User:Narayan Madhushala

LANGAUGE OF CHEMISTRY

Chemistry: The branch of experimental science which deals with the study of matter, its composition, preparation, properties and transformation is chemistry. The universe is composed of energy and matter.

Matter: Any substance in the universe which occupies space and possesses mass is called matter. It is classified into 2 types:

Physical Classification: Depending upon the physical state, matters are classified into three states:

Solid: The matter which has definite volume and definite shape is called solid. Ex: Wood, Salt, etc.

Liquid: The matter which has definite volume but variable shape is called liquid state. Ex: Different liquids.

Gas: The matter which has neither definite volume nor definite shape is called gas. Ex: Oxygen, Hydrogen, etc.

Chemical Classification: Depending upon the composition, matter is of two types:

Pure Matter: The matter containing one and only one types of substance is called pure matter. It is further classified into two types:

Elements: The smallest particle of an element which may or may not be capable of independent existence and can take parts in chemical reaction is called atom. Ex: Hydrogen, Oxygen, etc. = Atoms of these have no independent existence. Iron, Copper, etc. = Atoms of these have independent existence. Atoms are composed of equal numbers of electrons and protons. Atoms are neutrally charged. Atoms form molecules and ions.

The simplest and purest form of matter which can neither be split into simpler substances nor can be prepared (built) by combining two or more simpler substances by any physical or chemical process is called element. In terms of atomic theory, element is composed of atoms of the same kind. Ex: Gold, Iron, Hydrogen, Oxygen, etc. Recently 113 elements have been known, out of which 92 are natural and rest are artificial. All known elements are arranged on a chart called the Periodic Table of Elements. Elements are of four types:

Metals: The element which has tendency to lose electron from the valence shell of its atom is called metals. Ex: Gold, Iron, Copper, etc.

Non-metals: The element which has tendency to gain electron into the valence shell of its atom is called non-metals. Ex: Chlorine, Hydrogen, Sulphur, etc.

Metalloids: The elements which show some properties of metals and some properties of non-metals and behave as semi-conductors are called metalloids. Ex: Arsenic, Antimony, Bismuth, Germanium, Boron, Silicon, etc.

Inert gases: The elements which neither gain nor lose any electron by their atoms are called inert gases. They are also called as inactive. They are also called as noble gases because they were newly discovered gases with respect to other elements. Ex: Helium, Neon, Argon, etc. Compounds: A group of atoms bonded together, representing the smallest fundamental unit of a chemical compound which possesses the properties of that compound and can take part in a chemical reaction is called molecule. It cannot be subdivided without destroying its characteristic properties. Ex:	He, Ne, Ar are monatomic molecules. H2, N2, O2 is diatomic molecules. O3 and S8 are polyatomic molecules. CH4 and PCl5 are heteroatomic molecules. The complex and purest form of matter which is produced by the combination of two or more than two elements in definite proportion by weight and can be split into its components by suitable chemical method are called compounds. In terms of atomic theory, compound is composed of atoms of the different kind. Ex: Water (containing the elements hydrogen and oxygen), CO2 (containing the elements carbon and oxygen, Sugar (containing the elements C, H and O), etc. Compounds are of two types:

Organic compound: The compounds which are usually obtained from living sources i.e. animals, plants, etc. are called organic compound. Ex: Carbohydrates, Fats, Protein, Urea, etc.

In-organic compound: The compound which are usually obtained from non-living sources i.e. rocks, minerals, etc. are called in-organic compound. Ex: Common salt, Marble, Lime, Sand, etc.

Impure matter or Mixture: The matter containing two or more than two different substances so that individuals do not lose their identity is called impure matter or mixture. It is further classified into two types:

Homogenous Mixture: The impure matter which is perfectly uniform in its composition throughout i.e. each and every sample of mixture show identical composition and properties is called homogenous mixture. It means all the components of homogenous mixture can't be seen even under a powerful compound microscope. Ex: Air, Sea water, Brass, Salt solution, etc.

Heterogeneous Mixture: The impure matter which is not perfectly uniform in its composition throughout i.e. different sample of mixture show different composition and properties is called heterogeneous mixture. It means the components of heterogeneous mixture can be seen even sometimes with necked eye. Ex: Mixture of sugar and sulphur, Water and oil, sandy water, etc.

Separation of Mixture: Mixtures can be separated into individual components by different processes. Methods of separation depend on the physical characters of individual components of the mixture. Some commonly used laboratory processes for separation of mixtures of substances are as follows:

Filtration: The process of separating an insoluble solid component from the liquid completely by passing through a porous membrane is called filtration. This principle is based on the fact that solvent molecules and molecules or ions present in the solution can pass through the porous membrane (e.g. - filter paper) while suspended particles are retained on a porous membrane. The liquid collected after passing through a porous membrane is called filtrate, whereas insoluble particles left in the porous membrane are called residue. A typical experimental setup for this process is shown in the figure below. Fig: Filtration Sedimentation and decantation: This method is generally employed for the separation of the constituents of the mixture in which one component is liquid and the other component is in the form of coarse solid particles heavier than liquid. This method is based on the effect of gravity. The coarse solid particles being heavy settle down (sedimentation) and the upper clear layer of liquid is poured carefully into another container (decantation). For example- muddy river water is purified by this method. This method is not suitable for the mixture containing very fine particles. The typical setup for this experiment is shown below: Sublimation: The process of converting solid substances directly into the vapor state without converting it into the intermediate liquid state by applying heat is called sublimation. The vapors on cooling give back solid and it is called sublimate. This method is used to separate the solid components from the mixture which are directly converted into vapors on heating whereas remaining components are not affected by heat. Some of the substances which sublimate on heating are camphor, ammonium chloride, naphthalene, benzoic acid etc. The typical setup for this experiment is shown below:

Evaporation: The process of converting liquid into the vapors state at any temperature is called evaporation. This method is used for recovering soluble solid solute from the solution. In this method, the solution containing solid solute is heated in porcelain basin. The solid solute is left in the porcelain basin, whereas the liquid is evaporated. The typical setup for this experiment is shown below:

Crystallization: This technique is used for obtaining a solid compound in pure and geometrical form. The impure sample of the solid substance is dissolved in the suitable solvent to make the saturated solution at the higher temperature. When such solution is cooled, the substance appears in the form of crystals. The solution left behind is called mother liquor, which consists of all the impurities. The crystals thus obtained can be separated with the help of the spatula. The typical setup for this experiment is shown below:

Distillation: The process of converting liquid into the vapors in heating and the vapor back to liquid on cooling is called distillation. It is of two types:

Simple Distillation: This technique is used for separating liquids having boiling points differing by 10-20ºC. The liquid having lower boiling point distills first leaving another liquid behind. For distillation process, the liquid mixture is taken in distillation flask fitted with the thermometer and a condenser. To avoid bumping of liquid, few glass beads are used. The distillation flask is then heated on the sand bath. The liquid having low boiling point boils first and its vapor leaves the flask. These vapors are passed through the condenser and condensed into liquid. This condensed liquid is called distillate, which is collected in the receiver, whereas the liquid having the high boiling point is left behind in the distillation flask. The typical setup for this experiment is shown below: Fractional distillation: When the boiling points of two liquids present in the mixture do not differ much or they boil within a narrow range of temperatures, simple distillation doesn't work. Thus, fractional distillation is used. In fractional distillation, vapors of liquid are made to pass through the fractionating column, a glass column packed with glass beads or specially designed column. The vapors of liquid having high boiling point get condensed in this column and return back to the flask, whereas the vapors of liquid having low boiling point leave the column from the exit. These vapors enter the condenser and get condensed, which are collected in the receiver. The liquid collected in the receiver consists of pure more volatile liquid and the less volatile liquid remains in the distillation flask. The typical setup for this experiment is shown below:

Chromatography: Chromatography is an important experimental technique for the separation, purification, and identification of constituents of a mixture. This method is based on the differential distribution of the components of the mixture between two phases commonly called stationary phase and a mobile phase. The mobile phase may be liquid or gas. The components of the mixture have different affinities for two phases and thus move through the system at different rates. The component which has a high affinity for mobile phase moves relatively quickly, whereas a component which has a high affinity for stationary phase moves slowly. Due to the difference in rate, complete separation becomes possible. The common type of chromatography is column chromatography.

Some technical terms related to matters and its constituents: Symbol: The abbreviation used for representing the lengthy name of an element called symbol. A symbol is usually the first alphabet of the name of the element and acts as the short hand representation of an element.

