This lesson focuses on performing calculations involving chemical equations, moles, reacting masses, gas volumes, and solution concentrations.

1. Core Concepts (Short Notes)

5.1 Mole Concept

A mole is the SI unit for amount of substance.

• 1 mole contains 6.02 × 10²³ particles (Avogadro's number).

• Relates mass, volume, and number of particles.

• 
  

5.2 Molar Mass (Mr or M)

Sum of the atomic masses of all atoms in a compound.

• Example: H₂O → (2×1) + 16 = 18 g/mol.

  
  

5.3 Mole Calculations

Key relationships:

• Moles = mass / molar mass

• Mass = molar mass × moles

• Number of particles = moles × Avogadro number

  
  

5.4 Chemical Equations

Balanced equations show mole ratios between reactants and products. These ratios are essential for:

• Finding limiting reagents

• Calculating yields

• Comparing reacting masses

  
  

5.5 Limiting Reagent

The reactant that gets used up first. It determines how much product forms. Steps:

1. Convert masses → moles.

2. Compare mole ratios with the balanced equation.

3. Identify limiting reagent.

   
   

5.6 Percentage Yield

Shows the efficiency of a reaction.

• % Yield = (actual yield / theoretical yield) × 100

  
  

5.7 Gas Calculations

At room temperature and pressure (RTP):

• 1 mole of gas = 24 dm³

Formula:

• Moles = volume / 24 dm³

  
  

5.8 Solution Concentration

• Concentration (mol/dm³) = moles / volume (dm³)

• Or: moles = concentration × volume

Used in titrations and neutralization calculations.

5.9 Titration Calculations

Use the relationship:

• C₁V₁ / n₁ = C₂V₂ / n₂ Where n = stoichiometric coefficient.

2. Key Formulas to Memorize

Mass–Mole Relationship

• n = m / M

• m = nM

Gas Calculations

• n = V / 24 (at RTP)

Concentration

• C = n / V

• n = CV

Percentage Yield

• % yield = (actual / theoretical) × 100

Stoichiometric Ratio

Use coefficients from the balanced equation.

3. Tips & Tricks for Exams

• Always convert cm³ → dm³ by dividing by 1000.

• When stuck, write a clear table: mass → moles → ratio.

• Balance the chemical equation before calculations.

• Identify the limiting reagent; the smallest mole ratio is limiting.

• For titrations, write the neutralization equation (acid + base → salt + water).

• Check units carefully; most mistakes occur in unit conversion.

• Use 24 dm³/mol only at RTP.

4. Important Points to Remember

• Moles link mass, particles, and volume.

• Balanced equations are essential for accurate calculations.

• Limiting reagents determine the maximum product.

• Percentage yield shows real-world reaction efficiency.

• Concentration calculations are central to titration questions.

Correct unit conversions drastically reduce errors.