NON-METALS : CARBON
Carbon:
Carbon has been known to chemists since long in the form of coal, diamond, graphite, etc. Most of the compounds include carbon as its constituent element. All the living bodies are composed from almost 18% carbon. Lavoisier, in 1775 A.D, proved that when diamond was burnt, carbon dioxide was produced. Tennant, in 1792, further proved that diamond was purest form of carbon. Mackenzie, in 1800, proved the existence of graphite.
Allotropes of Carbon :
Carbon is known to exist in many allotropic forms which may be broadly classified as crystalline and amorphous.
It should be noted that all allotropic forms of carbon differ only in their physical properties but are chemically identical. Equal weight of the allotropic forms yields the same weight of carbon dioxide when burnt in air in the presence of oxygen.
C + O -----------------------> CO2
1.Crystalline Allotropes of Carbon :
A) Diamond
Diamond is considered to be the purest form of carbon and is believed to be formed from coal when high pressure develops on Coal beds in the earth. Diamond was discovered first in India and the honour of producing world famous diamonds like Kohinoor Regent lies with India. But presently India occupies very low position in the list of countries producing diamonds. Main Diamond producing countries at present at South Africa Belgian Congo Brazil etc.
Diamond offers in the form of transparent octahedral crystals and when uncut do not sign. They are cut at proper angle which is very specialised job. This imparts large total internal reflection with lends them the usual sign.
Properties
1] Diamond is the hardest substance known and can scratch marble and glass.
2] It is transparent to X-rays.
3] It has a very high refractive index i.e. 2.417.
4] It is a bad conductor of heat and electricity.
5] It changes to graphite above 1800oC.
6] Its density is also very high (3.51 at 15oC).
7] It is a resistance towards almost all chemical reagents but is oxidised to carbon dioxide when heated to about to about 900oC in the presence of air.
C + O -----------------------> CO2
Structure :
Diamond is a big three-dimensional structure in which each carbon atom join to four other surrounding carbon atoms by covalent bonds. Each carbon-carbon bond is 1.54A and each angle 109.5o. Each carbon atoms by covalent bonds of regular tetrahedron. As these covalent bonds are very strong which explain the hardness and high density of diamond. As high energy is required to break these bonds that is why its melting point is very high 3500 degree Celsius. Further, no free electrons are available with any carbon atom, it is not a good conductor of electricity.
Uses :
1] It is used for cutting glass marble and graphite.
2] It is used for grinding and polishing of hard surfaces.
3] It is used as a precious stones in jewellery as a gem because of its brilliant shine.
B) Graphite
Graphite is another crystal in allotropic form of carbon. It is also known as Black lead. It is usually found in Siberia Sri lanka Italy Bavaria and USA.
Graphite has been prepared artificially by heating mixture of sand and coke in electric furnace at about 3000 degree Celsius.
SiO2 + 3C ---------------> CO2
SiC ------------------------> Si + C
Properties
1] It is a soft to touch, dark grey substance and has metallic lustre.
2] Its specific gravity is 2.2 which less than diamond.
3] It is a only non- metal that is good conductor of heat and electricity.
4] It marks paper black, so it is called Black lead. (Lead pencil is a mixture of graphite and clay.)
5] It is resistant toward nearly all of chemical reagents.
6] It burns in air on strong heating to yield carbon dioxide.
7] When heated with Conc. HNO3 a yellow mass called graphite acid, C11H4O5 is obtained
8] With alkaline permanganate, it is oxidised to oxalic acid and metallic acid, C6(CooH)6
Structure
Graphite is a two-dimensional layer structure. In each layer, the carbon atoms are arranged in regular hexagonal rings. Each carbon atom is joined to three other atoms by covalent bonds. Each carbon-carbon bond is 1.42 A0 and each angle is 1200
The two successive layers of graphite are 3.4Ao apart. Thus these layers can slip over each other. Hence graphite are quite soft. Each carbon atom has still one electron free which can move from one point to the other. Thus graphite is a very good conductor of electricity.
Uses
- Used in making a pencil.
- Used as a dry lubricant.
- For making electrodes.
- For polishing iron articles.