Symbols from different sources From English Name: Hydrogen = H		Boron = B			Barium = Ba Chlorine = Cl		Chromium = Cr		Oxygen = O Zinc = Zn			Carbon = C			Cadmium = Cd Beryllium = Be		Cobalt = Co Calcium = Ca		Nitrogen = N

From Latin Name: Copper 	= Cuprum 	= Cu		Gold 		= Aurum 	= Au Sodium 	= Natrium 	= Na		Antimony 	= Stibium 	= Sb Iron 	= Ferrum 	= Fe 		Lead 		= Plumbum	= Pb Mercury 	= Hydrargyrum= Hg		Potassium	= Kalium 	= K Silver 	= Argentum 	= Ag 		Tin 		= Stannum 	= Sn

From German Name: Tungsten	= Wolfram	= W

From Scientist's Name: Curium		= Mdm. Curie		= Cm Mendelevium	= Dmitri Mendeleev 	= Md Nobelium		= Alfred Nobel		= No Einsteinium	= Albert Einstein         = Es Fermium		= Enrico Fermi		= Fm

From the name of Countries, Cities, Laboratories: Californium	= University of California	= Cf Polonium		= Poland 			= Po Americium		= America			= Am Germanium	= Germany 			= Ge Berkelium 		= City of Berkley		= Bk

From the name of Planets: Uranium		= Uranus	= U Neptunium	= Neptune	= Np Plutonium		= Pluto		= Pu

Significances of Symbol: A symbol is not only for an abbreviation for the full name of the element but it has qualitative and quantitative significance. The significances of Symbols are:

Let us take 'Ca' for example: Qualitative Significance: A symbol represents name of a particular element i.e. "Ca" represents Calcium.

Quantitative Significance: A symbol of an element represents: 1 mole of the element i.e. Calcium. 6.023 * 1023 atoms of the element i.e. Calcium. 1 gm atomic weight of the element i.e. Calcium (40 gm).

Molecular formula: The symbolical representation of any molecule of a compound in the terms of alphabet(s) and number(s) is called molecular formula. It is the short representation of a molecule. A molecular formula shows the actual number of atoms of all the involved elements in one molecule of the substance. Ex: H2O is the molecular formula of water.

Process to write Molecular Formula Valency of an atom or a radical should be identified. Valency of each atom or a radical should be written on the top end of the atom or radical. Electronegative part is to be placed on the right hand side and electropositive part is to be placed on the left hand side. The electropositive part and the electronegative part should be combined together in an inverse numerical ratio of their valency i.e. valencies of each parts are brought in criss-cross subscript term and the common numerical value, if present, should be removed.

Significances of Molecular Formula: A chemical molecular formula has both qualitative and quantitative significance. A chemical formula gives the following information:

Let us take NH3 for example: Qualitative Significances: The name of the given particular substance i.e. NH3 represents ammonia. The name of the components of the particular substance i.e. Ammonia is composed of nitrogen and hydrogen.

Quantitative Significances: 1 molecule of ammonia. 1 mole of ammonia contains 6.023 * 1023 molecules of ammonia. 1 molecule of ammonia contains 1 atom of nitrogen and 3 atoms of hydrogen. The molecular weight of ammonia is 17 (14+3). 17 parts by weight of ammonia contains 14 part by the weight of nitrogen and 3 parts by weight of hydrogen.

Some chemical substances and its molecular formula:

S.N.	General Name	Chemical Name	Molecular Formula	Valency 1.	Water		H2O	0 2.	Heavy water		D2O	0 3.	Common salt, Table salt or Rock salt	Sodium chloride	NaCl	0 4.	Glauber’s Salt	Sodium Sulphate	Na2SO4.10H¬2O	0 5.	Chile Salt Petre	Sodium nitrate	NaNO3	0 6.	Baking Soda	Sodium bicarbonate	NaHCO3	0 7.		Sodium hydroxide	NaOH	0 8.	Soda lime (Mixture of caustic soda and quick lime)		NaOH + CaO	0 9.	Sodium carbonate i.e. Washing Soda or Soda ash or Decahydrate		Na2CO3.10H2O	0 10.	Potassium Chloride		KCl	0 11.	Caustic Soda	Potassium hydroxide	KOH	0 12.	Heptahydrate or Epsom salt	Magnesium sulphate	MgSO4.7H2O	0 13.	Magnesia	Magnesium Oxide	MgO	0 14.	Quick lime or Lime	Calcium oxide	CaO	0 15.	Slaked lime or Lime water	Calcium hydroxide	Ca (OH)2	0 16.		Calcium Chloride	CaCl2	0 17.	Plaster of paris	Calcium sulphate hemihydrates	2CaSO4. H2O	0 18.	Zypsum salt	Calcium sulphate dichydrate	CaSO4.2H2O	0 19.	Bleaching powder	Calcium chloro hypochlorite	CaOCl2	0 20.	Marble chips, lime stone or chalk	Calcium carbonate	CaCO3	0 21.	Milk of magnesia	Magnesium hydroxide	Mg (OH)2	0 22.	Cement		MgCl2.5MgO.XH2O	0 23.	Boric acid		H3PO3	0 24.	Borax	Sodium Tetraborate	Na2B4O7.10H2O	0 25.	Diborane		B2H6	0 26.	Coke, Coal or Charcoal		C	0 27.		Carbon monoxide	CO	0 28.		Carbon dioxide	CO2	0 29.	Water gas		CO + H2	0 30.	Producer gas		CO + N2	0 31.	Semi water gas		CO + H2 + N2	0 32.	Oil gas		Mixture of gaseous hydrocarbons, CO, H2, etc.	0 33.	Coal gas		Mixture of H2, C2H4, C2H2, etc.	0 34.	L.P. gas		Methane, Ethane, etc. but in liquid form. 0 35.	Petrol gas		Mixture of air and petrol vapours. 0 36.	Indane gas		Mainly liquid isobutane under pressure. 0 37.	Sand, Quartz or Silica	Silicon dioxide	SiO2	0 38.	Laughing gas	Nitrous oxide	N2O	0 39.		Nitric oxide	NO	0 40.	Nitrogen peroxide	Nitrogen dioxide	NO2	0 41.		Nitrogen trioxide	N2O3	0 42.		Ammonia	NH3	0 43.	Sal ammoniac	Ammonium chloride	NH4Cl	0 44.	Nitrous acid		HNO2	0 45.	Nitric acid		HNO3	0 46.	Phosphine		PH3	0 47.		Phosphorous trioxide	P2O3	0 48.		Phosphorous pentoxide	P2O5	0 49.	Hypophosphorous acid		H3PO2	0 50.	Orthophosphorous acid		H3PO3	0 51.	Orthophosphoric acid		H3PO4	0 52.	Permonophosphoric acid		H3PO5	0 53.	Metaphosphoric acid		HPO3	0 54.	Hypophosphoric acid		H4P2O6	0 55.	Pyrophosphoric acid		H4P2O7	0 56.	Perdiphosphoric acid		H4P2O8	0 57.	Ozone		O3	0 58.		Hydrogen sulphide	H2S	0 59.		Sulphur dioxide	SO2	0 60.		Sulphur trioxide	SO3	0 61.	Hypo	Sodium thiosulphate	Na2S2O3	0 62.	Hypo	Sodium thiosulphate pentahydrate	Na2S2O3.5H2O	0 63.	Sulphurous acid		H2SO3	0 64.	Sulphuric acid, Oil of vitriol		H2SO4	0 65.	Hydrofluoric acid		HF	0 66.	Hydrochloric acid		HCl	0 67.	Hydrobromic acid		HBr	0 68.	Hydroiodic acid		HI	0 69.	Black oxide of Copper	Cupric oxide	CuO	0 70.	Red oxide of Copper	Cuprous oxide	Cu2O	0 71.	Blue vitriol	Copper sulphate pentahydrate	CuSO4.5H2O	0 72.	Zinc white or philosopher’s wool	Zinc oxide	ZnO	0 73.	White vitriol	Zinc sulphate heptahydrate	ZnSO4.7H2O	0 74.	Corrosive sublimate	Mercuric chloride	HgCl2	0 75.	Calomel	Mercurous chloride	Hg2Cl2	0 76.		Ferric chloride	FeCl3	0 77.	Green vitriol	Ferrous sulphate heptahydrate	FeSO4.7H2O	0 78.	Mohr’s salt	Ferrous ammonium sulphate hexahydrate	FeSO4 (NH4)2SO4.6H2O	0 79.	Horn silver	Silver chlorine	AgCl	0 80.	Lunar caustic	Silver nitrate	AgNO3	0 81.	Methane		CH4	0 82.	Ethane		CH3– CH3 i.e. C2H6	0 83.	Ethene or Ethylene		CH2=CH2 i.e. C2H4	0 84.	Ethyne or Acetylene		CH≡CH i.e. C2H2	0 85.	Chloroform 		CCl4	0 86.	Spirit, Methyl alcohol or Methanol		CH3OH	0 87.	Alcohol, Ethyl alcohol or Ethanol		CH3CH2OH	0 88.	Oxalic acid		C2H2O4	0 89.	Acetic acid, Vinegar		CH3COOH	0 90.	Sugar or Sucrose		C12H22O11	0 91.	Glucose		C6H12O6	0 92.	Urea		NH2.CO.NH2	0

Ion: An atom or molecule with a net electric charge due to the loss or gain of one or more electrons is called ion. Or, the charged atom or group of atoms separated from an ionic compound either by melting it or by dissolving it in water is called ion. An ion carries a charge, which means that the number of electrons and protons do not match. It can be classified as:

Depending upon the nature of charge: Ions are of two types:

Cation: The ion which carries +ve charge on it is called cation. Ex: H+, Na+, K+, NH4+, Zn++, Mg++, Al+++, etc.

