S-BLOCK.pdf

S-BLOCK.pdf
INORGANIC CHEMISTRY
S-BLOCK Hydrogen peroxide Laboratory Preparation: (i) From Sodium peroxide: It is prepared in the laboratory by adding small amounts ofsodium peroxide to ice cold water. Na2 O2 + 2H2 O  2NaOH + H2 O2 In place of cold water, dilute sulphuric acid (20%) can be used. Sodium peroxide in small amounts ata time is added to cold 20% sulphuric acid. Na2 O2 + H2 SO4  Na2 SO4 + H2 O2 The crystals of hydrated sodium sulphate (Na2 SO4 ·10H2 O) are removed by cooling the solution. The solution ofhydrogen peroxide obtained always consists some dissolved sodiumsulphate. The concentration of H2 O2 is about 3%. BaO2 ·8H2 O + H2 SO4 = BaSO4 + H2 O2 + 8H2 O The barium sulphate formed is filtered off and a solution of H2 O2 is obtained. The use of sulphuric acid has a disadvantage as it catalyses the decomposition of hydrogen peroxide formed. In place of sulphuric acid, weak acids like orthophosphoric acid, carbonic acid are preferred. Barium peroxide on treatment with orthophosphoric acid gives a precipitate of barium phosphate and H2 O2 which goes into the solution. 3BaO2 + 2H3 PO4  Ba3 (PO4 )2 + 3H2 O2 ppt. Insoluble bariumphosphate is filtered off. The filterate consists ofhydrogen peroxide. The barium phosphate is decomposed by dilute sulphuric acid. Ba3 (PO4 )2 + 3H2 SO4  3BaSO4 + 2H3 PO4 BaSO4 is removed by filtration and orthophosphoric acid is used again. Merck’s process: H2 O2 can be obtained by passing a current of CO2 through a cold pasty solution of barium peroxide in water. BaO2 + CO2 + H2 O  BaCO3 + H2 O2 Barium carbonate being insoluble is filtered off. Manufacture of Hydrogen Peroxide (i) Auto oxidation of 2-butyl anthraquinol (ii) By Oxidation of isopropyl alcohol (iii) Electrolytic process: In this process, the electrolysis of 50% sulphuric acid is carried out at low temperature using platinumelectrodes and a current of high density. Proxy disulphuric acid is formed. 2H2 SO4 2H+ + 2HSO4 – 2HSO4 –  H2 S2 O8 + 2e (anode) peroxy disulphuric acid Peroxydisulphuric acid is distilled. Hydrolysis occurs and a distillate containing about 30% H2 O2 is obtained. H2 S2 O8 + 2H2 O  2H2 SO4 + H2 O2 In place of 50% H2 SO4 , ammonium hydrogen sulphate dissolved in excess of sulphuric acid can be used for electrolysis. NH4 HSO4 NH4 SO4 – + H+ At anode 2NH4 SO4 –  (NH4 )S2 O8 + 2e Ammonium peroxy disulphate At cathode 2H+ + 2e  H2 (g)
The solution containing ammonium peroxy disulphate is heated at 43 mm pressure when its hydrolysis occurs forming hydrogen peroxide. (NH4 )2 S2 O8 + 2H2 O  2NH4 ·HSO4 + H2 O2 Hydrogen peroxide along with water distils over. Ammonium bisulphate can be used again. This method gives 30–40% aq. solution of hydrogen peroxide. Properties of H2 O2 Physical Properties: (i) Pure anhydrous hydrogen peroxide is a syrupy liquid. It is colourless but gives a bluish tinge in thick layers. It is odourless. (ii) It is soluble in water, alcohol and ether. (iii) It has bitter taste. It is injurious to skin (blisters are formed). Chemical Properties: (i) Stability: It is unstable in nature. It decomposes on standing and heating. It is an example ofauto oxidation-reduction reaction. 2H2 O2 = 2H2 O + O2 (ii) Acidic nature: The pure liquid has weak acidic nature but its aqueous solution is neutral towards litmus. It reacts with alkalies and carbonates to give their corresponding peroxides. H2 O2 + 2NaOH = Na2 O2 + 2H2 O H2 O2 + Ba(OH)2 = BaO2 + 2H2 O H2 O2 + Na2 CO3 = Na2 O2 + CO2 + H2 O (iii) Oxidising nature: It is a powerful oxidising agent. It is a electron acceptor in acidic and alkaline solutions. H2 O2 + 2H+ + 2e = 2H2 O (In acidic solutions) H2 O2 + 2e = 2OH (In alkaline solutions) The reactions are generally slow in acid solutions but fast in alkaline solution. Oxidising nature of hydrogen peroxide can be interpreted on account of the possession of label oxygen atom. The potential equation for its oxidising nature can be written as, H2 O2  H2 O + O the following examples show the oxidising nature of H2 O2 : (a) It oxidises black lead sulphide (PbS) to which lead sulphate (PbSO4 ). PbS + 4H2 O2  PbSO4 + 4H2 O (b) It oxidises nitrites to nitrates. NaNO2 + H2 O2  NaNO3 + H2 O (c) It oxidises sulphites into sulphates. Na2 SO3 + H2 O2  Na2 SO4 + H2 O (d) It oxidises arsenites into arsenates Na3 AsO3 + H2 O2  Na3 AsO4 + H2 O (e) It liberates iodine from potassium iodide 2KI + H2 O2  2KOH + I2 (f) It oxidises H2 S into sulphur H2 S + H2 O2  2H2 O + S (g) It oxidises acidified ferrous sulphate to ferric sulphate 2FeSO4 + H2 SO4 + H2 O2  Fe2 (SO4 )3 + 2H2 O (h) It oxidises acidified potassium ferrocyanide to potassium ferricyanide 2K4 Fe(CN)6 + H2 SO4 + H2 O2  2K3 Fe(CN)6 + K2 SO4 + 2H2 O (i) It oxidises formaldehyde to formic acid. This oxidation occurs in presence of pyrogalloland inalkaline medium. HCHO + H2 O2  HCOOH + H2 O or HCHO + H2 O2  2HCOOH + H2
