Zn amalgam is prepared by electrolysis of aqueous ZnCl2 using Hg cathode (9 gm). How much current is to be passed through ZnCl2 solution for 1000 seconds to prepare a Zn amalgam with 25% Zn by wt. (Zn = 65.4)
Correct answer: C. 8.85 amp
- A. 5.6 amp
- B. 7.2 amp
- C. 8.85 amp
- D. 11.2 amp
Explanation
To calculate the current needed, use Faraday's first law of electrolysis, which states that the mass of a substance deposited or liberated at an electrode during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte. Here, we want to achieve a Zn amalgam that is 25% zinc by weight. Given that the Hg cathode weighs 9 g, the total weight of the amalgam will be 9 g / 0.75 = 12 g. Therefore, the weight of zinc needed is 12 g * 0.25 = 3 g.Using the equation: mass = (Atomic mass of Zn * Current * Time) / (n * Faraday's constant), solve for the current: Current = (3 g * 2 * 96500 C/mol) / (65.4 g/mol * 1000 s) = 8.85 A.Options 5.6 A, 7.2 A, and 11.2 A are incorrect because they do not match the calculated current required to achieve the specified amalgam composition.
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