- As a moderator in the nuclear furnace.
C) Fullerene
It was discovered in 1985 before it only two allotropes were known. It was discovered by three scientists, viz. R.E. Smalley and R.F. Curl and H.W. Kroto in the year 1985. It was the third crystalline allotrope of carbon. They also shared the 1996 Nobel Prize in chemistry for this discovery.
Preparation and Separation : Fullerenes constitute a new family of carbon allotropes consisting of large spheroidal molecules of composition, C2n, where n>=30. These were first prepared evaporation of graphite using a powerful laser. However in 1990, Kratschmer and his colleagues developed a contact arc discharge method for microscopic production, known as the Kratschmer-Huffman method this is a more practical method for production of fullerenes in microscope quantities, involves heating of graphite in an electric arc in an inert gas such as a Helium or Argon when sooty material so formed mainly contains C60 fullerenes with smaller quantity of C70 and traces of other fullerenes consisting of even number of carbon atoms 350 or above. The C60 and C70 fullerenes can be readily separated from the fullerene soot by extraction with benzene or toluene followed by chromatography over alumina.
A small amount of fullerenes can also be prepared by the combustion of benzene and acetylene.
Note that unlike graphite a diamond the fullerenes dissolved in organic solvents. A solution of C60 fullerene in toluene is purple whereas that of C70 in in orange red. In fact, fullerenes are the only pure form of carbon because they do not have dangling age of surface bonds which attract other atoms as is the case of graphite of diamond.
Structure : Of all the fullerenes, C60 is the most stable.It looks like soccer ball and is sometimes called bucky ball. It contains 20 six membered rings and 12 five membered rings. Six membered rings are used both to order 6 membered rings and five membered rings but the five-member rings are connected to only six membered rings.
In nature, fullerenes, especially the C60 sphere, are highly symmetrical. Fullerenes have a similar structure to graphite, which is made up of a sheet of connected hexagonal rings, but they have pentagonal (or sometimes heptagonal) rings that prevent the sheet from being planar. Buckyballs and buckytubes are terms used to describe them depending on their shape. Cylindrical fullerenes are referred to as nanotubes. C60 is the most common fullerene, with no two pentagons sharing an edge. A C60 molecules' average carbon-carbon bond length is 1.44 angstrom.
C70 fullerene on the other hand, resembles a rugby ball. It consists 12 five membered rings and 25 six membered rings. As in C60 fullerenes, the pentagons are isolated from each other. Fullerenes are found in three different forms, viz. spherical, elliptical and in the form of tubes.
Properties of C60 (fullerenes):
Physical properties:
| C60 |
| 720.64 |
| Dark needle-like crystals |
| 280 °C |
| 800K - sublimes |
| 1.72 g/cm3 (mass); 1.44 x 1021/cm3 (molecular) |
| N/A |
| 2.2 (600 nm) |
| Hexagonal cubic |
| 1014 ohms m-1 |
| 0.4W/mK (300 K) |
| 720 |
| 720 |
Chemical properties:
- Buckminsterfullerene can easily be reduced electrochemically to form fulleride ion, It reacts with group-1 metals forming solid K3C60 , which acts as a superconductor below 18K.
- Hydrogenation: C60 addition with hydrogen to give polyhydroxy fullerenes. Buckminsterfullerene exhibits a small degree of aromatic character so it also undergoes Birch reduction.
- Halogenation: Halogens undergo addition reaction with C60 produces the following compounds such as C60Br8 and C60Br24.
- Addition of oxygen: Ozonation of C60 in 1,2-xylene at 257K gives an intermediate ozonide C60O3, which can be decomposed to form epoxide C60O.
- Formation of metal complexes: Fullerenes act as ligands in transition metal complexes due to the immense π system. Osmium tetroxide, a powerful oxidizing agent. When OsO4 is reacted with C60 and 4-tert-butylpyridine, it producing C60(OsO4)(4-t-butylpyridine)2.
- Compounds containing encapsulated metals. These may contain one, two, or three metals inside the fullerene sphere. Examples: UC60.
Uses:
- Fullerenes are used in the medical field as light-activated antimicrobial agents.
