Sodium Peroxides (Na 2 O 2 ): Preparation: It is formed by heating the metal in excess of air or oxygen at 300, which is free from

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1 S-Block Elements Generally one question was asked every year from this topic. This is completely theoretical and little memory based. Last minute revision generally helps. The general trends in the properties of compounds of S-block have to be emphasized. i.e. The stability, action of heat, basic nature and solubility of oxides, hydroxides, halides, carbonates, bicarbonates and sulphates. Sodium Oxide (Na 2 O): (i) It is obtained by burning sodium at 18 C in a limited supply of air or oxygen and distilling off the excess of sodium in vacuum. 18 2Na + O 2 Na 2 O (ii) By heating sodium peroxide, nitrate or nitrate with sodium. Na 2 O 2 + 2Na 2Na 2 O 2NaNO 3 + 1Na 6Na 2 O + N 2 2NaNO 2 + 6Na 4Na 2 O + N 2 Properties : (i) It is white amorphous mass. (ii) It decomposes at 4 C into sodium peroxide and sodium 2Na 2 O 4 C Na 2 O 2 + 2Na (iii) It dissolves violently in water, yielding caustic soda. Na 2 O + H 2 O 2NaOH Sodium Peroxides (Na 2 O 2 ): It is formed by heating the metal in excess of air or oxygen at 3, which is free from moisture and CO 2. 2Na + O 2 Na 2 O 2 (i) It is a pale yellow solid, becoming white in air from the formation of a film of NaOH and Na 2 CO 3. (ii) In cold water (~ C) produces H 2 O 2 but at room temperature produces O 2. In ice-cold mineral acids also produces H 2 O 2. Na 2 O 2 + 2H 2 O 2NaOH + H 2 O 2 25 C 2Na 2 O 2 + 2H 2 O 4NaOH + O 2 Na 2 O 2 + H 2 SO 4 Na 2 SO 4 + H 2 O 2 (iii) It reacts with CO 2, giving sodium carbonate and oxygen and hence its use for purifying air in a confined space e.g. submarine, ill-ventilated room, 2Na 2 O 2 + 2CO 2 2Na 2 CO 3 + O 2 (iv) It is an oxidising agent and oxidises charcoal, CO, NH 3, SO 2. 3Na 2 O 2 + 2C 2Na 2 CO 3 + 2Na [deposition of metallic Na] CO + Na 2 O 2 Na 2 CO 3 SO 2 + Na 2 O 2 Na 2 SO 4 2NH 3 + 3Na 2 O 2 6NaOH + N 2 (v) It contains peroxide ion [ O O ] 2

2 Oxides of Potassium: K 2 O, K 2 O 2, K 2 O 3, KO 2 and KO 3 Colours: White White Red Bright Yellow Orange Solid (i) 2KNO 3 + 1K Heating 6K 2 O + N 2 K 2 O Heating K 2 O (White) (Yellow) K 2 O + H 2 O 2KOH (ii) Controlled 2K + O 2 K air at 3 C 2 O 2 [Props: Similar with Na 2 O 2 ] (iii) Passage of O 2 through a blue solution of K in liquid NH 3 yields oxides K 2 O 2 (white), K 2 O 3 (red) and KO 2 (deep yellow) i.e O2 K in liq. NH 3 K 2 O 2 K 2 O 3 KO 2 white red yellow KO 2 reacts with H 2 O and produces H 2 O 2 and O 2 both 2KO 2 + 2H 2 O 2KOH + H 2 O 2 + O 2 1 to 15 C KO 3 : KOH + O 3 (ozonised oxygen) KO 3 (Dry powdered) (orange solid) Calcium Oxide (CaO): It is commonly called as quick lime or lime and made by decomposing lime stone at a high temperature about 1 C. CaCO 3 CaO + CO cal (i) It is white amorphous powder of m.p. 257 C. (ii) It emits intense light (lime light), when heated in oxygen-hydrogen flame. (iii) It is an basic oxide and combines with some acidic oxide e.g. CaO + SiO 2 CaSiO 3 CaO + CO 2 CaCO 3 (iv) It combines with water to produce slaked lime. CaO + H 2 O Ca(OH) 2 Magnesium Peroxide (MgO 2 ) and Calcium Peroxide (CaO 2 ): These are obtained by passing H 2 O 2 in a suspension of Mg(OH) 2 and Ca(OH) 2. Sodium Hydroxides: (i) Caustication of Na 2 CO 3 (Gossage's method): Na 2 CO 3 + Ca(OH) 2 2NaOH + CaCO 3 (suspension) Since the K sp (CaCO 3 ) < K sp (Ca(OH) 2 ), the reaction shifts towards right. (i) It is white crystalline, deliquescent, highly corrosive solid. (ii) It is stable towards heat. (iii) It's aqueous solution alkaline in nature and soapy in touch.

