www.thechemistryguru.com 1 Dry Tests Physical Examination In physical examination of compound colour, smell, density etc, are observed. Physical Examination Observation Inference (A) colour of Compound 2+ 2 (i) Blue, Whose aqueous Hydrated salts of Cu (except CO3 solution is also blue. and Cl-) (ii) Blue, Whose aqueous Anhydrous salts of cobalt solution is pink (iii) Colourless substance Transition metals absent (except some salts of Mn2+) (iv) Green, Whose aqueous Slats of Ni2+, Cr3+ solution is also green and on dilution colour is not changed too much (v) yellow-green, aqueous Salts if Fe2+ solution is light green or almost colourless (vi) Yellow-brown, aqueous Salts of Fe3+ solution is yellow (vii) Violet-pink, aqueous Salts of cobalt solution is pink www.thechemistryguru.com 2 (viii) Black, Substance. CuO, Nio, SnO, FeS, CuS, HgS, PbS, NiS, CoS, CuBr2, Ag2S, Cu2S, MnO2, Fe3O4, FeO, Co3O4, Ni2O3 etc. (ix) Brown Substance CdO, PbO2, SnS, Bi2S3 MnCO3 (pale brown), CuCrO4, SnS. (x) Yellow substance Bi2O3, CdS, SnS2, As2S3, PbI2, Chromates, As2S5, AgI etc. (xi) Red substance Cu2O, HgO, Pb3O4, HgI2 etc. 2 (xii) Orange substance Cr2 O 7 salts, Sb2S3 etc. (xiii) Green substance K2MnO4, Carbonate or Chloride ofCu2+ (xiv) Light pink Hydrated Mn2+ salts (xv) Purple. KMnO4 & other permanganates, some Cr3+ salts. (B) Odour of Compound (i) Ammonical smell NH4 salts (ii) Vinegar like smell Acetates (iii) Like smell from rotten S2- salts. eggs. (C) Density (i) Mixture or salt is heavy Hg and Pb salts (ii) Mixture or salt is light. Salts of Zn, Al, Bi, Ca, Ba, Sr, Mg etc. (Chiefly carbonates) (D) Exposure of Air www.thechemistryguru.com 3 (i) Colourless, deliquescent SbCl3, ZnCl2, CaCl2, Zn(NO3)2 substance which is changed to paste. (ii) Coloured, deliquescent Cu(NO3)2, FeCl3, Fe(NO3)2, MnCl2 substance stance which is etc. changed to paste. (iii) Colour of substance is Cd salts changed from white to yellow (iv) Colour of substance is Pb or Bi salts. changed from white to black NOTE: 1. When mixture contains more than one coloured salts, then original colour of salt may change. 2. Some ammonium salts and sulphide do not give smell. 2. Effect of Heating In a clean, dry test tube, substance is first heated gently and then strongly. Effect of heating Observation Inference 1. Substance melts Slats of alkali metals chloride of Hg, Pb, Ag etc. having water of crystallization 2. Substance cracks KI, NaCl, Pb(NO3)2, Ba(NO3)2 etc. 3. Substance swells Alum, borates, phosphates etc www.thechemistryguru.com 4 4. Colour of residue obtained after heating Hot Cold (i) Orange White Zn salts yellow (ii) Brown Yellow salts of Pb, Bi or Sn (iii) Red or Brown Cd salts black (iv) white Blue Cupric salts (CuSO4) (v) Blue Blue-red COCl2 (vi) Green Dark red CoBr2 (vii) Violet Dark red CoI2 (viii) Yellow Green Ni salts (ix) Green Violet Cr salts (x) Black Black CuO, MnO2, NiO (non-fusible) (xi) Dark red Light brown Fe2O3 brown (non-fusible) (xii) Dark Light orange- HgO orange-red red 5. Substance sublimes on heating and colour of sublimate is www.thechemistryguru.com 5 (i) White HgCl2, Hg2Cl2, As2O3, AlCl3, NH4 , halides, Sb2O3 etc. (ii) Greyish black HgS (iii) Yellow S, As2S3, HgI2 etc (iv) Yellow-blue or violet vapour I2 (v) Grey (having garlic odour) As 6. Observation of gases evolved (A) Colourless and odourless gas: (i) Which supports the Nitrates of alkali metals combustion of burning match stick (O2). 2 2 (ii) Which turns the lime water CO3 or C 2 O 4 salts milky (CO2). (B) Colourless, odorous gas: (i) Smell of ammonia (NH3). Ammonium salts. (ii) Smell of burning sulphur Sulphite salts or FeSO4 (SO2). (iii) Smell of rotten eggs (H2S) Sulphide salts. (iv) Pungent smelling gas, which Hydrated chloride salt gives white fumes with NH4OH. (C) Coloured odorous gases: (i) Brown gas which turns starch- Nitrates or nitrites of heavy iodide paper blue (NO2) metals www.thechemistryguru.com 6 (ii) Red-brown gas which turns Bromide salts starch-paper yellow. (iii) Violet gas which turns starch Iodide salts paper blue (iv) Yellow-green gas which Chloride salts decolorizes the litmus paper. 3. Smell of Compound Smell of a compound also gives idea about the salt. S. Smell Inference No. 1. Bitter almond type Cyanides smell 2. Ammonical smell Ammonium salts 3. Chlorine like smell Hypochlorites 4. Vinegar like smell Acetates 4. Solubility of Salts S. No. Observation Solubility in water 1. Nitrates and All metal salts are water soluble. nitrites 2. Acetates All metal acetates are water soluble. 3. Chlorides All are water soluble except AgCl, Hg2Cl and PbCl2. www.thechemistryguru.com 7 4. Bromides All are water soluble except AgBr, Hg2Br2, PbBr2 and HgBr2. 5. Iodides All are water soluble except AgI, Hg2I2, PbI2, HgI2. 6. Sulphates All are water soluble except CaSO4, SrSO4, BaSO4, PbSO4, Hg2SO4, Ag2SO4 7. Sulphides All are water insoluble except gp. 1 & 2 sulphides and (NH4)2S. 8. Carbonates All are water insoluble except gp. 1 carbonates and (NH4)2CO3. 9. Phosphates All are water insoluble except gp. 1 phosphates and (NH4)3PO4. 