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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

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(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

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(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

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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

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 (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

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(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.

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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     

2Pb OHeat 6PbO O  3 4  2   yellow  Red     

Heat PbO2 2PbO O 2    Brown   

Heat 2Ag2 O 4Ag O 2 

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(b) Some carbonates liberate CO2:

CaCOHeat CuO CO  3  2   Black  Green     

ZnSOHeat 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 SORed Hot Al O 3SO 2 43 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

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(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:

2Zn NOHeat 2ZnO 4NO  O  32 2 2 White Brown

Heat 2Cu(NO3 ) 2 2CuO 4NO 2  O 2

2PB NOHeat 2PbO 4NO  O  32 2 2

2Mg NOHeat 2MgO 4NO  O  32 2 2

2Ca NOHeat 2CaO 4NO  O  32 2 2

Heat 2LiNO3 Li 2 O 2NO 2  1/2O 2

Hg NOHeat Hg 2NO  O  32 2 2

Heat 2AgNO3 2Ag 2NO 2  O 2 Heat 2Co NO 2CaO 4NO  O  32 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

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(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 OHeat N Cr O  4H O  42 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

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CH COO PbHeat PbCO CH COCH  32 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 210H2 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. Because chlorides are more volatile then other salts, so other salts are converted into chlorides.

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S. Colour of Flame Inference No. With naked eye Cobalt glass 1. Golden yellow Invisible Na 2. Pink violet (Lilac) Crimson red K 3. Brick red Light green Ca 4. Dark red Violet Sr 5. Apple green Blue green Ba

3 6. Green Blue green Cu, BO3 7. Blue Visible Pb, Cu, As, Sb, Bi 8. Crimson red Li

NOTE: 1. Wire must be cleaned with conc. HCl and HCl must be pure. 2. If Pb, Sb, Bi, Sn or As may be present in the mixture then flame test must not be performed because they form alloy with Pt and spoil the wire. 3. Golden yellow colour of Na exists for long time and so other flame tests must be performed after removing Na. 4. Nichrome wire may also be used in place of Pt but results are not good. 5. Ca-salts give colour immediately while Ba or Sr salts, gives colour after sometime. 6. Be and Mg do not impart colour to flame due to high I.E.

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6. Charcoal Cavity Test

In this test, salt is fused with anhydrous Na2CO3 or oxidizing fusion mixture in a cavity on charcoal block in reducing flame. Reaction yield metal oxides. Some metal oxides are reduced to metal by action of charcoal while some form incrustation on cold parts of charcoal block. The fusion reactions may be represented as given below:

CaCl2 Na 2 CO 3 CuCO 3  2NaCl

CuCO3 CuO CO 2

CuO C Cu  CO

Observation Inference (A) Metallic bead is formed (i) Lustrous, white, malleable which leaves Ag no stain on paper and form no incrustation. (ii) White, malleable, leaves no stain on Sn paper (iii) Greyish white, soft which marks paper Pb (iv) Red-white, brittle Bi (v) White, brittle which fumes when hot Sb (vi) Red Cu (B) Incrustation is formed (i) White, which turns yellow and when not Sn or Zn (ii) White Sn (iii) Red-brown Cd

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(iv) White with odour of garlic As (v) Yellow which turns orange on heating Bi (vi) Yellow which turns red-brown or heating Pb (C) Residue is left behind (i) Grey or black residue without any Fe, Co, Ni or Mn incrustation (ii) Red-brown with incrustation Cd (iii) White, infusible residue which shines on Al, Zn, Ca, Sr, heating Ba, Mg.

7. Cobalt-nitrate Test This test is performed only when a white, infusible mass is obtained in charcoal cavity. It is based on fact that some metal oxides form coloured double oxides when heated with cobalt oxide in oxidizing flame. To perform this test, white infusible mass obtained in charcoal cavity test is taken in charcoal cavity with cobalt nitrate and mixture is heated in oxidizing flame.

S. Observation Composition Inference No.

3 3 1. Blue residue CoO.Al2O3 Al, PO4 or BO3 2. Green-residue CoO.ZnO Zn 3. Pink-dirty CoO.MgO Mg residue 4. Bluish Green CoO.SnO Sn

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NOTE: (i) Cobalt nitrate should not be used in excess otherwise black coloured cobalt oxide may be formed. In presence of this black coloured oxide, it is difficult to identify other colours. (ii) This test can also be performed with filter paper ash. For this test solution of substance under testing and cobalt nitrate solution are mixed and a filter paper is dipped in it. it is burnt and colour of ash is observed.

8. Borax-bead Test Some substance give coloured bead when heated with borax bead on platinum loop. Colour of head gives idea of substance. The reactions taking place may be represented as

 Na2 B 4 .10H 2 O Na 2 B 4 O 7  2NaBO 2 B 2 O 3 10H2 O  Glassy borax bead (mixture of sodium metaborate and boric anhydride) This borax bead form coloured bead with metal salts. e.g.,

 CuSO4 CuO SO 3

CuO B O Cu BO 2 3 2 2 Copper metaborate (Blue) The colour of bead is different in oxidizing and reducing flames. e.g., coloured copper metaborate may be reduced to colourless cuprous metaborate or to metallic copper.

2Cu BO C 2CuBO  B O  CO  22 2 2 3

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2Cu BO 2C 2Cu  2B O  2CO  22 2 3

Colour of the bead in Metal Oxidizing-flame Reducing-flame Hot Cold Hot Cold Green Blue Colourless Brown-red Copper Brown- Pale-yellow Bottle green Bottle green Iron yellow Green Green Green Green Chromium Blue Blue Blue Blue Cobalt Violet Amethyst Grey Grey Manganese red Red-brown Brown Colourless Colourless Nickel

NOTE: (i) Borax-bead must be performed for coloured substances only. (ii) Small amount of substance must be used otherwise transparent bead is obtained.

9. Microcosmic Salt Bead Test This test is similar to borax bead test and in it microcosmic salt bead in used in place of borax bead.

Na NH4 HPO 4 NaPO 3 NH 3  H 2 O Sodium metaphosphate

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Sodium metaphosphate combines with metallic oxides to form orthophosphates which are usually coloured. The conclusions can be made on the basis of table given in borax-bead test.