3 (iv) (v) (vi) (vii) NH 4 Cl + NaOH NaCl + NH H 2 O FeCl 3 + 3NaOH Fe(OH) 3 + 3NaCl Brown ppt ZnCl 2 + 2NaOH Zn(OH) 2 + 2NaCl Zn(OH) 2 + 2NaOH Na 2 ZnO 2 + 2H 2 O [Same with AlCl 3, SnCl 2, PbCl 2 ] soluble Acidic and amphoteric oxides gets dissolved easily e.g. CO 2 + 2NaOH Na 2 CO 3 + H 2 O Al 2 O 3 + 2NaOH 2NaAlO 2 + H 2 O Aluminium and Zn metal gives H 2 from NaOH 2Al + 2NaOH + 2H 2 O 3H 2 + 2NaAlO 2 Several non metals such as P, S, Cl etc. yield a hydride instead of hydrogen.e.g. 4P + 3NaOH + 3H 2 O PH 3 + 3NaH 2 PO 2 (Disproportionation reaction) Potassium Hydroxide: Same as NaOH (a) It is stronger base compared to NaOH. (b) Solubility in water is more compared to NaOH. (c) In alcohol, NaOH is sparingly soluble but KOH is highly soluble. (d) As a reagent KOH is less frequently used but in absorption of CO 2, KOH is preferably used compared to NaOH. Because KHCO 3 formed is soluble whereas NaHCO 3 is insoluble and may therefore choke the tubes of apparatus used. Magnesium Hydroxide: (i) It can be dried at temperature upto 1 C only otherwise it breaks into its oxide at higher temperature. Mg(OH) 2 MgO + H 2 O (ii) It is slightly soluble in water imparting alkalinity. (iii) It dissolves in NH 4 Cl solution Mg(OH) 2 + 2NH 4 Cl MgCl 2 + 2NH 4 OH Thus, Mg(OH) 2 is not precipitated from a solution of Mg +2 ions by NH 4 OH in presence of excess of NH 4 Cl. Sodium Carbonate: (i) (ii) Leblanc Process: NaCl + H 2 SO 4 (conc.) Mild heating NaHSO 4 + HCl Strong heating NaCl + NaHSO 4 Na 2 SO 4 + HCl (Salt Cake) Na 2 SO 4 + 4C Na 2 S + 4CO- Na 2 S + CaCO 3 Na 2 CO 3 + CaS Solvay Process: NH 3 + H 2 O + CO 2 NH 4 HCO 3 NaCl + NH 4 HCO 3 NaHCO 3 + NH 4 Cl 15 C 2NaHCO 3 Na 2 CO 3 + H 2 O + CO 2

4 (i) Anhydrous Na 2 CO 3 is called as soda ash, which does not decompose on heating but melts at 852 C. (ii) Na 2 CO 3 absorbs CO 2 yielding sparingly soluble sodium bicarbonate which can be calcined at 25 to get pure sodium carbonate. Na 2 CO 3 + H 2 O + CO 2 2NaHCO 3 (iii) It dissolved in acid with effervescence of CO 2 and causticised by lime to give caustic soda. Na 2 CO 3 + HCl 2NaCl + H 2 O + CO 2 Na 2 CO 3 + Ca(OH) 2 2NaOH + CaCO 3 Potassium Carbonate: By leblance process, it can be prepared but by solvay process it cannot be prepared because KHCO 3 is soluble in water. It resembles with Na 2 CO 3, m.p. is 9 C but a mixture of Na 2 CO 3 and K 2 CO 3 melts at 712 C. Calcium Carbonate: It occurs in nature as marble, limestone, chalk, coral, calcite etc. It is prepared by dissolving marble or limestone in HCl and removing iron and aluminium present, by precipitating with NH 3 and then adding (NH 4 ) 2 CO 3 to the solution. CaCl 2 + (NH 4 ) 2 CO 3 CaCO 3 + 2NH 4 Cl (i) It dissociates above 1 C as follows: CaCO 3 CaO + CO 2 (ii) It dissolves in water containing CO 2 forming Ca(HCO 3 ) 2 but is precipitated from the solution by boiling. CaCO 3 + H 2 O + CO 2 Ca(HCO 3 ) 2 Sodium bicarbonates: By absorption of CO 2 in Na 2 CO 3 solution. Na 2 CO 3 + H 2 O + CO 2 2NaHCO 3 Uses: It is used in medicine and as baking powder. Potassium bicarbonate: Prepared by Le-Blanc process and can t be prepared by solvey process due to its more solubility. It is more alkaline and more soluble in water compared to NaHCO 3. Magnesium Sulphate: (i) It is obtained by dissolving kieserite. MgSO 4. H 2 O in boiling water and then crystallising the solution as a hepta hydrate. i.e. MgSO 4. 7H 2 O. It is called as Epsom salt. (ii) It is also obtained by dissolving magnesite in hot dil. H 2 SO 4. MgCO 3 + H 2 SO 4 MgSO 4 + H 2 O + CO 2 (iii) or by dissolving dolomite (CaCO 3, MgCO 3 ) in hot dil. H 2 SO 4 and removing the insoluble CaSO 4 by filtration. (iv) It is isomorphous with FeSO 4. 7H 2 O, ZnSO 4.7H 2 O

5 Calcium Sulphate: It occurs as anhydrite CaSO 4 and as the dihydrate CaSO 4. 2H 2 O, gypsum, alabaster or satin-spar. 12 C 2 C (i) Gypsum (Plaster of paris) an.caso H2O H2O 4 (Dead burnt. Plaster) (ii) Solubility of CaSO 4 at first increases upto a certain point and then decreases with rise of temperature. (iii) Plaster paris is used in mould making due to its porous body. P-Block Elements This is one of the most important topics in inorganic chemistry Analysis of previous year s papers reveals that questions were asked more frequently on the chemistry of Boron, Silicon, Nitrogen, Phosphorus and Sulphur. About these non metals the following areas are to be emphasized. (i) Occurrence and isolation (ii) Preparation and structures of hydrides (iii) Preparation, Properties and structures of oxides (iv) Acidic nature, heating effect and structures of oxyacids (v) Preparation, stability orders, hydrolysis and structures of halides The general chemistry of halogens has to be revised once.