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 :

Options

A. 200
B. 225
C. 400
D. 446

Explanation

No. of moles of `Na^+=2`
2NaCl `-=2Na`
`underset("moles" 2)(Na)+ underset(2)(Hg) to underset(2)(Na(Hg))`
By electrolysis we can get a maximum of 2 moles of sodium which can combine with exactly 2 moles of mercury to give 2 moles of amalgam. ltbr. `therefore` Maximum weight of Na amalgam (assuming equimolar Na and Hg) = 46 + 400 = 446 g.