Empirical Formula

• What does the formula of a compound show?

  Relative number of atoms of each element
• How can the formula of a substance be determined?

  Through experimentation or empirical evidence
• What is an empirical formula?

  It is the simplest whole number ratio
• What does a molecular formula indicate?

  Actual number of atoms in one molecule
• What are the empirical and molecular formulas for alkenes like Ethene and Propene?

  • Ethene:
  • Empirical Formula: CH₂
  • Molecular Formula: C₂H₄
  • Propene:
  • Empirical Formula: CH₂
  • Molecular Formula: C₃H₆
• What is the empirical formula for the first four members of the alkene series?

  CH₂ for all compounds
• How can the molecular formula be calculated from the empirical formula?

  Using the empirical formula and Mᵣ of the molecule
• If the empirical formula is C₄H₃O₂ and Mᵣ is 166, what is the molecular formula?


  C₈H₆O₄
• What is the relative mass (Mᵣ) of the empirical formula C₂H₅?

  29
• How do you calculate the number of empirical units in a molecule?

  Divide Mᵣ by the empirical formula mass
• What is the empirical formula for copper oxide?

  CuO
• Why is it meaningless to talk about molecular formulas for giant covalent structures?

  They do not contain molecules
• What is the definition of a hydrated compound?

  Contains water of crystallisation
• What is an anhydrous compound?

  Does not contain water of crystallisation
• How do you find the value of n in a hydrated compound formula?

  Calculate moles of water and compound
• If a sample of magnesium sulfate loses 3.78g of water, what is the mass of magnesium sulfate left?

  3.60g
• How do you calculate the ratio of amounts in a hydrated compound?

  Divide moles of each component
• What is the formula for hydrated copper sulfate?

  CuSO₄.xH₂O
• How do you calculate the empirical formula from mass percentages?

  Convert percentages to moles
• If a compound contains 40.0g of carbon, 6.7g of hydrogen, and 53.5g of oxygen, what is the relative molecular mass?

  60
• What is the empirical formula for a compound with 54.5% carbon, 9.10% hydrogen, and 36.4% oxygen?

  C₃H₆O
• How do you find the empirical formula from mass data of a compound?

  Use mass to calculate moles
• What is the empirical formula for nitroglycerin based on its composition?

  C₃H₅N₃O₆
• What is the molecular formula for dichloroethane with 24.3% carbon and 4.1% hydrogen?

  C₂H₄Cl₂
• How do you calculate the empirical formula for a liquid with a molecular weight of 44.0?

  Convert mass percentages to moles
• If a compound contains 58.8% carbon, 9.8% hydrogen, and 31.4% oxygen, what is its molecular formula?

  C₄H₈O₂
• What are the steps to calculate the empirical formula from mass data?

  1. Convert mass to moles for each element
  2. Divide by the smallest number of moles
  3. Write the empirical formula using whole numbers
• What is water of crystallisation and its significance?

  • Water molecules incorporated into a compound's structure
  • Essential for the crystal structure
  • Describes hydrated compounds
• What is the formula for hydrated calcium nitrate?

  Ca(NO₃)₂.xH₂O
• How do you find the value of x in a hydrated compound formula?

  Calculate moles of water and compound
• If a sample of hydrated barium chloride loses mass upon heating, how do you find its formula?

  Calculate the mass lost and moles
• What is the formula for a hydrate containing 85.25% barium chloride?

  BaCl₂.xH₂O
• How do you calculate the empirical formula from mass percentages?

  Convert percentages to moles
• If a compound contains 40.0g of carbon, 6.7g of hydrogen, and 53.5g of oxygen, what is the relative molecular mass?

  60
• What is the empirical formula for a compound with 54.5% carbon, 9.10% hydrogen, and 36.4% oxygen?

  C₃H₆O
• How do you find the empirical formula from mass data of a compound?

  Use mass to calculate moles
• What is the empirical formula for nitroglycerin based on its composition?

  C₃H₅N₃O₆
• What is the molecular formula for dichloroethane with 24.3% carbon and 4.1% hydrogen?

  C₂H₄Cl₂
• How do you calculate the empirical formula for a liquid with a molecular weight of 44.0?

  Convert mass percentages to moles
• If a compound contains 58.8% carbon, 9.8% hydrogen, and 31.4% oxygen, what is its molecular formula?

  C₄H₈O₂