Introduction Occurance Melting point and Uses of Group 14 of P- block element.

Introduction.

Carbon is widely widespread in nature.It is the essential constituent of all living matter as proteins, carbohydrate and fat.Carbon dioxide is essential in photosynthesis and used in the course of respiration.Organic chemistry is used in the chemistry as for the devoid containing compounds . Inorganic compounds produce on a large scale include carbon black, coke graphite, carbonates, carbon dioxide, carbon monoxide,urea,calcium carbide, calcium cyanamide and carbon bisulphite. There is a great interest in the organometallic compound , carbonyls and pie bonding complexes .

The discovery that flints (hydrated siO₂) had a sharp cutting edge was very important in the development of human technology. Nowadays silicon is important in a number of materials produce in high tonnages. These includes cement , ceramics , clays, bricks, glass, and the silicone polymers . The very pure element is important in the microelectronics industries .

Germanium is little known , but tin and lead are very known and have been used as metal since before biblical times. The lead sheet was used on the floor in the hanging garden of Babylon to prevent water escaping .

Occurrence of the element.

The elements are all well known , apart from germanium . Carbon is the seventeenth and silicon is the most abundant element by weight in the earth crust.Germanium minerals are very rare . Ge occurs as traces in the ores of other metal in coal , but it is not well known. Both Si and GE are also used in the portion of organic chemistry for the use of both semiconductors as well as for the use of the transistor.The occurrence of the tin, as well as lid, are used in low amount., they occur as concentrated ores which are easy to extract both metals have been well known since beforeBiblical times.

Carbons occur in large quantities combined with other element and compounds mainly as coal , crude , oil and carbonates in rocks such as calcite CaCO₃ and magnesite MgCO₃ and dolomite (MgCO₃, CaCO₃).

Carbon is also found in the native form large amount of graphite are mined, and extremely small quantities of diamond are mined too. Both CO₂ and CO are important industrially...Silicon occurs very widely as silica (SiO₂) sand and quartz and in a wide variety in the of silicon mineral and clays. Germanium is only found in traces in some silver and zinc ores, and in some types of coal.Tim is mined as cassiterite SnO₂, and lead is found as the ore galena PbS.

Extraction and used of Carbon, Silicon, Germanium, Tin and lead.

(i) Carbon.

Carbon black is produced in large amounts 1991. It is made of the incomplete combustion of the hydrocarbons from natural gas or oil.The particle size is very small.Over 90% is used in the rubber industry to make tyres and other main used in the newspaper ink.Coke is produced in very large amount.Fifty-one million tonnes were produced in the by distillation heavier petroleum oils.Coke is extremely important in the metallurgical extraction and many other metals.

This is usually found in the mixture with mica, silicates, and quartz.which contain 10% carbon.Graphite is separated from most of the impurities by flotation.Finally, it is purified by heating with HCl and HF in a vacuum to remove the last traces of silicon compound as SiF₄.Sedentary deposits of carbon are mined in Mexico.This was once through to be amorphous carbon but is now regarded as microcrystalline graphite.Nearly as much is made synthetically as in mined.

$$3C+SiO_2\xrightarrow[]{heat}SiC+2CO\overset{2500^{\circ}{c}}{\rightarrow}C_(graphite)+Si_(g)$$

Graphite is used for making electrodes in steel making and metal foundries, for crucibles, as lubricants and in pencils, brake lining, and brushes for electric motors. It is used as the moderator in the cores of a gas cooled nuclear reactions, where it slows down neutrons.Activated charcoal is made by heating or chemically oxidising sawdust or peat.World production was 864200 tonnes in 1991.activated carbon has an enormous surface area , and is used to purify and decolourise sugar and other chemicals.It is also used to absorb poisonous gases in gas masks, in filter beds at sewage plants and as the catalyst for some neutrons.

(ii) Silicon.

