MOLE CONCEPT

  Al D. Deacon 

Founder: Gold'N Geniuz 

Physicist and Educator 

1. Define Mole and Molar Mass

  • Mole (mol): The amount of substance that contains 6.022 × 10²³ particles (atoms, molecules, or ions).
  • Molar Mass (g/mol): The mass of 1 mole of a substance. It is numerically equal to the relative atomic or molecular mass but expressed in grams per mole (g/mol).
    • Example:
      • Molar mass of H₂O = (2 × 1.008) + 16.00 = 18.02 g/mol
      • Molar mass of NaCl = 22.99 + 35.45 = 58.44 g/mol

2. Perform Calculations Involving the Mole

Basic Mole Calculations

  • Number of Moles (n) = Mass (m) / Molar Mass (M)

    • Example:
      • How many moles in 36 g of H₂O?
        n = 36 g / 18.02 g/mol = 2.00 moles

  • Number of Particles = Moles × Avogadro’s Number

    • Example:
      • How many molecules in 2 moles of H₂O?
        Particles = 2 × (6.022 × 10²³) = 1.204 × 10²⁴ molecules

  • Mass = Moles × Molar Mass

    • Example:
      • Find the mass of 0.5 moles of NaCl.
        m = 0.5 × 58.44 g/mol = 29.22 g

3. State Avogadro’s Law

  • Statement: Equal volumes of gases, at the same temperature and pressure, contain the same number of molecules.
  • Implication:
    • 1 mole of any gas at STP (0°C, 1 atm) occupies 22.4 L.
    • At room temperature (25°C, 1 atm), 1 mole of gas occupies 24.0 L.
  • Example Calculation:
    • Find the volume occupied by 3 moles of CO₂ at STP.
      V = 3 × 22.4 L = 67.2 L

4. State the Law of Conservation of Matter

  • Statement: Matter cannot be created or destroyed in a chemical reaction; the total mass of reactants = total mass of products.
  • Example:
    • In the reaction 2H₂ + O₂ → 2H₂O,
      • The total number of H and O atoms before and after remains the same.

5. Write Balanced Equations

  • Balancing Rules:

    1. Write correct formulas for reactants and products.
    2. Count atoms of each element on both sides.
    3. Adjust coefficients to balance atoms.
    4. Check that total mass and charge are conserved.

  • Example (Unbalanced → Balanced):

    • Unbalanced: Fe + O₂ → Fe₂O₃
    • Balanced: 4Fe + 3O₂ → 2Fe₂O₃

6. Apply the Mole Concept to Equations (Ionic & Molecular)

Mole Ratio from Equations

  • The coefficients in a balanced equation show the ratio of moles of reactants and products.

Example:
Consider the reaction:
2H₂ + O₂ → 2H₂O

  • 2 moles of H₂ react with 1 mole of O₂ to form 2 moles of H₂O.
  • If given 5 moles of H₂, the amount of H₂O formed = 5 moles H₂ × (2 moles H₂O / 2 moles H₂) = 5 moles H₂O.

Ionic Equations

  1. Write molecular equation:
    • NaCl + AgNO₃ → NaNO₃ + AgCl (s)
  2. Write full ionic equation:
    • Na⁺ + Cl⁻ + Ag⁺ + NO₃⁻ → Na⁺ + NO₃⁻ + AgCl (s)
  3. Write net ionic equation (removing spectator ions):
    • Ag⁺ + Cl⁻ → AgCl (s)

7. Define Standard Solution

  • Definition: A solution of accurately known concentration used in titrations.
  • Preparation Steps:
    1. Weigh a known mass of solute.
    2. Dissolve it in distilled water.
    3. Transfer to a volumetric flask and make up to the required volume.
  • Example:
    • A 1.00 M NaCl solution contains 58.44 g of NaCl in 1.00 L of solution.


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