CARBON AND ITS COMPOUND -I

       CARBON AND ITS COMPOUNDS -I

Carbon

Carbon is generally a non-metallic black solid. It occurs as diamond, graphite, coal. It occurs as wood, petroleum, natural gases, metallic trioxocarbonates (iv) and carbon (iv) oxide in the combined form. Carbon is the first four (4) element in the periodic table. It has the atomic number of six (6). Its electronic configuration is 1s2 2s2, 2p2. It has the atomic mass of twelve (12). Carbon is contained in all living cells. It is an important source of heat and light energy.

Allotropes of Carbon

Allotropy is the existence of an element in two or more structural form in the same physical state. Carbon, tin, sulphur and phosphorous exist in different structural forms in their free states. Carbon exists in two main crystalline allotropic forms called diamond and graphite. It also exist in a non crystalline allotropic form known as amorphous carbon.

Diamond

Diamonds is found in Africa, India, Brazil, Republic of Guyana etc.

 structure of diamond

It has a network structure. Diamond is octahedral in shape. When cut and polished, it has an amazing luster which makes it valuable as jewelry. It is the hardest substances known. It is therefore used in making glass cutters and rock borers. It is also used as dies for drawing metal wires.

In diamond each carbon is covalently bonded to four other carbon atoms at tetrahedral positions about it. Thus, since each of the four valence electrons is involved in a strong covalent bond, there is no free electron to conduct electricity. Diamond is therefore a poor conductor of electricity. It has a high melting point. It is resistant to high temperature and chemical attack. It sublimes at 3500oC.

 Graphite:

Graphite is found in West Germany, Madagascar, Mexico, China, Australia etc.

 Structure of graphite

Graphite occurs naturally as an opaque black solid called plumbago. It has a layer structure. One layer solid slides over another. Because it is soft and slippery, it is used a lubricant. In graphite each carbon atom is bonded to three other carbon atoms and the fourth electron is free or delocalized. It is free to move round the whole structure. Thus, because one electron from each atom in graphite structure is mobile, graphite is a good conductor of electricity. It is inert, and it is often used as electrodes in electroplating and in dry cells. A mixture of graphite and clay is used as 'lead' in pencils. Graphite has a high melting point.

14.5. Amorphous Carbon

Non crystalline allotropic forms of carbon are called amorphous carbon. Amorphous forms of carbon include the following:

Coal, coke, carbon black, lamp black or soot, charcoal and carbon fibres.

Carbon black, lamp black or soot:

Carbon black is formed when natural gas (methane) and petroleum products is burnt in a limited supply of air. Lamp black is formed from an incomplete combustion of fuel (kerosene). It is found in the chimney of a kerosene lamp. Soot as formed in the kitchen chimney or above fire place where wood is used as a source of fuel. Carbon black, lamp black and soot are black and powdery in nature. They are used in making printers' ink, shoe polish and carbon papers.

CH4 + O2 C + 2H2O

Large quantity of carbon black can be prepared by heating natural gas to a very high temperature in the absence of air. CH4 C + 2H2

Carbon fibres:

Carbon fibres are formed or produced when fibres are heated to a very high temperature in the absence of air. The fibres char to form carbon. Some examples of fibre materials are: Nylon 6,6,Terylene, Polyester, Rayon etc.

Charcoal: different types of charcoal are wood charcoal, animal charcoal and sugar charcoal.

Wood charcoal is prepared or formed when wood is heated in the absence or limited supply of air. Animal charcoal is formed when bones and animal refuse are heated in the absence or limited supply of air. Sugar charcoal is made by dehydrating sugar with concentrated H2SO4 or by heating the sugar in a limited supply of air.

C12H22O11 H2SO4 + 11H2O

Wood charcoal contains sulphur as an impurity while animal charcoal contains calciumtetraoxophophates(v) as an impurity. Charcoal has a high adsorptive capacity. Not all gases are however adsorbed by charcoal. Carbon(iv) oxide is one of the gases that cannot be adsorbed by charcoal or CO2 cannot be adhered to the internal surfaces of charcoal.

 Chemical Properties of Carbon

1. Carbon reacts with oxygen to form its oxide.

When carbon burns in a limited supply of air, a toxic gas called carbon(ii)oxide is formed. 2C + O2 2CO

Limited supply carbon(ii)oxide. If oxygen is in excess supply, carbon(iv)oxide is formed.

C + O2 CO2 Excess supply carbon(iv)oxide

If diamond, graphite and amorphous carbon are heated separately in an excess, supply of air, the same carbon(iv)oxide is formed.

2. Carbon reacts with some elements to form its binary compounds.

3C(s) + 4Al(s) Al4C3(s) alluminium carbide;   2C(s) +Ca(s) CaC2(s) calcium carbide

C(s) + 2S(s) CS2(l) carbon(iv)sulphide;         C(s) + 2H2 CH4(g) methane

3. Carbon reduces some metallic and non-metallic oxide to their respective metals and nonmetals.

Fe2O3(s) + 3C(s) 2Fe(s) + 3CO(g);      2ZnO(s) + C(s) 2Zn(s) + CO2(g) ;   CO2(g) + C(s) 2CO(g)

H2O(g) + C(s) CO(g) + H2(g)

4.Carbon is oxidized to carbon(iv)oxide by strong oxidizing acids.

