Chemical reaction involve interaction of atoms and molecules. A large number of atoms/molecules (approximately `6.022xx10^(23)`)are present in a few grams of any chemical compound varying with their atomic/molrcular mass. To handle such a large numbers conveniently, the mole concept was introduced. This concept has implications in diverse areas such as analytical in diverse areas such as analytical chemistry, biochemistry, electrochemistry and radiochemistry. The following example illustrates a typical case, involving chemical/ electrochemical reaction, which requires a clear understanding of the mole concept.
A 4.0 molar aqueous solution of NaCl is prepared and 500 mL of this solution is electrolysed. This leads to the evolution of chlorine gas at one of teh electrodes (atomic mass: Na=23, Hg=200, 1F=96500 coulombs)
If 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

Answer

D

Explanation

500 ml of 4.0 molar NaCl has 2 mole of NaCl.
By electrolysis we can get a maximum of 2 mole of sodium which can combine with exactly 2 moles of mercury to give amalgam.
`therefore` The maximum weight of amalgam which can be formed from this solution
=weight of 2 mole of sodium+weight of 2 mole of mercury
`=2xx23+2xx200=446`g.