(j) Benzene in presence of ferrous sulphate is oxidised to phenol. (k) It dissolves the chromic hydroxide precipitate present in NaOH solution forming a yellow solution of sodium chromate. 2Cr(OH)3 + 4NaOH + 3H2 O2  2Na2 CrO4 + 8H2 O (l) A solutionofchromic acid insulphuric acid or acidified potassiumdichromate is oxidised to blue peroxide of chromium (CrO5 ) which is unstable, however, it is soluble in ether and produces blue coloured solution. K2 Cr2 O7 + H2 SO4 + 4H2 O2  2CrO5 + K2 SO4 + 5H2 O Peroxide of chromiumdecomposes to form chromic sulphate and oxygen. 4CrO5 + 6H2 SO4  2Cr2 (SO4 )3 + 6H2 O + 7O2 Peroxide of chromiumis represented as (m) In acidic solution, mercury is oxidised to mercuric oxide. Hg + H2 O2 H SO 2 4     HgO + H2 O (n) Bleaching action: Due to its oxidising nature, it acts as a bleaching agent. Coloured material + O  Colourless It bleaches materials like silk, hair, ivory, cotton, wool, etc. (iv) Reducing nature: It can also act as a reducing agent towards powerful oxidising agents. H2 O2  2H+ + O2 + 2e– In alkaline solution, however, its reducing action is more effective. H2 O2 + 2OH–  2H2 O + O2 + 2e– The potential equation when H2 O2 acts as a reducing agent can be expressed as, H2 O2 + O  H2 O + O2 (a) Ag2 O is reduced to silver Ag2 O + H2 O2  2Ag + H2 O + O2 (b) It reduces ozone to oxygen. H2 O2 + O3  H2 O + 2O2 (c) Manganese dioxide in acidic medium is reduced to manganous salt. MnO2 + H2 SO4  PbO + H2 O + O2 (e) Red lead in presence of HNO3 is reduced to plumbous salt. Pb3 O4 + 6HNO3 + H2 O2  3Pb(NO3 )2 + 4H2 O + O2 (f) Chlorine and bromine are reduced to corresponding hydracids. Cl2 + H2 O2  2HCl + O2 This reaction can be shown in following steps: Cl2 + H2 O2  2HCl + O2 Similarly, Br2 + 2 O2  2HBr + O2 (g) It reduces acidified KMnO4 solution, i.e., acidified KMnO4 is decolorised by H2 O2 . 2KMnO4 + 3H2 SO4 + 5H2 O 2  K2 SO4 + 2MnSO4 + 8H2 O + 5O2 (h) Potassium ferricyanide (alk. solution) is reduced to potassium ferrocyanide. 2K3 Fe(CN)6 + 2KOH + H2 O2  2K4 Fe(CN)6 + 2H2 O + O2 (i) Hypohalites are reduced to halides NaOCl + H2 O2  NaCl + H2 O + O2 (j) KIO4 is reduced to KIO3 KIO4 + H2 O2  KIO3 + H2 O + O2 Uses: (a) for restoring colour of old paintings. (b) as ‘antichlor’to remove traces of chlorine and hypochlorite.
(c) Highly concentrated solution (about 40%) of H2 O2 is used to oxidise petrol, alcohol, and hydrozine hydrate for the propelling of rockets and torpedoes. NH2 ·NH2 + 2H2 O2  N2 + 4H2 O Compounds of Sodium 1. Sodium Oxide, Na2 O : It is prepared by heating sodiumnitrate or sodium nitrite with sodium. 2NaNO3 + 10Na  6Na2 O + N2 2NaNO2 + 6Na  4Na2 O + N2 Pure sodium oxide is formed when the mixture of sodiumazide and sodium nitrite is heated. 3NaN2 + NaNO2  2Na2 O + 5N2 Na2 O + H2 O  2NaOH + heat On heating at 4000 C, it disproportionates forming sodium peroxide and metallic sodium vapour. 2Na2 O 4000 C     Na2 O2 + 2Na Sodamide is formed when it reacts with liquid ammonia Na2 O + NH3  NaNH2 + NaOH It is used as dehydrating and polymerising agent in organic chemistry. 2. Sodium Peroxide, Na2 O2 : It is formed by heating sodium in excess of air free frommoisture and carbon dioxide or in excess of pure oxygen . 2Na + O2 (excess) 3500 C     Na2 O2 It is a pale yellow powder. On exposure, it becomes white moisture and carbon dioxide 2Na2 O2 + 2H2 O  4NaOH + O2 2Na2 O2 + 2CO2  2Na2 CO3 + O2 At low temperature, it forms H2 O2 with water and acids. It combines with CO and CO2 Na2 O2 + CO  Na2 CO3 2Na2 O2 + 2CO2  2Na2 CO3 + O2 It acts as a powerful oxidising agent. (a) Chromic compounds are oxidised to chromates 2Cr(OH)3 + 3Na2 O2  2Na2 CrO4 + 2NaOH + 2H2 O (b) Manganous salt is oxidised to sodium manganate. MnSO4 + 2Na2 O2  Na2 NO4 + Na2 SO4 (c) Sulphides are oxidised to corresponding sulphates Na2 S + 4O  Na2 SO4 Benzoyl peroxide (bleaching agent) is formed when C6 H5 COCl reacts with Na2 O2 2C6 H5 COCl + Na2 O2  (C6 H5 CO)2 O2 + 2NaCl Benzoyl peroxide 3. Sodium Hydroxide (Caustic Soda), NaOH : (a) Methods involving sodium carbonate as a starting material: Two methods are used. These are: (i) Causticisation process (Gossage process): This process depends on the reaction between suspension of lime (milk of lime, calcium hydroxide) and sodium carbonate. This reaction is reversible. Na2 CO3 + Ca(OH)2 CaCO3 + 2NaOH Na2 CO3 + Fe2 O3  2NaFeO2 + CO2 The sodium ferrite is cooled and thrown into hot water. The hydrolysis of sodium ferric occurs forming a solution of sodium hydroxide and insoluble ferric oxide.
