CARBON & ITS COMPOUNDS
The compounds obtained from ‘Carbon’ are widely used as clothes, medicines, books, food, fertilizer, fuel etc. all living structures are carbon based. The amount of carbon present in the earth’s crust and in the atmosphere is quite merge. The earths crust has only 0.02% carbon in the form of mineral (like carbonates, hydrogen-carbonates, coal and petroleum) and the atmosphere has 0.03% of carbon dioxide. In spite of this small amount of carbon available in nature, the importance of carbon seems to be immense. Carbon forms a large number of compounds with hydrogen which are known as hydrocarbons. In addition to hydrogen, carbon compound may also contain some other element such as oxygen, halogen, nitrogen, phosphorus, sulphur etc. The number of compounds of carbon is more than three million which is much larger than the compounds formed by all other element put together.
BONDING IN CARBON COMPOUNDS
Carbon forms covalent bonds in its compounds with other atoms. In each compound the valency of carbon is four. That is, carbon has tetravalent character. But what is covalent bond and what is meaning of tetravalent ?
COVALENT BOND: A chemical bond formed between two atoms of the same element or two atoms of different elements by sharing of electron is called a covalent bond.
Necessary conditions of the formation of covalent bond:
- The combining atoms should have nonmetallic character.
- The combining atoms should contain 4 to 7 electrons in their respective valence shell.
- In hydrogen there is only 1 valence electron, but it also forms covalent bond.
- The combining atoms need 1, 2, 3 or 4 electrons to complete their octet (hydrogen completes its duplet)
- The combining atoms should contribute equal number of electrons to form pair of electrons to be shared.
- After sharing the pair of electrons each combining atoms should attain stable electronic configuration like its nearest noble gas.CLASSIFICATION OF COVALENT BOND: On the basis of the number of electrons shared by two combining atoms, the covalent bond are of three types.
- Single Covalent Bond: A single covalent bond is formed by the sharing of one pair of electrons between the two atoms. It is represented by one short line (–––) between the two atoms.
Example: H–H, Cl –Cl, H–Cl, CH3–CH3.
- Double Covalent Bond: A double covalent bond is formed by the sharing of two pairs of electron between the two combining atoms. It is represented by putting (=) two short lines between the two bonded atoms.
Examples: O = O (O2), CO2 (O = C = O), H2C = CH2
- Triple covalent bond: A triple bond is formed by the sharing of three pair of electrons between the two combining atoms. It is represented by putting three short line (º) between two bonded atoms. Example: N2 (N≡N), CH≡CH.Formation of single covalent compounds:
- Formation of hydrogen molecule (H2): A molecule of hydrogen is composed of two H-atoms. The electronic configuration of H-atom is.
H – H Bond in terms of energy shells (orbits)
- Formation of chlorine molecule (Cl2). The atomic number of chlorine is 17, thus there are 17 electrons in an atom of chlorine. Electronic configuration of Cl atom –
Shells K L M
Electrons 2 8 7 } Incomplet Octet
Electonic configuration of Ar atom
Shells K L M
Electrons 2 8 8 } complet octet
Chlorine atom needs one electron more to complete its octet –
Cl – Cl bond in terms of energy shell orbits
Formation of hydrochloric acid (HCl):
- H atom has one valence electron. It needs 1 electron more to complete its duplet and chlorine atom has 7 valence electrons. It need 1 electron more to complete its octet and acquire stable electronic configuration (2, 8, 8) like noble gas argon.
- Formation of oxygen (O2): The atomic number of O atom is 8. There are 6 electron in the valence shell of oxygen atom it needs 2 more electrons to attain the nearest stable inert gas Neon (2, 8) configuration :
- Formation of nitrogen molecule (N2): The atomic number of nitrogen is 7 and its electronic configuration is K(2), L(5). It needs 3 electrons more to complete its octet like noble gas neon (2, 8).
- Formation of ammonia molecule (NH3): The atomic number of N is 7. It’s electronic configuration is 2, 5 there are 5 electrons in its valence shell. It needs 3 electrons more to complete its octet like noble gas neon (2, 8).
- Formation of H2O molecule: The electronic configuration of hydrogen is K (1) and that of oxygen is K(2) L(6) thus each hydrogen require one and oxygen required two electrons to achieve the stable electronic configuration.
- Formation of CO2 molecule: The atomic number of C is 6 and the electronic configuration of C is K(2), L(4) and that of oxygen is K(2), L(6) thus each carbon require 4 and oxygen require two electrons to achieve the stable electronic configuration.
- Formation of CH4 molecule: Methane is a covalent compound containing 4 covalent bond. It contains one carbon atom and four hydrogen atom covalently bonded to central carbon atom.
- Formation of carbon tetrachloride molecule (CCl4): The electronic configuration of carbon and chlorine atoms are (2, 4) and (2, 8, 7) respectively. Carbon atom needs four electrons and chlorine atom needs one electron to attain the stable electronic configuration.
- Formation of ethylene or ethene molecule (C2H4): The electronic configuration of carbon atom is 2, 4. There are 4 valence electrons in one C atom. Each H atom contains 1 valence electron. Thus, there are 12 valence electrons present in ethene molecule.
- Formation of Acetylene or ethyne molecule (C2H2) :
Non polar and polar covalent compounds:
Non polar covalent bond:
A covalent bond formed between two atoms of the same element or same electronegativity is called a non-polar covalent bond.
Example: H2, N2, O2, Cl2 etc.
Polar covalent bond:
The covalent bond between the atoms of two elements having different electronegativities is called a polar covalent bond. Molecule in which the atom are bonded by a polar covalent bond are called polar molecules. Note: In a polar covalent bond, the shared pair of electrons lies more toward the atom which is more electronegative.
