Mole Concept and Calculating Number of Moles

Jul 6, 2024

Mole Concept and Calculating Number of Moles

Key Concepts

  • Relative Masses and Molar Masses

    • Relative atomic masses:
      • Carbon: 12 amu
      • Oxygen: 16 amu
      • Nitrogen: 14 amu
    • Molar masses (gram atomic masses):
      • Carbon: 12 g
      • Oxygen: 16 g
      • Nitrogen: 14 g
    • Molar masses allow us to see and work with atoms (e.g., 12 g of Carbon contains 6.023 x 10^23 atoms of Carbon).

  • Avogadro's Number

    • 6.023 x 10^23 atoms/molecules/ions = 1 mole (e.g., 1 dozen = 12 items)
    • Avogadro's Number (~6.023 x 10^23) serves as a standardized quantity.

Definitions

  • Mole
    • One mole of any atom = its molar mass.
    • 1 mole of Carbon = 12 g, containing 6.023 x 10^23 atoms.
    • 1 mole of Oxygen = 16 g, containing 6.023 x 10^23 atoms.
    • 1 mole of Nitrogen = 14 g, containing 6.023 x 10^23 atoms.

Relationships

  • m-relationship (mass relationship)
    • Example: 1 mole of Oxygen = 16 g
  • n-relationship (number relationship)
    • Example: 1 mole of Oxygen = 6.023 x 10^23 atoms

Calculation Examples

  • Mass-based calculations

    1. Calculate number of moles in 32 g of Oxygen:
      • 1 mole of Oxygen = 16 g
      • 32 g = 2 moles of Oxygen
    2. Calculate number of moles in 6 g of Carbon:
      • 1 mole of Carbon = 12 g
      • 6 g = 0.5 moles of Carbon
    3. Calculate number of moles in 4 g of Hydrogen:
      • 1 mole of Hydrogen = 1 g
      • 4 g = 4 moles of Hydrogen

  • Number-based calculations

    1. Calculate number of moles in 12 x 10^23 atoms of Oxygen:
      • 1 mole of Oxygen = 6 x 10^23 atoms
      • 12 x 10^23 atoms = 2 moles of Oxygen
    2. Calculate number of moles in 18 x 10^23 atoms of Carbon:
      • 1 mole of Carbon = 6 x 10^23 atoms
      • 18 x 10^23 atoms = 3 moles of Carbon

  • Intermediate Level Calculations

    1. Calculate number of moles in 28 g of Nitrogen atom:
      • 1 mole of Nitrogen atom = 14 g
      • 28 g = 2 moles of Nitrogen atom
    2. Calculate number of moles in 28 g of Nitrogen gas (N2):
      • Molar mass of N2 = 14 + 14 = 28 g
      • 28 g = 1 mole of N2 gas
    3. Calculate number of moles in 49 g of H2SO4:
      • Molar mass of H2SO4 = 2(1) + 32 + 4(16) = 98 g
      • 49 g = 0.5 moles of H2SO4

Conclusion

  • 1 mole = molar mass or 6.023 x 10^23 particles
  • Use m-relationship for mass-based questions and n-relationship for number-based questions.