Tiêu đề 05-Compounds of common use (some imp. chem. compound ).pdf ✅

5 CHAPTER CONTENTS ➢ INTRODUCTION ➢ IMPORTANT TERMS & CONCEPT ➢ INTRODUCTION  Types of Salt : When cation replaces H+ of an acid, salt is formed. There are various types of salts. (i) Sulphate : Those salts which are obtained by replacing hydrogen of sulphuric acid are called sulphates, e.g., (ii) Chlorides : When hydrogen of hydrochloric acid is replaced by cation, chloride salt are formed, e.g., Sodium Chloride Calcium Chloride Aluminium Chloride Copper chloride Nickel chloride Potassium chloride Magnesium chloride Iron (III) chloride Arsenic chloride Antimony chloride NaCl CaCl2 AlCl3 CuCl2 NiCl2 KCl MgCl2 FeCl3 AsCl3 SbCl3 (iii) Nitrates : Those salts which are obtained by replacing hydrogen of nitric acid by action are called nitrate salts, e.g., Sodium nitrate Potassium nitrate Ammonium nitrate Lead nitrate Calcium nitrate Magnesium nitrate Aluminium nitrate Copper nitrate NaNO3 KNO3 NH4NO3 Pb(NO3)2 Ca(NO3)2 Mg(NO3)2 Al(NO3)3 Cu(NO3)2 (iv) Carbonates : When hydrogen of carbonic acid is replaced by metal ion, carbonate salts are formed, e.g., Sodium carbonate Zinc carbonate Iron (II) carbonate Potassium carbonate Copper carbonate Lead carbonate Na2CO3 ZnCO3 FeCO3 K2CO3 CuCO3 PbCO3 Sodium sulphate Potassium sulphate Zinc sulphate Copper sulphate Magnesium sulphate Calcium sulphate Ferrous sulphate or Iron (II) sulphate Stannous sulphate Ferric sulphate or Fe (III) sulphate Aluminium sulphate Chromium sulphate Nickel sulphate Manganese sulphate Barium sulphate Cobalt sulphate Mercury (II) sulphate Lead sulphate Na2SO4 K2SO4 ZnSO4 CuSO4 MgSO4 CaSO4 FeSO4 SnSO4 Fe2(SO4)3 Al2(SO4)3 Cr2(SO4)3 NiSO4 MnSO4 BaSO4 CoSO4 HgSO4 PbSO4 SOME IMPORTANT CHEMICAL COMPOUNDS
2. Salts. Salts are also obtained by reaction of acid with base. Cation is derived from base anion is derived from acid. The salts derived from sodium hydroxide are called sodium salts. The salt derived from potassium hydroxide are called potassium salts. Calcium hydroxide gives calcium salts, magnesium hydroxide gives magnesium slats, copper hydroxide gives copper salts and so on. 3. Diplacement Reactions. Those reactions in which more reactive metal can displace less reactive metal from its salt solution. 4. Hydrogen Carbonates. Those salts which are obtained by replacement of one hydrogen of H2CO3 are called hydrogen carbonates or bicarbonates e.g., Sodium hydrogen carbonate Potassium hydrogen carbonate Calcium hydrogen carbonate Magnesium hydrogen carbonate NaHCO3 KHCO3 Ca(HCO3)2 Mg(HCO3)2 5. Hydrogen Sulphates. Those salts which formed by replacement of one atom of hydrogen of sulphuric acid by metal ion are called hydrogen suphates e.g. 6. Monoprotic Acids. Those acids which give one H+ ion in aqueous solution are called monoprotic acids, e.g., HCl, HBr, HI, HNO3, HNO2 (nitrous acid), CH3COOH (acetic acid), HCOOH (formic acid). They form only one type of salts. 7. Diprotic Acids. Those acids which give two H+ ions in aqueous solution are called diprotic acids, e.g., H2SO4, H2CO3 (carbonic acid), H2SO3 (sulphuric acid), (COOH)2 (oxalic acid). They form two series of salts, one by replacing one hydrogen and another by replacing both the hydrogen atoms. Sodium hydrogen phosphate Sodium phosphate Disodium hydrogen phosphate NaH2PO4 Na3PO4 Na2HPO4 8. Triprotic Acids. Those acids which give three protons i.e. three H+ ions in aqueous solution are called triprotic acid, e.g., H3PO4 (phosphoric acid). They form three series of salts. 9. Chemical in Common Salt. The main chemical present in common salt is sodium chloride. It is obtained by neutralization reaction of sodium hydroxide with HCl (Hydrochloric acid). It is obtained on a large scale from sea water. It is found in large deposits called rock salt. 10. Uses of Common Salt. (i) It is used in daily food. (ii) It is used as preservative (iii) It is used for manufacture of Na metal and Cl2 (g) by electrolysis in molten state. (iv) It is used for manufacture of caustic soda. (v) It is used for manufacture of baking soda and washing soda by Solvay process. 