Example: HCl, H2O & NH3
Note: δ means partial
Characteristics of covalent bond and covalent compounds:
Characteristics of covalent bond:
- Covalent bond are formed by mutual sharing of electrons
Note: Shared pair of electrons is also called bonding pair of electrons.
- Covalent bond is directional in nature because shared pair of electrons remain localized in a definite space between the two atoms.
Characteristics of covalent compounds:
Physical State: The covalent compounds are generally gases or liquids, but compounds with high molecular masses are solids.
Example: Solid: Urea, Glucose, Naphthalene.
Liquids: Water, ethanol, benzene.
Gases: Methane, chlorine, hydrogen, oxygen
- Melting and boiling points: Covalent compounds have low melting and low boiling points because intermolecular forces (cohesive forces) in covalent compounds are weaker than those in ionic compounds.
Note: Some exception like diamond and graphite which are covalent solids have very high M.P. & B.P. l
- Solubility: Covalent compounds generally dissolve readily in organic solvents but they are less soluble in water.
For example: Napthalene which is an organic compound dissolves readily in organic solvents like ether but is insoluble in water. However some covalent compounds like urea, glucose, sugar etc. are soluble in water. Some polar covalent compounds like ammonia and hydrochloric acid are soluble in water.
- Conductivity: Covalent compounds do not conduct electricity because they contain neither the ions nor free electrons necessary for conduction, So they do not conduct electricity
For example: Covalent compounds like glucose, alcohol, carbon tetrachloride do not conduct electricity.
Differences between ionic and covalent compounds :
The chemical compounds which are present in living organisms (plant and animal) are called organic compounds. The belief that formation of organic compounds was possible only in plants and animals led the scientists of early days to propose that Vital Force was necessary for the formation of such compounds. But the experimental work of Friedrich Wohler (German chemist) denied the idea of vital force when he prepared urea in his laboratory. (urea is an organic compound and waste product of urine).
Allotropy / allotropes of carbon:
The phenomenon of existence of allotropic forms of an element is called allotropy. Allotrops are the different forms of the same element having different physical properties but almost similar chemical properties. There are three allotrops of carbon these are diamond, graphite and fullerene.
Diamond: Diamond is a crystalline allotrope of carbon. Its atomic symbol & empirical formula is ‘C’.
Structure of Diamond
Structure: In diamond, each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement. This tetrahedral arrangement of carbon atoms gives a rigid, three dimensional structure to diamond It is due to this rigid structure that diamond.
- Is very hard crystalline structure.
- Has high melting point.
- Is non conductor of heat and electricity.
Properties: Pure diamond is a transparent and colourless solid.
- Polished diamond sparkles brightly because it reflects most of the light (refractive index of diamond is 2.45)
- Diamond are not attacked by acids, alkalis and solvents like water, ether, benzene or carbon tetrachloride but diamond is attacked by fluorine at 750°C.
C (Diamond) +2 F2
Carbon Fluorine Carbontetrafluoride
- The density of diamond is 3.51 g per cm3 at 20°C.
- A saw fitted with diamond is used for sawing marbles.
- A chip diamond is used for glass cutting.
- Black diamonds are used in making drill.
- Diamonds are used for making dice for drawing very thin wires of harder metals.
- Diamonds are also used for making high precision tools for use in surgery such as, for the removal of cataract.
- Diamond are used for making precision thermometers and protective windows for space crafts.
Graphite is also known as black lead it marks paper black. The name graphite has been taken from the Greek word ”graphein” (which means to write) in reference to its uses as ‘lead’ in lead pencils.
Structure: Graphite is an opaque and dark grey solid. In a crystal of graphite the carbon atoms are arranged in hexagonal patterns in parallel planes. In a layer of graphite each carbon atom is strongly bonded to three carbon atoms by covalent bonds. Thus, one valence electron of each carbon atom is free in every layer of graphite crystal. The free electron makes graphite a good conductor of electricity. Each layer is bonded to the adjacent layers by weak forces. As a result, each layer can easily slide over the other.
- Graphite is greyish -black, opaque material having metallic (shiny) lustre.
- It is soft and has a soapy (slippery) touch.
- Graphite is lighter than diamond. The density of graphite is 2.26 g per cm3 at 20°C.
- Graphite is a good conductor of heat and electricity.
- Graphite has a very high melting point.
- Graphite is insoluble in all common solvent.
- For making electrodes in dry cells and electric arc furnaces.
- Graphite is a good dry lubricant for those parts of machines where grease and oil cannot be used.
- For making crucibles for melting metals.
- For manufacturing lead pencils.
- Graphite is used as neutron moderator in nuclear reactors.
- For the manufacture of gramophone records and in electrotyping.
- For the manufacture of artificial diamond.Fullerene:
- Fullerene was discovered in 1985 by Robert F. Curl Jr, Harold Kroto and Richard E. Smally.
- This molecule containing sixty atoms of carbon has been named Buckminster fullerene.
Fullerens has been named after American architect and engineer R. Buckminster-fuller whose geodesic domes follow similar building principles.
Types of fullerene: C60, C70, C74 and C78 are the members of the fullerene family. But C60 is the most stable and most studied form of fullerenes.Structure of fullerene :
- Buckminster fullerene molecule (C60) is nearly spherical.
- It consists of 12 pentagonal faces and 20 hexagonal faces giving it 60 corners. Thus, Buckminster fullerene has a hollow, cage-like structure.
- In figure, ball like molecules containing C atoms.
- By electrically heating a graphite rod in atmosphere of helium.
- By vaporising graphite by using laser.
- Fullerene is soluble in benzene and forms deep violet colour solution.
