Chemical Calculations

PlantUML Diagram

6.5 Chemical Calculations

6.5.1 Mole-Mass Calculations

Example 6.3: Calculating Mass of One Mole of a Substance

  • Sodium (Na): 1 mole = 23 g
  • Nitrogen (N₂): 1 mole = 28 g
  • Sucrose (C₁₂H₂₂O₁₁): 1 mole = 342 g

Problem-solving Strategy:

  • For metals: Molar mass = Atomic mass in grams
  • For molecular elements: Molar mass = Molecular mass in grams

Example 6.4: Calculating Mass of Given Moles

Problem: 9.05 moles of ozone (O₃)

Solution:

  • Molar mass of O₃ = 48 g
  • Mass = Molar mass × Number of moles
  • Mass of 9.05 moles O₃ = 48 g × 9.05 = 434.4 g

Example 6.5: CO₂ Formation from Natural Gas Combustion

Problem: Mass of 0.25 moles CO₂

Solution:

  • Molar mass of CO₂ = 44 g
  • Mass of 0.25 moles CO₂ = 44 g × 0.25 = 11 g

Example 6.6: Converting Grams to Moles

  • a) 5 g of hydrogen (H₂)
  • Molar mass of H₂ = 2.016 g/mol
  • Moles = 5 g ÷ 2.016 g/mol = 2.48 moles
  • b) 100 g of ice (H₂O)
  • Molar mass of H₂O = 18.016 g/mol
  • Moles = 100 g ÷ 18.016 g/mol = 5.55 moles

6.5.2 Mole-Particles Calculations

Example 6.7: Calculating Number of Atoms in Given Moles

  • 1.25 moles of Zn
  • Number of atoms = 6.022 × 10²³ × 1.25 = 7.53 × 10²³ Zn atoms
  • 0.2 moles of Al
  • Number of atoms = 6.022 × 10²³ × 0.2 = 1.2044 × 10²³ Al atoms

Example 6.8: Calculating Number of Molecules in Given Moles

  • 0.5 moles of methane (CH₄)
  • Number of molecules = 6.022 × 10²³ × 0.5 = 3.011 × 10²³ molecules
  • 1.6 moles of H₂O₂
  • Number of molecules = 6.022 × 10²³ × 1.6 = 9.635 × 10²³ molecules

Key Concepts:

  • Mole-mass conversions use molar mass (g/mol)
  • Mole-particle conversions use Avogadro's number (6.022 × 10²³)
  • For metals, molar mass equals gram atomic mass
  • For molecular substances, molar mass equals gram molecular mass

Problem-solving Steps:

  • Identify the substance (metal, molecular, ionic)
  • Determine molar mass
  • Use appropriate conversion factor (molar mass or Avogadro's number)
  • Perform calculations