11. Manufacture of Sodium Hydroxide. Sodium hydroxide is the most important alkali and is made commercially by electrolysis of saturated brine solution (sodium chloride). Three kinds of cells are used : Castner-Kellner Cell. In this cell, mercury flows along the bottom of the cell and is made cathode in outer compartments as shown in figure. The anode consists of number of graphite blocks. Cl2 +ve carbon anodes Moving mercury cathode (–ve) Strong brine in Hg in Na/Hg Out Spent brine out At the anode + 2Cl– –→ Cl2 + 2e– At the cathode – Na+ + e– –→ Na Na + Hg –→ NaHg Sodium amalgam Fig. THE CASTNER-KELLNER CELL Thee electrolysis of brine solution takes place. Since hydrogen has a over voltage (i.e.more energy Sodium hydrogen sulphate Calcium hydrogen sulphate Potassium hydrogen sulphate Magnesium hydrogen sulphate NaHSO4 Ca(HSO4)2 KHSO4 Mg(HSO4)2
is required to discharge H+ ion) at mercury cathode, sodium is preferentially discharged at cathode forming amalgam with mercury. Sodium amalgam flows out and is reacted with H2O to give NaOH. 2NaHg + 2H2O –→ 2NaOH + 2Hg + H2 The mercury is recirculated in the cell. H2 and Cl2 are two important by-products. 12. Properties of Sodium Hydroxide. (i) It is deliquescent solid and absorbs moisture and CO2 finally forming solid hydrated carbonate. (ii) It can precipitate cations like Zn2+, Al3+, Pb2+ , Sn2+ but these precipitates get dissolved in excess of NaOH. Zn(OH)2 + 2OH– –→ [Zn(OH)4] 2– (Zincate ion) Al(OH)3 + 3OH– –→ [Al(OH)6] 3– (Aluminate ion) Sn(OH)2 + 4OH– –→ [Sn(OH)6] 3– (Stannate ion) Pb(OH)2 + 2OH– –→ [Pb(OH)4] 2– (Plumbate ion) 13. Uses of Sodium Hydroxide. (i) It is used in soap industry. (ii) It is used in paper industry (iii) It is used in textile industry (iv) It is used for preparation of pure fats and oils. (v) It is used in preparation of artificial silk (rayon). (vi) It is used in petroleum industry. (vii) It is used in absorbing poisonous gases. (viii) It is used as reagent in laboratory. 14. Washing Soda. Its chemical formula is Na2CO3.10H2O, i.e. sodium carbonate decahydrate, i.e. one mole of Na2CO3 contains 10 moles of water of crystallization. Anhydrous sodium carbonate is called soda ash. 15. Solvay Process. It is used for manufacture of washing soda. It is also called Ammonia Soda process. Raw materials. Sodium chloride (NaCl), ammonia (NH3) and limestone (CaCO3). Process. (i) In this process a cold and concentrated solution of sodium chloride (called brine) is saturated with ammonia. (ii) The ammonical brine is fed from the top of the carbonating tower packed with perforated plates. (iii) Carbon dioxide (CO2) is introduced from the base of the tower which reacts with NH3 and H2O to form ammonium bicarbonate (ammonium hydrogen carbonate). NH3 + H2O + CO2 –→ (NH4)HCO3 .....(i) (iv) Ammonia hydrogen carbonate reacts with sodium chloride (NaCl) to form sodium hydrogen carbonate and ammonia chloride. (NH4)HCO3 + NaCl ––→ NaHCO3 + NH4Cl Ammonium Hydrogen carbonate Sodium chloride Sodium Hydrogen carbonate Ammonium chloride .......(ii) (v) CO2 used in first reaction is produced by heating limestone in lime kiln (furnace). CaCO3 ––→ CaO + CO2 Limestone Quicklime Carbon dioxide heat (vi) Quiklime reacts with H2O to form slaked lime. CaO + H2O ––→ Ca(OH)2 Calcium oxide Water Calcium hydroxide (vii) Slaked lime reacts with ammonium chloride produced in reaction (ii) to generate ammonia which can be used again in reaction (i). Ca(OH)2 + 2NH4Cl ––→ CaCl2 + 2NH3 + 2H2O Calcium hydroxide Ammonium chloride Calcium chloride Ammonia Water Thus, most of ammonia can be recovered and reused, therefore, this process is economical. Secondly, calcium chloride is obtained as a by- product. (viii)Sodium hydrogen carbonate, formed in reaction (ii) is sparingly (partially) soluble in water and can be separated by filtration. (ix) Sodium hydrogen carbonate is heated to form sodium carbonate. 2NaHCO3 ––→ Na2CO3 + H2O + CO2 Sodium hydrogen carbonate Sodium carbonate Water Carbon dioxide heat CO2 formed is recirculated., i.e. used again in reaction (i). (x) Sodium carbonate is recrystallized by dissolving in water to get washing soda.