- Crystalline fullerene has semiconductor properties.
- Compounds of fullerene with alkali metals are called fullerides and they are superconductors.
- As a superconductor.
- As a semiconductor.
- As a lubricants and catalyst.
- As fibres to reinforce plastics.
Versatile Nature of Carbon
About three million (or thirty lakh) compounds of carbon are known. The existence of such a large number of organic compounds is due to the following characteristic features of carbon.
(1) CATENATION: Tendency to form Carbon-Carbon bond: “The property of forming bonds with atoms of the same element is called catenation”. Carbon has the maximum tendency for catenation in the periodic table. This is because of strong carbon carbon bonds as compared to other atoms.
Note: Silicon also show catenation.
- When two or more carbon atoms combine with one another, they form different types of chain such as (i) Straight chains
(ii) Branched chains
(iii) Closed chain or ring chains
- The property of catenation is due to
(i) small size of C atom
(ii) Great strength of carbon – carbon bond.
- When two or more carbon atoms combine with one another, they form different types of chain such as (i) Straight chains
(2) Tetravalency of Carbon:
- The atomic number of carbon is 6.
- The electronic configuration of carbon atom is 1s2,2s2,2p2.
- It has four electrons in the outermost shell, therefore its valency is four.
Thus carbon forms four covalent bonds in its compounds.
(3) Tendency to form multiple bonds: Due to small size, carbon can easily form double or triple bonds (called multiple bonds) with itself and with the atoms of other elements as nitrogen, oxygen, sulphur etc.
“A series of organic compounds having similar structures and similar chemical properties in which the successive members differ in their molecular formula by –CH2 group”.
The different members of the series are called homologous.
Characteristics of Homologous Series:
- All the member of a homologous series can be described by a common general formula.
Example: All alkane can be described by the general formula CnH2n+2.
- Each member of a homologous series differ from its higher and lower neighbouring members by a common difference of –CH2 group.
- Molecular masses of the two adjacent homologues differ by 14 mass units, because molecular mass of –CH2 group is 12 + 2 = 14.
- All the members of a homologous series show similar chemical properties.
- All the members of the series can be prepared by similar methods known as the general method of preparation.
Table: Some members of alkane, alkene and alkyne homologous series.
Activity : Calculate the difference in the formulae and molecular masses for
(a) CH3OH and C2H5OH
(b) C2H5OH and C3H7OH and (c) C3H7OH and C4H9OH
Homologous series containing functional groups.
HCHO, CH3CHO, CH3CH2CHO, CH3CH2CH2CHOl
- Carboxylic acids: HCOOH, CH3COOH, CH3CH2COOH, CH3CH2CH2COOH
- Amines: CH3NH2, CH3CH2NH2,CH3CH2CH2NH2.
- Ketones: CH3COCH3, CH3COCH2CH3, CH3COCH2CH2CH3
- Haloalkanes: CH3X, CH3CH2X, CH3CH2CH2X, CH3CH2CH2–CH2XHow do physical properties change in a homologous series of hydrocarbons.
The physical properties of the various members of a homologous series change regularly with an increases in the molecular mass.(i) Melting and boiling points: Melting point and boiling point of hydrocarbon in a homologous series increases with an increase in molecular mass.
(ii) Physical State
- Hydrocarbons containing lesser number of carbon atoms are gases.
- Hydrocarbons containing large number of carbon atoms are solids.
- Hydrocarbon containing intermediate number of carbon atoms are liquid.
Example : Hydrocarbon containing 1-4 carbon atoms are gases, these containing 5–13 carbon atoms are liquid and those containing more than 14 carbon atoms are solids.
Compounds formed from combination of carbon and hydrogen are known as Hydrocarbon. Hydrocarbon on the basis of chain are mainly classified into two parts.
Saturated and unsaturated hydrocarbon :
(1) Saturated Hydrocarbon:
- The hydrocarbons which contain only single carbon-carbon covalent bonds are called saturated hydrocarbons.
- They are also called alkanes.
- General formula for alkanes is CnH2n+2 where ‘n’ is the number of carbon atoms.
General formula of saturated hydrocarbon (CnH2n+2)
(2) Unsaturated hydrocarbons: The hydrocarbon in which two carbon atoms are bonded to each other by a double (=) or a triple (≡) bond is called an unsaturated hydrocarbon.
- Unsaturated hydrocarbons are of two types viz. alkenes and alkynes.
(I) Alkenes : ()
- The hydrocarbon in which the two carbon atoms are bonded by a double bond are called alkenes.
- Their general formula is CnH2n where “n” is the number of carbon atoms.
General formula of alkenes: CnH2n
|No. of C atoms||Name||Formula||Structure|
(II) Alkyne (– C ≡ C –)
- The hydrocarbon in which two carbon atoms are bonded by a triple bond are called alkyne.
- Their general formula is CnH2n–2 where ‘n’ is the number of carbon atoms.General formula of alkynes: CnH2n–2
|No. of ‘C’atoms||Name||Formula||Structure|
CHAINS, BRANCHES AND RINGS: The hydrocarbons may also have branched, closed chains or ring or cyclic structures.
Branched structure: The alkanes containing three or less carbon atoms do not form branches.
CH4 CH3–CH3 CH3–CH2–CH3
Methane Ethane Propane
- The alkane containing four carbon atoms (C4H10) has two types of arrangement of carbon atoms.
- Closed chains or cyclic hydrocarbon:
These hydrocarbons contains closed chain or rings of atoms in their molecules. These are of two types:
(A) Alicyclic hydrocarbon :
- These hydrocarbons contain a ring chain of three or more carbon atoms.
- These cyclic compounds are named by prefixing cyclo before the name of corresponding straight chain hydrocarbon.
