Question

Chemical reactions involve interaction of atoms and molecules. A large number of atoms/ molecules (approximately $6.023\times 10^{23}$) 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, which requires a clear understanding of the mole concept.
A $4.0$ 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).
The total number of moles of chloride gas evolved is

• A. $0.5$
• B. $1.0$
• C. $2.0$
• D. $3.0$

Answer 1

Answer: (B)

$500mL$ of $4.0$ molar $NaCl$ solution contains $2$ moles of $NaCl$. The chlorine content of this sample will i be evolved as chlorine gas.
The number of moles of $NaCl=$ Number of moles of $C{l}^{-}$
$=2$ moles
$\therefore$ Number of moles of $C{l}_2$ gas evolved
$=\frac{2}{2}=1$ mole $(2NaCl\to C{l}_2)$