Anion: The ion which carries -ve charge on it is called anion. Ex: OH–, Cl–, O–2, S–2, SO4–2, PO4–2, N–3, etc.

Depending upon the no. of charge or valency: Ions are of four types:

Monovalent ion: The ion having only one charge is called monovalent ion. Ex: Na+, H+, X–, etc.

Di or Bivalent ion: The ion having two charges is called bivalent ion. Ex: Zn++, Mg++, O–2, S–2, SO4–2, etc.

Trivalent ion: The ion having three charges is called trivalent ion. Ex: Fe+++, Al+++, N–3, PO4–3, etc.

Tetravalent ion: The ion having four charges is called tetravalent ion. Ex: Sn++++, Pb++++, C–4, Fe (CN)6–4, etc.

Radical: An atom, molecule or ion that has an unpaired valence electron is called radical. The atoms or a group of atoms which behave as a single unit during a chemical reaction and carry positive or negative charge are called radical. The molecule of a compound is usually made up of two parts which are separately known as radicals. For example, the radicals present in NaCl molecule are Na+ and Cl–. A radical has an unpaired electron, but does not have a net charge because the number of protons equals the number of electrons. It is classified by two methods in two types:

Depending upon the nature of charge: Radicals are of two types:

Electro-positive Radical: The radical which carries +ve charge on it is called electro-positive radical. The electro-positive radical present in a salt is called basic radical. It is called so because it is derived from base during the formation of the salt by neutralization. Ex: All positive radicals except H+ are basic radicals i.e. Na+, K+, Zn++, Mg++, Al+++, NH4+, etc. Explanation: NaOH	 	+ 	HCl 	→ 	Na+Cl- + H2O (Base)			(Acid)		(Salt) CuO	 	+ 	H2SO4 	→ 	Cu++ SO4-- + H2O (Base)			(Acid)		(Salt) Here, Na+ and Cu++ are electro-positive radical in salt, has been derived from base during the formation of salt by the process of neutralization, hence, it is called basic radical.

Some electro-positive radicals and its symbol and valency are as follows:

S.N.	Name of Radical	Symbol	Valency 1.	Hydrogen	H	1 2.	Sodium	Na	1 3.	Potassium	K	1 4.	Silver	Ag	1 5.	Ammonium	NH4	1 6.	Magnesium	Mg	2 7.	Barium	Ba	2 8.	Calcium	Ca	2 9.	Cobalt	Co	2 10.	Cadmium	Cd	2 11.	Nickel	Ni	2 12.	Zinc	Zn	2 13.	Aluminum	Al	3 14.	Antimony	Sb	3 15.	Arsenic	As	3 16.	Bismuth	Bi	3 17.	Chromium	Cr	3 18.	Copper	Cu	Cuprous = 1	ous = Cu2 = 2 Cupric = 2	ic = Cu = 2 19.	Gold	Au	Aurous = 1 Auric = 3 20.	Iron	Fe	Ferrous = 2 Ferric = 3 21.	Mercury	Hg	Mercurous = 1	Hg2 = 2 Mercuric = 2	Hg = 2 22.	Lead	Pb	Plumbous = 2 Plumbic = 4 23.	Manganese	Mn	Manganous = 2 Mangamic = 4 24.	Tin	Sn	Stannous = 2 Stannic = 4

Electro-negative Radical: The radical which carries -ve charge on it is called electro-negative radical. The electro-negative radical present in a salt is called acid radical. It is called so because it is derived from acid during the formation of the salt by neutralization. Ex: All negative radicals except O--, OH- are acid radicals. Ex: O Explanation: NaOH	 	+ 	HCl 	→ 	Na+Cl- + H2O (Base)			(Acid)		(Salt) CuO	 		+ 	H2SO4 	→ 	Cu++ SO4-- + H2O (Base)			(Acid)		(Salt) Here, Cl- and SO4-- are electro-negative radicals in the salt have been derived from acid during the formation of salt by the process of neutralization, hence it is acid radical.

Some electro-negative radicals and its symbol and valency are as follows:

S.N.	Name of Radical	Symbol	Valency 1.	Hydride	H	1 2.	Hydroxide	OH	1 3.	Halide	X = F, Cl, Br, I	1 4.	Hypochlorite	ClO	1 5.	Chlorite	ClO2	1 6.	Chlorate	ClO3	1 7.	Perchlorate	ClO4 8.	Nitride	N	3 9.	Nitrite	NO2	1 10.	Nitrate	NO3	1 11.	Sulphide	S	2 12.	Sulphite	SO3	2 13.	Sulphate	SO4	2 14.	Thiosulphate	S2O3	2 15.	Hydrogen sulphite or Bisulphite	HSO3	1 16.	Hydrogen sulphate or Bisulphate	HSO4	1 17.	Phosphide	P	3 18.	Phosphite	PO3	3 19.	Phosphate	PO4	3 20.	Cyanide	CN	1 21.	Acetate	CH3COO	1 22.	Permangateate	MnO4	1 23.	Hydrogen carbonate or Bicarbonate	HCO3	1 24.	Cyanate	CNO	1 25.	Sulpho cyanate or Thiocyanate	CNS	1 26.	Oxide	O	2 27.	Peroxide	O2	2 28.	Oxalate	C2O4	2 29.	Manganate	MnO4	2 30.	Carbonate	CO3	2 31.	Chromate	CrO4	2 32.	Dichromate	Cr2O7	2 33.	Zincate	ZnO2	2 34.	Stannate	SnO2	2 35.	Silicate	SiO3	2 36.	Nitroprusside	Fe (CN)5NO	2 37.	Borate	BO3	3 38.	Ferricyanide	Fe (CN)6	3 39.	Ferrocyanide		4 40.	Sulpho nitroprusside or Thionitroprusside	Fe (CN)5NOS¬	4

Depending upon the no. of components atoms: Radicals are of two types:

Simple radical: The radicals which contain only one atom are called simple radicals. Ex: Na+, H+, X-, etc.

Compound or Complex radical: The radicals which contain two or more atoms are called compound radicals. Ex: NH4+, ZnO2--, SO4--, NO3-¬, etc.

Valency: The combining capacity of an atom or radical with other atom or radical is called the valency.

According to classical concept: Valency of an element can be determined by counting number of hydrogen atom (taken as standard) with which one atom of the particular element combines.

According to the electronic or modern concept: Valency of an element can be determined by counting the number of electrons lost, gained or shared by an atom or a radical of other element to acquire the nearest stable configuration state. Ex: The valency of hydrogen is 1 and the valency of zinc is 2.

Variable Valency: There are several elements which show more than one valency. An atom of such elements combines with different number of atoms of another element to form two or more different compounds.

Chemical Reaction: The process by which chemical composition and properties of any substances are completely changed is called chemical reaction. It is a chemical change which takes place by simple contact, heat, light, pressure, etc. Any chemical change, which is represented by symbol and formula, is known as a chemical equation. Ex: When zinc is treated with dil. Sulphuric acid then zinc sulphate and hydrogen gas is obtained.

Types of Chemical Reaction: Based on direction: Chemical reactions are classified into two types:

Reversible reaction: The reaction which occurs in both directions, lie forward as well as backward direction is called reversible reaction. Here, products decomposes and react with each other under suitable condition to give back reactants. Law of mass action and Le-Chateliers principle can be applied. It is denoted by double headed arrow (⇔). Ex:

Irreversible reaction: The reaction which occurs in only one direction, lie only in forward direction is called irreversible reaction. Here, products never give back reactants. Law of mass action and Le-Chateliers principle cannot be applied. It is denoted by a single headed arrow (→). Ex:

Synthesis or Combination or Association Reaction: The chemical reaction in which a compound is formed by the direct combination of two or more simpler forms is called the combination reaction. Combination reaction is carried out by the application of heat, pressure, electricity or light. Ex:	2H2 (g) + O2 (g) □(→┴ ) 2H2O (l) 2Mg + O2 □(→┴ ) 2MgO

Analysis or Decomposition or Dissociation Reaction: The chemical reaction in which a chemical substance is broken down into two or more of its constituents is called analysis reaction. Ex:	CaCO3 □(→┴ ) CaO + CO2 2HgO □(→┴ ) 2Hg + O2

Replacement or Displacement Reaction: The chemical reaction in which a one of the constituent of a compound is removed (replaces) and the vacancy is occupied by another substance or element is called displacement reaction. There are two types of displacement reaction:

Single displacement reaction: The chemical reaction in which one element displaces the other element from a compound is called single displacement reaction. Representation of this reaction:	A + BX □(→┴ ) AX + B