2Na2 FeO2 + H2 O  2NaOH + Fe2 O3 The solution is filtered and evaporated to dryness to get flakes of sodium hydroxide. (b) Methods involving sodium chloride as starting material: Methods used are electrolytic as the electrolysis ofsodium chloride solution is carried out in an electrolytic cell. Principle: A sodium chloride solution contains Na+ , H+ , Cl– and OH– ions. NaCl Na+ + Cl– H2 O H+ + OH– Hydrogen is liberated at cathode, Cl2 gas is liberated. The solution on electrolysis becomes richer in Na+ and OH– ions. Since chlorine reacts with sodium hydroxide solution even in cold forming sodium chloride and sodium hypochlorite, it is necessary that chlorine should not come in contact with sodium hydroxide during electrolysis. 2NaOH + Cl2  NaCl + NaClO + H2 O To overcome this problem, the anode is separated from the cathode in the electrolytic cell either byusing a porous diphragm or by using a mercury cathode. (i) Porous diaphragm process (Nelson cell process): Nelson cell consists of a perforated steel tube lined inside with asbestos. The tube acts as a cathode. A graphite rod dipped in sodium chloride solution serves as anode. (ii) Castner-Kellner cell: This is the common cell in which mercury is used as cathode. Two graphite electrodes act as anodes and a series of iron rods fitted in the inner compartment act as cathode. Mercury in the outer compartments acts as cathode while in the inner compartment it acts as anode by induction. The cell is kept rocking with help of an eccentric wheel. When electricityis circulated, sodiumchloride inthe outer compartments is electrolysed. Chlorineis evolved at the graphite anode while Na+ ions are discharged at the Hg cathode. The liberated sodium forms amalgam with mercury. NaCl Na+ + Cl– At Anode 2Cl–  2Cl + 2e  Cl2 At Cathode Na+ + e  Na Na + Hg  Amalgam The sodiumamalgamthus formed comes inthe inner compartment due to rocking. Here, the sodiumamalgam acts as the anode and iron rods act as cathode. At Anode Na-amalgam  Na+ + Hg + e At Cathode 2H2 O + 2e  H2  + 2OH– The concentrated solution of sodium hydroxide (about 20%) is taken out from inner compartment and evaporated to dryness to get solid NaOH. (iii)Kellner-Solvay cell: This is the modified cell. The flowing mercury acts as cathode. A number of graphite rods dipping in sodium chloride solution acts as anode. Chemical Properties: (a) Action of atmosphere: 2NaOH + CO2  Na2 CO3 + H2 O (b) Strong alkali: Sodium hydroxide is a strong alkali as it dissociates completely in water furnishing OH– ions. NaOH Na+ + OH–
(i) It reacts with acids forming corresponding salts. NaOH + HCl  NaCl + H2 O 2NaOH + H2 SO4  Na2 SO4 + 2H2 O NaOH + HNO3  NaNO3 + H2 O 3NaOH + H3 PO4  Na3 PO4 + 3H2 O NaOH + CH3 COOH  CH3 COONa + H2 O (ii) It combines with acidic oxides to form salts. 2NaOH + CO2  Na2 CO3 + H2 O Sodium carbonate 2NaOH + SO2  Na2 SO3 + H2 O Sodium sulphide 2NaOH + 2NO2  NaNO3 + NaNO2 + H2 O Sodium Sodium Nitrate Nitrite (iii) Amphoteric oxides ofaluminium, zinc, tin and lead dissolve in sodiumhydroxide forming corresponding salts. Al2 O3 + 2NaOH  2NaAlO2 + H2 O Sodium meta aluminate ZnO + 2NaOH  Na2 ZnO2 + H2 O Sodium zincate SnO + 2NaOH  NaSnO2 + H2 O Sodium stannite SnO2 + 2NaOH  NaSnO3 + H2 O Sodium stannate PbO + 2NaOH  NaPbO2 + H2 O Sodium plumbite PbO2 + 2NaOH  NaPbO3 + H2 O Sodium plumbate (c) Action on non-metals: Non metals like halogens, P(yellow), S, Si, B, etc. are attacked by NaOH. (i) Halogens: Hypohalites and halides are formed with cold and dilute solution of NaOH. Cl2 + 2NaOH  NaCl + NaClO + H2 O (cold and dilute) Sodium hypo chlorite Br2 + 2NaOH  NaBr + NaBrO + H2 O (cold and dilute) Sodium hypo bromite I2 + 2NaOH  NaI + NaIO + H2 O (cold and dilute) Sodium hypo iodate Halogens form helates and halides with hot and concentrated solution of NaOH. 3Cl2 + 6NaOH  5NaCl + NaClO3 + 3H2 O (hot and conc.) Sodium chlorate 3r2 + 6NaOH  5NaBr + NabrO3 + 3H2 O (hot and conc.) Sodium bromate 3I2 + 6NaOH  5NaI + NaIO3 + 3H2 O (hot and conc.) Sodium iodate (ii) Yellow phosphorus (white) when heated with NaOH solution evolves phosphine gas (PH3 ) alongwith the formation of sodium hypophosphite. P4 + 3NaOH + 3H2 O  3NaH2 PO2 + PH3 Sodium Phosphine hypophosphite
