Avogadro's Constant and Mole Calculations

Objective

• Use Avogadro's constant to calculate the number of molecules and atoms in a given sample.
• Targeted at higher students, not foundation level.

Key Concepts

• Avogadro's Constant: 6.02 x 10^23, used to represent the number of particles in a mole.

Calculating Moles of Atoms

Example 1: Water (H2O)

• Formula: H2O
• Atoms per Molecule: 2 hydrogen, 1 oxygen = 3 atoms
• Moles of Atoms: 1 mole of water molecules = 3 moles of atoms

Example 2: Methane (CH4)

• Formula: CH4
• Atoms per Molecule: 1 carbon, 4 hydrogen = 5 atoms
• Moles of Atoms: 1 mole of methane molecules = 5 moles of atoms

Example 3: Calcium Hydroxide (Ca(OH)2)

• Formula: Ca(OH)2
• Atoms per Molecule: 1 calcium, 2 oxygen, 2 hydrogen = 5 atoms
• Moles of Atoms: 1 mole of calcium hydroxide = 5 moles of atoms

Calculating Number of Atoms

Example 1: Hydrogen Chloride (HCl)

• Formula: HCl
• Atoms per Molecule: 1 hydrogen, 1 chlorine = 2 atoms
• Number of Atoms: 1 mole of HCl = 6.02 x 10^23 molecules
  • Total: 2 x 6.02 x 10^23 = 1.204 x 10^24 atoms

Example 2: Sodium Oxide (Na2O)

• Formula: Na2O
• Atoms per Molecule: 2 sodium, 1 oxygen = 3 atoms
• Number of Atoms: 1 mole of Na2O = 6.02 x 10^23 molecules
  • Total: 3 x 6.02 x 10^23 = 1.806 x 10^24 atoms

Additional Resources

• More questions and exercises available in the revision workbook.