Avogadro's Constant and Mole Calculations

Introduction

• Focus on using Avogadro's constant to calculate the number of molecules and atoms in a given sample.
• Relevant for higher level students.
• One mole is Avogadro's constant: (6.02 \times 10^{23}).

Calculating Atoms in a Given Mass

1. Equation Used:

   • Number of moles = (\frac{\text{Mass in grams}}{\text{Relative Atomic Mass}})

2. Example: Calculate atoms in 48g of Magnesium

   • Given mass = 48g
   • Relative atomic mass of Magnesium = 24
   • Calculation: (\frac{48}{24} = 2) moles
   • Total atoms = Avogadro's constant (\times 2 = 1.24 \times 10^{24}) atoms.

3. Practice Problem: Calculate atoms in 28g of Lithium

   • Given mass = 28g
   • Relative atomic mass of Lithium = 7
   • Calculation: (\frac{28}{7} = 4) moles
   • Total atoms = Avogadro's constant (\times 4 = 2.48 \times 10^{24}) atoms.

Calculating Atoms in a Compound

1. Example: Calculate atoms in 56g of Calcium Oxide (CaO)

   • Relative atomic mass: Calcium = 40, Oxygen = 16
   • Relative formula mass = 40 + 16 = 56
   • Calculation: (\frac{56}{56} = 1) mole
   • Total atoms = Avogadro's constant (\times 2 = 1.24 \times 10^{24}) atoms.

2. Practice Problem: Calculate atoms in 54g of Water (H(_2)O)

   • Relative atomic mass: Hydrogen = 1, Oxygen = 16
   • Relative formula mass of Water = 2(1) + 16 = 18
   • Calculation: (\frac{54}{18} = 3) moles
   • Total molecules = Avogadro's constant (\times 3 = 1.86 \times 10^{24}) molecules
   • Total atoms = (1.86 \times 10^{24} \times 3 = 5.418 \times 10^{24}) atoms._

Conclusion

• Able to calculate number of molecules and atoms using Avogadro's constant.
• Practice these calculations using questions from the vision workbook.