(iii) Sulphur on heating with sodium hydroxide solutionforms sodium thiosulphate 4S + 6NaOH  Na2 S2 O3 + 2Na2 S + 3H2 O Sodium sodium thio sulphate sulphide (iv) Silicon evolves hydrogen when heated with NaOH solution 2NaOH + Si + H2 O  Na2 SiO3 + 2H2 Sodium silicate (v) Boron also evolves hydrogen when fused with NaOH. 2B + 6NaOH  2Na3 BO3 + 3H2 Sodium borate (d) Action on metals: Metals like Zn, Al, Sn, Pb react with sodiumhydroxide solution and evolve hydrogen. Zn + 2NaOH  Na2 ZnO2 + H2 2Al + 2NaOH + 2H2 O  2NaAlO2 + 3H2 Sn + 2NaOH + H2 O  Na2 SnO3 + 2H2 Pb + 2NaOH + H2 O  Na2 PbO3 + 2H2 [However, Sn and Pb when fused with NaOH form Na2 SnO2 and Na2 PbO2 , respectively. Sn + 2NaOH  Na2 SnO2 + H2 Pb + 2NaOH  Na2 PbO2 + H2 ] (e) Action on salts: Sodiumhydroxide reacts with metallic salts to formhydroxides which maybe insoluble or dissolve in excess of NaOH to form salts of oxyacids. Some of the hydroxides decompose its insoluble oxides. (i) Insoluble hydroxides: Salts of nickel, iron, manganese, copper, etc., form insoluble hydroxides. Ni(NO3 )2 + 2NaOH  Ni(OH)2 + 2NaNO3 FeSO4 + 2NaOH  Fe(OH)2 + Na2 SO4 FeCl3 + 3NaOH  Fe(OH)3 + 3NaCl Red ppt. CrCl3 + 3NaOH  Cr(OH)3 + 3NaCl Green ppt. MnSO4 + 2NaOH  Mn(OH)2 + Na2 SO4 Buff coloured ppt. CuSO4 + 2NaOH  Cu(OH)2 + Na2 SO4 Blue coloured ppt. (ii) Insoluble hydroxides which dissolve in excess of NaOH. ZnSO4 + 2NaOH  Zn(OH)2 + Na2 SO4 White insoluble Zn(OH)2 + 2NaOH  Na2 ZnO2 + 2H2 O Sodium zincate (soluble) AlCl3 + 3NaOH  Al(OH)3 + 3NaCl White ppt. Al(OH)3 + NaOH  NaAlO2 + 2H2 O Sodium meta aluminate(soluble) SnCl2 + 2NaOH  Sn(OH)2 + 2NaCl White ppt. Sn(OH)2 + 2NaOH  Na2 SnO2 + 2H2 O Sodium stannite (Soluble) (iii) Unstable hydroxides 2AgNO3 + 2NaOH  2AgOH + 2NaNO3 2AgOH  Ag2 O + H2 O (Brown)
HgCl2 + 2NaOH  Hg(OH)2 + 2NaCl Hg(OH)2  HgO + H2 O (Yellow) (f) Action of ammonium salts: Ammonium salts are decomposed on heating with sodium hydroxide solution with the evolution of ammonia gas. NH4 Cl + NaOH  NH3  + NaCl + H2 O (NH4 )2 SO4 + 2NaOH  Na2 SO4 + 2NH3  + H2 O (g) Action of carbon monoxide: NaOH reacts with carbon monoxide under pressure at 150–2000 C to form sodium formate. NaOH + CO 150 200 5 10 0       C atm HCOONa Sodium formate (h) Caustic property: Sodium hydroxide bereaks down the proteins of skin to a pasty mass. On account of this property, it is commonly called as Caustic soda. 4.Sodium Carbonate orWashing Soda (Na2 CO3 .10H2 O) The most important one is Solvayprocess. The following are the three main processes for the manufacture of sodium carbonate. (a) Le-Blanc process, (b) Solvay, ammonia soda process, and (c) Electrolytic process. (a) Le- Blanc process: The raw materials of this process are common salt (NaCl), sulphuric acid, coke and calcium carbonate (CaCO3 ). It involves the following steps: (i) Conversion of NaCl into Na2 SO4 : The common salt a heated with calculated quantity of sulphuric acid (concentrated) in the furnace. NaCl + H2 SO4  NaHSO4 + HCl Sodium hydrogen sulphate The paste is heated at higher temperature when sodiumhydrogensulphate is converted into sodiumsulphate. NaHSO4 + NaCl  Na2 SO4 + HCl Sodium sulphate, thus formed is technically called salt cake. The HClevolved is dissolved in waterto form hydrochloric acid. (ii) Conversion of salt-cake into black ash: The solid residue is called black ash. This