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analytical chemistry

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Analytical Chemistry 1. When sodium hydroxide solution is added first drop by drop and then in excess to the salt solutions of magnesium, iron (II), iron (III), copper (II), zinc and lead, following observations are made as shown in table below : Ion Colour of salt solution Mg2+ Magnesium chloride (Colourless) Iron (II) Sulphate (light green) Iron (III) chloride (reddish brown) Copper (II) Sulphate (blue) Zinc Sulphate (colourless) Fe2+ Fe3+ Cu2+ Zn2+ Pb2+ Lead nitrate(colourless) Colour of ppt. when NaOH is Colour of ppt/sol with excess added drop by drop of NaOH sol. Dull white ppt. insoluble in Mg(OH)2 dull white ppt. excess. Dirty green ppt. insoluble in Fe(OH)3 Dirty green ppt. excess. Fe(OH)3 Reddish brown ppt Reddish brown ppt. insoluble in excess. Pale blue ppt. insoluble in Cu(OH)2 Pale blue ppt. excess. Zn(OH)2 White gelatin like Colourless sol. due to the formation ppt. of sodium zincate Colourless sol. due to the Pb(OH)2 Chalky white ppt. formation of sodium plumbite 2. Action of sodium hydroxide on soluble salts of Mg2+, Fe2+, Fe3+, Cu2+, Zn2+ and Pb2+. Given salt + NaOH Sodium Salt + Precipitate 2NaCl + Mg(OH)2 1. MgCl2 + 2NaOH Mg(OH)2 is a dull white ppt. insoluble in excess of NaOH Na2SO4 + Fe(OH)2 2. FeSO4 + 2NaOH Fe(OH)2 is a dirty green ppt. insoluble in excess of NaOH 3NaCl + Fe(OH)3 3. FeCl3 + 3NaOH Fe(OH)3 is a reddish brown ppt. insoluble in excess of NaOH. Na2SO4 + Cu(OH)2 4. CuSO4 + 2NaOH Cu(OH)2 is pale blue ppt. insoluble in excess of NaOH. 1 Key Points Na2SO4 + Zn(OH)2 5. ZnSO4 + 2NaOH Zn(OH)2 is a gelatin like white ppt. soluble in excess of NaOH. 2NaNO3 + Pb(OH)2 6. Pb(NO3)2 + 2NaOH Pb(OH)2 is a chalky white ppt., soluble in excess of NaOH. 3. When ammonium hydroxide solution is added first drop by drop and then in excess to the salt solution of magnesium, iron (II), iron (III), copper (II), zinc and lead, following observations are made as shown in table below : Ion Mg2+ Magnesium chloride (Colourless) Colour of ppt. when NaOH is Colour of ppt./sol. with excess added drop by drop of NH4OH sol. Dull white ppt. insoluble in Mg(OH)2 dull white ppt. excess. Fe2+ Iron (II) Sulphate (light green) Iron (III) chloride (reddish brown) Copper (II) Sulphate (blue) Fe(OH)2 Dirty green ppt. Zn2+ Zinc Sulphate (colourless) Zn(OH)2 White gelatin like Pb2+ Lead nitrate (colourless) Pb(OH)2 Chalky white ppt. Fe3+ Cu2+ Colour of salt solution Fe(OH)3 Reddish brown ppt Cu(OH)2 Pale blue ppt. Dirty green ppt. insoluble in excess. Reddish brown ppt. insoluble in excess. deep blue or inky blue sol. due to the formation complex salt [Cu(NH3)]4SO4 Colourless sol. due to the formation of complex salt [Zn(NH3)4] SO4 Chalky white ppt. insoluble in excess. 4. Action of ammonium hydroxide on soluble salts of Mg2+, Fe2+, Fe3+, Cu2+, Zn2+ and Pb2+. Given salt + NH4OH Ammonium salt + precipitate 2NH4Cl + Mg(OH)2 MgCl2 + 2NH4OH (NH4)2SO4 + Fe(OH)2 FeSO4 + 2NH4OH 3NH4Cl + Fe(OH)3 FeCl3 + 3NH4OH (NH4)2SO4 + Cu(OH)2 CuSO4 + 2NH4OH (NH4)2SO4 + Zn(OH)2 ZnSO4 + 2NH4OH 2NH4NO3 + Pb(OH)2 Pb(NO3)2 + 2NH4OH 2 Key Points

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