2H2SO4(aq) + C(s) 2H2O(l) + 2SO2(g) + CO2(g);  4HNO3(aq) + C(s) 2H2O(l) + 4NO2(g) + CO2(g)

WK 2       CARBON AND ITS COMPOUND –II

Coal and Coke

Coal and coke are among the examples of amorphous carbon as already mentioned.

Coal:

Coal is a black impure carbon formed from vegetations buried under the earth for many millions of years. These plants under high pressure underwent metamorphosis into the hard black rock, which are now known as coal.

Uses of coal

In the home, it is used as a domestic fuel. It is used for cooking. It is used in power stations for generating electricity. Railway locomotive engines run on coal. Coal is used in making or manufacturing many chemicals and drugs.

Types of coal

Four main types of coal are:

1. Peat

2. lignite (brown coal)

3. Bituminous coal (soft coal)

4. Anthracite (hard coal)

Peat is not a true coal. It is the first stage of coal formation. Peat consists of about 50% carbon.

Lignite (brown coal) is a further stage in the process of coal formation. It consists of about 60% carbon.

Bituminous coal (soft coal) is the most plentiful of the four types of coal. It consist of about 80% carbon.

Anthracite (hard coal) is the final product of the coal making process. It consists of over 90% carbon. Anthracite is the oldest and hardest form of coal.

Coal formation: Peat Lignites Bituminous Anthracite

Destructive distillation of coal

Destructive distillation of coal is heating coal to a very high temperature (about 1,250oC) in the absence of air so that it decomposes into four main products namely: coal gas, coal tar, ammonical liquor and coke. These four products are known as the products of destructive distillation of coal. The first three products are volatile. The only residue left after they have all been distilled off (and collected at different temperatures) is coke. Coal is used for the generation of heat energy for domestic purposes and chemical industries.

Coal gas is a mixture of these gases: ethane, methane, carbon (ii) oxide, hydrogen, sulphur (iv)oxide (very small) and hydrogen sulphide (very small). It is used as fuel in industries. Coal tar is a thick, brownish black liquid. It is a mixture of many organic chemicals like toluene, nephthalene, benzen, phenol etc. It is used in the production of many chemicals such as disinfectants, dyes, drugs etc. Ammonical liquor is made up of ammonia. It is used in the making of ammonium compounds. For instance ammonium tetraoxosulphate(vi), NH4SO4, which is manufactured with this liquor is used as a fertilizer.

Coke

It has already been pointed out that coke is the only residence left after all the volatile substances had been distilled off after the destructive distillation of coal. Coke is a light, porous, black carbon. Coke is amorphous in that it contains about 90% amorphous carbon. It is used in the making of calcium carbide used in the production of ethyne.

Distillation of coke: Coke is a light, porous, black carbon. Coke is amorphous in that it contains about 90% amorphous carbon. It is used in the making of calcium carbide used in the production of ethyne.

Ca(s) + 2C(s) CaC2(s)

               Coke      Calcium carbide

CaC2(s) + 2H2O(l)                Ca(OH)2(aq) + C2H2(g)

Calcium carbide                               Calcium hydroxide               Ethylene

1 Vol                                               1 Vol.

Coke is used in the extraction of metals from their ores. It reduces the oxides of the less active metals (e.g ZnO, Fe2O3, CuO, PbO etc) to the metals.

2ZnO(s) + C(s) 2Zn(s) + CO2(g)

                  Coke

Coke is also used as fuel.

Gasification of coke

Coke can be converted or turned into gas by making it to combine with either the oxygen of the air or with steam.

Producer gas: Producer gas is formed when air is passed into thick layer of red-hot coke.

2C + O2 + N2 2CO(g) + 4N2(g) + Heat

          Air        2 Vol.          4 Vol.

Producer Gas

Producer gas is therefore a mixture of carbon (ii) oxide and nitrogen in the ration of 1:2

Water gas: Water gas is formed when steam is blown over white-hot coke.

              H 20 ( g )+ C C 0 + H 2

Water gas is a mixture of carbon (ii) oxide and hydrogen in the ration of 1:1. Both producer gas and water gas are used as fuel in heating. Water gas has more calorific value than producer gas because both carbon(ii)oxide, CO and hydrogen, H2 are combustible. Town gas is a name often given to a mixture of coal gas and water gas.

Destructive distillation of wood

Wood is a complex substance like coal except that the percentage composition of elements present in it different. For example, wood has a higher percentage of carbon than coal.

Destructive distillation of wood yields these four fractions: (1) wood charcoal (2) pyroligneous acid (3) wood tar (4) wood gas.

Pyrolignous acid, which is the liquid fraction, contain mainly ethanoic acid, propanone, methanol and some other compound.

Summary of destructive distillation of coal

Products of distillation of coal	State	constituents	uses
Coke	solid	Carbon	Fuel, extraction of metals from their ores, producer gas
Ammoniacal liquor	liquid	Ammonia and water	Fertilizer, industries
Coal tar	liquid	Benzene, toluene, nephthalene	Paints, insecticides,drugs,plastics, dyes, perfumes,tarring of roads,explosive
Coal gas	gas	H2,CH4, CO2 and small other gases	In making gaseous fuel