- It is also used in several biomedical applications including the design of high-performance MRI contrast agents, X-ray imaging contrast agents, photodynamic therapy and drug and gene delivery.
- Buckminsterfullerene is used in drug delivery systems, in lubricants and as a catalyst.
- It is also used as a conductor.
- Some types of fullerene can be used as an absorbent for gases.
- It is used in making cosmetic products.
- C60 based films are used for photovoltaic applications.
- Fullerenes are used in making carbon nanotubes based fabrics and fibres.
2) Amorphous allotropes of carbon
A) Charcoal
It is the amorphous form of carbon. It is a soft, black and highly porous. Different types of charcoal are:
a. Wood Charcoal : It is made by destructive distillation of wood. It is highly porous and has a vast internal surface area. Upon the surface charcoal absorbs many times its volume of gases.
Uses:
- Fuel Feedstock
- Reducing Agent
- Filtration Agent & Gas Masking
- Decolorizing Agent
- Gastric Medicine
- Sketches & Paints
- Soil Conditioning
- Gunpowder
b. Animal charcoal : Animal charcoal or bone black is the carbonaceous residue obtained by the dry distillation of bones. It contains only about 10% carbon, the remaining being calcium and magnesium phosphates (80%) and other inorganic material originally present in the bones.
Uses : It may be used for refining sugar, manufacture of superphosphate of lime(fertilizer) and phosphorus, for decoloring organic chemicals.
c. Sugar charcoal : It is obtained by the action of conc. H2SO4 on sugar.
2C12H22O11 + H2SO4(conc)→ 12C + 5H2O + H2SO4(dil)
It is the purest form of amorphous carbon.
Uses : It may be used to remove coloring matter, as black pigment.
Activated charcoal
All form of charcoal are highly porous substance and can absorb many times their own volume of the gases which increases further by heating charcoal at 1000oC in a current of superheated steam. This treatment removes the impurities sticking in the wall. Thus prepared is called activated charcoal.
B. Lamp Black
Lamp black is obtained by burning natural gases and other compounds in a limited supply of air. The soot obtained is made to stick on the wet blanket hung in the chamber. After drying the shoot is removed from the blanket.
The black soot is one of the purest varieties of amorphous carbon containing 98.6% carbon and 1.4% hydrogen.
Uses:
It was one of the major black pigment in early American house paints. Currently, lampblack is used as a black pigment in
1] cements
2] ceramics
3] inks
4] Linoleum
5] crayons
6] shoe polishes
6] Carbon paper
C. Gas Carbon
A black deposit obtained on the roof and sides are retort during the destructive distillation of coat (in the manufacture of oil gas) is called gas carbon. It is good conductor of electricity and used for making electrodes in dry cell.
D. Coke
It is residue obtained in destructive distillation of coal. It is pure for of carbon.
Uses : It may be used as a reducing agent in metallurgy, fuel, etc.
E. Coal
It is formed by slow decomposition of vegetable matter under the influence of high temperature, high pressure and in the absence of air. This process is called carbonization.
Uses :
1] It is used as fuel
2] In the manufacture of producer gas.
3] It is used as reducing agent.
Preparation and properties of Carbon Monoxide (CO)
Carbon Monoxide
Three oxides of carbon are known with the formulae CO, CO2 and C3O2 (carbon suboxide). The oxidation state of carbon in CO is +2; +4 in CO2 and +4/3 in carbon suboxide.
Laboratory preparation
1. In the laboratory carbon monoxide is prepared by heating of oxalic acid crystals with concentrated sulphuric acid.
(COOH)2 + H2SO4(conc.) -----------> CO2 + CO + (H2SO4.H2O)
Concentrated sulphuric acid dehydrates oxalic acid on heating and a mixture of carbon monoxide sulphuric acid.
2. In the laboratory pure carbon monoxide is prepared by heating formic acid with concentrated sulphuric acid.
HCOOH + H2SO4(conc.) ----------------> CO + (H2SO4.H20)
3. In the laboratory carbon monoxide is also prepared by heating Potassium ferrocyanide with concentrated sulphuric acid.
