Calculating Percentage by Mass

• What is the formula for calculating the percentage by mass of an element in a compound?

  Percentage by mass = (total relative atomic mass of the element / relative formula mass of the compound) × 100
• What does the percentage by mass of an element in a compound indicate?

  • It shows the proportion of the compound's mass that comes from a specific element.
  • It is calculated using the relative atomic mass of the element and the relative formula mass of the compound.
• What is the relative atomic mass of magnesium?

  24
• What is the relative atomic mass of oxygen?

  16
• How do you determine the relative formula mass of magnesium oxide?

  By adding 24 (magnesium) and 16 (oxygen) to get 40.
• What is the relative formula mass of magnesium oxide?

  40
• How would you calculate the percentage by mass of magnesium in magnesium oxide?

  60%
• What is the formula for calcium chloride?

  Ca₂Cl₂
• What is the relative formula mass of calcium chloride?

  111
• What is the relative atomic mass of calcium?

  40