Lecture Notes: Conversion Factors and Mole Ratios

Key Concepts

• Conversion Factors: Used to convert units by canceling out unwanted units.

  • Example: Converting lenses per spider or hands per person to total lenses or hands.
  • Important to identify and use the correct fraction of the conversion factor to cancel out units.

• Chemical Formulas and Mole Ratios:

  • Mole ratios come from chemical formulas and are used to determine the amount of elements in a compound.
  • Example: In calcium carbonate (CaCO₃), the constituent elements are calcium, carbon, and oxygen.
  • The mole ratio derived from the formula: 1 mole of CaCO₃ contains 1 mole of calcium, 1 mole of carbon, and 3 moles of oxygen.

Example Problems

Problem 1: Moles of Oxygen in Calcium Carbonate

• Objective: Determine the number of moles of oxygen in 1.7 moles of calcium carbonate.
• Mole Ratio:
  • 1 mole of CaCO₃ = 1 mole of Ca = 1 mole of C = 3 moles of O
• Solution: Use the mole ratio to find the moles of oxygen.

Problem 2: Mass of Sodium in Sodium Chloride

• Objective: Convert grams of sodium to grams of sodium chloride.
• Steps:
  1. Start with the given mass of sodium (e.g., 2.4 grams).
  2. Convert grams of sodium to moles using the conversion factor (1 mole Na = 22.99 grams Na).
  3. Use the mole ratio (1 mole NaCl = 1 mole Na).
  4. Convert moles of sodium chloride to grams using the conversion factor (1 mole NaCl = 58.44 grams NaCl).
• Result: Calculate the mass in grams of sodium chloride.

Important Notes

• Conversion between grams of two different substances requires an intermediate conversion to moles.
• Key conversion factors:
  • Grams to Moles: Use molar mass.
  • Moles to Grams: Use molar mass for the specific compound.

Study Tips

• Practice problems repeatedly to understand conversion processes.
• Review chapters 2 and 6 to solidify your understanding of conversions and mole calculations.
• Seek help if you're struggling with concept application or problem-solving.