contains about 45% sodium carbonate. (iii) Recovery of Na2 CO3 : The black ash is crushed and extracted with water. The sodium carbonate dissolves and the insoluble impurities mainlyconsisting CaS are left behind. The insoluble materialis called sludge or alkaliwaste. The solutionconsisting sodiumcarbonate is evaporated to gen solid sodiumcarbonate. (b) Solvay ammonia soda process: This is the modern process used for the manufacture of sodium carbonate.The raw materials required in this process are the common salt, ammonia and limestone. NH3 + H2 O + CO2  NH4 HCO3 Ammonium bicarbonate NaCl + NH4 HCO3  NaHCO3 + NH4 Cl Sodium bicarbonate 2NaHCO3     Na2 CO3 + H2 O + CO2
(c) Electrolytic process: In this process sodium chloride is first converted into sodium hydroxide by electrolysis. In the Nelson cell used for the manufacture of sodium hydroxide, carbon dioxide number pressure is blown along with steam. The sodium hydroxide produced will then react withcarbon dioxide to form sodium carbonate. The solution is concentrated and crystallised. 2NaOH + CO2  Na2 CO3 + H2 O Physical Properties: The common form is decahydrate, Na2 CO3 .10H2 O. This form is called washing soda. The decahydrate form on standing in air effloresces and crumbles to powder. It is the monohydrate form, Na2 CO3 .H2 O. It also forms a heptahydrate, Na2 CO3 .7H2 O. Chemical Properties: (a) Action of acids: It is readily decomposed by acids with evolution of carbon dioxide. The reaction occurs in two steps. Na2 CO3 + HCl  NaHCO3 + NaCl NaHCO3 + HCl  NaCl + H2 O + CO2 (b) Action of CO2 : On passing CO2 through the concentrated solution of sodium carbonate, sodium bicarbonate gets precipitated. Na2 CO3 + H2 O + CO2  2NaHCO3 (c) Action of silica: When the mixture of sodium carbonate and silica is fused, sodium silicate is formed. Sodium silicate is called soluble glass or water glass as it is soluble in water. Na2 CO3 + SiO2  Na2 SiO3 + CO2  (d) Action of slaked lime: Sodium hydroxide is formed when the solution of sodium carbonate and slaked lime is heated. Na2 CO3 + Ca(OH)2  2NaOH + CaCO3 (e) Action with sulphur and sulphur dioxide: When aqueous solution of sodium carbonate containing sulphur is treated with sulphur dioxide, sodium thiosulphate (Na2 S2 O3 ) is formed. Na2 CO3 + SO2 H O 2     Na2 SO3 + CO2  Na2 SO3 + S  Na2 S2 O3 (f) Action on salts of non-alkali metals: Sodium carbonate reacts with metal salts (except alkali metal salts) to forminsoluble or basic carbonates. CaCl2 + Na2 CO3  CaCO3 + 2NaCl BaCl2 + Na2 CO3  BaCO3 + 2NaCl 2MgCl2 + 2Na2 CO3 + H2 O  MgCO3 ·Mg(OH) + 4NaCl + CO2 Basic Magnesium Carbonate 5ZnSO4 + 5Na2 CO3 + 4H2 O  [2ZnCO3 ·3Zn(OH)2 ]·H2 O + 5Na2 SO4 + 3CO2 Basic zinc Carbonate CuSO4 + Na2 CO3  CuCO3 + Na2 SO4
2CuSO4 + 2Na2 CO3 + H2 O  Cu(OH)2 ·CuCO3 + CO2 + Na2 SO4 Basic copper Carbonate 3(CH3 COO)2 Pb + 3Na2 CO3 + H2 O  2PbCO3 Pb(OH)2 + CO2 + 6CH3 COONa Basic lead Carbonate 2AgNO3 + Na2 CO3  Ag2 CO3 + 2NaNO3 Carbonates of metals like Fe, Al, Sn, etc., When formed are immediately hydrolysed to hydroxides. Fe2 (SO4 )3 + 3Na2 CO3  Fe2 (CO3 )3 + 3Na2 SO4 Fe2 (CO3 )3 + 3H2 O  2Fe(OH)3 + 3CO2 Uses: As a laboratory reagent. The mixture of Na2 CO3 and K2 CO3 is used as a fusion mixture. 5. Sodium Bicarbonate (Baking Soda), NaHCO3 It is obtained as the intermediate product in the solvay ammonia soda process. Normal carbonated canbe changed to bicarbonate by passing carbon dioxide through its saturated solution. Na2 CO3 + CO2 + H2 O  2NaHCO3 Sparingly soluble Properties: It is a white crystalline solid, sparingly soluble in water. The solution is alkaline in nature due to hydrolysis. The solution is weakly basic. NaHCO3 + H2 O NaOH + H2 CO3 The solution gives yellow colour with methyl orange but no colour with phenolphthalein. On heating, it loses carbon dioxide and water forming sodium carbonate. 