Ex:	Zn (s) + H2SO4 (aq) □(→┴ ) ZnSO4 +H2 Fe (s) + CuSO4 (aq) □(→┴ ) Cu (s) + FeSO4

Double displacement reaction: The chemical reaction in which radicals or constituents of two different reacting substances are mutually exchanged to give new compounds is called the double displacement reaction. This type of reaction involves the decomposition and recombination. Representation of this reaction:	AX + BY □(→┴ ) AY + BX

It is of two types:

Neutralization reaction¬: The double displacement reaction occurring between an acid and a base to give salt and water is called neutralization reaction. Neutralization reaction simply means the acid-base reaction to produce salt and water. In this type of reaction in which the reacting species are acid and base and they are said to neutralize each other producing salt and water. It is also called 'water forming reaction'. Ex:	HCl (aq) + NaOH (aq) □(→┴ ) NaCl (aq) + H2O (l) H2SO4 (aq) + KOH (aq) □(→┴ ) K2SO4 (aq) + H2O (l) H2SO4 + CaO □(→┴ ) CaSO4 + H2O

Precipitation: The double displacement reaction occurring between two clear solutions resulting in the formation of at least on insoluble product is called precipitation. Ex:	HCl + AgNO3 □(→┴ ) AgCl ↓ + HNO3 H2SO4 + BaCl2 □(→┴ ) BaSO4 ↓ + 2HCl

Hydrolysis Reaction: The chemical reaction which occurs due to the presence of water is called hydrolysis reaction. Water is here a hydrolyzing agent.

Ex:	Na2CO3 + 2H2O ↔ 2NaOH + H2CO3 2Na + 2H2O ↔ 2NaOH + H2 FeCl3(s) + 3H2O (l) ↔ Fe (OH)3 + 3HCl

Isomerism or Rearrangement Reaction: The chemical reaction in which a new compound is formed due to the internal change in the position of constituent's atoms of the older compound without any loss or gains of atoms is called rearrangement reaction.

Ex:	NH4CNO □(→┴(              Δ                     ) ) NH2.CO.NH2 (Ammonium cyanate)	       (Urea) Polymerization Reaction: The chemical reaction in which two or more molecules of simple substances with low molecular weight combine to form a single molecule of complex compound with high molecular weight is called polymerization reaction. It means that the process in which several small monomers combine to form a large polymer. Ex:	n (CH2=CH2) □(→┴ ) -(CH¬2-CH2)n- (Ethene)				(Polythene)

Condensation Reaction: The chemical reaction in which two or more molecules condense to each other by losing water molecule is called condensation reaction. Ex:	H2SO4 + H2SO4 □(→┴(                      Condensation                     ) ) H2S2O7

Thermo Chemical Reaction: The chemical reaction which occurs by the absorption of heat or with the evolution of heat is called thermo chemical reaction. It is of two types:

Endothermic Reaction: The thermo chemical reaction which takes place only by the absorption of heat is called endothermic reaction. Ex:	CO2 + C □(→┴ ) 2CO - 39 Kcal. N2 + O2 □(→┴ ) 2NO - 43.2 Kcal.

Exothermic Reaction: The thermo chemical reaction which takes place along with the evolution of heat is called exothermic reaction. Ex: 	C + O2 □(→┴ ) CO2 + 95 Kcal. 2SO2 + O2 □(→┴ ) 2SO3 + 45 Kcal.

Factors responsible for a chemical reaction: There are many factors responsible for a chemical reaction. Some of the methods of bringing a chemical reaction are as follows: By simple contact: A simple contact between the reactants is essential for any reaction to occur. By contact with an aqueous solution: Some of the reactions are carried out in the presence of aqueous solution. By application of Heat: Generally, heat is required to break the strong inter nuclear bonds and initiate the reaction. By application of Pressure: High pressure is required for some reactions to occur By application of Electricity: For combination, decomposition or any other chemical change, electricity is required. By application of Light: Photochemical reactions proceed only in the presence of light. By application of Catalyst: Catalyst is required to speed up or slow down the rate of reaction. Sound: Some chemical reaction like decomposition of acetylene into carbon and hydrogen occurs in presence of sound.

Chemical Equation: The symbolic representation of all the substances in involved in an actual chemical change or reaction in terms of alphabets, numbers and signs is called the chemical equation. The substances which undergo the chemical change are called reactants. The substances which are produced as a result of the change are called products. Ex:	When hydrogen is burnt in air we get water. Hydrogen + Oxygen □(→┴(               Burn in air                   ) ) Water 2H2 	      +       O2       □(→┴(                            ∆                            ) ) 2H2O (Reactants)	                       (Products)

Types of Chemical Equation:

Skeleton Equation: The chemical equation in which no. of atoms of all involved elements are not equal or have not been equalized on both sides by multiplying appropriate species with the appropriate no. is called skeleton equation.

Ex:	Zn + HCl            →                 ZnCl2 + H2

Balanced Equation: The chemical equation in which no. of atoms of all involved elements are equal or have been equalized on both sides by multiplying appropriate species with the appropriate no. is called balanced equation. Ex:	Zn + HCl            →                 ZnCl2 + H2

Essentials of a chemical equation: To be perfect and meaningful, a chemical equation should have following properties: Chemical change must be true. Ex:	Mg + O2 □(→┴(                  Burn in air                  ) ) MgO2 + Mg3O4  	(Wrong) Mg + O2 □(→┴ ) 2MgO		(Correct)

It should be written in molecular form (except metal and inert gas). Ex:	H + O □(→┴ ) H2O		(Wrong) H2 + O2 □(→┴ ) H2O		(Correct)

It should be balanced i.e. total atoms in left side (reactants) are equal to total atoms in right hand side (products).A chemical equation should be balanced. Ex: N2 + 3H2 □(→┴ ) 2NH3

Significances of a chemical equation:

Ex: When hydrogen is burnt in air we get water. 2H2 	      +       O2       □(→┴(                            ∆                            ) ) 2H2O

Qualitative significance: This equation represents language: When hydrogen is burnt in air we get water.

Quantitative significance: This equation represents: The number of molecules: Two molecules of hydrogen combine with one molecules of oxygen to give two molecules of water. The number of atoms: 4 atoms of hydrogen combine with 2 atoms of oxygen to give 2 molecules of water. The number of volumes: Two volumes of hydrogen combine with one volume of oxygen to give two volumes of steam. The number of moles: Two moles of hydrogen combine with one mole of oxygen to give two moles of steam. The number of parts (by mass): 4 parts by the weight of hydrogen combine with 32 parts by the weight of oxygen to give 36 parts by the weight water. Limitations of a chemical equation: The limitations of chemical equations are as follows: A chemical equation does not tell us about the physical states of the reactants and products. It does not tell us about the conditions only under which a reaction occurs. It does not tell us about the thermo-chemical nature (whether heat is absorbed or evolved) of a reaction. It does not tell us about the concentration of the reacting solutions. It does not tell us about the reversibility of a reaction. It does not tell us about the rate of reaction.

Ways to remove limitations of a chemical equation // Ways to make a chemical equation more informative: The limitations of a chemical equation can be removed and the equation can be made more informative in the following ways: Some letters or signs i.e. (s), (l), (g), (aq), (alc), ↑ for gas, ↓ for ppt., can be used to give the information that the substance is solid, liquid, gas or it evolves out, precipitate or it settles down as ppt, aqueous solution or the solution in water, alcoholic solution or the solution in alcohol respectively.

Ex:	2Na (s) + 2H2O (l) □(→┴ ) 2NaOH (aq) + H2 (g) Zn (s) + H2SO4 (aq) □(→┴ ) ZnSO4 (aq) + H2 (g) AgNO3 (aq) + NaCl □(→┴ ) AgCl ↓ + NaNO3 (aq) (ppt)

The information about the reaction conditions like presence of catalyst, need of temperature, light, pressure, etc. are written just above the arrow sign (→) separating reactants and products, if possible. Ex:	N2 (g) + 3H2 (g) □(→┴(                450 C,   200 atm                           ) ) 2NH3 (g)

To give the information about the thermo chemical nature of a reaction, amount of heat is added at the last on the product side providing +ve sign if the reaction is exothermic and -ve sign if the reaction is endothermic. Ex:	C + O2 □(→┴ ) CO2 + 95 Kcal [Exothermic reaction] CO2 + 2C □(→┴ ) 2CO – 39 Kcal [Endothermic reaction]

Concentration of the reacting solution is informed by adding dil. (for dilute solution) and conc. (for concentration solution) just below or by the side of the reactant.

Ex:	Zn + H2SO4 □(→┴ ) ZnSO4 + H2 ↑ (dil)		             (aq) Zn + 2H2SO4 □(→┴ ) ZnSO4 + 2H2O + SO2 ↑ (conc)		(aq)

Information about the reversibility of a reaction can be provided by putting double headed half arrows in between reactants and products to show that the same products can again interacts under suitable condition to give back the same original reactants.

