What is corrosion? write the colour of silver, copper and iron corrosion.
Answers
Corrosion
The corroding activity on surface of metals due to air, moisture or any chemical is called corrosion.
Corrosion On Metals
Silver — When corrosion takes place on silver then it's colour changes into black.
This happens as follows :
The air contains some amount of sulphur in form of Hydrogen Sulphide (H₂S). When this compound comes in contact with Silver then,
- H₂S + Ag → Ag₂S (Silver Sulphide)
is formed, which is black and dump in colour.
Copper — The colour due to corrosion in copper changes to green.
This happens as follows :
When Copper comes in exposure to Carbon Dioxide (CO₂) and water vapour (H₂O) then basic calcium carbonate (basic. CuCO₃) is formed which is greenish in colour
- Cu + CO₂ + H₂O → CuCO₃ + H₂
Iron — The corrosion of Iron is specifically called “Rusting” which eats up iron slowly making it week. The colour of rust is mostly Brownish and sometimes greenish in colour.
This happens as follows :
The iron reacts with moisture and oxygen to form hydrated Iron Oxide which makes the metal week and ugly.
- Fe + O₂ + H₂O → Fe₂O₃.xH₂O
In order to prevent this reaction painting, galvanisation or alloys can be used.
When a metal is atacked by its surrounding air , moisture , acid etc it is said to be corroded . The process is called corrosion.
Electrochemical corrosion of metals occurs when electrons from atoms at the surface of the metal are transferred to a suitable electron acceptor or depolarizer. Water must be present to serve as a medium for the transport of ions.