Question

Some articles made of silver, copper and iron get coloured coating over them when they are exposed to air. Identify the colour and chemical name of the substance of coating in each case.

Answer 1

Hint: When metals are exposed to air then they get coloured coating over them and get converted to stable form like hydroxide, oxide, this process is called as corrosion.

Complete step by step answer:
- When articles made of silver, copper and iron get exposed to air then following observations are made:
- Let’s discuss about it in each case:
- It is observed that when silver is exposed to air then following reaction takes place:
\[4Ag+{{O}_{2}}\to 2A{{g}_{2}}O\]
Here, we can see that silver gets a white coloured coating over it. And the chemical name of it is Silver Oxide.
- It is observed that when copper is exposed to air then following reaction takes place:
\[4Cu+{{O}_{2}}\to 2C{{u}_{2}}O\]
Here, we can see that copper gets a green coloured coating over it. And the chemical name of it is Copper Oxide.
-It is observed that when iron is exposed to air then following reaction takes place:
\[4Fe+6{{H}_{2}}O\to 2F{{e}_{2}}{{O}_{3}}+6{{H}_{2}}\]
Here, we can see iron that gets a brown coloured coating over it. And the chemical name of it is Iron Oxide.
- We can protect the metals from being corroded by applying coatings to metals, painting and cathodic protection etc.

Note:
We should not get confused in corrosion and rusting. As both of these processes are different. The main difference between these two is that corrosion can occur on different surfaces of metals, wood etc. Whereas, rusting usually occurs on surfaces of iron and its alloys.