2NaHCO3  Na2 CO3 + H2 O+ CO2 The metal salt which forms basic carbonate with sodium carbonate, gives normal carbonate with sodium bicarbonate ZnSO4 + 2NaHCO3  ZnCO3 + Na2 CO3 + H2 O+ CO2 6. Sodium Thiosulphate, Na2 S2 O3 .5H2 O It is the sodium salt of an unstable acid, thiosulphuric acid (H2 S2 O3 ). It is also known as hypo. The following methods can be used for its preparation. (i) It is obtained by boiling sodium sulphite solution with flowers of sulphur. Na2 SO3 + S  Na2 S2 O3 The unreacted sulphur is filtered offand the filtrate is evaporated to crystallization. (ii) Spring’s reaction: The mixture of sodium sulphite and sodium sulphide is treated with calculated quantityof iodine. Na2 S + I2 + Na2 SO3  Na2 S2 O3 + 2NaI The resulting solutionis concentrated and allowed to crystallise when crystals ofsodiumthiosulphate being less soluble separate out first. (iii) When the solution containing sodium carbonate and sodium sulphide is treated with sulphur dioxide, sodium thiosulphate is formed with evolution of carbon dioxide. 2Na2 S + Na2 CO3 + 4SO2  3Na2 S2 O3 + CO2  (iv) Sodiumthiosulphate is formed when sulphur is heated with caustic soda solution. 4S + 6NaOH  Na2 S2 O3 + 2Na2 S + 3H2 O With excess of sulphur, sodium pentasulphide is formed, Na2 S + 4S  Na2 S5 (v) On passing SO2 gas through the solution of Na2 CO3 in presence of sulphur we get sodiumthiosulphate. Na2 CO3 + SO2  Na2 SO3 + CO2 Na2 SO3 + S  Na2 S2 O3
Properties: (i) It is a colourless crystalline solid consisting of5 molecules ofwater as water ofcrystallization. It has the formula, Na2 S2 O3 ·5H2 O. It is soluble in water. It melts at 480 C. (ii) Action of heat: It is efflorescent substance. The water molecules are completely lost when heated at 2150 C. Na2 S2 O3 ·5H2 O 2150 C     Na2 S2 O3 + 5H2 O When strongly heated above 2230 C, it decomposes forming sodium sulphate and sodium pentasulphide. 4Na2 S2 O3  3Na2 SO4 + Na2 S5 (iii)Action of acids: Dilute acids decompose it with evolution of SO2 and precipitation of sulphur. Na2 S2 O3 + 2HCl  2NaCl + SO2 + S + H2 O Na2 S2 O3 + H2 SO4  Na2 SO4 + SO2 + S + H2 O (iv) Oxidation : It is oxidised by iodine quantitatively 2Na2 S2 O3 + I2  2NaI + Na2 S4 O6 Sodium tetrathionate Colour ofiodine disappears. (v) Reducing action: It is oxidised by chlorine and bromine water. Sulphur is precipiated. Na2 S2 O3 + Cl2 + H2 O  Na2 SO4 + 2HCl + S It reduces FeCl3 to FeCl2 2Na2 S2 O3 + 2FeCl3  Na2 S4 O6 + 2FeCl2 + 2NaCl (vi) Action ofAgNO3 : Awhite precipitate of silver thiosulphate is obtained which changes to yellow, brown and finallyblack due to the formation of silver sulphide. 2AgNO3 + Na2 S2 O3  Ag2 S2 O3 + 2NaNO3 Ag2 S2 O3 + H2 O  Ag2 S + H2 SO4 (vii) Action of silver halides: Halides form complexes with sodium thiosulphate. Silver bromide forms argento thiosulphate complex. AgBr + 2Na2 S2 O3  Na3 [Ag(S2 O3 )2 ] + NaBr Sodium argentothiosulphate (colourless) Similar reactions are observed with AgCl and AgI. This propertyis utilised in photographyfor fixing the negative and positive of black and white photography. It removes undecomposed AgBr present on the film. (viii) Action on copper sulphate: Cuprous thiosulphate is formed which dissolves in excess of sodium thiosulphate to form a complex. CuSO4 + Na2 S2 O3  CuS2 O3 + Na2 SO4 Cupric thiosulphate 2Cu2 S2 O3 + Na2 S2 O3  Cu2 S2 O3 + Na2 S4 O6 Cuprous thiosulphate 3Cu2 S2 O3 + 2Na2 S2 O3  Na4 [Cu6 (S2 O3 )5 ] Sodium cupro thiosulphate Uses: Sodium thiosulphate is used : (a) as an antichlor to remove excess of chlorine from bleached fabrics. Sodium Chloride (Common salt), NaCl Sodium chloride is the most common of the salts of sodium. It is also called common salt or table salt or rock salt or sea salt.
