2.4 Molecular & Empirical Formulas

• What does the molecular formula of a substance show?

  The actual number of atoms of each element present in a compound or molecule
• What is the molecular formula for glucose?

  C6H12O6
• How many carbon atoms are in a glucose molecule?

  6 carbon atoms
• What is the empirical formula of glucose?

  CH2O
• What does the empirical formula represent?

  The simplest, whole number ratio of atoms of each element in a compound
• What is the ratio of carbon to hydrogen to oxygen in glucose's empirical formula?

  1 : 2 : 1
• What is the process to find the empirical formula from a molecular formula?

  1. Identify the molecular formula.
  2. Determine the ratio of atoms.
  3. Simplify the ratio to the smallest whole numbers.
• What is the empirical formula of ethane, given its molecular formula C2H6?

  CH3
• How do you simplify the ratio of C : H atoms in ethane from 2 : 6?

  By dividing both sides by 2 to get 1 : 3
• How to find the molecular formula from the empirical formula and Mr?

  1. Determine the empirical formula.
  2. Find the molar mass (Mr) of the empirical formula.
  3. Divide the given Mr by the empirical formula's Mr.
  4. Multiply the empirical formula by this ratio to get the molecular formula.
• If an unknown compound has an empirical formula of CH3 and an Mr of 30, what is its molecular formula?

  C6H12
• What is the molecular formula of a compound with an empirical formula of CH2O and an Mr of 180?

  C8H12O4
• How to find the empirical formula from masses or percentages?

  1. Convert percentages to grams (assuming 100g total).
  2. Find the number of moles of each element.
  3. Divide by the smallest number of moles to get the simplest ratio.
  4. Write the empirical formula based on this ratio.
• What is the empirical formula for a compound containing 50.05% sulfur and 49.95% oxygen by weight?

  SO2
• What is the empirical formula of a compound that contains 46.3% lithium and 53.7% oxygen?

  Li2O
• What is the empirical formula of a compound that contains 15.9% boron and 84.1% fluorine?

  BF3
• What is the empirical formula for a compound that is 43.7% phosphorus and 56.4% oxygen?

  PO