(B) Aromatic hydrocarbon:
- These have at least one benzene ring in their molecules.
It is a special type of ring of six carbon atoms with three double bonds in alternate positions.
Will you be my friend? (Functional group):
- Carbon forms many compounds with hydrogen. But carbon also forms bonds with other atoms such as halogen, oxygen, nitrogen and sulphur. Therefore, carbon is said to be very friendly element. These compounds are obtained by replacing one or more hydrogen atoms by other atoms such that the valency of carbon remains satisfied. The atom replacing the hydrogen atom is called heteroatom or Functional group.
- Different organic compounds having same functional group have almost same properties these are called families.
Example: l Properties of CH3–OH and CH3–CH2OH are similar and it is due to the presence of –OH (hydroxyl) group.l This group is known as alcoholic group.l Family of compounds having –OH group is called alcohols.
- Properties of CH3–OH and CH3–CH2OH are similar and it is due to the presence of –OH (hydroxyl) group.
- This group is known as alcoholic group.
- Family of compounds having –OH group is called alcohols.
Some Functional Groups in Carbon compounds
Nomenclature of carbon compounds: Carbon compounds can be called by their common names, but, then remembering millions of compounds by their individual names may be very difficult. Due to this reason, the International Union of Pure and Applied chemistry (IUPAC) has devised a very systematic method of naming these compounds. Naming a carbon compound can be done by the following methods.
- The number of carbon atoms in the molecule of a hydrocarbon is indicated by the following stems.
Example: Saturated hydrocarbon.
Alkane → Meth + ane = Methane
Alkene → Eth + ene = Ethene
Alkyne → Eth + yne = Ethynel
- In case of functional group is present, it is indicated in the name of compound with either a prefix or a suffix.
- Identify the longest continuous chain of carbon atoms. This gives the name of parent hydrocarbon.
- In the case of any substituent appropriate prefix is added before the name of parent hydrocarbon.
- In the case of a functional group, the ending ‘e’ in the name of the parent hydrocarbon is replaced by the appropriate suffix.
⇒ Functional Group: “Functional group may be define as an atom or a group of atoms which is responsible for most of the characteristic chemical properties of an organic compound”.
The prefixes and suffixes of some substituents/functional group
Definition: Compounds having same molecular formula show different physical and chemical properties are called isomers and the phenomenon is called isomerism. The difference in properties of isomers is due to the difference in the relative arrangements of various atoms present in their molecules. Organic compound show following types of structural isomerism on the basis of their difference in structural arrangement of atoms.
- Type of Isomerism: The following figure shows the pictorial representation of different types of isomerism
- Chain isomerism: Organic compounds having same molecular formula but difference in the nature of length carbon chain are called chain isomers. For example, Let us consider the molecular formula of an alkane C4H10.
- Position isomerism: Compounds having same molecular formula but differ in the position of, functional group, double bond or triple bond in the carbon chain are called position isomers. This type of isomerism is shown by Alkene, Alkyne, Alcohol, Amine, Haloalkane etc.
Ex.1 Let us consider the molecular formula of an alcohol (CnH2n + 2O)C3H8O
Ex.2 Let us consider the molecular formula of alkene C4H8(CnH2n)
- Functional isomerism: Compounds having same molecular formula but differ in nature of functional group are called functional isomers.
Ex.1 Alcohol and ether have same molecular formula (CnH2n+2O) but have different functional group hence show functional isomerism. C2H6O
Ex.2 Aldehyde and Ketone having same molecular formula (CnH2nO)C3H6O
- Metamerism: The compounds having same molecular formula but different number of carbon atoms (or alkyl groups) on either side of functional group, are called metamers.
E.g. ethers, thioethers, secondary amines, ketones, esters etc.
- Tautomerism: This is a special type of functional isomerism in which the isomers differ in the arrangement of atoms but they exist in dynamic equilibrium with each other. For exmaple, acetaldehyde and vinyl alcohol are tautomers.
♦ Knowledge Enhance:
Stereoisomerism was exhibit by compounds which have same structural formula and sequence of bonds but differ in the relative position of atoms or groups of atoms in space. It is majorly of two types
1. Geometrical Isomerism
2. Optical Isomerism
1. Geometrical Isomerisms also called cis trans isomerism is exhibited by alkanes because of the presence of double bond. This is due to the restricted rotation around carbon-carbon double bond. As a result, the position of the groups attached to these carbons is fixed in space. Here cis-isomer have identical group on either side where as intrans-isomer identical groups are at opposite side of C = C.
2. Optical Isomerism is shown by substances which can rotate the plane of polarished light. For exmaple this type of isomerism is shown by amino acid alanine.
Note: You will study about stereoisomerism in detail in higher classes.
⇒ Chemical Properties of Carbon compound :
All carbon compounds show some common characteristic properties. As most of the fuels we use are either carbon or its compounds. Some such properties are described here :
Combustion: Combustion is a chemical process in which heat and light (in the form of flame) are given out The process of combustion, is a rapid oxidation reaction of any substance in which heat and light are produced.
Combustion of some common substance:
- Combustion of Carbon: Carbon (or charcoal) burn in air or oxygen to give CO2 producing heat and light.
C(s) + O2(g) CO2(g) + Heat + light
Carbon Oxygen Carbon dioxide
- Combustion of Hydro Carbon: Hydrocarbons burn to produce carbon dioxide (CO2), water (H2O) and heat and light.
Note: Natural gas and biogas contain methane. So, burning of natural gas and biogas are also combustion reactions.
Burning of LPG (Butane) produces CO2, H2O heat and light.
- Combustion of cellulose: Combustion of cellulose (like wood, cotton cloth and paper) gives CO2, H2O heat and light. Cellulose is a carbohydrate and can be described by the formula (C6H10O5)n.
