Relative formula mass

• What is the purpose of relative formula mass in chemistry?

  It is used in conservation of mass calculations.
• How can relative formula masses be calculated?

  By summing the relative atomic masses of the atoms in the chemical formula.
• What is the smallest part of an element that can exist?

  An atom.
• What does mass measure in an object?

  The amount of matter it contains.
• In what units is mass measured?

  In kilograms (kg) or grams (g).
• What is relative atomic mass?

  The mean relative mass of the atoms of the different isotopes in an element.
• What is the symbol for relative atomic mass?

  A_r.
• How is the relative atomic mass of an element defined?

  It is the number of times heavier an atom is than one-twelfth of a carbon-12 atom.
• Where can the A_r values for elements be found?

  In the periodic table.
• What is the relative formula mass symbol?

  M_r.
• How do you calculate the relative formula mass of a substance?

  By adding the A_r values for all the atoms in the formula.
• What is the process to calculate the relative formula mass of carbon dioxide (CO₂)?

  • Identify the number of each atom: 1 carbon (C) and 2 oxygen (O).
  • Use A_r values: C = 12, O = 16.
  • Calculate: M_r = 12 + (2 × 16) = 12 + 32 = 44.
• What is the relative formula mass of calcium hydroxide, Ca(OH)₂?

  M_r = 74.
• How is the relative formula mass of magnesium nitrate, Mg(NO₃)₂ calculated?

  M_r = 148.
• What is an ionic compound?

  • Formed when a negative ion joins with a positive ion.
  • Involves the transfer of electrons.
  • Examples include sodium chloride (NaCl).
• What is the formula for calculating the relative formula mass of a substance?

  M_r = sum of A_r values of all atoms in the formula.
• Why do relative formula masses have no units?

  Because they are relative masses.
• How do relative formula masses of ionic compounds differ from molecular compounds?

  Ionic compounds do not exist as molecules but are calculated similarly.
• What are the steps to calculate the relative formula mass of a compound?

  1. Identify the number of each type of atom in the formula.
  2. Find the A_r values for each element.
  3. Multiply the A_r by the number of atoms.
  4. Sum all the values to get M_r.