Calculating Moles of an Element

Introduction

• Topic for higher tier only
• Aim: Calculate the number of moles of an element
• Understanding that concepts may be tricky
• Importance of reviewing video examples

Relative Atomic Mass

• Defined as the mass of a single atom of an element
• Calculated from average masses of isotopes, weighted for abundance
• Found on the periodic table; provided in exams
• Example:
  • Carbon: relative atomic mass = 12
  • Oxygen: relative atomic mass = 16
• Note: Relative atomic mass has no units

The Concept of Moles

• A mole represents a very large number (Avogadro's number)
• One mole corresponds to the relative atomic mass of an element in grams
• Example:
  • 12 grams of carbon = 1 mole of carbon atoms
  • 16 grams of oxygen = 1 mole of oxygen atoms
• General rule: mass of an element in grams = one mole of atoms of that element
• Useful for calculating the number of atoms in a chemical reaction

Calculating Number of Moles

• Formula:
  • Number of moles = Mass (g) / Relative atomic mass
• Importance of learning this equation

Example Calculations

1. Magnesium Calculation

   • Mass given: 48 grams
   • Relative atomic mass of magnesium: 24
   • Calculation:
     • Moles = 48 g / 24 = 2 moles

2. Calcium Calculation

   • Mass given: 120 grams
   • Relative atomic mass of calcium: 40
   • Calculation:
     • Moles = 120 g / 40 = 3 moles

3. Iron Calculation

   • Mass given: 252 grams
   • Relative atomic mass of iron: 56
   • Calculation:
     • Moles = 252 g / 56 = 4.5 moles

4. Sulfur Calculation

   • Mass given: 4064 grams
   • Relative atomic mass of sulfur: 32
   • Calculation:
     • Moles = 4064 g / 32 = 127 moles

Conclusion

• Mole calculations can be manageable with practice
• More examples available in revision workbook
• Encouragement to practice and learn