Question

: What is the chemical formula of rust?
(A) Fe$_3$O$_4$
(B) Fe$_2$O$_4$
(C) Fe$_2$O$_3$
(D) Fe$_3$O$_2$

Answer 1

Hint:Rust is related to the rusting of iron, also known as ferric oxide. It occurs through a redox reaction between the oxygen, and an iron with atmosphere having moisture. From the chemical name of rust, we can identify the chemical formula.

Complete step by step solution:First, let us discuss the rusting of iron. As mentioned it is the method of formation of rust.
> Now, we know it is the reaction between oxygen, or air, and the iron is chemically attacked, resulting in the formation of reddish brittle coating on iron.
> A reddish coating is the characterization of rusting of iron.
> The rusting of iron is considered to be an example of corrosion of metals.
> Thus, we can say that in other terms, corrosion of iron objects relates to the rusting of iron.
> Now, there is an increase in oxidation state of iron in consideration with the rusting, and rust is said to be a mixture of two different oxides.
- Thus, first is iron with +2 oxidation state i.e. iron (II) oxide, with the chemical formula FeO.
- The second we have the iron (III) oxide, having +3 oxidation state, known as ferric oxide, and the chemical formula is Fe$_2$O$_3$.
- In the last, we can conclude that the chemical formula of rust is Fe$_2$O$_3$.
Hence, the correct option is (C).

Note: Don’t get confused about how there is an increase in oxidation state of iron. We know that oxygen is an oxidizing agent, and iron is a reducing agent. So, here iron will lose its electrons very fast, when there is a reaction with the oxygen.