A constante de Faraday e os aspectos quantitativos da eletroquímica (relação carga x massa).

Introduction

This tutorial explains the Faraday constant and its relationship to electrochemistry, particularly how charge relates to mass. We will also solve a practical problem involving the electroplating of silver on Olympic medals, specifically addressing how to calculate the required average electric current. This knowledge is essential for understanding processes like electrolysis and its applications in real-world scenarios.

Step 1: Understand the Faraday Constant

• The Faraday constant (F) is approximately 96485 C/mol and represents the amount of electric charge per mole of electrons.
• It is crucial for calculating the relationship between the electric charge (Q) and the amount of substance transformed during electrochemical reactions.
• The fundamental equation to remember is:
  • Q = i × t
  • Where Q is the charge in coulombs, i is the current in amperes, and t is the time in seconds.

Step 2: Relate Charge to Mass

• To find the relationship between charge and mass, you can use the formula:
  • m = (Q × M) / (n × F)
  • Where:
    • m is the mass of the substance deposited (in grams),
    • Q is the total charge (in coulombs),
    • M is the molar mass of the substance (in g/mol),
    • n is the number of electrons transferred per ion in the reaction,
    • F is the Faraday constant.

Step 3: Identify the Problem Parameters

• In our problem, we need to deposit 65.5 grams of silver (Ag) in 2 hours.
• The molar mass of silver (Ag) is approximately 107.87 g/mol.
• For silver, n = 1 since one electron is involved in the reduction to deposit silver.

Step 4: Calculate Total Charge Needed

• First, calculate the number of moles of silver needed:

  • n_moles = mass / M
  • n_moles = 65.5 g / 107.87 g/mol ≈ 0.607 moles

• Next, calculate the total charge (Q) required:

  • Q = n_moles × n × F
  • Q = 0.607 moles × 1 × 96485 C/mol ≈ 58620 C

Step 5: Convert Time to Seconds

• Convert the time from hours to seconds for the calculation:
  • 2 hours = 2 × 3600 seconds = 7200 seconds

Step 6: Calculate the Average Current

• Finally, use the charge and time to find the average current (i):
  • i = Q / t
  • i = 58620 C / 7200 s ≈ 8.14 A

Conclusion

You have learned how to calculate the average electric current needed to deposit a specific mass of silver using the Faraday constant and electrochemical principles. By understanding the relationship between charge, mass, and current, you can apply these concepts to various electrochemical processes, including electroplating and battery technologies. If you wish to delve deeper into the electrolysis process, consider exploring additional resources or videos provided in the description.