Manufacture from sea water: The sea water is allowed to dry up under summer heat in small tanks or pits. The solid crust so formed is collected. Potassium: Compounds of potassium: Potassium chloride is the starting material for the preparation of various potassium compounds. It is obtained from carnallite, KCl·MgCl2 ·6H2 O, by fractionalcrystallisation. The carnalities ground and extracted with a 20 percent solution of MgCl2 . The carnallite dissolves while NaCl and MgSO4 remain undissolved. The clear solution is put to crystalline when crystals of KCl separate out. Oxides: Three oxides of potassium are known: (a) Potassium monoxide, K2 O (b) Potassium dioxide (tetraoxide or superoxide), KO2 or K2 O4 (c) Potassium sesquioxide, K2 O3 KO2 is prepared by burning potassium in excess of oxygen free from moisture. K + O2  KO2 It is also obtained by reacting dry potassium hydroxide with ozone. 2KOH + O3  2KO2 + H2 O K2 O3 is obtained when oxygen is passed through liquid ammonia containing potassium. 4K (dissolved in liquid NH3 ) 3 2 O    2K2 O3 Potassium superoxide, KO2 , is a chrome yellow powder. it dissolves in water giving H2 O2 and O2 . 2KO2 + 2H2 O  2KOH + H2 O2 + O2
It reacts directly with CO and CO2 . 2KO2 + CO  K2 CO3 + O2 2KO2 + CO2  K2 CO3 + (3/2)O2 On heating with sulphur, it forms potassium sulphate. 2KO2 + S  K2 SO4 KO2 is used as an oxidising agent. It is used as air purifier in space capsules, submarines and breathing masks as it both produces oxygen and removes carbon dioxide. Potassium Hydroxide, KOH It is manufactured like sodium hydroxide, i.e. by electrolysis of KCl solution. It is used for the absorption of gases like CO2 , SO2 , etc. It is often called as caustic potash and its aq. solution is knwon as potash Iye. It is used for making soft soaps. Alcoholic caustic potash is a usefulreagent in organic chemistryas it eliminates hydrogen halidesfrom alkyl halides. C2 H5 Br + KOH(alc.)  C2 H4 + KBr + H2 O Potassium carbonate, K2 CO3 It is also called Potash or Pearl ash. It cannot be made bythe use of Solvayprocess as potassiumbicarbonate is more soluble than sodiumbicarbonate. However, it can be prepared by Le-Blanc process. KCl is first converted into K2 SO4 ·K2 SO4 is then heated with CaCO3 and carbon. KCl + K2 SO4  KHSO4 + HCl KHSO4 + KCl  K2 SO4 + HCl K2 SO4 + CaCO3 + 2C  K2 CO3 + CaS + 2CO2 It is a white powder, deliquescent in nature. It is highly soluble in water. It is used in the maufacture of hard glass. The mixture of K2 Co3 adn Na2 CO3 is used as a fusion mixture in laboratory. COMPOUNDS OF MAGNESIUM Magnesium Oxide, MgO, (Magnesia) Preparation: It can be prepared by following reactions. 2Mg + O2 Burning    2MgO Mg(OH)2 Heated     MgO + H2 O 2Mg(NO3 )2 Heated     2MgO + 4NO2 + O2 MgCO3 Heated     MgO + CO2 Properties: It is a light infusible white powder. It fuses at 2800o C. It is slightly soluble in water and forms magnesium hydroxide. MgO + H2 O  Mg(OH)2 It is basic in nature. It reacts with acids to form corresponding salts. MgO + 2HCl  MgCl2 + H2 O MgO + H2 SO4  MgSO4 + H2 O It is reduced by carbon at very high temperature. MgO + C  Mg + CO Magnesium oxide when mixed with a saturated solution of magnesium chloride sets to a hard mass like cement known as magnesia cement or sorel’s cement. The composition is MgCl2 .5MgO.xH2 O.
Magnesium Hydroxide, Mg(OH)2 Preparation: It is prepared by dissolving magnesium oxide in water or by treating magnesiumsalt with an alkali. MgO + H2 O  Mg(OH)2 MgCl2 + Ca(OH)2  Mg(OH)2 + CaCl2 MgCl2 + 2NaOH  Mg(OH)2 + 2NaCl Properties: It is a white powder. It is sparingly soluble in water. It is basic in nature and forms salts with acids. It decomposes on heating. It readily dissolves in strong solution of NH4 Cl. Mg(OH)2 + 2NH4 Cl MgCl2 + 2NH4 OH Uses: A suspension of Mg(OH)2 in water is used in medicine as an antacid under the name, milk of magnesia. Magnesium Carbonate, MgCO3 It is found in nature as magnesite (MgCO3 ) and dolomite (MgCO3 .CaCO3 ). Preparation: It can be prepared by adding sodium bicarbonate to a hot solution of magnesium salt. MgSO4 + 2NaHCO3  MgCO3 + Na2 SO4 + H2 O + CO2 The magnesium carbonate cannot be obtained by the addition of sodium carbonate to the solution of magnesium salt. A white precipitate of a basic acarbonate of composition 3MgCO3 .Mg(OH)2 .2H2 O is obtained. It is known as magnesia alva. It is suspended in water and CO2 is passed when magnesium bicarbonates known as fluid imagines is formed. The solution is boiled when normal magnesium carbonate separates out. 2MgSO4 + 2Na2 CO3 + H2 O  MgCO3 .Mg(OH)2 + 2Na2 SO4 + CO2 MgCO3 .Mg(OH)2 + 3CO2 + H2 O  2Mg(HCO3 )2 Mg(HCO3 )2  MgCO3 + CO2 + H2 O Properties: It is a white powder, insoluble in water. It dissolves readily in water containing excess of carbon dioxide. MgCO3 + CO2 + H2 O  Mg(HCO3 )2 It dissolves in acids foming salts with evolution of CO2 . MgCO3 + 2HCl  MgCl2 + H2 O + CO2 MgCO3 + H2 SO4  MgSO4 + H2 O + CO2 On heating, it decomposes with evolution of CO2 . MgCO3  MgO + CO2 It forms double carbonates with alkali carbonates. MgCO3 + Na2 CO3  Na Mg CO So le 2 3 2 ( ) lub Magnesium chloride, MgCl2 .6H2 O It occurs as mineral carnallite, KCl.MgCl2 .6H2 O and bischrofite, MgCl2 .H2 O. It is found in sea water, mineral springs, etc. Preparation: (a) It is extracted from carnallite mineral. The mineral is fused and cooled to 176o C when whole of KCl is deposited while MgCl2 .6H2 O remains in the fused state. (b) It can also be obtained by dissolving Mg, MgO, Mg(OH)2 or MgCO3 in dilute hydrochloric acid. The preparationofanhydrous magnesiumchloride has alreadybeen described inthe extraction ofmagnesium.
