Question

Define corrosion. What is meant by rust? Write the chemical form.

Answer 1

Hint: Corrosion is a process that causes damage to metal; numerous new compounds like oxide, hydroxide, or sulphide are formed. Rust is related to the iron compound formed due to the corrosion. The chemical formula of rust could be known.

Complete step by step answer:
-Firstly, let us define the corrosion. It is a natural process, and a dangerous problem. It is a natural process occurring from the electrochemical series, in which atoms on the same meta surface get oxidized. It causes damage to the entire surface.
-In the process of corrosion, atoms lose electrons to oxygen in the air (atmosphere), or in the water, and the atoms get oxidized, leading to the formation of an oxide.
-The well-known example of corrosion is the rusting of iron; when the objects made of iron, or iron alloys get corroded.

-Other examples include-
Copper Corrosion: The copper coating which is their in the statue of liberty is changing its color to bluish green due to the formation of $C{{u}_{4}}S{{O}_{4}}{{(OH)}_{6}}$which is green in color
Silver jewellery gets tarnished due to formation of $A{{g}_{2}}S$which is black in color.
-Now, talking about rust; rusting of iron further refers to the formation of rust. It is composed of iron oxide, present on the surface of iron objects.
-Rusting of iron is a redox type of reaction, and it is of red colour, that smashes into a powder form.
-Now, we have to write the chemical formula of rust, as mentioned it is a hydrated form of iron oxide. So, it can be written as $F{{e}_{2}}{{O}_{3}}.n{{H}_{2}}O$
-Here, Fe exists in +3 oxidation state, and the amount of water molecules is variable, so, its represented with n.
-The reaction involved in rusting is given below-

\[\text{Iron}+\text{Oxygen}(\text{from environment})+Water(Humidity)\to \text{Iron oxide (Rust)}\]
At anode- \[\]
\[Fe\to F{{e}^{+2}}+2{{e}^{-}}\]
At cathode- \[\]
\[4F{{e}^{2+}}+{{O}_{2}}\to 4F{{e}^{+3}}+2{{O}^{2-}}\]
Overall Reaction-
\[4F{{e}^{+2}}(aq)+{{O}_{2}}(g)+(4+2x){{H}_{2}}O\to 2F{{e}_{2}}{{O}_{3}}.x{{H}_{2}}O+8{{H}^{+}}(aq)\]

-In the last we can conclude that these terms are kind of dependent on each other.

Note:
Don’t get confused between the no. of water molecules present, as these reactions occur in the air, or in the water present in the atmosphere. So the amount of water molecules would vary. The second is the existence of Fe in +3 oxidation state; oxygen is a good oxidizing agent, and it increases the oxidation state of iron from +2 to +3.