Ex:	N2 (g) + 3H2 (g) □(→┴ ) 2NH3 (g) 2SO2 (g) + O2 (g) □(→┴ ) 2SO3 (g)

Information about the time taken for the completion of a reaction cannot provide. To express the rate of a reaction i.e. whether the reaction occurs slowly or quickly, words "slow" or "fast" is written above the arrow or sometimes at the back on the products side inside the brackets. Ex:	Pb (s) + 2HCl □(→┴ ) PbCl2 (aq) + H2 ↑ (dil) Pb (s) + 2HCl □(→┴ ) PbCl2 (aq) + H2 ↑ (conc)

Balancing Chemical Equation

Balancing of chemical equation means total atoms in the reactants (L.H.S.) are equal to total atoms in products (R.H.S.). For balancing a chemical equation, we discuss four methods:

Hit and trial method: In this method the equation is balanced by trial and error methods. There are no definite rules to balance the equation but simple guessing. Generally, hit and trial method is applicable for simple chemical equations. The atom which occurs at minimum number of places on both sides should be selected first and the one occurring maximum number of times should be taken last of all.

Na2S2O3 + I2 □(→┴ ) Na2S4O6 + NaI Na2S2O3 + I2 □(→┴ ) Na2S4O6 + 2NaI		S + NaOH □(→┴ ) Na2S + Na2S2O3 + H2O 3S + 4NaOH □(→┴ ) Na2S + Na2S2O3 + H2O CuFeS2 + O2 □(→┴ ) Cu2S + FeS + SO2 2CuFeS2 + O2 □(→┴ ) Cu2S + 2FeS + SO2		Ag2S + NaCN □(→┴ ) Na[Ag(CN)2] + Na2S Ag2S + 4NaCN □(→┴ ) 2Na [Ag (CN)2] + Na2S H2SO4 + Al(OH)3 □(→┴ ) Al2(SO4)3 + H2O 3H2SO4 + 2Al (OH)3 □(→┴ ) Al2(SO4)3 + 3H2O		NO + H2O + O2 □(→┴ ) HNO3 4NO + 2H2O + 3O2 □(→┴ ) 4HNO3 K4[Fe(CN)6] + FeCl3 □(→┴ ) Fe4[Fe(CN)6]3 + KCl 3K4 [Fe (CN)6] + 4FeCl3 □(→┴ ) Fe4[Fe(CN)6]3 + 12KCl		NH3 + O2 □(→┴ ) NO + H2O 4NH3 + 5O2 □(→┴ ) 4NO + 6H2O

Partial Equation Methods: Equations are balanced by partial equation method when equations contain many reactants and products and hence cannot be balanced by the hit and trial method. This method is very important because in this method, we know how to decompose large molecule into simpler smaller molecules, how to carry out possible reactions, how to cancel nascent hydrogen, oxygen and chlorine atom by multiplying with suitable numbers, and at last adding and subtracting all reactants and products to get balanced chemical equation. This step is completed in 5 steps:

Large molecule is decomposed into two or more simple molecules. Possible reactions are carried out i.e. acid-base or oxidation and reduction reaction. Each partial equation is separately balanced by the hit and trial method. These balanced partial equations are multiplied with suitable coefficients in order to exactly cancel out those common substances which do not appear in the overall chemical equations. The balanced partial equations so obtained, are added to arrive at the balanced chemical equation.

Oxidizing agent: The compound which produce oxygen is called oxidizing agent.

Preparation of Nascent Oxygen: HNO3 dissociates as (ABC → AB + BC + C) i.e.	2HNO3 □(→┴ ) H2O + N2O + 4O (Dilute and cold nitric acid) 2HNO3 □(→┴(                        1:1                             ) ) H2O + 2NO + 3O (Moderately conc. nitric acid) 2HNO3 □(→┴ ) H2O + 2NO2 + O (Hot and conc. nitric acid)

KMnO4 dissociates as (ABC → AB + BC + C) i.e.	2KMnO4 □(→┴ ) K2O + 2MnO + 5O (Acidified) 2KMnO4 □(→┴ ) K2O + 2MnO2 + 3O (Neutral) 2KMnO4 + 2KOH □(→┴ ) 2K2MnO4 + H2O + O (Alkaline)

K2Cr2O7 dissociates as (ABC → AB + BC + C) i.e. K2Cr2O7 □(→┴ ) K2O + Cr2O3 + 3O (Acidified)

H2O2 □(→┴ ) H2O + O (Hydrogen peroxide)

O3 □(→┴ ) O2 + O (Ozone)

H2SO4 □(→┴ ) H2O + SO2 + O (conc.)

Halogen (X2) reacts with water to give acid and nascent oxygen. X2 + H2O □(→┴ ) 2HX + O

Chemical properties of Nascent Oxygen: Nascent oxygen combines with metals and non-metals to give their oxides.

Metals + O □(→┴ ) Metal oxide 2K + O □(→┴ ) K2O Zn + O □(→┴ ) ZnO 2Cr + 3O □(→┴ ) Cr2O3

Remember: Oxides of metals (generally group 1-2) are basic oxides i.e. base anhydrides and hence they react with acid to give salt and water but combined with water to give hydroxides (alkalies).

MO + Acid □(→┴ ) Salt + Water K2O + 2HCl □(→┴ ) 2KCl + H2O ZnO + 2HNO3 □(→┴ ) Zn (NO3)2 + H2O CuO + 2HNO3 □(→┴ ) Cu (NO3)2 + H2O Cr2O3 + 3H2SO4 □(→┴ ) Cr2 (SO4)3 + H2O

Base anhydride (MO) + Water □(→┴ ) Hydroxides (Alkalies) CaO + H2O □(→┴ ) Ca (OH)2 MgO + H2O □(→┴ ) Mg (OH)2 Na2O + H2O □(→┴ ) NaOH

Non-metals + O □(→┴ ) Non metal oxide 2H + O □(→┴ ) H2O C + O □(→┴ ) CO2 S + 2O □(→┴ ) SO2 2P + 5O □(→┴ ) P2O5 2B + 3O □(→┴ ) B2O3

Remember: Oxide of non-metals (group 14-17) are acidic oxides i.e. acid anhydrides and hence they reacts with bases to give salt and water but combined with water to give acid.

Acid anhydride (NmO) + Base □(→┴ ) Salt + Water SO2 + 2NaOH →┴ Na2SO3 + H2O

Acid anhydride (NmO) + Water □(→┴ ) Acid

SO2 + H2O □(→┴ ) H2SO3 SO2 + 2H2O □(→┴ ) H2SO4 + 2H (SO2 + Excess of water)    (Sulphuric acid + nascent hydrogen) SO3 + H2O □(→┴ ) H2SO4 CO2 + H2O □(→┴ ) H2CO3 P2O5 + 3H2O □(→┴ ) 2H3PO3 B2O3 + 3H2O □(→┴ ) 2H3BO3

Nascent oxygen combines with lower oxides of non-metals to give their oxides.

CO + O □(→┴ ) CO2 SO2 + O □(→┴ ) SO3

Nascent oxygen combines with metallic sulphide (MS), metallic sulphite (MSO3) and metallic-thio sulphate (MS2O3) to give metallic sulphate (MSO4).

MS + 4O □(→┴ ) MSO4 MSO3 + O □(→┴ ) MSO4 MS2O3 + O □(→┴ ) MSO4 + S

Nascent oxygen combines with metallic nitrite (MNO2) to give metallic nitrate (MNO3).

MNO2 + O □(→┴ ) MNO3

Nascent oxygen combines with "ous" compound in the presence of suitable acid to give "ic" compound and water.

"ous" compound + O + suitable acid □(→┴ ) "ic" compound + H2O

2FeCl2 + O + 2HCl □(→┴ ) Fe2Cl3 + H2O (Ferrous chloride)	                      (Ferric chloride) FeSO4 + O + H2SO4 □(→┴ ) Fe (SO4)3 + H2O (Ferrous sulphate)	                         (Ferric sulphate)

Nascent oxygen combine with hydrogen sulphide (H2S), hydrogen peroxide (H2O2) and hydrogen halide (HX) to give water as common product.

H2S + O□(→┴ ) H2O + S H2O2 + O □(→┴ ) H2O + O2 2HX + O □(→┴ ) H2O + X2

Nascent oxygen combines with organic compound containing not more than carbon, hydrogen and oxygen to give only CO2 + H2O.

