Free Science Lessons: Calculating Masses Using Moles

Introduction

• Focus of the lesson: Using moles to calculate masses of reactants and products in chemical reactions.
• Target audience: Higher tier students.

Key Concepts

• Moles in Chemistry:
  • Moles represent amounts in chemical equations.
  • Understanding the relationship between moles and mass is crucial to solving chemistry problems.

Examples and Calculations

Example 1: Magnesium Chloride

• Equation: 1 mole of Magnesium + 1 mole of Chlorine → 1 mole of Magnesium Chloride.
• Problem: Calculate the mass of Magnesium Chloride from 146 g of Hydrochloric Acid (HCl).
  • Step 1: Analyze equation - 2 moles of HCl produce 1 mole of Magnesium Chloride.
  • Step 2: Find moles of HCl - Mass (146 g) / Relative Formula Mass (36.5) = 4 moles.
  • Step 3: Calculate moles of Magnesium Chloride - 4 moles HCl → 2 moles Magnesium Chloride.
  • Step 4: Calculate mass - Moles (2) × Relative Formula Mass of Magnesium Chloride (95) = 190 g.

Example 2: Sodium Sulfate

• Problem: Calculate mass from 240 g of Sodium Hydroxide (NaOH).
  • Step 1: Analyze equation - 2 moles of NaOH make 1 mole of Sodium Sulfate.
  • Step 2: Find moles of NaOH - Mass (240 g) / Relative Formula Mass (40) = 6 moles.
  • Step 3: Calculate moles of Sodium Sulfate - 6 moles NaOH → 3 moles Sodium Sulfate.
  • Step 4: Calculate mass - Moles (3) × Relative Formula Mass of Sodium Sulfate (142) = 426 g.

Example 3: Hydrogen Peroxide

• Problem: Calculate mass from 64 g of Oxygen.
  • Step 1: Analyze equation - 2 moles of Hydrogen Peroxide make 1 mole of Oxygen.
  • Step 2: Find moles of Oxygen - Mass (64 g) / Relative Formula Mass (32) = 2 moles.
  • Step 3: Calculate moles of Hydrogen Peroxide - Need 4 moles Hydrogen Peroxide for 2 moles Oxygen.
  • Step 4: Calculate mass - Moles (4) × Relative Formula Mass of Hydrogen Peroxide (34) = 136 g.

Conclusion

• With practice, calculating reacting masses using moles can become straightforward.
• Additional practice questions available in the vision workbook.

Additional Resources

• Vision workbook for more practice on calculating reacting masses.