Question

The volume of $KI$ solution used for $CuS{{O}_{4}}$ is:
a.$1L$
b.$2L$
c.$4L$
d.$5L$

Answer 1

We know that Iron is put in the reactivity series above copper. In this order, elements placed above are more reactive than those placed underneath them. Iron is, therefore, more reactive than copper.

Complete step by step solution:
Let us first understand the type of reaction happening in the experiment mentioned in the question; Copper ions are displaced by iron from an aqueous copper sulfate solution because iron is more reactive than copper as per the reactivity series.
This type of reaction involves the displacement of one metal by another more reactive metal and hence it is known as a single displacement reaction. In detail, a single replacement reaction also referred to as a single displacement reaction, is a reaction in which another element in a complex is replaced by one element. Pure components are often the starting materials.
According to the reaction, $1~mol\left( ~CuS{{O}_{4}} \right)\equiv 1~mol\left( ~{{S}_{2}}O_{3}^{2-}~ \right)\equiv \dfrac{1}{2}~mol~\left( {{I}_{2}} \right)\equiv 2~mol~\left( KI \right)$
$1~mol\left( ~CuS{{O}_{4}} \right)\equiv 0.4\times 2=0.8~mol$
Therefore, $0.2M\times \left( V \right)=0.8$
$\Rightarrow V=4~L$

Therefore, correct answer is option C.

Additional information:
For certain forms of reactions, including single replacement reactions, the reactivity series, also called the activity series, lists elements in order of their reactivity. In the reactivity order, the more reactive elements will replace the less reactive elements, but not the other way around. For elements that form cations and elements that form anions, there are different rankings.

Note:
Remember that in fact, in a single displacement reaction, anion can be substituted by elements that form anions in a compound, and the cation can be substituted in a compound by elements that form cations. Usually metals will form cations.