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

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.