CH4 + 4O □(→┴ ) CO2 + H2O (Methane)

C6H12O6 + 2O □(→┴ ) CO2 + H2O (Glucose)

C2H2O4 + O □(→┴ ) CO2 + H2O (Oxalic acid)

NH2.CO. NH2 □(→┴ ) No reaction (Urea)

Oxidation and Reduction Method:

Ion-Electron Method:

REDOX REACTION

Classical Concept of Oxidation and Reduction:

Oxidation: The chemical process involving addition of oxygen or electronegative element or removal of hydrogen or electropositive element or increase in valency of an element is called oxidation. Ex: 2MgO + O2 □(→┴ ) 2MgO 	(Addition of oxygen) FeCl2 + 3/2Cl2 □(→┴ ) FeCl2 		(Addition of electronegative element) H2S + Cl2 □(→┴ ) 2HCl + S 	(Removal of hydrogen) Hg2Cl2 □(→┴ ) HgCl2 + Hg 	(Removal of electropositive element) Reduction: The chemical process involving removal of oxygen or electronegative element or addition of hydrogen or electropositive element or decrease in valency of an element is called reduction. Ex: NH3 + HCl □(→┴ ) 	NH4Cl 		(Addition of hydrogen) 2Na + H2O □(→┴ ) 	2NaOH 	(Addition of electropositive element) 2KClO3 □(→┴ ) 	2KCl + 3Cl2 	(Removal of oxygen) H2S □(→┴ ) H2 + S 		(Removal of electropositive element)

Redox Reaction: The chemical reaction which involves both oxidation and reduction simultaneously is called redox reaction.

Oxidizing agent or Oxidant: The chemical substance which releases oxygen or any other electronegative radical to another substance or removes hydrogen or any other electropositive radical from another substance is called oxidizing agent.

Reducing agent or Reductant: The substance which releases hydrogen or any other electropositive radical to another substance or removes oxygen or any other electronegative radical from another substance is called oxidizing agent.

Modern or Electronic Concept of Oxidation and Reduction:

Oxidation: The chemical process which involves de – electronation or loss (removal) of electron which results increase in positive charge or decrease in negative charge is called oxidation. Reaction taking place at anode of electrochemical cell. Oxidation process can accurately be termed as oxidation half as it is the partial equation isolated form a redox reaction which involves the loss of electron(s) only. Ex: Na0 □(→┴ ) Na+ + e–	(Na is oxidized to Na+, loss of e–) Sn++ □(→┴ ) Sn++++ + 2e– 	(Sn2+ is oxidized to Sn4+, ↑ in +ve charge) 2Cl– □(→┴ ) Cl2 + 2e–	(Cl– is oxidized to Cl2, ↓ in –ve charge)

Reduction: The chemical process which involves electronation or gain (addition) of electron which results decrease in positive charge or increase in negative charge is called reduction. Reaction taking place at cathode of electrochemical cell. Reduction process can accurately be termed as reduction half as it is the partial equation isolated form a redox reaction which involves the gain of electron(s) only. Ex: O2 + 4e– □(→┴ ) 2O– –	(O2 is reduced to O– –, gain of e–) Cu++ + 2e– □(→┴ ) Cu	(Cu++ is reduced to Cu, ↓ in +ve charge) MnO4– + e– □(→┴ ) MnO4– – 	(Permanganate is reduced to Manganate, ↑ in –ve charge)

Redox Reaction: The chemical reaction which involves the transfer of electron(s) from one reactant to another is called redox reaction. Ex:	Zn +  CuSO4  □(→┴ )  ZnSO4  +  Cu

In ionic form: Zn0 +  Cu++  □(→┴ )  Zn++  +  Cu0

Taking oxidation half: Zn0 □(→┴ )  Zn++  +  2e– Taking reduction half: Cu++ +  2e–  □(→┴ )  Cu

Remember: Double displacement, complex formation, neutralization, hydrolysis, formations of carbonyls and amalgams are not redox reactions. In neutralization and double displacement reaction, there is no change in oxidation number. Combustion of food, burning of fuel, rusting of ions, formation of aqua regia, dissolving of noble metals in aqua regia, formation of colloidal gold, cellular respiration, etc. are redox reactions. Oxidizing agent or Oxidant: The chemical substance involved in a redox reaction that gains electrons and is thereby reduced to a low valency state and whose oxidation state decrease i.e. itself get reduced (itself undergoes reduction) and helps another substance to undergo oxidation is called oxidizing agent. It makes the other substance loss in electron or increase in oxidation number.

Ex:	Zn +  CuSO4  □(→┴ )  ZnSO4  +  Cu

In ionic form: Zn0 +  Cu++  □(→┴ )  Zn++  +  Cu0

Here, Cu++ is an oxidizing agent as it accepts 2e–s provided by Zn and it itself undergoes reduction.

All lewis acids are oxidants. E.g: F2 >Cl2 >Br2 > I2, O2, O3, H2SO4, HNO3, HClO4, FeCl3, HgCl2, KMnO4, K2Cr2O7, KClO3, etc. Fluorine is the strongest oxidizing agent or weakest reducing agent. Oxyacids of halogen are oxidizing agents. Order of oxidizing power of oxyacids of halogens HClO4 < HClO3 < HClO2 < HClO but acid strength is reversed. It is the only element to show –ve oxidation state only. Starch iodine paper is used to test presence of oxidizing agent. Bleaching action of chlorine is due to oxidation and is permanent. Molecules made up of electronegative elements are oxidizing agent. Compounds containing an element which is in the highest oxidation state, are oxidizing agent. Ex: KMnO4, K2Cr2O7, Na2Cr2O7, CrO3, H2SO4, HNO3, FeCl3, HgCl2, KClO4, H2O2, CO2, SO3, etc. are oxidizing agent. Ex: Oxides of Mg2+, Cu2+, Cr2+, CO2, P4O10, etc. are oxidizing agent.

Strength of oxidizing agent: O2- (Superoxide) > O2-- (Peroxide) > O2 (Monoxide)

Reducing agent or Reductant: The chemical substance involved in a redox reaction that loses electrons and is thereby oxidized to a higher valency state and whose oxidation state increase i.e. itself get oxidized (itself undergoes oxidation) and helps another substance to undergo reduction is called oxidizing agent. It makes the other substance gain in electron or decrease in oxidation number.

Ex:	Zn +  CuSO4  □(→┴ )  ZnSO4  +  Cu

In ionic form: Zn0 +  Cu++  □(→┴ )  Zn++  +  Cu0

Here, Zn is a reducing agent as it supplies 2e–s to Cu++ and it itself undergoes oxidation.

All lewis bases are reductants. E.g.: H2S, H2C2O4, FeSO4, SnCl2, Na2S2O3, etc. Lithium is the strongest reducing agent in solution but Caesium (Cs) is the strongest reducing agent in the absence of water i.e. in gas. Reducing property increase down the group in periodic table. Among the alkaline earth metals, Ba is the strongest reducing agent. Bleaching action of SO2 is due to reduction and is temporary. All metals, non-metals, hydracids e.g. HCl, HBr, HI, H2S, etc, compounds containing an element in its lowest oxidation state e.g. FeCl2, FeSO4, SnCl2, Hg2Cl2, Cu2O, etc, metallic hydrides e.g. NaH, LiH, etc. are reducing agent. Remember: Both oxidizing and reducing agent are: H2O2 (acts as oxidant, reductant, and an acid), O3, HNO2 (acts as oxidizing, reducing, and complex forming properties), SO2, H2SO3, Na2SO3, NaNO2, etc. Halogens are oxidizing agent but halogen acids are reducing agent.

Oxidation Number: The total number of electrons that an atom either gains or losses in order to form a chemical bond with another atom is called oxidation number.

Difference between Oxidation number and Valency

S.N.	Oxidation Number	Valency 1.	The total number of electrons that an atom either gains or losses in order to form a chemical bond with another atom is called oxidation number. The combining capacity of its atom which is equal to the no. of electrons lost, gained or shared as it combines with the atom of another element is called valency. 2.	O.N. of an element may be +ve, -ve or 0. Valency of an element is a no. assigned with no any +ve or –ve sign. 3.	O.N. may have a fractional value too. Valency is always a whole no. 4.	O.N. of an element may be different in different compounds. Valency of an element is always fixed; it has been found to be variable in some transitional and inner transitional metals.

Method to determine O.N.: We assign oxidation numbers to the elements in a compound by using the following rules: For each bond between two atoms, less electronegative atom is given +1 oxidation number and more electronegative atom is given –1 oxidation number. It implies that, oxidation no. of any element in isolated form and in natural state is 0 because of same electronegative value i.e. 0. Ex: H2, He, O2, Cl2, etc.

