Question

Yellow color solution of \[FeC{l_3}\] changes to light green when …..
(A) \[SnC{l_2}\]is added
(B) Zn is added
(C) \[{H_2}S\]gas is passed
(D) all true

Answer 1

 Hint: Ferrous Chloride solution is light green in color. If any reducing agent react with \[FeC{l_3}\] then, \[FeC{l_3}\] gets converted to \[FeC{l_2}\] because \[FeC{l_3}\] is an oxidizing agent.

Complete answer:
Let’s see what will happen when \[FeC{l_3}\] react with the compounds given in the options.
- When \[SnC{l_2}\]is added to the \[FeC{l_3}\] solution, a redox reaction occur because \[SnC{l_2}\] is a reducing agent and \[FeC{l_3}\] is an oxidizing agent. Reaction is shown as below.
\[2FeC{l_3} + SnC{l_2} \to 2FeC{l_2} + SnC{l_4}\]
So, \[FeC{l_2}\] solution is light green in color, hence we can say that solution of \[FeC{l_3}\] will turn light green when we will add \[SnC{l_2}\] to it.
- Zn metal is also a reducing agent and it can reduce Iron from its solutions. So, in this reaction also \[FeC{l_3}\] gets converted to \[FeC{l_2}\]. Reaction is as shown below.
\[2FeC{l_3} + Zn \to ZnC{l_2} + 2FeC{l_2}\]
Here also \[FeC{l_2}\]gets formed in the solution and is responsible for the light green coloration.
- \[{H_2}S\]is also a reducing agent and reduces the \[FeC{l_3}\] in its solution. Here’s the reaction.
\[2FeC{l_3} + {H_2}S \to 2FeC{l_2} + 2HCl + S\]
We will get light green also because of the presence of \[FeC{l_2}\].
So, Correct option is (D) all true.

Additional Information:
- Iron is mostly seen in two oxidation states, +2 and +3. Iron has relatively the same stability in both of these oxidation states. So, whenever any redox reagent is available to react then these compounds can undergo redox reactions.
- The compounds that contain \[F{e^{2 + }}\] , may act as a reducing agent because it can be oxidized to \[F{e^{3 + }}\] state. Same way compounds that contain \[F{e^{3 + }}\] , may act as an oxidizing agent because it can be oxidized to \[F{e^{2 + }}\] state.

Note: Do not think that metals cannot react with the liquid solutions. If metal is reactive enough, it will react accordingly. Whenever option like (D) is given in the question, always try to see other possibilities as well because it may be possible that we commit a mistake there.