypton gas at STP?

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