Calculating Moles of a Compound

• What is a mole described as in the video?

  A very large number
• How do you calculate the number of moles of an element?

  By using the equation: number of moles = mass in grams / relative atomic mass
• What do we need to revise to calculate the number of moles of a compound?

  The idea of relative formula mass
• What is the formula for carbon dioxide?

  CO₂
• What is the relative atomic mass of carbon?

  12
• What is the relative atomic mass of oxygen?

  16
• How do you calculate the relative formula mass of carbon dioxide?

  By adding the relative atomic masses of its components: 12 + 2(16) = 44
• What is the symbol for relative formula mass?

  M
• Does relative formula mass have units?

  No, it has no unit
• What is the equation to calculate the number of moles of a compound?

  Number of moles = mass in grams / relative formula mass
• If you have 300 g of calcium carbonate, how do you calculate the number of moles?

  Divide 300 g by the relative formula mass of calcium carbonate
• What is the formula for calcium carbonate?

  CaCO₃
• What is the relative atomic mass of calcium?

  40
• How do you calculate the relative formula mass of calcium carbonate?

  Add the relative atomic masses: 40 (Ca) + 12 (C) + 3(16) (O) = 100
• How many moles of calcium carbonate are in 300 g?


  3 moles
• If you have 380 g of magnesium chloride, how do you calculate the number of moles?

  Divide 380 g by the relative formula mass of magnesium chloride
• What is the formula for magnesium chloride?

  MgCl₂
• What is the relative atomic mass of magnesium?

  24
• What is the relative atomic mass of chlorine?

  35.5
• How do you calculate the relative formula mass of magnesium chloride?

  Add the relative atomic masses: 24 (Mg) + 2(35.5) (Cl) = 95
• How many moles of magnesium chloride are in 380 g?

  4 moles
• If you have 990 g of lithium sulfate, how do you calculate the number of moles?

  Divide 990 g by the relative formula mass of lithium sulfate
• What is the formula for lithium sulfate?

  Li₂SO₄
• What is the relative atomic mass of lithium?


  7
• What is the relative atomic mass of sulfur?

  32
• How do you calculate the relative formula mass of lithium sulfate?

  Add the relative atomic masses: 2(7) (Li) + 32 (S) + 4(16) (O) = 110
• How many moles of lithium sulfate are in 990 g?

  9 moles
• If you have 64.5 g of barium hydroxide, how do you calculate the number of moles?

  Divide 64.5 g by the relative formula mass of barium hydroxide
• What is the formula for barium hydroxide?

  Ba(OH)₂
• What is the relative atomic mass of barium?

  137
• What is the relative atomic mass of hydrogen?

  1
• How do you calculate the relative formula mass of barium hydroxide?

  Add the relative atomic masses: 137 (Ba) + 2(16) (O) + 2(1) (H) = 43
• How many moles of barium hydroxide are in 64.5 g?

  1. 5 moles
• What are the steps to calculate the number of moles of a compound?

  1. Determine the formula of the compound.
  2. Calculate the relative formula mass.
  3. Use the equation: number of moles = mass in grams / relative formula mass.
• What are the relative atomic masses of common elements mentioned?

  • Carbon: 12
  • Oxygen: 16
  • Calcium: 40
  • Magnesium: 24
  • Chlorine: 35.5
  • Lithium: 7
  • Sulfur: 32
  • Barium: 137
  • Hydrogen: 1