K4[Fe(CN)6] + 3H2SO4 ----------------> 2K2SO4 + FeSO4 + 6HCN
6HCN + 12H2O --------------------------> 6COOH + 6NH3
6HCOOH ----------------------------> 6H2O + 6CO
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K4[Fe(CN)6] + 6H2SO4 + 8H2O ---------------------------> 2K2SO4 + FeSO4 + 3(NH4)2SO4 +6CO
Physical properties
Carbon monoxide is:
1] Highly poisonous,
2] Colourless
3] Odourless
4] Tasteless gas.
5] Very flammable and mixes well with air, easily forming explosive mixtures.
6] Melting Point: -205°C
7] Boiling Point: -191°C
8] Vapour density: 0.967 (air=1)(at 25°C)
Chemical properties
1. Action towards litmus : It is neutral to litmus.
2. Combustibility : It is a non supporter of combustion but burns itself in the presence of air or oxygen to produce carbon dioxide with blue flame.
2CO + O2 -------------------> 2CO2
3. Formation of addition products : Carbon monoxide is an unsaturated compound gives addition reaction. It is because oxidation number of carbon in carbon monoxide is + 2 and extend upto +4. The following reactions for that carbon monoxide and unsaturated compound.
a) Action with hydrogen : Carbon monoxide reacts with hydrogen under certain condition to form methanol (CH3OH).
CO (g) + 2H2(g) → CH3OH (g)
b) Action with sulphur : When carbon monoxide and sulphur vapours are heated together carbonyl sulphide is produced.
CO + S -----------------> OCS
c) Action with chlorine : A mixture of carbon monoxide and chlorine reacts in the presence of sunlight to yield phosgene which is very poisonous gas.
CO + Cl2 -----------------------> COCl2
d) Formation of metal carbonyls : Carbon monoxide combines with transition metals like Nickel, iron, Cobalt, to form addition compound called metal carbolysis.
Ni + 4CO ------------------> Ni(CO)4
Fe + 5CO -------------------> Fe(CO)5
2Co +8CO → [Co(CO)4]2
Nickel tetracarbonyl decomposes when heated at 180°C to yield black nickel. Therefore this reaction is used for the purification of nickel.
e) Action with sodium hydroxide: Sodium formate is obtained when carbon monoxide is passed through heated caustic soda (200°C) under pressure.
CO + NaOH -----------------> HCOONa
f) Action with Haemoglobin : Blood contains haemoglobin, a red pigment. Carbon monoxide, when combines with this pigment yield stable carboxyhemoglobin.
Haemoglobin + CO -------------------> Carboxyhemoglobin
This prevents hemoglobin to carry oxygen to the different parts of body from lungs and causes suffocation and even death. Thus carbon monoxide act as a poisonous gas. Therefore it is advised that a room being heated by burning coal should be well ventilated.
(4) Reducing character: Carbon monoxide is easily oxidised to carbon dioxide, therefore, it behaves as a very good reducing agent. For example,
(i) Reducing of metal oxides:
PbO + CO -------------> Pb + CO2
ZnO+ CO --------------> Zn +CO2
Fe304 + 4CO ---------------> 3Fe + 4CO2
(ii) Reduction of Tollen's Reagent: Ammonical silver nitrate solution is called Tollen's Reagent. When CO is passed through it, silver is obtained in the form of mirror.
2[Ag(NH3)2]+OH- + CO ----------> 2Ag + CO2 +H2O + 4NH3
(iii) Reduction of Fehling Solution:
Cu(OH)2 + CO ---------> Cu2O(Red ppt) +H2O + CO2
Uses of Carbon Monoxide
(i) As its burning is an exothermic reaction, it is used as a fuel in combination with hydrogen (Water gas)
(ii) It is very good reducing agent and is used in metallurgical operations.
(iii) It is used for the extraction of Nickel and Iron by forming their Volatile Carbonyls.
(iv) By combining with Chlorine a poisonous gas phosgene is produced which is used in warfare.
Tests of Carbon Monoxide
(i) It burns with a blue flame.
(ii) When a filter paper soaked in platinic chloride in contact with Carbon monoxide turns green, pink or black due to reduction of the metal chloride by carbon monoxide.