Relative formula mass

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

  Relative formula mass and related calculations
• How can we 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 atomic mass denoted by?

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

  35.5
• How do we 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 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 (MgCl₂)?

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

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

  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 calculating the percentage mass of an element in a compound?

  (ar of the element × number of atoms) / mr of the compound × 100
• What is the formula of calcium hydroxide?

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

  (16 × 2) / 74 × 100
• What is the relative atomic mass of calcium?

  40
• 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)?

  40 + 2 × 16 + 2 × 1 = 74
• What is the percentage mass of oxygen in calcium hydroxide?

  43.2%
• What are the steps to calculate the percentage mass of an element in a compound?

  1. Find the relative atomic mass (ar) of the element.
  2. Multiply ar by the number of atoms of that element.
  3. Divide by the relative formula mass (mr) of the compound.
  4. Multiply by 100 to convert to a percentage.
• What is the process to find the relative formula mass of a compound?

  1. Identify the molecular formula of the compound.
  2. Find the relative atomic masses of each element.
  3. Add together the relative atomic masses of all atoms in the formula.