Combustion of alcohol :
C2H5OH(l) + 3O2(g) 2CO2(g) + 3H2O(g) + heat + light
Ethanol oxgyen (in air)
Activity: To observe the combustion of given organic compounds.
Materials : Benzene, naphthalene, Camphor, alcohol (ethanol). Spirit, acetone.
1. Take each compound oniron spatula and burn them in Bunsen burner.
2. Record the type of flame produced.
3. Put a metal plate above the flame and observe whether or not there is black carbon deposition.
Compound used Flame Produced Deposit
Benzene Smoky flame Carbon deposited Naphthalene Smoky flame Carbon deposited Camphor Smoky flame Carbon deposited Alcohol Non-Luminous flame No Carbon deposited Spirit Non-Luminous flame No Carbon deposited Acetone Non-Luminous flame No Carbon deposited
Conclusion: Benzene, naphthalene, camphor burn with smoky flame and carbon particles get deposited they undergo incomplete combustion due to excess of carbon content.
Alcohol, spirit and acetone burn with non-Luminous flame and no carbon gets deposited. They under go complete combustion, therefore produce more heat.
Activity: To study the different types of flames / presence of smoke.
Material required: Bunsen burner.
1. Light the bunsen burner.
2. Close the air hole and observe thecolour of the flame.
3. Put a metal plate over it and observe the nature ofdeposit.
4. Open the air regulator to allowflow of air.
5. Observe thecolour of flame.
6. Put a metal plate and observe the nature ofdeposit.
Conclusion: Keep the air regulator open to get oxidising, non-sooty flame which has high temperature and does not lead to black deposits.
Combustion and the nature of flame:
(i) Saturated hydrocarbon such as, methane, ethane, propane, butane and natural gas and LPG burn with a blue flame in the presence of sufficient / excess of air / oxygen.
(ii) In the presence of limited amount of air / oxygen, saturated hydrocarbon, such as, methane, butane. etc give smoky flame.
(iii) Unsaturated hydrocarbon such as ethene, ethyne etc. burn with a luminous / yellow smoky flame.
(iv) The gas / kerosene stove used at home has inlets for air so that a sufficiently oxygen rich mixture is burnt to give a clean blue flame. If you carefully observe the bottoms of vessels getting blackened, it is clear indication that the air holes are blocked and the fuel is getting wasted.
(v) Fuels, such as coal and petroleum, have some amount of nitrogen and sulphur in them. Combustion of coal and petroleum results in formation of oxides of sulphur and nitrogen (such as sulphur dioxide, nitric oxide, nitrogen peroxide) which are major pollutants in the environment.
Formation of Coal and Petroleum: Coal and petroleum have been formed from biomass which has been subjected to various biological and geological processes. Coal is a naturally occurring black mineral and is a mixture of free carbon and compounds of carbon containing hydrogen, oxygen, nitrogen and sulphur. It is not only a good fuel but is also a source of many organic compounds. It is found in coal mines deep under the surface of earth. Coal is believed to be formed from fossils which got buried inside the earth during earthquakes and volcanoes which occurred about 300 million years ago. Due to huge pressure and temperature inside the earth and in the absence of air, the fossils fuels (vegetable matter or wood, etc.) were converted into coal. The slow chemical processes of the conversion of wood into coal is called carbonization. Since coal is formed by slow carbonization of plants and fossils, it produces many important carbonisation products like peat, lignite, bituminous and anthracite etc. and is itself known as fossil fuel. Coal is also a non-renewable source of energy.
Petroleum is a complex mixture containing various hydrocarbons (compounds of carbon and hydrogen) in addition to small amounts of other organic compounds containing oxygen, nitrogen, and sulphur. It is a dark coloured, viscous and foul smelling crude oil. The name petroleum is derived from latin words : “petra” meaning rock and “oleum” meaning oil. Since petroleum is found trapped between various rocks, it is also known as rock oil.
Carbon and its compounds can be easily oxidised on combustion (or burning). During combustion / burning, the compounds gets oxidised completely to different products, depending upon the nature of the oxidising agents.
Carbon gives carbon monoxide or carbondioxide depending upon the oxygen available.
2C(s) + O2(g) → 2CO(g)
Carbon Oxygen(limited) Carbon monoxide
C(s) + O2(g) → CO2(g)
(excess) Carbon dioxide
- Hydrocarbon when oxidised give different product as follows:
- Alcohols also give different products on oxidation depending upon the reaction conditions.
Alcohols on oxidation with certain oxidising agents such as chromic anhydride in acetic acid, yield corresponding aldehydes,where as on oxidation with alkaline potassium permanganate (or acidified potassium dichromate) corresponding carboxylic acid is formed, as given below :
Activity: To study the reaction of ethanol with alkaline potassium permanganate:
Material required: Ethanol, alkaline KMnO4, test tube.
- Take about 3 ml of ethanol in a test tube.
- Add 5% solution of alkaline KMnO4 drop by drop into this solution.
- Observe the colour of alkaline KMnO4 after adding initially as well as finally.Observation: The colour of KMnO4 gets discharged in the beginning. When excess of KMnO4 is added, the colour of KMnO4 does not disappear because whole of ethanol gets oxidised to ethanoic acid.
Addition reaction: All unsaturated hydrocarbons (unsaturated carbon compounds) react with a molecule like H2. X2. H2O etc. to form another saturated compounds are called addition reactions. Unsaturated hydrocarbons add hydrogen, in the presence of catalysts, such as nickel or palladium to give saturated hydrocarbons.
Note: Catalysts are substance that cause a reaction to occur or proceed at a different rate without the reaction it say being affected.
