3.1 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 an 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 atomic mass denoted by?

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

  35.5
• How do you find 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 relative formula mass of magnesium chloride (MgCl₂)?

  95
• How do you calculate the relative formula mass of sulfuric acid (H₂SO₄)?

  By calculating \(2 \times 1 + 1 \times 32 + 4 \times 16 = 98\)
• How do you find the percentage mass of sulfur in sulfuric acid?

  By using the formula \(\frac{32 \times 1}{98} \times 100\)
• What is the percentage mass of sulfur in sulfuric acid?

  32.7%
• How do you find the percentage mass of oxygen in calcium hydroxide (Ca(OH)₂)?

  By calculating \(\frac{16 \times 2}{74} \times 100\)
• What is the percentage mass of oxygen in calcium hydroxide?

  43.2%
• What is the process to calculate the relative formula mass of a compound?

  • Identify the molecular formula of the compound.
  • Find the relative atomic masses of each element.
  • Multiply the relative atomic mass by the number of atoms of that element.
  • Sum all the values to get the relative formula mass (mr).
• What is the formula for calculating the percentage mass of an element in a compound?

  • Formula: \(\frac{\text{ar of element} \times \text{number of atoms}}{\text{mr of compound}} \times 100\)