The metallic impurities present in the impure copper can be either more/less reactive. More reactive metals like iron pass into the solution and remain there. Less reactive metals like gold and silver collect at the bottom in the form of anode mud .
CORROSION:-
The eating up of metals by the action of air, moisture or a chemical on their surface.
The corrosion of iron is called Rusting. When an iron object is left in damp air for a considerable time, it gets covered with a red-brown flaky substance called rust.
Rust is mainly hydrated iron (III) oxide, Fe2O3. xH2O
Conditions necessary for rusting :-
presence of air (oxygen) and Water ( moisture)
Prevention of rusting :-
Corrosion of Aluminum :-
Due to formation of a dull layer of aluminium oxide on exposure to air, the aluminium vessel loses its shine very soon. It protects it from further corrosion.
The layer of aluminium oxide can be made thicker by electrolysis - ANODISING. ( by making it anode during electrolysis of dilute sulphuric acid.)
Corrosion of copper :-
It is very slow and copper vessels can be cleaned with dilute acid solution.
Corrosion of silver :-
Silver objects get tarnished and turn black due to the formation of a thin silver sulphide layer by the action of hydrogen sulphide gas present in air.
Gold and Platinum do not corrode.
ALLOYS :-
It is a homogeneous mixture of two or more metals or a metal and a non-metal to improve its properties. It is prepared by mixing the various metals in molten state in required proportions and then cooling their mixture to the room temp.
Alloy of aluminium with copper, magnesium and manganese - Duralumin
Alloy of aluminium with magnesium - Magnalium
Alloy of copper and zinc – Brass
Alloy of iron and carbon - Steel
Alloy of copper and tin - Bronze
Alloy of lead and tin - Solder
Alloy of mercury with one or more metals – Amalgam
Alloy of pure gold, silver, copper- 22 carat gold
