Science: Metals and Non-Metals: Methods of Prevention of Corrosion (For CBSE, ICSE, IAS, NET, NRA 2022)

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Methods of Prevention of Corrosion

Painting

This is a common method of preventing iron from rusting. This painting prevents rusting by providing a coating over iron objects.

Oiling and Greasing

oil and grease on the iron objects also prevents them from rusting. Iron parts of various machines and vehicles are oiled and greased to prevent rusting and to minimize friction.

Galvanization

In this method we put a layer of zinc metal on the iron objects and this process is known as galvanization. This method is used on large scale for making galvanized iron sheets for making boxes and for roof covering. Galvanized iron sheets are used to make drum, trunks and other iron containers. Galvanized iron sheets are also used for building roofs and manhole covers. In brief, galvanization prevents rusting in a big way.

Alloying

This is a very good method for improving the quality of different metals. In this method a particular metal with other metal or non-metal is mixed in a fixed proportion. . For example, iron metal cannot be used for making utensils because it will rust but when it is mixed with nickel and chromium metal it becomes stainless steel.

Reactivity of Metals

A more reactive metal displaces a less reactive metal from its salt solution. The arrangement of metals in the decreasing order of their activity is known as activity or reactivity series. It is also known as electrochemical series. A portion of this series is given below.

In this series only few metals are shown:

Reactivity of Metals

For example: Fe is placed in a solution of CuSO4 it replaces Cu from the solution according to the following reaction.

Fe (s) + CuSO4 (aq) ⇾ FeSO4 (aq) + Cu (s)

Fe is more reactive than Cu and copper is more reactive than silver.

Source of Metals

  • The Earth crust is the major source of metals. Some metal salts are also present in sea.
  • These salts are also source of certain metals like sodium, magnesium etc. The constituents of earth crust which contain these metals, or their compounds are known as minerals. minerals contain a high percentage of a particular metals and the metal can be profitably extracted from it; such minerals are called ores.
  • The process of obtaining metals from its ore is called metallurgy.

Chemical Reaction of Non-Metals

Reaction of Non-Metals with Oxygen, Water and Some Common Acids and Bases

Non-metals react with oxygen on heating or burning to form their oxides

S (s) + O2 (g) SO2 (g)

C (s) + O2 (g) CO2 (g)

2H2 (g) + O2 (g) 2H2O (l)

Nature of Oxides of Non- Metals

In general oxides of non-metals are acidic in nature or after dissolving in water they form acids

Carbon dioxide forms carbonic acid with water CO2 (g) + H2O (l) ⇾ H2CO3 (aq)

(carbonic acid)

Halogens (F, Cl, Br, I) are also non-metals and they react with metals to form halides. For example, NaCl, NaBr, KCl, KBr, KI. Important source of these halides is sea. Oxides of halogens are not very important as compared to their salts. NaCl which is obtained from sea, is used as a raw materials for the manufacture of many important chemicals.

Uses of Metals

  • Many metals like iron , copper and aluminum are used to make containers.
  • Metals like copper, aluminum, iron and stainless steel are used to make utensils and fry pans.
  • Ductile metals like copper and aluminum are used for making electrical wires. Steel ropes are used in cranes to lift heavy objects in making bridges.
  • Iron and steel are used to make machines
  • Zinc, lead, mercury, lithium are used to make cells and batteries.
  • Malleable metals like iron and aluminum are used to make sheets which are used for various construction purposes.
  • Gold, silver and platinum metals are used to make jewelries due to their luster, high malleability and inert nature.
  • Alloys of different metals and non-metals are used for various purposes e. g. Stainless steel for making utensils.

Uses of Non-Metals

  • Hydrogen is used in manufacturing of ammonia gas which is further used in the manufacturing of urea (fertilizer) .
  • Hydrogen is a constituent of many industrial fuels like water gas (CO + H2) and coal gas (H2 + CH4) .
  • Silicon is used in making transistors, chips for computers and photovoltaic cells.
  • Silicon is used in steel industry to deoxidize steel and it produces high quality corrosion resistant steel.
  • Most of the phosphorous is used for making phosphoric acid H3PO4 which is used in the manufacturing of phosphate fertilizers.
  • White phosphorous as (P4S3) is used in the match industry.
  • Phosphates are added to the detergents as they help in the removal of dirt from soiled cloths.
  • Sulphur is used in agriculture to control fungus and pests.
  • Sulphur is used in the manufacturing of gun powder, which is an intimate mixture of Sulphur, charcoal and potassium nitrate.
  • Most of Sulphur is converted into sulphuric acid which is called the king of chemicals and is used to make variety of other chemicals.

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