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)
The total number of moles of chlorine gas evolved is :
A. 0.5
B. 1
C. 2
D. 3

Answer 1

500 mL of 4.0 molar NaCl solution contains 2 moles of NaCl. The chlorine content of this sample will be evolved as chlorine gas.
The number of moles of NaCl = number of moles of Cl = 2 moles
`therefore` Number of moles of `Cl_2` gas evolved
`=2/2=1mole (2NaCl to Cl_2)`