Question

Chemical reactions involve interaction of atoms and molecules. A large number of atoms and molecules (approximately `6.022 xx 10^(23)`) are present in a few grams of any chemical compound varying with their atomic/molecular masses. To handle such a large number conveniently, the mole concept was introduced. This concept has implications in diverse areas such as analytical chemistry, biochemistry, electrochemistry adn radiochemistry. The following examples illustrate a typical case involving chemical/electrochemical reaction which requires a clear understanding of mole concept.
A 4.0 molar aqueous solution of NaCl is prepared and 500 mL of the solution is electrolysed. This lead to the evolution of chlorine gas at one of electrodes (atomis mass : Na = 23 , Hg = 200 , 1F = 96500 C)
If the cathode is a Hg electrode, the maximum weight (g) of amalgam formed from the solution is :
A. 200
B. 225
C. 400
D. 446

Answer 1

Correct Answer - D
`Na + Hg rarr Na//Hg` (Amalgam)
By electrolysis, 2 moles of NaCl can produce 2 moles of sodium at cathode
From the above equation, it is evident that
2 moles of Na can combine with Hg
`= 200 mol = 2 xx 200 = 400 g`
`:.` Maximum weight of amalgam formed
`= 46 + 400 = 446 g`.