- Addition of hydrogen to ethene :
- Addition of hydrogen to ethyne :
- Addition of hydrogen to a unsaturated carbon compound is called hydrogenation reaction.
Certain vegetable oils such as ground nut oil, cotton seed oil and mustard oil, contain double bonds (C = C) and are liquids at room temperature. Because of the unsaturation, the vegetable oils undergo hydrogenation, like alkenes, to from saturated products called vanaspati ghee. Which is semi-solid at room temperature.
The reactions in which one or more hydrogen atoms of a hydrocarbon are replaced by some other atoms or groups are called substitution reaction.
Example: Methane reacts with chlorine (or bromine) in the presence of sunlight and undergo substitution reaction. It is called photochemical reaction because it takes place in presence of sunlight.
⇒ Some important carbon compounds :
⇒ Ethanol (Ethyl alcohol, C2H5OH): Ethanol is the second member of the homologous series of alcohols. Preparation: By the fermentation of carbohydrates (sugar or starch). Ethanol is prepared on commercial scale by fermentation of sugar. Fermentation is allowed to take place at 298 – 303 K in the absence of air. This is ethanol (ethyl alcohol) gets oxidised to ethanoic acid(acetic acid) in the presence of air.
C12H22O11 + H2O C6H12O6 + C6H12O6
Sucrose Glucose Fructose
C6H12O6 2C2H5OH + 2CO2(g)
Glucose/Fructose Ethanol (ethyl alcohol) Carbon dioxide
- Physical state / colour and odour: Pure ethanol is a colourless liquid having a pleasant smell and a burning taste.
- Boiling and Freezing points: It is a volatile liquid with a boiling point of 78.1°C, and freezing point is –118°C.
- Density: Ethanol is lighter than water as its density is 0.79 g ml–1 at 293 K.
- Solubility: Ethanol is miscible with water in all proportions, due to the formation of hydrogen bonds with water molecules.
- Conductivity: Ethanol is a covalent compound and does not ionise easily in water, hence it is a neutral compound.
- Action on Litmus: Ethanol is a neutral compound. So, it has no effect on the colour of litmus
⇒ Chemical properties of ethanol:
- Combustion (or burning): Ethanol is highly inflammable liquid and readily burn in air with blue flame to form water vapour, carbon dioxide and evolving heat. Thus, combustion of ethanol is an exothermic reaction.
C6H5OH (l) + 3O2(g) 2CO2(g) + 3H2O(g) + Heat
- Reaction with sodium metal : Ethanol reacts with sodium metal to produce sodium ethoxide and hydrogen gas is evolved.
2C2H5OH (l) + 2Na(s) → 2C2H5ONa + H2(g)
Ethanol Sodium metal Sodium ethoxide HydrogenActivity: To study the reaction of ethanol with sodium metal.
Materials: Ethanol, dry piece of sodium metal test tube.
- Take ethanol in a test tube.
- Add a dry piece of sodium metal.
- Bring a burning matchstick near the gas evolved to test it and record observation.
Observation: The gas burns in air with a pop sound which is the characteristics of hydrogen gas. Conclusion: Alcohol react with sodium metal to liberate hydrogen gas.
- Reaction with ethanoic acid (Esterification reaction) :
The reaction in which an alcohol reacts with acetic acid in the presence of conc. H2SO4 to form an ester is called esterification.
Note: Ester are sweet-smelling compounds and are used for making perfumes.
Reaction with conc. sulphuric acid (Dehydration):
Ethanol when heated with excess of concentrated sulphuric acid at 443 K, gets dehydrated to give ethene.
Note: The concentrated sulphuric acid can be regarded as a dehydrating agent which remove water from ethanol.
Uses of ethanol:
- Ethanol is present in alcoholic beverages such as beer, wine, whisky.
- As a solvent for paints, varnishes-dyes, cosmetics, perfumes, soaps and synthetic rubber etc.
- Ethanol is used in cough syrups, digestive syrups and tonics.
- A mixture of 80% rectified spirit and 20% petrol is called power alcohol. It is used as fuel in cars and aeroplanes.
- A mixture of ethanol and water has lower freezing point than water this mixture is known as antifreezing and is used in radiators of vehicles in cold countries and at hill stations.
- As an antiseptic to sterilize wounds and syringes in hospitals.
- For the manufacture of terylene and polythene.
- As a preservative for biological specimens.
- Ethyl alcohol is used as hypnotic (induces-sleep).Harmful effects of Alcohols:
- Consumption of small quantities of dilute ethanol causes drunkenness. Even though this practice is condemned, it is a socially widespread practice. However, intake of even a small quantity of pure ethanol (called absolute alcohol) can be lethal. Also long-term consumption of alcohol leads to many health problems.
- When large quantities of ethanol are consumed, it tends to slow metabolic processes and to depress the central nervous system. This results in lack of coordination, mental confusion, drowsiness, lowering of normal inhibitions and finally stupor (unconscious state of wild)
- Drinking of alcohol over a long period of time damages liver.Denatured Alcohol: Ethanol to which certain poisonous and nauseating substances like methyl alcohol, pyridine etc. have been added is termed denatured alcohol.
Note: To prevent the misuse of ethanol (Alcohol), industrial alcohol is coloured blue so that it can be recognised easily.
Harmful effects of denatured alcohol:
- Methanol is highly poisonous compound for human beings. Methanol when taken, even in small amount, can cause death.
- Methanol gets oxidised to methanal in the liver, which causes coagulation of protoplasm.
- Methanol also effects the optic nerve and cause blindness.
⇒ Ethanoic acid (acetic acid) CH3COOH:
- Ethanoic acid is commonly called acetic acid and belongs to the homologous series of carboxylic acid and is represented as CH3COOH.
