Question

The total number of moles of chlorine gas evolved is:
A: 0.5
B: 1.0
C: 2.0
D: 3.0

Answer 1

The mole concept is very significant and useful in chemistry. It is actually the base of stoichiometry and it provides the best option to express the amounts of reactants as well as products that are consumed and formed during a chemical reaction.

Complete Step by step answer: To calculate the number of moles, we generally use the following formula:
$Number{\text{ }}of{\text{ }}moles = \dfrac{{Given{\text{ }}mass{\text{ }}}}{{{\text{ }}Molecular{\text{ }}mass{\text{ }}of{\text{ }}the{\text{ }}given{\text{ }}species}}$
Alternatively, we can also depict the number of moles from the balanced chemical equation. The coefficients actually represent the number of moles which react, not just only molecules.
In this case let us assume that a 4.0 M aqueous $NaCl$ solution is prepared out of which 500mL of this solution has been electrolysed. This process usually leads to the evolution of chlorine gas at one electrode. Now we have to calculate the total number of moles of chlorine gas evolved.
In this question we will try to write the balanced chemical equation to depict the number of moles of chlorine gas.
Moles of NaCl$$$$ = 4 \times 0.5 = 2\;moles (Since 500 mL = 0.5 L)
2 moles of $NaCl$= 2 moles of $C{l^ - }$
$2C{l^ - } \to C{l_2} + 2{e^ - }$
This balanced chemical equation clearly depicts that 2 moles of $C{l^ - }$ yields 1 mole of $C{l_2}$ gas.
Therefore, 1 mole of $C{l_2}$gas has been evolved.

Hence, the correct answer is Option B.

Note: A balanced chemical equation simply obeys the law of conservation of mass. Balancing the chemical equations is a significant guiding principle in chemistry. A balanced chemical equation helps you to predict the amount of reactants required and the amount of products formed.