Question

If zinc pieces are added to yellow $\text{FeC}{{\text{l}}_{\text{3}\,\,}}$ solution, it turns to very light green. It is because:
(A) $\text{FeC}{{\text{l}}_{3}}$ Solution is acidic due to hydrolysis and zinc added produce nascent hydrogen causing reduction of $\text{FeC}{{\text{l}}_{\text{3}}}$ to $\text{FeC}{{\text{l}}_{\text{2}}}$
(B) $\text{FeC}{{\text{l}}_{\text{3}\,\,}}$ Solution is basic and zinc added produces ${{\text{H}}_{\text{2}}}$ which reduce $\text{FeC}{{\text{l}}_{\text{3}\,\,}}$to$\text{FeC}{{\text{l}}_{\text{2}}}$.
(C) Zinc reduces $\text{FeC}{{\text{l}}_{\text{3}\,\,}}$ to $\text{FeC}{{\text{l}}_{\text{2}}}$
(D) None of the above is correct

Answer 1

Hint: Metal in the top of the electrochemical series is a strong electropositive element.
- Metal lies in the top of the electrochemical series and a less electropositive metal lies below in the series from there salt solution.


Complete Solution :
Reactivity of metal is determined by how easily they lose the electron. In electrochemical series zinc ($\text{Zn}$) metal placed above the iron ($\text{Fe}$) metal, so zinc is more reactive metal than iron. It will displace$\text{Fe}$ from its salt solution.
$\text{Zn}\,\,\text{+}\text{2FeC}{{\text{l}}_{\text{3}\,\,}}\to \,\,\text{ZnC}{{\text{l}}_{\text{2}}}\,\,\text{+}\,\,\text{2FeC}{{\text{l}}_{\text{2}}}$
In this redox reaction $\text{Zn}$ is oxidised into $\text{Z}{{\text{n}}^{\text{2+}}}$ and get $\text{Fe}$ reduced from ferric ($\text{F}{{\text{e}}^{\text{3+}}}$) to ferrous ($\text{F}{{\text{e}}^{\text{2+}}}$) ion.

\[\begin{align}
& \text{Zn}\,\,\to \,\text{Z}{{\text{n}}^{\text{2+}}}\text{+}\,\,\text{2}{{\text{e}}^{\text{-}}} \\
& \text{2F}{{\text{e}}^{\text{3+}}}\text{+}\,\text{2}{{\text{e}}^{\text{-}}}\to \,\text{F}{{\text{e}}^{\text{2+}}} \\
\end{align}\]
Zinc is a highly active metal. $\text{FeC}{{\text{l}}_{\text{3}\,\,}}$ Compound is yellowish in colour. After addition of a piece of zinc metal in the $\text{FeC}{{\text{l}}_{\text{3}\,\,}}$ solution, it will reduce ferric ion to ferrous ion and the colour of the solution will change from yellow to green.
(A) Aqueous solution of $\text{FeC}{{\text{l}}_{\text{3}\,\,}}$ is acidic in nature, it on hydrolysis form $\text{HCl}$. $\text{HCl}$ is dissociated into ${{\text{H}}^{\text{+}}}$ in the solution. In term of oxidation $\text{Zn}$ metal is oxidised into $\text{Z}{{\text{n}}^{\text{2+}}}$ and ${{\text{H}}^{\text{+}}}$ ion in the solution get reduce into nascent $\text{F}{{\text{e}}^{\text{2+}}}$ gas. Loss of electron causes reduction of $\text{FeC}{{\text{l}}_{\text{3}}}$ into $\text{FeC}{{\text{l}}_{2}}$. So, option this statement is correct.
(B) $\text{FeC}{{\text{l}}_{\text{3}}}$ Solution is acidic in nature, so addition of $\text{Zn}$ metal causes release of ${{\text{H}}_{\text{2}}}$ gas it leads to reduction of $\text{FeC}{{\text{l}}_{\text{3}}}$ into $\text{FeC}{{\text{l}}_{2}}$. So this statement is wrong.
(C) In this redox reaction zinc metal acts as a reducing agent, it will reduce $\text{F}{{\text{e}}^{\text{3+}}}$ into $\text{F}{{\text{e}}^{\text{2+}}}$ ion. So this statement is also true.
So, the correct answer is “Option A and C”.

Note: In a redox reaction an oxidizing agent is reduced , however a reducing agent gets oxidised.
- $\text{Zn}$ Metal is placed above the hydrogen in the electrochemical series, so zinc metal is capable of replacing hydrogen gas when it reacts with the hydrogen containing compounds such as dilute acid and water.