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					Mole-Mass and Mole-Volume
      Relationships
    The Mole-Mass Relationship
• To convert the mass of a substance to the
  number of moles of the substance you have to
  use the molar mass of an element or
  compound.

• Mass = # of moles x (mass/1mole)
    The Mole-Mass Relationship
• EX: the molar mass of NaCl is 58.5 g/mol, so
  the mass of 3.00 mol NaCl is calculated:
  o Mass of NaCl = 3 mol x (58.5 g/1 mol)
  o = 176 g


• When you measure 176 g of NaCl on a
  balance, you are measuring 3.00 moles of
  NaCl.
 The Mole-Mass Relationship Practice
• What is the mass of 9.45 mol of aluminum
  oxide (Al2O3)?
  – First add up all the masses
     • Al = 27g x 2 = 54g
     • O = 16g x 3 = 48g
     • Al2O3 = 102 g
  – Then convert from moles to grams:
     • 9.45 mol Al2O3 x (102g/1 mol Al2O3) = 963.9g
 The Mole-Mass Relationship Practice
• 16. Find the mass, in grams, of 4.52 x 10-3 mol
  C20H42.
 The Mole-Mass Relationship Practice
• 17. calculate the mass, in grams, of 2.50 mol
  of iron(II) hydroxide Fe(OH)2.
 The Mole-Mass Relationship Practice
• You can calculate the number of moles using
  the same relationship you use to find the mass
  of moles by inverting the conversion factor.

• Moles = mass x (1mole/mass)
   The Mole-Mass Relationship Practice
• How many moles of iron(III) oxide are contained
  in 92.2 g of pure Fe2O3?

• Fe2O3 = 159.6 g = 1 mol

• 92.2 g Fe2O3 x (1 mol/159.6 g Fe2O3) = 0.578 mol
  Fe2O3
 The Mole-Mass Relationship Practice
• 18. Find the number of moles in 3.70 x 10-1 g
  boron.
 The Mole-Mass Relationship Practice
• 19. Calculate the number of moles in 75.0 g of
  dinitrogen trioxide (N2O3)
   The Mole-Volume Relationship
• Avogadro’s hypothesis states that equal
  volumes of gases at the same temperature
  and pressure contain equal numbers of
  particles.

• Because of variations due to temperature and
  pressure, the volume of a gas is usually
  measured at a standard temperature and
  pressure.
   The Mole-Volume Relationship
• Standard temperature and pressure (STP)
  means a temperature of 0C and a pressure of
  101.3 kPa, or 1 atmosphere (atm).
   The Mole-Volume Relationship
• At STP, 1 mol or 6.02 x 1023 representative
  particles, of any gas occupies a volume of 22.4
  L.

• The quantity, 22.4 L, is called the molar
  volume of a gas.
   The Mole-Volume Relationship
• The molar volume is used to convert a known
  number of moles of gas to the volume of the
  gas at STP.

• Volume of gas = moles of gas x (22.4L/1mol)
   The Mole-Volume Relationship
• Determine the volume, in liters, of 0.60 mol
  SO2 gas at STP.

• 1 mol SO2 = 22.4 L SO2

• Volume = 0.60 mol SO2 x (22.4L/1mol)
• = 13 L SO2
    The Mole-Volume Relationship -
              Practice
• 20. What is the volume of these gases at STP?
  – A. 3.20 x 10-3 mol CO2
  – B. 3.70 mol N2
    The Mole-Volume Relationship -
              Practice
• 21. at STP, what volume do these gases
  occupy?
  – A. 1.25 mol He
  – B. 0.335 mol C2H6
 Calculating Molar Mass from Density
• Different gases have different densities.
  Density of a gas is measured in grams per liter
  (g/L) and at a specific temperature.

• Molar mass = (grams/L) x (22.4 L/1 mole)
 Calculating Molar Mass from Density
• The density of a gaseous compound
  containing carbon and oxygen is found to be
  1.964 g/L at STP. What is the molar mass of
  the compound?

• Molar mass = (1.964 g/L) x (22.4 L/1 mol)
• = 44 g/mol
Calculating Molar Mass from Density -
              Practice
• 22. a gaseous compound has a density of 3.58
  g/L at STP. What is the molar mass of this gas?
 Calculating Molar Mass from Density
• 23. What is the density of krypton gas at STP?

				
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posted:9/22/2012
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