ELECTROCHEMISTRY

By Al D. Deacon – Physicist | Educator | Researcher

📧 al.deaconjr@gmail.com | 🌐 www.goldengeniuzonline.com


1. Conduct Investigations Leading to the Classification of Substances as Conductors or Nonconductors

  • Conductors: Materials that allow electricity to flow due to the presence of free-moving charge carriers (electrons or ions).
    • Examples: Metals (Cu, Al, Fe), graphite, aqueous salt solutions.
  • Nonconductors (Insulators): Materials that do not allow electricity to flow because they lack free charge carriers.
    • Examples: Plastic, wood, glass, distilled water.
  • Investigation:
    • Set up a simple circuit with a battery, bulb, and test material.
    • Observe whether the bulb lights up (conductor) or remains off (nonconductor).

2. Distinguish Between Metallic and Electrolytic Conduction

Metallic Conduction:

  • Occurs in metals and graphite.
  • Due to the movement of delocalized electrons.
  • No chemical changes occur.
  • Conductivity remains constant at constant temperature.

Electrolytic Conduction:

  • Occurs in electrolytes (ionic solutions or molten salts).
  • Due to the movement of free ions (cations and anions).
  • Chemical reactions occur at the electrodes.
  • Conductivity depends on the ion concentration and strength of the electrolyte.

3. Classify Electrolytes as Strong or Weak Based on Their Conductivity

Strong Electrolytes:

  • Completely ionize in solution.
  • High conductivity.
  • Examples: HCl, H₂SO₄, NaCl, KOH.

Weak Electrolytes:

  • Partially ionize in solution.

  • Low conductivity.

  • Examples: CH₃COOH (acetic acid), NH₄OH, H₂CO₃ (carbonic acid).

  • Experiment: Measure conductivity using a conductivity meter or observe the brightness of a bulb in an electrolyte solution.

4. Define Electrolysis, Cathode, Anode, Cation, Anion

  • Electrolysis: The decomposition of an electrolyte using electricity.
  • Cathode: The negative electrode where reduction occurs.
  • Anode: The positive electrode where oxidation occurs.
  • Cation: A positively charged ion that moves to the cathode.
  • Anion: A negatively charged ion that moves to the anode.

5. Identify Ions Present in Electrolytes

  • Example: Electrolysis of NaCl solution (Brine):
    • NaCl dissociates into Na⁺ and Cl⁻.
    • Water dissociates into H⁺ and OH⁻.
    • At the electrodes:
      • Cathode: H⁺ is reduced (H₂ gas released).
      • Anode: Cl⁻ is oxidized (Cl₂ gas released).

6. Predict the Electrode to Which an Ion Will Drift

  • Cations (+) move to the cathode (-).
  • Anions (-) move to the anode (+).
  • Example:
    • In CuSO₄ solution: Cu²⁺ moves to the cathode, SO₄²⁻ moves to the anode.

7. Predict Chemical Reactions Using the Electrochemical Series

  • Electrochemical Series determines which ions are discharged during electrolysis:
    • At the cathode, the less reactive metal or hydrogen is deposited.
    • At the anode, the halide ion (Cl⁻, Br⁻, I⁻) is discharged before OH⁻.
Cations (Cathode) Anions (Anode)
K⁺, Na⁺ (not discharged) SO₄²⁻, NO₃⁻ (not discharged)
Ca²⁺, Mg²⁺ (not discharged) OH⁻ (discharged as O₂)
Zn²⁺, Fe²⁺ Cl⁻, Br⁻, I⁻ (discharged as Cl₂, Br₂, I₂)
H⁺ (discharged as H₂)

Example Prediction:

  • Electrolysis of CuSO₄ solution with copper electrodes:
    • Cathode: Cu²⁺ + 2e⁻ → Cu (copper deposits).
    • Anode: Cu → Cu²⁺ + 2e⁻ (copper dissolves).

8. Discuss the Electrolysis of Certain Substances

Electrolyte Cathode Product Anode Product
Molten NaCl Na (sodium metal) Cl₂ (chlorine gas)
NaCl solution H₂ (hydrogen gas) Cl₂ (chlorine gas)
H₂SO₄ solution H₂ (hydrogen gas) O₂ (oxygen gas)
CuSO₄ solution Cu (copper metal) O₂ (oxygen gas, unless Cu anode is used)

9. Define the Faraday Constant

  • Faraday Constant (F): The charge of one mole of electrons.
    • F = 96,500 C/mol (approx. 96,500 coulombs per mole of electrons).

10. Calculate the Masses and Volumes of Substances Liberated During Electrolysis

  • Faraday’s Laws of Electrolysis:
    • 1st Law: Mass deposited ∝ charge passed.
      • m = (Q × M) / (n × F)
      • where m = mass, Q = It (charge = current × time), M = molar mass, n = electrons transferred, F = Faraday constant.
    • 2nd Law: For the same charge, the mass deposited depends on the equivalent weight.

Example Calculation:

  1. How much copper is deposited when 2A current passes through CuSO₄ for 30 min?
    • Charge, Q = It = (2A × 1800s) = 3600 C
    • Molar mass of Cu = 63.5 g/mol, n = 2
    • m = (3600 × 63.5) / (2 × 96,500) = 1.18 g

11. Describe Industrial Applications of Electrolysis

1. Extraction of Metals (Electrometallurgy)

  • Aluminium Extraction (Hall-Héroult Process)
    • Electrolysis of molten Al₂O₃ in cryolite.
    • Cathode: Al³⁺ + 3e⁻ → Al (liquid aluminium).
    • Anode: O²⁻ → O₂ + 4e⁻ (oxygen reacts with carbon anode to form CO₂).

2. Electroplating

  • Coating an object with a metal layer using electrolysis.
  • Example: Silver Plating
    • Electrolyte: AgNO₃ solution.
    • Cathode: Object to be plated (e.g., spoon).
    • Anode: Pure silver.

3. Manufacture of Chlorine, Hydrogen, and Sodium Hydroxide (Chlor-Alkali Process)

  • Electrolysis of brine (NaCl solution).
  • Products:
    • Cathode: H₂ gas.
    • Anode: Cl₂ gas.
    • Solution: NaOH formed.

4. Electrorefining of Copper

  • Impure copper anode dissolves into solution.
  • Pure copper cathode gains Cu²⁺ ions.

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