More than a million silicon tonnes of Si have produced annually.Most of it is added to steel to deoxidize it.This is important in the manufacture of high silicon corrosion resistant steels. For this purpose, it is convenient to use ferrosilicon.This is an alloy of Fe and Si.It is made by reducing SiO₂ and scrap iron with coke.

$$SiO_2+Fe+2C→FeSi+2CO$$

The element Si is obtained by reducing SiO₂ with high purity coke.There must be an excess of SiO₂, to prevent the formation of the carbide SiC.Si is a shiny blue-grey colour and has an almost metal-like lustre, but it is a semiconductor, not a metal.High purity Si is made by converting Si to SiCl₄, purifying this by distillation, and reducing the chlorine with Mg or Zn.

$$SiO_2+2C→Si+2CO$$

$$Si+2Cl_2→SiCl_4$$

$$SiCl_4+2Mg→Si+MgCl_2$$

For the final processes of purification, a process called zone refining is used.This is an excellent method for small quantities.A rod of the element, which has already been purified extensively, is placed in a lo9ng quartz tube filled with an inert gas.A heating coil melts a thin disc of the rod.The heater moves slowly from end to another end, and pure Si or metal crystallises from the melt.The impurities are more stable in the liquid and are carried to the end of the rod, where they are cut off and discarded.Semiconductor quality Si can make by sodium reduction of Na₂[SiF₆], which is a by-product from making phosphate fertilisers from fluorapatite.

$$Na_2[SiF_4]+4Na→Si+6NaF$$

(iii) Germanium.

Ge has been recovered from coal ash, but it is now recovered from the flue dust from smelting Zn ores.A number os steps are required in the recovery of Ge from flue dust to concentrate and purify it.These give pure GeO2 which is reduced by H₂ to Ge at 500DC.Transistors grade material is obtained by zone refining.World production was about 50 tonnes in 1993.

It is mainly used for making transistors and semiconductor devices.It is transparent to infra-red light and is therefore also used for making prisms, and lenses and also windows in infra-red spectrophotometers and scientific apparatus.

(iv) Tin.

The only the important ore is cassiterite SnO₂.Mine production was 177000 tonnes.The main supplies now come from china.In the U.K tin was also now uneconomic.SnO₂ is reduced to the metal carbon at 1200-1300DC in an electric furnace.The product often contains traces of Fe, which make the metal hard.Fe is removed by blowing air through the molten mixture to oxidise the iron to FeO, which then float to the surface.

The main uses of the Sn are electroplating steel to make tinplate, and making the alloy.Tinplate is extensively used for making cans for food and drinks.The most important alloy is solder, but there are many other including bronze, gun metal, and pewter.SnO₂ is used as a glaze in ceramics and is often mixed with another metal oxide as pigments for pottery.

(v) Lead.

The main ore of lead is galena PbS. This is black, shiny, and very shiny and dense.The main sources are the USSR 17%, Australia 14%, The USA 10%, Canada 9%, Peru, Mexico and China 6% each. Galena is mined and separated from other minerals by froth flotation.There are two methods of extraction of the element.Roast in air to give PbO, and then reduce with coke or CO in a blast furnace.

1.Roast in air to give PbO, and then reduce with coke or CO in a blast furnace.

$$2PbS+3O_2→2PbO\xrightarrow[]{+c}2Pb_(liquid)+CO_2(gas)+SO_2$$

2.PbS is partially oxidised by heating and blowing air through it. After sometimes the air is turned off and heating is continued, and the mixture undergoes self-reduction.

$$3PbS\xrightarrow[]{heat\, in\, air}PbS+2PbO\xrightarrow[]{heat \,in \,absence\, of\, air}3Pb(liquid)+SO_2(gas)$$

The metals contain a number of metallic impurities: Cu,Ag, Au, Sn, As, Sb, Bi, and Zn.These are removed by cooling to near the freezing point of Pb, when first Cu then Zn-containing most of the Ag and Au solidify preferential oxidation converts As, Sb,and Sn, to As₂O₃, Sb₂O₃, and SnO₂ which float on the surface of the molten metal and may be skimmed off.

Uses.

1. Pb is used to making lead acid storage.
2. It is used for the storage batteries.
3. It is used for the lead pigmented (red lead Pb₃O₄), litharge(PbO), chrome yellow.
4. It is used for the production of the lead chamber of manufacture of H₂SO₄.
5. Preparation for the lead sulphide photocells.
6. To makes the bullet, shots etc.
7. It is used to make tubes, sheets, lead pipes.
8. To make the protective sheath for the telephone and telegraph wires which are buried under the earth.
9. In making alloys, brass, bronze. Etc.

Reference.

F.A.Cotton and Wilkinson G. Basic inorganic Chemistry. John,Wiley and Sons (Asia), 2007.

Lee., J.D. Concise Inorganic Chemistry. fifth edition. New Delhi: Oxford University Press., 2008.

Sharma, M.L and P.N Chaudhary. A textbook of B.S.C chemistry. Kathmandu Nepal: Ekta Books Thapathali Kathmandu, 2011.