Relative Formula Mass

• What is the topic covered in today's video?

  Relative formula mass and related calculations
• How can you find the mass number of any element?

  By looking in the top left corner of its nuclear symbol
• What does the mass number represent?

  The number of protons plus the number of neutrons in the nucleus
• What is relative formula mass denoted by?

  mr
• What is the relative atomic mass of chlorine as an element?

  35.5
• How do you calculate the relative formula mass of a compound?

  By adding together the relative atomic masses of all the atoms in its molecular formula
• What is the molecular formula of magnesium chloride?

  MgCl₂
• What is the relative atomic mass of magnesium?

  24
• How do you calculate the relative formula mass of magnesium chloride?

  24 + 35.5 × 2 = 95
• What is the molecular formula of sulfuric acid?

  H₂SO₄
• What is relative atomic mass denoted by?

  ar
• How do you calculate the relative formula mass of sulfuric acid?

  2 × 1 + 32 + 4 × 16 = 98
• How do you calculate the percentage mass of sulfur in sulfuric acid?

  (32 × 1) / 98 × 100
• What is the percentage mass of sulfur in sulfuric acid?

  32.7%
• What is the formula for calcium hydroxide?

  Ca(OH)₂
• How do you find the relative atomic mass of each element in calcium hydroxide?

  40 for calcium, 16 for oxygen, and 1 for hydrogen
• How do you calculate the percentage mass of oxygen in calcium hydroxide?

  (16 × 2) / 74 × 100
• What is the final percentage mass of oxygen in calcium hydroxide?

  43.2%
• What are the steps to calculate the relative formula mass of a compound?

  1. Identify the molecular formula.
  2. Find the relative atomic masses of each element.
  3. Multiply the relative atomic mass by the number of atoms for each element.
  4. Add all the values together to get the relative formula mass.
• What is the formula to calculate the percentage mass of an element in a compound?

  • Percentage mass = (ar of element × number of atoms) / mr of compound × 100