- 5-8% solution of acetic acid in water is called vinegar and is used for preservating foods like sausage, pickles.
- At ordinary temperature, ethanoic acid is a colourless liquid with a strong pungent smell and sour taste.
- Its boiling point is 391 K and its density at 273 K is 1.08 (heavier than water).
- It is miscible with water due to the formation of hydrogen bonds with water molecules.
- On cooling at 289.6 K, it turns in ice-like crystals, hence named as glacial acetic acid.
- It dissolves sulphur, iodine and many other organic compounds.
- It dimerise when dissolved in benzene.
Activity: To determine pH of acetic acid and hydrochloric acid.
Material: Acetic acid (1M), HCl (1M), blue litmus paper, universal indicator.
Procedure: Take two strips of blue litmus paper.
- Put a few drops of HCl on one of them and few drops of acetic acid on the other.
- Observe the change in colour.
- Take 1 ml of acetic acid in a test tube and add a few drops of universal indicator.
- Take 1 ml of HCl in a test tube and add few drops of universal indicator.Observation: Both acetic acid and HCl turn blue litmus red showing that they are acidic in nature. pH of acetic acid and HCl are not equal.
Conclusion: HCl is strong acid than CH3COOH, therefore, pH of HCl will be lower than that of acetic acid.
- Reaction with alcohols (Esterification reaction):
Ethanoic acid reacts with ethanol in the presence of conc. H2SO4 to form ethyl ethanoate which is an ester.
CH3COOH(l) + C2H5OH(l) CH3COOC2H5 + H2O
Ethanoic acid Ethanol Ethyl ethanoate (ester)
the reaction of carboxylic acid with an alcohol to form an ester is called “esterification”.
Note: Ester can be hydrolysed in the presence of an acid or a base to give back the parent carboxylic acid and the alcohol.
(i) Ethyl ethanoate on acid hydrolysis gives ethanoic acid and ethanol.
CH3COOC2H5(l) + H2O(l) → CH3COOH(aq.) + C2H5OH
(ii) Hydrolysis of ester in the presence of base (alkali) is called “Saponification reactions”.
CH3COOC2H5(l) + NaOH(aq) → CH3COONa + C2H5OH
Ethyl ethanoate Sodium Hydroxide Sodium ethanoate EthanolNote: Alkaline hydrolysis of higher esters is used in the manufacture of soaps.
Activity: To study the esterification process using ethanol and acetic acid.
Materials: Beaker, water, test tube, ethanol, acetic acid.
Conc. H2SO4 etc.
Procedure: Take 2ml of ethanol in a test tube.
- Add 2ml of ethanoic acid (acetic acid) in to it.
- Add few drops of conc. H2SO4.
- Warm it in a beaker containing water.
Observation: Pleasant fruity smelling compound (called ester) is formed.
Conclusion: Acetic acid reacts with alcohol in presence of conc.
which act as a dehydrating agent to form ester.
Reaction with sodium carbonate and sodium hydrogen carbonate :
Ethanoic acid decomposes sodium hydrogen carbonate and sodium carbonate with a rapid evoluation of carbon-dioxide gas.Note; Reactions of ethanoic acid with NaOH, NaHCO3, Na2CO3 and active metals show that the hydrogen present in the carboxyl (–COOH) group is acidic in nature.
Activity: To study the reaction of carboxylic acid with sodium carbonate and sodium hydrogen carbonate. Material: Ethanoic acid, Sodium carbonate, Sodium hydrogen carbonate.
- Take 1g of Na2CO3 and add 2ml of ethanoic acid into it.
- Pass the gas formed through lime water and note down the observation.
- Repeat the same procedure with sodium hydrogen carbonate and record observation.Observation: Brisk effervescence due to carbon dioxide formed which turns lime water milky. Conclusion: Acetic acid react with Na2CO3 and NaHCO3 to liberate CO2 gas.Uses of ethanoic acid:
- Ethanoic acid is used in the manufacture of various dyes, perfumes and rayon.
- It is used for making vinegar.l It is used for making white lead [2PbCO3 . Pb(OH)2] which is used in white paints.
- Its 5% solution is bactericidal (destroys bacteria).
- It is used in preparation of cellulose acetate which is used for making photographic film.
- It is used for coagulation of the latex.l It is used for preparation of 2, 4-dichloro phenoxy ethanoic acid which is used as herbicide.
- Aluminium acetate and chromium acetate are used as mordants in dyeing and water proofing of fabrics.
Soap and detergents: Soap and detergents are substances which are used for cleaning. There are two types of detergents:
2. Synthetic detergents
Soap: A soap is the sodium or potassium salt of a long-chain fatty acids (carboxylic acid or glycerol).
To test tube B, add a few drops of soap solution. Now shake both the test tubes vigourously for the same period of time.
Can you see the oil and water layers separately in both the test tubes immediately after you stop shaking them.
Leave the test tubes undisturbed for some time and observe. Does the oil layer separate out ? In which test tube does this happen first ? this activity demonstrate effect of soap in cleasing as we know that most of the dirt is oily in nature and oil does it dissolve in water.
But know the question arise what are soap ? What are the detergent which one is more effect. How the work. Soap is sodium or potassium salt a long change fatty acid (Carboxylic acid or Glycerol) A soap has large non ionic hydrocarbon group and an ionic group. COONa.
Ex.of soap are :
(1) Sodium stearate (C17H35COONa)
(2) Sodium plamitate (C15H31COONa)
Soap are basic in nature so soap solution turn red litmus to blue.
