Lecture on Moles and Calculations

Introduction

• Concept of a mole: Relative atomic/molecular mass in grams
• Example: Sodium (atomic mass = 23) = 1 mole is 23g

Calculating Molecular Mass

• Sodium Chloride (NaCl): Total mass of sodium and chlorine = 58.5g
• 58.5g of NaCl = 1 mole

Moles in Gases

• 1 mole of any gas occupies 24 dm³ at room temperature and pressure
• Avogadro's Law: Equal volumes of gases have the same number of particles
  • Avogadro's constant: 6.02 x 10²³ (number of particles in 1 mole)

Calculations for Moles

Mass-Based Calculations

• Number of moles = Mass (g) / Molecular mass (MR)

Volume-Based Calculations for Gases

• Number of moles = Volume (dm³) / 24

Solution-Based Calculations

• Number of moles = Concentration (mol/dm³) x Volume (dm³)

Problem Solving Examples

Example 1: Sulfuric Acid Calculation

• Given: Volume = 20 cm³, Concentration = 1 mol/dm³
• Convert volume to dm³, then calculate moles: 0.02 mol

Example 2: Phosphoric Acid Concentration

• Mass = 7.84g, Volume = 400 cm³
• Calculate moles using mass, then find concentration using volume

Example 3: Reaction with Sodium Carbonate

• Given mass of Na₂CO₃, calculate moles using MR
• Use balanced equation for stoichiometric calculations

Practical Applications

• Convert volumes, calculate concentrations
• Use stoichiometry and balance equations for calculations

Additional Examples

Example 4: Hydrocarbon Combustion

• Deduce formula of CₓHᵧ from given volumes of gases

Example 5: Basic Lead Carbonate

• Determine X and Y in compound formula from mass data

Yield and Purity Calculations

Percent Purity

• Formula: (Mass of pure substance / Mass of impure) x 100
• Example calculation using given volumes and masses

Percent Yield

• Formula: (Actual yield / Theoretical yield) x 100
• Example calculation with hydrogen and ammonia

Limiting Reactant Concepts

• Determine limiting and excess reactants from given data
• Perform calculations based on the limiting reactant

Conclusion

• Emphasize understanding of stoichiometry, conversions, and Avogadro's constant
• Practice and application of concepts in varied problems