Na amalgam is prepared by electrolysis of NaCl solution using liquid Hg as cathode. How long should the current of 10 amp. is passed to produce 10% Na − Hg on a cathode of 10 gm Hg. (atomic mass of Na = 23).
Correct answer: A. 7.77 min
- A. 7.77 min
- B. 9.44 min
- C. 5.24 min
- D. 11.39 min
Explanation
To solve this problem, we use Faraday's laws of electrolysis. First, calculate the amount of sodium needed to form a 10% Na-Hg amalgam on 10 g of Hg. This requires 1 g of Na since 10 g * 10% = 1 g. Using the molar mass of Na (23 g/mol), we find that 1 g of Na is approximately 0.0435 mol. According to Faraday's first law, the mass (m) of a substance deposited is directly proportional to the charge (Q) passed through the electrolyte:m = (Z * Q), where Z = electrochemical equivalent.For Na, equivalent weight = atomic mass = 23, so Z = 23/96500 (Faraday constant).Q = It, where I = 10 A and t = time in seconds.Substituting the values, we calculate t to be approximately 466.2 seconds, which is around 7.77 minutes. Therefore, Option A is correct. The other options either underestimate or overestimate the time based on incorrect calculations.
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