Preparation of Soap:
The soap is prepared by heating animal fats or vegetable oils (olive oils, castor oil or palm oil) with sodium hydroxide or potassium hydroxide. The process of formation of soap by the hydrolysis of fat or oil with alkali is called saponification.
Oil or Fat + Sodium hydroxide → Soap + glycerol
- A soap molecule contains two parts that interact differently with water, one part is a long hydrocarbon (non-polar) chain, and other belongs to the –COONa group (Hydrophillic). A soap molecule may be represented as :
Cleansing action of soap:
The molecules of soap are sodium or potassium salts of long chain carboxylic acids. The ionic end of soap dissolves in water while the carbon chain dissolves in oil. The soap molecules, thus form structures called micelles where one end of the molecules is towards the oil droplet while the ionic end faces outside. This form an emulsion in water. The soap micelle thus helps in dissolving the dirt in water and we can wash out clothes clean.
Effect of soap in cleaning
Differences between soaps and synthetic detergents :
- The hydrocarbon chain is non-polar and water -hating (hydrophobic), while the other part is polar or water loving (hydrophilic).
- Hydrophilic part makes the soap soluble in water and hydrophobic part makes the soap insoluble.
- When soap is added to water, the soap molecules assume a configuration which increases the interaction of the water loving heads with the water molecuels, and decreases the interaction between the water hating tails with the water molecules.
- The hydrophobic part of the soap molecules traps the dirt and the hydrophilic part makes the entire molecules soluble in water. Thus, the dirt gets washed away with the soap.
- The water-hating, non polar tails clump together in a radial fashion with the water-loving, polar heads remaining at the periphery of the clump, these clumps or droplets of soap molecules are called micelles.Disadvantage of soap:
- Soaps are not effective in hard water : Hard water contains calcium ions (Ca2+) and magnesium ions (Mg2+). These ions react with the carboxylate ions (RCOO–) of the soap forming an insoluble precipitate called scum. For example, soap like sodium stearate (C17H35COONa) reacts with calcium and magnesium ions as per the following chemical equation.
2C17H35COONa + Ca2+(aq) → (C17H35COO)2 Ca ↓ + 2Na+ (aq)
Sodium stearate (In hard water) Calcium stearate
Sodium ion2C17H35COONa + Mg2+(aq) → (C17H35COO)2 Mg ↓ + 2Na+ (aq)
Sodium stearate (In hard water) Magnesium stearate(scum) Sodium ionThe scum gets attached to the clothes, utensils and even skin and thus, interferes with the cleansing ability of the additional soap and makes the cleansing of clothes difficult. Moreover, large amount of soap is wasted in reacting with calcium and magnesium ions present in hard water.
- Soaps are not effective in acidic medium: In presence of hydrogen ions (H+ ions), i.e. in acidic medium, the carboxylate ions of soap (RCOO– ion) interact with hydrogen ions (H+) to form undissociated (free) fatty acid as represented below :
C17H35COO–(aq) + H + → C17H35COOH
carboxylate ion Carboxylic acid (Unionised)As the fatty acids are weak acids, so they do not get ionised and hence, micelle formation is hindered, thus, adversely affecting the cleansing property of soaps.
You will observe that the amount of foam in the two test tubes in different. The foam is formed to a greater extent in test tube ‘B’ (containing detergent solution), while formation of a curdy white mass will be observed in test tube ‘A’. This activity clearly indicates that detergents can be used for cleansing purpose, even with hard water.
- Synthetic detergents are called soapless soap because they are not prepared from fatty acid and alkali.
- Synthetic detergents are sodium salts of sulphonic acids, i.e. detergents contain a sulphonic acid group (–SO3H), instead of a carboxylic acid group (–COOH), on one end of the hydrocarbon chain.
Properties of synthetic detergents:
- Synthetic detergents do not react with the ions present in hard water. Hence, synthetic detergents have no problem in forming lather with hard water, i.e. their efficiency is not affected by hard water. l
- Synthetic detergents can be used even in acidic solution and sea water, whereas soap cannot be used in the acidic solution (due to precipitation of free acids)
- Synthetic detergents do not form insoluble salts of calcium or magnesium with hard water. Hence, lesser amounts of synthetic detergents are required for washing.Washing powder:
- Washing powders used for washing clothes contain only about 15 to 30 percent detergents by mass. The remaining part is made of the following.
(i) Sodium sulphate and sodium silicate which keep the powder dry.
(ii) Sodium tripolyphosphate or sodium carbonate which maintains alkalinity for removing dirt.
(iii) Carboxymethylcellulose (CM-Cellulose) which keep the dirt particle suspended in water.
(iv) Sodium perborate (a mild bleaching agent) which impart whiteness to the materials (clothes, etc.) being washed.
- Carbon is versatile element that forms the basis of all living things.
- Carbon can form a vast variety of compounds because of its tetravalency and the property of catenation.
- Covalent bonds are formed between two similar or different atoms by sharing electrons in their valence shell, such that both of them can achieve the structure of nearest noble gas.
- Carbon forms covalent bonds with itself as well as atoms of hydrogen, oxygen, nitrogen, sulphur and halogens.
- Carbon can form compounds having a straight chain between carbon atoms with a single bond, or double bond or triple bond. It can also form compounds with branched chains and closed chains.
- logous series of carbon compounds is a group of carbon compounds having the same functional group with the same general formula.
- The functional groups such as alcohols, aldehydes, ketones, carboxylic acids and halogens impart characteristic properties to the carbon compounds.
- Carbon and its compounds are the major sources of fuels.
- Ethanol and ethanoic acid are most important compounds of carbon in our daily life.
- The soaps and detergents have cleansing action, because of the presence of hydrophobic and hydrophilic groups in their molecules, which help in emulsifying oil, and hence, in the removal of dirt.