10. Hydroxides All are water insoluble except gp. 1 hydroxides Ba(OH)2, Sr(OH)2 and Ca(OH)2. NOTE: Action of Heat on Different Compounds: (a) Some oxides liberate O2: Heat 2HgO 2Hg O2 Red Silvery deposit Heat 2Pb O 6PbO O 3 4 2 yellow Red Heat PbO2 2PbO O 2 Brown Heat 2Ag2 O 4Ag O 2 www.thechemistryguru.com 8 (b) Some carbonates liberate CO2: CaCOHeat CuO CO 3 2 Black Green Heat ZnSO ZnO CO 3 2 Yellow hot White White cold Heat 2AgCO2 3 4Ag2CO 2 O 2 Heat CaCO3 CaO CO 2 Heat MgCO3 CaO CO 2 Heat Li2 CO 3 Li 2 O CO 2 (C) Some bicarbonates liberate CO2: 2NaHCO3 Na 2 CO 3 CO 2 H 2 O NH4 HCO 3 NH 3 CO 2 H 2 O (D) Some Sulphates liberate SO3: Heat Heat CuSO4 .5H 2 O CuSO 4 CuO SO 3 5H2 O Heat 2FeSO4 Fe 2 O 3 SO 2 SO 3 Al SORed Hot Al O 3SO 2 43 2 3 3 (E) Some Sulphates liberate SO2: Heat 2MgSO4 2MgO 2SO 2 O 2 Heat hightemp. 2ZnSO4 2ZnO 2SO 2 O 2 Heat 2BeSO4 2BeO 2SO 2 O 2 www.thechemistryguru.com 9 (F) Some Sulphates lose water of crystallization: Heat 2CaSO4 .2H 2 O 2 CaSO 4 .H 2 O 2H 2 O 700 C 100 0 C 450 0 C ZnSO4 .7H 2 O ZnSO 4 .6H 2 O ZnSO 4 .H 2 O ZnSO 4 H2 O 5H 2 O H 2 O (g) Some nitrates liberate NO2 and O2: Heat 2Zn NO 2ZnO 4NO O 32 2 2 White Brown Heat 2Cu(NO3 ) 2 2CuO 4NO 2 O 2 2PB NOHeat 2PbO 4NO O 32 2 2 2Mg NOHeat 2MgO 4NO O 32 2 2 2Ca NOHeat 2CaO 4NO O 32 2 2 Heat 2LiNO3 Li 2 O 2NO 2 1/2O 2 Hg NOHeat Hg 2NO O 32 2 2 Heat 2AgNO3 2Ag 2NO 2 O 2 Heat 2Co NO 2CaO 4NO O 32 2 2 (H) Some nitrates liberate O2: Heat 2NaNO3 2NaNO 2 O 2 Heat 2AgNO3 2AgNO 2 O 2 (I) Some nitrates liberates N2O: Heat NH4 NO 3 N 2 O 2H 2 O www.thechemistryguru.com 10 (J) Hydrated chlorides liberate HCl: Heat 2[AlCl3 .6H 2 O] Al 2 O 3 6HCl 9H 2 O Heat MgCl2 .6H 2 O MgO 2HCl 5H 2 O Heat ZnCl2 .2H 2 O Zn OH Cl HCl H 2 O Heat 2 ZnCl2 .6H 2 O Zn 2 OCl 2 2HCl H 2 O Heat 2[FeCl3 .6H 2 O] Fe 2 O 3 6HCl 9H 2 O Heat SnCl2 .2H 2 O Sn OH Cl HCl H 2 O (K) Some chlorides decompose as: Heat 2FeCl3 2FeCl 2 Cl 2 Heat 2CuCl2 Cu 2 Cl 2 Cl 2 Heat NH4 Cl NH 3 HCl Heat Hg2 Cl 2 HgCl 2 Hg (I) Some other salts decomposes as: NH Cr OHeat N Cr O 4H O 42 2 7 2 2 3 2 Orange Green Heat 4K2 Cr 2 O 7 4K 2 CrO 4 2Cr 2 O 3 3O 2 Heat NH4 NO 3 N 2 2H 2 O Heat NH4 NO 3 N 2 O 2H 2 O Heat 2Mg NH4 PO 4 Mg 2 P 2 O H 2 O 2NH 3 Heat 2Zn NH4 PO 4 Zn 2 P 2 O 7 H 2 O 2NH 3 www.thechemistryguru.com 11 CH COO PbHeat PbCO CH COCH 32 3 3 3 Heat FeC2 O 4 FeO CO 2 CO Heat SnC2 O 4 SnO CO 2 CO Heat CAaC2 O 4 CaCO 3 CO Heat K4 Fe CN 4KCN Fe 2C N 2 6 1000 C 160 0 Red Hot HBO3 3 HBO 2 HBO 2 4 7 BO 2 3 Heat 2KCIO3 2KCI 3O 2 Heat 2KMnO4 K 2 MnO 4 MnO 2 O 2 Na B O .10H )Heat Na B O Heat 2NaBO B O 2 4 7 210H2 O 2 4 7 2 2 3 Glassy bead Na NH4 HPO 4 NH 3 NaPO 3 H 2 O 5. Flame Test Some volatile substances (especially chlorides) provide colour to oxidizing Bunsen flame. Colour of flame depends upon the metal ion present in the substance. When a slat is brought in contact of oxidizing flame, it dissociates into ion. The electrons of ions are excited to higher energy level and when they de-excites to ground state, they emit in visible region.