Question

Identify the correct option
Rust contains$\left( {F{e_2}{O_3} \cdot {H_2}O} \right)$. Rust spots can be removed by:
(A) $N{a_2}{S_2}{O_3}$
(B) $S{O_2}$
(C) ${H_2}{C_2}{O_4}$
(D) $KMn{O_4}$

Answer 1

Hint: Rust is basically the iron oxide which forms a layer on the surface of the metal and eventually converts the metal entirely into rust. It is formed by the reaction of iron metal with oxygen in the presence of water or air moisture. It is reddish brown in color.

Complete step by step answer:
Rust consists of hydrated iron (III) oxides $\left( {F{e_2}{O_3} \cdot {H_2}O} \right)$ and iron (III) oxide – hydroxide $\left( {FeO\left( {OH} \right),Fe{{\left( {OH} \right)}_3}} \right)$. The process of formation of rust is known as rusting of iron. It may also generally be termed as oxidation as the process does involve the loss of electrons or the increased oxidation state of metal.
As we know that oxygen is a very good oxidizing agent and that the iron is a reducing agent. Therefore, iron atoms readily give up electrons when exposed to oxygen and then the oxidation number of iron is a reducing agent. Therefore, iron atoms readily give up electrons when exposed to oxygen and then the oxidation number of iron is further increased when moisture is present.
The series of chemical reactions followed in the process are:
$Fe \to F{e^{2 + }} + 2{e^ - }$ (reduction of iron)
$4F{e^{2 + }} + {O_2} \to 4F{e^{3 + }} + 2{O^{2 - }}$ (oxidation of iron)
Now, in the presence of moisture, the hydroxides of iron are formed which is shown in the following reaction:
$F{e^{2 + }} + 2{H_2}O \to Fe{(OH)_2} + 2{H^ + }$ and $F{e^{3 + }} + 3{H_2}O \to Fe{(OH)_2} + 3{H^ + }$
Then, the hydroxides of iron undergo dehydration and result in the formation of iron oxide. This process can be written as:
  4Fe{\left( {OH} \right)_2} + {O_2} + {H_2}O \to 2F{e_2}{O_3} + 5{H_2}O \\
  Fe{\left( {OH} \right)_3} \rightleftharpoons Fe\left( {OH} \right) + {H_2}O \\
  FeO\left( {OH} \right) \rightleftharpoons F{e_2}{O_3} + {H_2}O \\
It can be noted that all the above reactions are dependent on the presence of water and oxygen. Rust contains$\left( {F{e_2}{O_3} \cdot {H_2}O} \right)$. Iron is present in $ + 3$oxidation state. It reacts with an oxalic acid solution to form a soluble complex. Thus rust spots can be removed by the reaction with oxalic acid.
$F{e_2}{O_3} \cdot {H_2}O + {H_2}{C_2}{O_4} \to $ Soluble complex


Note:
We can remove rust by the simplest form of chemical rust remover which is usually about \[5\% \] acetic acid. Acetic acid, also known as ethanoic acid with the formula \[C{H_3}COOH\].