Na2CO3 + 10H2O ––→ Na2CO3.10H2O Sodium carbonate (anhydrous) Washing soda 16. Properties of Washing Soda (i) It is a transparent crystalline solid. (ii) It contains ten molecules of water of crystallization. (iii) It is efflorescent substance (i.e. loses water of crystallization) when exposed to air. It loses nine molecules of water and forms monohydrate. Na2CO3 . 10H2O ––→ Na2CO3.H2O + 9H2O Sodium carbonate (decahydrate) (Sodium carbonate) monohydrate (iv) Washing soda loses all the water of crystallisation on heating and becomes anhydrous (which does not contain water of cyrstallisation). It does not decompose on heating. Na2CO3 . 10H2O ––→ Na2CO3. + 10H2O Sodium carbonate (decahydrate) Soda ash (Anhydrous sodium carbonate)  ........(iii) (v) Washing soda dissolves in water to form an alkaline solution which turns red litmus blue. It shows that its aqueous solution is alkaline in nature. Na2CO3 + 2H2O 2NaOH + H2CO3 .....(iv) (vi) When treated with HCl or H2SO4, it liberates CO2 gas. Na2CO3 + 2HCl ––→ 2NaCl + H2O + CO2 ...(v) Na2CO3 + H2SO4 ––→Na2SO4 + H2O + CO2 ...(vi) (vii) When CO2 gas is passed through aqueous solution of sodium carbonate, sodium hydrogen carbonate gets precipitated. Na2CO3 + CO2 + H2O ––→NaHCO3 (vii) 17. Uses of Sodium Carbonate. (i) It is used in manufacture of glass, soap, paper and other sodium compounds like borax, caustic soda, etc. (ii) It is used in softening of hard water. (iii) It is used as washing soda in laundries. (iv) It is used as cleaning agent for domestic purposes. (v) It is used as laboratory reagent. (vi) It is used in textile and petroleum refining. (vii) It is used for preparation of carbonate of metals. (viii) It is used in fusion mixture (Na2CO3 + K2CO3) which helps in qualitative analysis i.e., in preparation of soda extract in case of insoluble salts. 18. Baking Soda (NaHCO3). Baking soda, chemically is sodium hydrogen carbonate. It is obtained as a first product in Solvay process as shown in reaction (ii). It can also be obtained by passing CO2 gas through aqueous solution of sodium carbonate as shown in reaction (vii). 19. Properties of Sodium Hydrogen Carbonate. (i) It is white crystalline solid. (ii) It is sparingly soluble in water. (iii) Its aqueous solution is alkaline in nature due to hydrolysis. The solution is weakly basic. NaHCO3 + H2O NaOH + H2CO3 This solution gives yellow colour with methyl orange (indicator) but no colour with phenolphthalein. (iv) On heating, it loses carbon dioxide and water forming sodium carbonate. 2NaHCO3 ––→ Na2CO3 + CO2 + H2O (Sodium hydrogen carbonate) heat (v) When it comes in contact with H2SO4. It gives CO2 which is used in fire extinguishers. 2NaHCO3 + H2SO4 ––→ Na2SO4 + 2H2O + 2CO2 20. Uses of Sodium Hydrogen Carbonate . (i) It is used as antacid (medicine) under the name soda bicarbonate to neutralize excess of acidity (hyper-acidity) in the stomach. (ii) It is an ingredient of baking powder which contains NaHCO3 and tartaric acid. When baking powder is heated, sodium hydrogen carbonate decomposes to give CO2 and sodium carbonate. CO2 causes bread and cake to rise. Tartaric acid helps to remove bitter taste due to formation of Na2CO3. (iii) It is used as additive in foods. (iv) It is used in making aerated soft drinks.