Electrolytic Cell and Quantitative Electrolysis

Key Concepts

• Electrolytic Cell: Uses current to drive a non-spontaneous redox reaction, requiring an external voltage source (e.g., a battery).

  • Electron Flow: Electrons come from the negative terminal of the battery.

• Reduction and Oxidation Processes:

  • Zinc Electrode: Zinc ions (Zn²⁺) in solution gain electrons to form solid zinc.
  • Copper Electrode: Solid copper loses electrons and forms Cu²⁺ ions, causing the copper electrode to lose mass over time.

Example Problem: Quantitative Electrolysis

• Objective: Calculate how much zinc in grams deposits on the zinc electrode after one hour of applying a current of 5.0 amps.

Calculation Steps

1. Current and Charge: Definition and Conversion

   • Formula: Current (I) = Charge (Q) / Time (t)
   • Given: Current = 5.0 amps, Time = 1 hour
   • Conversion: 1 hour = 3600 seconds (60 minutes * 60 seconds)

2. Calculate Charge (Q):

   • Formula: Q = I * t = 5.0 amps * 3600 seconds
   • Result: Q = 18,000 coulombs

3. Moles of Electrons Using Faraday's Constant

   • Faraday's Constant: 96,500 coulombs/mole of electrons
   • Calculation: Moles of electrons = 18,000 coulombs / 96,500 coulombs/mole = 0.19 moles of electrons

4. Relate Electrons to Moles of Zinc

   • Reduction Half-Reaction: Zn²⁺ + 2e⁻ → Zn (solid)
   • Mole Ratio: 2 moles of electrons are needed to reduce 1 mole of Zn²⁺ to Zn
   • Calculation: 0.19 moles of electrons ÷ 2 = 0.095 moles of Zn

5. Convert Moles of Zinc to Grams

   • Molar Mass of Zinc: 65.39 g/mole
   • Calculation: 0.095 moles * 65.39 g/mole = 6.2 grams of Zn

Final Answer

• Amount of Zinc Deposited: 6.2 grams

Additional Notes

• Methodology Preference: Step-by-step logical approach is preferred, though unit analysis can also be used.
• Understanding Units: An alternative method involves considering units throughout the problem to verify the mathematical steps.