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Electrochemistry - Coggle Diagram

- - - - Conductivity decreases with dilution due to fewer ions per unit volume.
      - Molar conductivity increases with dilution, especially for weak electrolytes.
    - - Plotting Λm against √c yields a straight line for strong electrolytes.
      - Intercept represents Λ°m and slope represents ‘-A’.
    - - Facilitates calculation of Λ°m for electrolytes.
      - Useful for determining dissociation constants of weak electrolytes.
    - - Values of molar conductivity at different concentrations for electrolytes like acetic acid and potassium chloride.
- - - - Components: Consists of two platinum electrodes coated with platinum black.
      - Arrangement: Electrodes placed at a fixed distance in a cell.
      - Measurement: Conductance of the solution measured using a conductivity meter.
    - - Definition: Ratio of distance between electrodes to their area.
      - Calculation: Determined using solutions of known conductivity.
    - - Process: Measured conductance multiplied by the cell constant.
      - Units: Typically expressed in Siemens per meter (S/m).
  - - - Represents the conductivity of a solution containing one mole of electrolyte.
    - - Formula: Λm = k × V, where k is the conductivity and V is the volume containing one mole of electrolyte.
      - Importance: Helpful in understanding the behavior of electrolytes at different concentrations.
    - - Strong Electrolytes: Molar conductivity slightly increases with dilution.
      - Weak Electrolytes: Molar conductivity significantly increases with dilution due to increased dissociation.
- - - - Example Regularity: Difference in Λ°m for NaX and KX electrolytes is nearly constant.
      - Specific Findings:
        
        For KCl and NaCl, difference in Λ°m ≈ 23.4 S cm² mol⁻¹.
        
        For NaBr and NaCl, difference in Λ°m ≈ 1.8 S cm² mol⁻¹.
  - - - Method: For any electrolyte, Λ°m is calculated from the Λ°m of individual ions.
      - Use in Weak Electrolytes: Determines Λ°m for weak electrolytes by using Kohlrausch's law.
    - - Process: For weak electrolytes, dissociation constants are determined using Λ°m values obtained from Kohlrausch's law.
    - - Insight: Provides understanding of the behavior of electrolytes in solutions, especially in very dilute solutions.
- - - - First Law
        
        Proportionality: The amount of chemical reaction at an electrode during electrolysis is proportional to the quantity of electricity passed through the electrolyte.
      - Second Law
        
        Substance Amounts: Amounts of different substances liberated are proportional to their chemical equivalent weights.
    - - Charge on one mole of electrons: 96487 C (Faraday, F).
      - Example Calculation: Using Faraday's laws to calculate the mass of copper deposited during electrolysis.
  - - - Reaction: Cu2+(aq) + 2e– → Cu (s).
      - Calculation: Using current and time to determine the mass of copper deposited.
  - - - Commercial Production: High amperage used for large-scale metal production.
      - Example: Electrolysis of CuSO4 for purifying copper.
- - - - Essentially galvanic cells converting chemical energy into electrical energy.
      - Must be light, compact, and maintain stable voltage.
    - - Single-use batteries that cannot be reused after discharge.
      - Examples:
        
        Dry Cell (Leclanche Cell)
        
        Components: Zinc container (anode), carbon (graphite) rod (cathode), moist paste of ammonium chloride (NH4Cl) and zinc chloride (ZnCl2).
        
        Electrode Reactions: Zinc at the anode and a complex reaction involving manganese dioxide at the cathode.
        
        Voltage: Approximately 1.5 V.
        
        Mercury Cell
        
        Suitable for low current devices like hearing aids and watches.
        
        Components: Zinc-mercury amalgam (anode) and a paste of HgO and carbon (cathode).
        
        Electrolyte: Paste of KOH and ZnO.
    - - Rechargeable batteries that can undergo multiple charging and discharging cycles.
      - Lead Storage Battery
        
        Commonly used in automobiles and inverters.
        
        Composition: Lead anode, lead dioxide cathode, and a 38% solution of sulfuric acid as electrolyte.
        
        Function: On discharging, lead and lead dioxide convert into lead sulfate and water. On charging, the reaction reverses.
  - - - More efficient than thermal power plants, converting chemical energy directly into electricity with minimal pollution.
      - Continuous feeding of reactants to the electrodes and removal of products from the electrolyte compartment.
    - - Highly successful example used in the Apollo space program.
      - Components: Hydrogen and oxygen fed through porous carbon electrodes into a concentrated aqueous sodium hydroxide solution.
      - Catalysts: Finely divided platinum or palladium.
      - Electrode Reactions: Oxygen reduction at the cathode and hydrogen oxidation at the anode.
      - Overall Reaction: 2H2(g) + O2(g) → 2H2O(l).
      - Efficiency: Approximately 70% in converting chemical energy into electricity.
- - - - Iron Oxidation: Fe (s) → Fe²⁺ (aq) + 2e⁻.
      - Anodic Reaction: At the anodic spot, iron loses electrons.
    - - Oxygen Reduction: O₂ (g) + 4H⁺ (aq) + 4e⁻ → 2H₂O (l).
      - Cathodic Reaction: Electrons move to another spot and reduce oxygen in the presence of H⁺.
    - - Atmospheric Oxidation: 2Fe²⁺ (aq) + 2H₂O (l) + ½O₂ (g) → Fe₂O₃ (s) + 4H⁺ (aq).
      - Electrode Potentials: Anode (E°(Fe/Fe²⁺) = -0.44 V), Cathode (E°(O₂/H₂O) = 1.23 V).
      - Cell Potential: E°(cell) = 1.67 V.
      - Final Product: Rust (hydrated ferric oxide, Fe₂O₃.xH₂O) along with the production of hydrogen ions.
    - - Protective Coatings
        
        Painting: Prevents metallic surfaces from contacting the atmosphere.
        
        Chemical Treatments: Using chemicals like bisphenol for protective covering.
      - Electrochemical Protection
        
        Sacrificial Anode: Using metals like Mg, Zn, etc., which corrode themselves to protect the main object.
        
        Galvanization: Covering iron with a layer of zinc to prevent rusting.