Metals and Nonmetals for (2009-2010)

Electrolytic refining In the process of electrolytic refining, the strip of impure metal is made anode and the thin strip of pure metal is made cathode. The solution of molten salt is taken as electrolyte. On passing electricity , the pure metal deposits at cathode.

Anode mud The insoluble impurities that settle down at the bottom of anode are known as anode mud. The soluble impurities go into the solution.

Corrosion. The process of slowly eating away of metals due to their conversion into oxides, carbonates, sulphides, sulphates, etc by the action of moisture and gases is called corrosion.

Corrosion of iron is called rusting Rusting. The process of depositing a brown flaky substance on the surface of iron due to air and moisture is called rusting. The brown substance is called rust. It is chemically Fe2O3.xH2O. Conditions for rusting are - presence of moisture and presence of air.

Prevention of rusting Rusting of iron can be prevented by painting, applying grease or oil, galvanization, chrome plating, anodizing, making alloys, etc.

1. Galvanization. The process of depositing a thick layer of zinc metal on iron objects is called galvanization.
2. Chrome plating. The process of depositing a layer of chromium (Cr) on iron objects is called chrome plating.
3. Alloying. The process of making homogeneous mixture of a metal with other metal or nonmetal in molten state is called alloying.

Alloy The homogeneous mixture of a metal with other metal or nonmetal in molten state is called an alloy.

1. Stainless steel is an alloy of iron, nickel and chromium.
2. Brass is an alloy of copper and zinc.
3. Bronze is an alloy of copper and tin.
4. Solder is an alloy of lead and tin. It has low melting point and is used for welding electrical wires together.

Objectives to make alloys. Alloys are made to

1. Increase hardness
2. Make resistant to corrosion
3. Decrease melting point
4. Change chemical reactivity
5. Decrease electrical conductivity
6. Increase colour and tensile strength

Meaning of 22-carat gold The pure gold which has no impurities is called 24 carat. 22 carat gold has 22 parts gold and 2 parts of silver or copper.

• The alloy of mercury metal with one or more other metals is called amalgam.
• Ores of many metals are oxides because oxygen is very reactive element and it is present in large amount on the earth.
• Galvanized objects remain protected against rusting even zinc coating is broken because when the zinc layer on the surface of galvanized iron object is broken, zinc continues to corrode as it is more reactive than iron.
• Highly reactive metals like aluminium, calcium, etc cannot be reduced by carbon because they have more affinity for oxygen than carbon.