(40) GCSE Chemistry Revision "Using Moles to Balance Equations"

Introduction to Balancing Chemical Equations Using Moles

• Focus: Higher tier chemistry students.

• Previous learning: Balancing equations through counting atoms.

• New approach: Using moles for balancing.

Example 1: Balancing the Reaction between Hydrogen and Chlorine

• Reaction: Hydrogen + Chlorine ⟶ Hydrogen Chloride

• Mass Data Given: 2 g of Hydrogen, 71 g of Chlorine, produces 73 g of Hydrogen Chloride.

• Calculation of Moles:

  • Hydrogen:

    • Mass = 2 g

    • Relative formula mass = 2

    • Moles = Mass / Formula Mass = 2 g / 2 = 1 mole

  • Chlorine:

    • Mass = 71 g

    • Relative formula mass = 71

    • Moles = Mass / Formula Mass = 71 g / 71 = 1 mole

  • Hydrogen Chloride:

    • Mass = 73 g

    • Relative formula mass = 36.5

    • Moles = Mass / Formula Mass = 73 g / 36.5 = 2 moles

• Ratios:

  • Lowest Ratio Calculation:

    • Hydrogen: 1/1 = 1

    • Chlorine: 1/1 = 1

    • Hydrogen Chloride: 2/1 = 2

• Balanced Equation:

  • H + Cl ⟶ 2 HCl

  • Remove '1' in front of H and Cl since it's convention.

Example 2: Reaction of Aluminium and Iron(II) Oxide

• Reaction: Aluminium + Iron(II) Oxide ⟶ Aluminium Oxide + Iron

• Mass Data Given: 54 g of Aluminium, 216 g of Iron(II) Oxide, produces 102 g of Aluminium Oxide and 168 g of Iron.

• Calculation of Moles:

  • Aluminium: 2 moles

  • Iron(II) Oxide: 3 moles

  • Aluminium Oxide: 1 mole

  • Iron: 3 moles

• Ratios:

  • Lowest Ratio Calculation:

    • Aluminium: 2/1 = 2

    • Iron(II) Oxide: 3/1 = 3

    • Aluminium Oxide: 1/1 = 1

    • Iron: 3/1 = 3

• Balanced Equation:

  • 2 Al + 3 FeO ⟶ 1 Al2O3 + 3 Fe

  • Remove '1' in front of Aluminium Oxide.

Example 3: Barium Chloride and Aluminium Sulfate Reaction

• Reaction: Barium Chloride + Aluminium Sulfate ⟶ Barium Sulfate + Aluminium Chloride

• Mass Data Given: 1,248 g of Barium Chloride, 684 g of Aluminium Sulfate, produces 1,398 g of Barium Sulfate and 534 g of Aluminium Chloride.

• Calculation of Moles:

  • Barium Chloride: 6 moles

  • Aluminium Sulfate: 2 moles

  • Barium Sulfate: 6 moles

  • Aluminium Chloride: 4 moles

• Ratios:

  • Lowest Ratio Calculation:

    • Barium Chloride: 6/2 = 3

    • Aluminium Sulfate: 2/2 = 1

    • Barium Sulfate: 6/2 = 3

    • Aluminium Chloride: 4/2 = 2

• Balanced Equation:

  • 3 BaCl2 + 1 Al2(SO4)3 ⟶ 3 BaSO4 + 2 AlCl3

  • Remove '1' in front of Aluminium Sulfate.

Conclusion

• Mastering moles for balancing equations is foundational for more complicated reactions.

• More practice can be found in related workbooks.