Relative Formula Mass

• What topic is covered in today's video?

  Relative formula mass calculations
• How is the mass number of an element determined?

  By adding protons and neutrons
• Where is the mass number located in a nuclear symbol?

  Top left corner
• What does the relative atomic mass (ar) represent?

  Average mass of all isotopes of an element
• What is the relative atomic mass of chlorine?

  35.5
• What is relative formula mass (mr)?

  Sum of relative atomic masses in a compound
• How do you calculate the relative formula mass of magnesium chloride (MgCl₂)?

  Add 24 and 35.5 times 2
• What is the relative formula mass of magnesium chloride?

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

  Add 2 times 1, 1 times 32, and 4 times 16
• What is the relative formula mass of sulfuric acid?

  98
• How do you calculate the percentage mass of an element in a compound?

  AR of element times number of atoms divided by MR
• 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)?

  Calculate 16 times 2 for oxygen
• What is the relative atomic mass of calcium, oxygen, and hydrogen?

  40 for Ca, 16 for O, 1 for H
• What is the relative formula mass of calcium hydroxide?

  74
• What is the 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.
  4. Sum all the values to get the relative formula mass.
• What is the formula for calculating percentage mass of an element in a compound?

  • Percentage mass = (AR of element × number of atoms) / MR of compound × 100