Properties: It is a colourless crystalline solid, highly deliquescent and highly soluble in water. It is the starting material for various magnesium compounds. Magnesium Sulphate, MgSO4 .7H2 O It occurs in nature as minerals kiesserite (MgSO4 .H2 O), epsom salt (MgSO4 .7H2 O) and kainite (KCl.MgSO4 .3H2 O). Preparation: It is formed by reacting magnesite (MgCO3 ) or dolomite with dilute sulphuric acid. MgCO3 + H2 SO4  MgSO4 + H2 O + CO2 MgCO3.CaCO Dolomite 3 + 2H2 SO4  MgSO4 + CaSO Inso le 4 ( lub ) + 2CO2 + 2H2 O It is commercially prepared by boiling kiesserite mineral in water. The crystals are obtained when the solution is cooled. MgSO4 .H2 O + 6H2 O  MgSO4 .7H2 O Properties: It is a colourless crystalline compound, soluble in water. The crystals are efflorescent and bitter in taste. It is isomorphous with ZnSO4 .7H2 O. It forms double sulphates with alkalimetal sulphates, K2 SO4 .MgSO4 .6H2 O (Schonite). Heating effect: Whenheated to 150o C, it changes to monohydrate. On further heating, it becomes anhdrous at 200o C. On strong heating, it decomposes into MgO. MgSO4 .7H2 O 150o C     MgSO4 .H2 O 200o C     MgSO4 Strong heating     MgO + SO2 + 1 2 2 O Magnesium sulphate is reduced by lampblack at 800o C. 2MgSO4 + C  2MgO + 2SO2 + CO2 CALCIUM COMPOUND OF CALCIUM Quick Lime, Slaked Lime and Lime Water Preparation: CaCO3 CaO + CO2 . The reaction moves towards right hand direction if CO2 formed is immediately removed from the kiln by allowing a blast of air to enter the kiln through fire boxes. The temperature for the decomposition of limestone should be near about 1000o C otherwise at higher temperature, the clay present in the limestone as impurity will react with it to form silicate.
When water is added to lime, a hissing sound is produced along with clouds of steam. In this process a large amount of heat energy is given out. The lime cracks with the formationof a powder called slaked lime [Ca(OH)2 ]. CaO Quick e lim + H2 O  Ca OH Slaked e ( ) lim 2 + Heat energy The process is known as slaking of lime. The paste of lime in water is called milk of lime while the filtered and clear solution is known as lime water. Chemically both are Ca(OH)2 . Limestone CaCO ( ) 3 10000 C    Quick Lime CaO ( ) H O 2     Slaked Lime Ca OH [ ( ) ] 2  Suspension Milk of Lime Ca OH ( ) ( )2  Suspended in water  Filter Clear Solution Lime water Ca OH ( ) ( )2 Mortar Slaked lime is mixed with three to four times its weight of sand. The mixture is made into a thick paste with gradual addition of water. This paste is called mortar and is used in building construction. Ca(OH)2 + CO2  CaCO3 + H2 O CaCl2 + Na2 CO3  CaCO3 + 2NaCl The precipitate of CaCO3 thus obtained is known as precipitated chalk. It is a white powder, insoluble in water. It dissolves in presence of CO2 due to formation of calcium bicarbonate. CaCO3 + H2 O + CO2  Ca(HCO3 )2
Calcium Sulphate, CaSO4 ·2H2 O (Gypsum) It is found in nature as anhydride (CaSO4 ) and gypsum (CaSO4 ·2H2 O). It can be prepared by reacting any calcium salt with either sulphuric acid or a soluble sulphate. CaCl2 + H2 SO4  CaSO4 + 2HCl CaCl2 + Na2 SO4  CaSO4 + 2NaCl Plaster of Paris, 2CaSO4 ·H2 O (Calcium sulphate hemihydrate) Preparation: (i) Plaster of paris is a white powder. (ii) It has the property of setting to a hard mass when a paste with water is allowed to stand aside for sometime. Slight expansion occurs during the setting as water is absorbed to reformCaSO4 ·2H2 O (gypsum). the setting process is exothermic. The process of setting takes place in two stages. In the first stage, there is conversion of Plaster of Paris into ortho-rhombic form of gypsum(setting step) and in the second stage ortho-rhombic formchanges into monoclinic form(hardening step). 2 4 2 CaSO H O Plaster of Paris  Setting H O     2 CaSO H O Otho r bic 4 2 2   hom Hardening     CaSO H O Monoclinic 4 2 2  The setting of plaster of paris may be catalysed by sodium chloride while it is retarded by borax or alum. Addition of alumto Plaster of Paris makes the setting very hard. The mixture is known as Keene’s cement. (iii) When Plaster ofParis is heated at 2000 C, it forms anhydrous calciumsulphate which is known as dead plaster. It has no setting property as it takes up water only very slowly.

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