Relative Formula Mass

• 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?

  Number of protons plus 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 is the relative atomic mass of an element calculated?

  By averaging the masses of its isotopes
• What is relative formula mass denoted by?

  mr
• How do you find the relative formula mass of a compound?

  Add the relative atomic masses of all atoms
• What is the relative formula mass of magnesium chloride (MgCl₂)?

  95
• What is the relative atomic mass of magnesium?

  24
• How do you calculate the relative formula mass of sulfuric acid (H₂SO₄)?

  98
• What is the formula to calculate the percentage mass of an element in a compound?

  (ar of element × number of atoms) / mr of compound × 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)?

  Calculate using ar and mr
• What is the relative atomic mass of oxygen?

  16
• What is the relative atomic mass of hydrogen?

  1
• What is the relative formula mass of calcium hydroxide (Ca(OH)₂)?

  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 (mr).
• What is the process to calculate the percentage mass of an element in a compound?

  1. Use the formula: (ar of element × number of atoms) / mr of compound × 100.
  2. Substitute the values for the specific element and compound.
  3. Calculate to find the percentage mass.