Using Moles to Balance Chemical Equations

Introduction

• Topic: Balancing chemical equations using moles.
• Level: Higher tier only.
• Previous Knowledge: Counting atoms method to balance equations.
• Objective: Learn to balance equations using moles.

Key Concepts

• Moles: A measure of quantity in chemistry, important for balancing equations.
• Relative Formula Mass: Used to calculate the number of moles.

Example 1: Hydrogen and Chlorine Reaction

• Given:
  • 2g of Hydrogen (H)
  • 71g of Chlorine (Cl)
  • 73g of Hydrogen Chloride (HCl)
• Steps to Balance:
  1. Calculate moles:
     • Moles of H = Mass / Relative Formula Mass = 2 / 2 = 1 mole
     • Moles of Cl = 71 / 71 = 1 mole
     • Moles of HCl = 73 / 36.5 = 2 moles
  2. Determine the lowest ratio:
     • Divide all moles by the smallest number (1 in this case):
       • H: 1/1 = 1
       • Cl: 1/1 = 1
       • HCl: 2/1 = 2
  3. Write balanced equation without the number one.

Example 2: Aluminium and Iron Oxide Reaction

• Given:
  • 54g of Aluminium (Al)
  • 216g of Iron (III) Oxide (Fe₂O₃)
  • 102g of Aluminium Oxide (Al₂O₃)
  • 168g of Iron (Fe)
• Steps to Balance:
  1. Calculate moles:
     • Al = 2 moles, Fe₂O₃ = 3 moles, Al₂O₃ = 1 mole, Fe = 3 moles
  2. Determine the lowest ratio:
     • Divide by the smallest number (1):
       • Al: 2/1 = 2
       • Fe₂O₃: 3/1 = 3
       • Al₂O₃: 1/1 = 1
       • Fe: 3/1 = 3
  3. Write balanced equation using the ratio.

Example 3: Barium Chloride and Aluminium Sulfate Reaction

• Given:
  • 1,248g of Barium Chloride (BaCl₂)
  • 684g of Aluminium Sulfate (Al₂(SO₄)₃)
  • 1,398g of Barium Sulfate (BaSO₄)
  • 534g of Aluminium Chloride (AlCl₃)
• Steps to Balance:
  1. Calculate moles:
     • BaCl₂ = 6 moles, Al₂(SO₄)₃ = 2 moles, BaSO₄ = 6 moles, AlCl₃ = 4 moles
  2. Determine the lowest ratio:
     • Divide by the smallest number (2):
       • BaCl₂: 6/2 = 3
       • Al₂(SO₄)₃: 2/2 = 1
       • BaSO₄: 6/2 = 3
       • AlCl₃: 4/2 = 2
  3. Write balanced equation using this ratio.

Conclusion

• Practice: Use the method to balance more complex equations.
• Additional Resources: More questions in Vision workbook, link provided.
• Goal Achieved: Ability to balance chemical equations using moles.