Ex: 0        0	H — H							f. H — O — S — O — H

H — Cl							g. H — O — S — O — O — H

O = C = O						h. C

H — C — H						i. P

H — O — O — H					j. Cr	Oxidation number of some element have fixed value in their compound as follow:

S.N.	Elements	Oxidation number Metals 1.	Alkali metals: Li, Na, K, Rb, Cs, Fr (The oxidation number of a Group 1 element in a compound is +1.)	+1 always 2.	Alkaline earth metal: Be, Mg, Ca, Sr, Ba, Ra (The oxidation number of a Group 2 element in a compound is +2.)	+2 always 3.	Al 	+3 always 4.	P-block metals shows variable oxidation state from	+2 and +4 5.	Transition metals or d-block metals give variable oxidation states generally. Generally, in transition metals, higher oxidation state compounds except that of gold are stable whereas in –block metals, lower oxidation state compounds are more stable. 6.	Minimum oxidation number of metal	0 7.	Maximum oxidation number of metal, Cr, Mn and Os	+6, +7 and +8 respectively 8.	The O.N of a metal in metal carbonyl or metal amalgam is zero. Ex: The O.N. of Ni in [Ni (CO)4] is 0 & Na in NaHg is 0. Non–Metals 7.	H-atom	+1 but in metal hydrides like MaH, CaH2, MgH2, LiH, etc. O.N is -1. 8.	O–atom	-2 but in peroxide like Na2O2, H2O2, etc. it is -1, in superoxide like KO2, NaO2, etc. it is (-1)⁄2, in di-oxygen difluoride like O2F2, it is +1 and in difluoride oxygen (OF2) it is +2 9.	S, Se

(Sulphur shows O.S. of -2, +2, +4 and +6. -2, +2 in ground state and +4 and +6 in excited state)	–2 as sulphide, selenide 10.	Nitrogen□(→┴ )

Phosphorus□(→┴ )

N, P, As□(→┴ ) –3 to +5 in the ground state due to small size and unavailable d-orbital. -3, +3 = Ground state +5 = Excited state

–3 as nitride, phosphide, Arsenide 11.	Element of group, IVA(C, Si, Ge, Sn, Pb), VA (N, P, As, Sb, Bi), VIA (O, S, Se, Te, Po), VIIA(Halogens) Except: O and F		Group no.–8 ≤ O.N.Element ≤ Group no. 12. F Cl, Br, I (The O.N. of a Group 17 element in a binary compound is -1.)	–1 always –1 as terminal atom in the form of halide 13.		The mixm O.N. of an atom of an element = no. of valence electron present in an atom. If an element has n valence electron then maxm O.N. = n. For ex.: The maxm O.N. of F, O, N is +7, +6, +5 respectively.

The minm O.N. of an element = No. of electrons required to attain nearest inert gas configuration. If an element has n valence electron then minm O.N. = (8–n). For ex.: The minm O.N. of F, O, N is -1, -2, -3 respectively.

Sum of oxidation number of all atoms in a species is equal to net charge present on that species. The algebraic sum of the ON of all the atoms of a compound is 0. Noble gases mainly do not form compound so their O.N. is 0. Elements except noble elements have two O.N., one is its free state is 0 or other in its combined state. The algebraic sum of the O.N of all the atoms of an ion is equal to the charge present on them. Oxidation State: The oxidation number per atom of a particular element in a particular compound is called oxidation state. Oxidation state and oxidation number are not necessarily equal. The oxidation state of an atom of an element is different in different compounds. No element can give its oxidation state more than its outermost shell electrons. For example, in HNO3, by rule, OS of N is +7 but actually, OS of N is +5. If element has several oxidation states, lower oxidation state compound is reducing agent, higher oxidation state compound is oxidizing agent and intermediate oxidation state compound shows both reducing and oxidizing behavior. Lower oxidation states oxides are basic, higher oxidation state oxides are acidic and intermediate oxidation state oxides are amphoteric. Lower oxidation state compounds are ionic those of higher are covalent in nature (Fajan's rule). Oxidation states of some element in compound are as follows:

O.S. of	Compound	Formula	O.S. Cr	Pot. Dichromate	K2Cr2O7	+6 Chromium pentaoxide	CrO5	+6 Fe	Pot. Ferrocyanide	K4[Fe(CN)6]	+2 Prussian blue/Ferricferro cyanide	Fe4[Fe(CN)6]3	+3 & +2 Pot. Ferricyanide	K3[Fe(CN)6]	+3 Brown ring	FeSO4.NO	+2 Dark brown ring 	[Fe(H2O)5NO]SO4	+1 Sodium nitroprusside	Na2[Fe(CN)5NO]	+2 Sod.sulphonitroprusside	Na4[Fe(CN)5NOS]	+2 Ferrous oxide	FeO	+2 Ferric oxide	Fe2O3	+3 Ferrosoferric oxide	Fe3O4	+8/2 (average) Haemoglobin	C2952H4664N812O832S8Fe4	+2 Methaemoglobin	– –	+3 C	Cane sugar 	C12H22O11	0 Glucose	C6H12O16	0 Dichloromethane	CH2Cl2	0 Pyrene/Carbon tetrachloride	CCl4	+4 S	Sod.tetrathionate	Na2S4O6	0 & +5 Marshall's acid	H2S2O8	+6 Sod.thiosulphate	Na2S2O3	-2 & +6 or +5 & -1 Caro's acid	H2SO5	+6 Oleum	H2S2O7	+6 N	Hydrazine	NH2- NH2	-2 Hydrazoic acid	N3H	-1/3 C & N	Prussic acid	H-CN	+2 & -3 Hydrogen isocyanide	H-C≡N	+2 & -3 Cl	Bleaching powder	CaOCl2	+1 & -1 Cl, O, N	Nitrosyl chloride	NOCl	-1, -2 & +3 Cu	Schweitzer's reagent	[Cu(NH3)4]SO4	+2 Mg	Chlorophyll	C55H72O5N4Mg	+2 Pt	-	[Pt(C2H4)Cl3]-	+2

Among the 3d series: Manganese (Mn) has highest oxidation state i.e. +7, chromium (Cr) wih +6. Among the transition elements: Ruthenium (4d) and Osmium (5d) of group VIII give highest oxidation state i.e. +8.

Q. Determine the oxidation number of underlined element. H2SO4 □(⇒┴ ) Here,	O.N. of each H–atom = +1 O.N. of S–atom = x (let) O.N. of each O–atom = –2 We know that, Sum of O.N. of all involved atoms = 0 Or, (+1) × 2 + (x) + (–2) × 4 = 0 Or, x + (–6) = 0 ∴ x = + 6

Hence, O.N. of S-atom in H2SO4 is + 6.

NH4NO3 □(⇒┴ ) Here,	O.N. of NH4–radical = +1 O.N. of N–atom = x (let) O.N. of each O–atom = –2 We know that, Sum of O.N. of all involved species = 0 Or, (+1) + (x) + (–2) × 3 = 0 Or, x + (–5) = 0 ∴ x = + 5

Hence, O.N. of N-atom in NH4NO3 is + 6.

Cr2O7– – □(⇒┴ ) Here,	O.N. of each Cr–atom = x (let) O.N. of each O–atom = –2 We know that, Sum of O.N. of all involved species = – 2 Or, (x) × 2 + (–2) × 7 = – 2 Or, 2x – 14 = – 2 Or, 2x = – 2 + 14 = +12 ∴ x = +6

Hence, O.N. of Cr-atom in Cr2O7– – is + 6.

Oxidation and Reduction in terms of O.N. Oxidation: The partial equation isolated from an overall chemical reaction which involves increase in oxidation number is called oxidation.

Reduction: The partial equation isolated from an overall chemical reaction which decrease in oxidation number is called reduction.

Redox Reaction: The chemical reaction which involves both increases and decreases in oxidation number from reactants to products is called redox equation. Ex: i.	PbO +  H2  □(→┴ )  Pb  +  H2O

As there is both increase and decrease in O.N. from reactants to products, the given reaction is a redox reaction.

ii. CuO +  H2SO4  □(→┴ )  CuSO4  +  H2O

As there is no any increase and decrease in O.N. from reactants to products, the given reaction is not a redox reaction. Types of Redox Reaction: There are mainly four types: Combination redox reaction: Combination reactions “combine” elements to form a chemical compound. As usual, oxidation and reduction occur together.

Decomposition or intramolecular redox reaction: Decomposition reactions are the reverse of combination reactions, meaning they are the breakdown of a chemical compound into its component elements.

Displacement or intermolecular redox reaction: Displacement reactions, also known as replacement reactions, involve compounds and the “replacing” of elements. They occur as single and double replacement reactions.

Combustion redox reaction: Combustion reactions always involve oxygen and an organic fuel. In the following image, we see methane combusting to release energy.

Dispropotionation or Auto redox reaction: The redox reaction in which same species simultaneously oxidized as well as reduced is called disproportion redox reaction. Ex:

P + NaOH + H2O □(→┴ ) PH3 + NaH2PO2

Remember: Fluorine does not give disporpotionation reaction due to its strongest oxidizing nature.

Balancing Redox Reaction: When balancing redox reactions, make sure that the number of electrons lost by the reducing agent equals the number of electrons gained by the oxidizing agent. Two methods can be used: Oxidation number method: The balancing redox equations:

Write the skeletal equation representing the chemical change.

Indicate the oxidation number of each atom on both sides of the equation.

Predict the reductant (species whose O.N. is ↑ed) and oxidant (species whose O.N. is ↓ed). Find out the increase and decrease in oxidation number per molecule of reductant and oxidant respectively. Let these be 'x' and 'y' respectively.

Take L.C.M. of 'x' and 'y'.

Multiply reductant by (L.C.M)/X and oxidant by (L.C.M)/y in the skeletal equation to equalize increase and decrease in O.N. This represents the no. of mole of reductant and oxidant involved in the reaction.

