Question

This question along with the next two were asked in the (IIT-JEE, 2007) exam. Let us try them out!

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 under-standing of the mole concept.

A 4.0 M aqueous solution of NaCl is prepared and 500 mL of this solutionn is electrolyzed. This leads to the evolution of chlorine gas at one of the electrodes (atomic mass of Na is 23 and Hg is 200) (1 F = 96500 C).

The total number of moles of chlorine gas evolved is

• A. 0.5
• B. 1
• C. 2
• D. 3

Answer 1

The correct option is B 1

So this is straightforward right? Just use mole concept and you can figure this out. You know the molarity and the volume consumed, the number of moles of sodium chloride is pretty direct from there. Let's solve this
4.0 M NaCl, 500 mL (0.5 L)
moles of NaCl = 4 $\times$ 0.5 = 2
2 moles NaCl $\equiv$ 2 moles $C{l}^{\ominus }$
$2C{l}^{\ominus }\to C{l}_2$
2 mol 1 mol