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Chemical reactions involve interaction of atoms and molecules.A large number of atoms/molecules are present in a few grams of any chemical compound varying with their atomic/molecular masses.To handle such large numbers conveniently,the mole concept was introduced.This concept has implications in diverse areas such as analytical chemistry,biochemistry,electrochemistry and radiochemistry.The following example illustrates a typical case involving chemical/electrochemical reaction.A H.O molar aqueous solution of NaCl is prepared and 500ml of this solution is electrolysed.This leads to the evolution of chlorine gas at one of the electrodes(atomic mass:Na=23,Hg=200;1 faraday=96500 coulombs).If the cathode is a Hg electrode,the maximum weight (g) of amalgam formed from this solution is

$\begin{array}{1 1}(a)\;200& (b)\;225 \\(c)\;400& (d)\;446\end{array} $

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Number of moles of $Na^+=2$
$2NaCl\equiv 2Na$
$Na+Hg\rightarrow Na(Hg)$
By electrolysis we can get a maximum of 2 moles of sodium which can combine with exactly 2 moles of mercury to give amalgam.
$\therefore$ Maximum weight of Na amalgam (assuming equimolar Na and Hg)=46+400=446g
Hence (d) is the correct answer.
answered Mar 25, 2014 by sreemathi.v

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