Balance all atoms except O and H by hit and trial method.

Finally, balance O and H.

If reaction is acidic then balance O by adding H2O on deficient side and balance H by adding H+ on deficient side.

If reaction is acidic then 1st balance O-atom by adding H2O molecules to the side deficient in oxygen. Then to balance H, add H2O molecules to the side deficient in H-atom and equal no. of OH- ions to the other side. Again while balancing one H-atom add one molecule of H2O, if balancing two H-atom, add two molecule of H2O, add n molecules of H2O in side deficient in H-atom and same no. of OH- ions to the other side.

Ion electron method: The balancing redox equations:

Write the skeletal equation representing the chemical change.

Indicate the oxidation number of each atom on both sides of the equation.

Divide the given equation into two half-reactions i.e. oxidation and reduction halt reaction. Increase in oxidation number is oxidation half and decrease in oxidation number is reduction half.

Balance the atoms other than O and H then balance O and H.

If reaction is acidic then balance O by adding H2O on deficient side and balance H by adding H+ on deficient side.

If reaction is basic then balance O by adding OH– on deficient side and balance H by adding OH– to the side having more H and add equal no. of H2O on opposite side.

Equalize the charge on the sides by adding suitable no. of electrons to the side deficient in negative charge or the side having more positive charge.

Multiply the two half reaction by suitable integer so that the total no. of electron gained in one half is equal to total no. of electrons lost in another half.

Add the two balanced half-reactions and cancel any term common to both side.

PROBLEMS: In the following reaction, the ratio of HNO3 acting as oxidant and acid is ? Cu +  HNO3  □(→┴ )  Cu(NO3)2  +  NO  +  H2O Solution: The steps to balance the equation are: Cu +  HNO3  □(→┴ )  Cu(NO3)2  +  NO  +  H2O

Cu +  HNO3  □(→┴ )  Cu(NO3)2  +  NO  +  H2O

Oxidant → HNO3 Reductant → Cu

Increase in O.N. = 2 – 0 = 2 → x (Let) Decrease in O.N. = 5 – 2 = 3 → y (Let)

L.C.M. of x and y = 6

3Cu +  2HNO3  □(→┴ )  Cu(NO3)2  +  NO  +  H2O

3Cu +  2HNO3  □(→┴ )  3Cu(NO3)2  +  NO  +  H2O 3Cu +  2HNO3  +  HNO3  □(→┴ )  3Cu(NO3)2  +  NO  +  H2O 3Cu +  2HNO3  +  6HNO3  □(→┴ )  3Cu(NO3)2  +  2NO  +  4H2O 3Cu +  8HNO3  □(→┴ )  3Cu(NO3)2  +  2NO  +  4H2O Hence, 2 HNO3 act as oxidant and 6 HNO3 act as acid. Therefore, the ratio is 2/6 = 1:3. Balance the given disproportionation reaction with oxidation number method. Cl2 +  NaOH  □(→┴ )  NaCl  +  NaClO3  +  H2O Solution: The steps to balance the equation are: Cl2 +  NaOH  □(→┴ )  NaCl  +  NaClO3  +  H2O

Cl2 +  NaOH  □(→┴ )  NaCl  +  NaClO3  +  H2O

Oxidant → Cl2 Reductant → Cl2

Increase in O.N. = 5 → x (Let) Decrease in O.N. = 1 → y (Let)

L.C.M. of x and y = 5

Adjust coefficients of NaCl and NaClO3 to balance the charges in oxidation number. Cl2 +  NaOH □(→┴ )  5NaCl+1NaClO3 + H2O

Balance atoms other than O and H. 3Cl2 + 6NaOH □(→┴ )  5NaCl + 1NaClO3 + H2O

Balance O and H. 3Cl2 + 6NaOH □(→┴ )   5NaCl + 1NaClO3 + 3H2O 3Cl2 + 6NaOH □(→┴ )   5NaCl + NaClO3 + 3H2O Hence, the given equation is balanced. Balance the given skeleton equation with ion electron method. Cr2O7 2 – +  Fe2 +  + H +  □(→┴ )  Cr 3 +  + Fe 3+  +  H2O

Solution: The steps to balance the equation are: Write the skeletal equation representing the chemical change. Cr2O7 2 – +  Fe2 +  + H +  □(→┴ )  Cr 3 +  + Fe 3+  +  H2O

Indicate the oxidation number of each atom on both sides of the equation.

Cr2O7 2 – +  Fe2 +  + H +  □(→┴ )  Cr 3 +  + Fe 3+  +  H2O

Separating the two half. Oxidation half: Fe2 + □(→┴ )  Fe 3+ Reduction half: Cr2O7 2 – □(→┴ )  Cr 3 +

Balancing atom on both side. Oxidation half: Fe2 + □(→┴ )  Fe 3+ Reduction half: Cr2O7 2 – + 14H +  □(→┴ )  2Cr 3 +  +  7H2O

Balancing charge on both sides. Oxidation half: Fe2 + □(→┴ )  Fe 3+  +  1e– Reduction half: Cr2O7 2 – + 14H +  +  6e–  □(→┴ )  2Cr 3 +  +  7H2O

Balancing electron on both side. Oxidation half: Fe2 + □(→┴ )  Fe 3+  +  1e–  ] × 6 6Fe2 + □(→┴ )  6Fe 3+  +  6e– Reduction half: Cr2O7 2 – + 14H +  +  6e–  □(→┴ )  2Cr 3 +  +  7H2O

Add the two half reaction. Cr2O7 2 – +  6Fe2 +  + 14H +  +  6e–  □(→┴ )  2Cr 3 +  +  6Fe 3+  +  7H2O +  6e– Cr2O7 2 – +  6Fe2 +  + 14H +  □(→┴ )  2Cr 3 +  +  6Fe 3+  +  7H2O Hence, the given equation is balanced.

For the redox reaction: 	MnO4 – +  C2O42 –  + H +  □(→┴ )  Mn2+  + CO2  +  H2O. The correct coefficient of the reactants MnO4 –, C2O42 – and H + are respectively. Solution: The steps to balance the equation are: Write the skeletal equation representing the chemical change. MnO4 – +  C2O42 –  + H +  □(→┴ )  Mn2+  + CO2  +  H2O

Indicate the oxidation number of each atom on both sides of the equation.

MnO4 – +  C2O42 –  + H +  □(→┴ )  Mn2+  + CO2  +  H2O

Separating the two half. Oxidation half: C2O42 – □(→┴ )  CO2 Reduction half: MnO4 – □(→┴ )  Mn2+ Balancing atom on both side. Oxidation half: C2O42 – □(→┴ )  2CO2 Reduction half: MnO4 – + 8H +  □(→┴ )  Mn2+  +  4H2O Balancing charge on both sides. Oxidation half: C2O42 – □(→┴ )  2CO2  +  2e– Reduction half: MnO4 – + 8H +  +  5e–  □(→┴ )  Mn2+  +  4H2O

Balancing electron on both side. Oxidation half: C2O42 – □(→┴ )  2CO2  +  2e–  ] × 5 5C2O42 – □(→┴ )  10CO2  +  10e–

Reduction half: MnO4 – + 8H +  +  5e–  □(→┴ )  Mn2+  +  4H2O ] × 2 2MnO4 – + 16H +  +  10e–  □(→┴ )  2Mn2+  +  8H2O

Add the two half reaction. 2MnO4 – +  5C2O42 –  + 16H +  +  10e–  □(→┴ )  2Mn2+  +  10CO2  +  8H2O  +  10e– 2MnO4 – +  5C2O42 –  + 16H +  □(→┴ )  2Mn2+  +  10CO2  +  8H2O Hence, The correct coefficient of the reactants MnO4 –, C2O42 – and H + are respectively 2, 5 and 16. For the given reaction, the ratio of the no. of electrons gained per molecule of oxidant to the no. of electrons lost per molecule of reductant is ? P4 +  OH –  □(→┴ )  PH3  +  H2PO2– Solution: Write the given equation representing the chemical change. P4 +  OH –  □(→┴ )  PH3  +  H2PO2–

Indicate the oxidation number of each atom on both sides of the equation.

P4 +  OH –  □(→┴ )  PH3  +  H2PO2–

Separating the two half. Oxidation half: P4 □(→┴ )  H2PO2– Reduction half: P4 □(→┴ )  PH3

Balancing atom on both side. Oxidation half: P4 +  8OH –  □(→┴ )  4H2PO2– Reduction half: P4 +  12H2O  □(→┴ )  4PH3  +  12OH –

Balancing charge on both sides. Oxidation half: P4 +  8OH –  □(→┴ )  4H2PO2–  +  4e– Reduction half: P4 +  12H2O  +  12e–  □(→┴ )  4PH3  +  12OH –

∴ No. of electrons gained by per molecule of oxidant = 12 ∴ No. of electrons lost by per molecule of reductant = 4 ∴ Ratio = 12/4 = 3:1