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Scheme for Systematic Analysis of a Mixture containing two Salts

Qualitative Analysis

 Tests For Anions

Preparation of Sodium Carbonate Extract:
One gram of the mixture is treated with thrice its weight of anhydrous Na2CO3 and about 20 to 25 ml of water and boil it for about 15 minutes. The mixture is then cooled and filtered . the filterate is known as Sodium Carbonate Extract. It is used to perform wet tests.
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EXPERIMENT
OBSERVATION

INFERENCE
DryTest

1 

 Action of dil HCl.

To a little of the mixture dil HCl is added and warmed.
  1. Brisk efferverscence with the evolution of colourless odourless gas turning lime water milky
  2. Colourless gas with the smell of rotten eggs, turning lead acetate paper black.
  3. Colourless gas with smell of burning matches.
  4. Reddish brown vapours with pungent smell
  1. Presence of CO32-
  1. Presence of S2-

 
 
  1. Presence of SO32-
  1. Presence of NO2-
 
2
 Action of Conc. H2SO4.

A little of the mixture is treated with conc H2SO4 and warmed. If there is no reaction to the above solution Copper turnings are added and warmed 
 
  1. Colourless gas forming thick white fumes with Conc. NH4OH at the mouth of the test tube.
  2. b)Fuming gas with reddish brown vapours, with the solution turning brown.
  3. Fuming gas with violet vapours, solution turning black.
  4. Smell of vinegar
  5. Reddish brown vapours on strong heating or on heating with Cu turnings.
  1. Presence of Cl-
  1. Presence of Br-

 
  1. Presence of I- 
  1. Presence of CH3COO-.
  2. Presence of NO3-
3
 Ammonium Molybdate test

A little of the mixture is warmed with Conc. HNO3 and Ammonium Molybdate.

 Bright Yellow precipitate of Ammonium Phospho molybdate is formed. Presence of PO43-
Wet test

4

 To a little of the salt solution or Sodium Carbonate extract after acidification with dil HCl BaCl2 solution is added. White precipitate which is insoluble in dil HCl is formed Presence of SO42-
  Confirmation test for Halides:

MnO2 Test

To a little of the mixture MnO2and Conc. H2SO4 is added and warmed
  1. Greenish Yellow gas with pungent smell turning KI paper brown.
  2. Reddish brown vapours condensing to form red droplets.
  3. Violet vapours condensing to form violet solid.
  1. Presence of Cl-
  1. Presence of Br-
  1. Presence of I- 
 
Wet Test
 AgNO3 Test.

The Sodium Carbonate extract is acidified with dil. HNO3 boiled and treated with AgNO3
  1. Curdy white precipitate soluble in excess of NH4OH solution.
  2. Pale Yellow ppt. sparingly soluble in NH4OH.
  3. Yellow precipitate insoluble in NH4OH.
  1. Presence of Cl-
  1. Presence of Br-
  1. Presence of I-
  Confirmation of Chloride

Chromyl Chloride Test.

The Mixture is mixed with solid K2Cr2O7 and warmed with Conc. H2SO4. The issuing vapours are passed into H2O in a test tube, followed by NH4OH and Lead Acetate solution
  1. Reddish brown gas dissolving in H2O forming yellow solution.
  2. Yellow ppt. is formed on adding lead acetate solution.
 Presence of Cl- confirmed.
  Confirmation of NO3-

Brown Ring Test.

The extract is mixed with dilute H2SO4 and freshly prepared FeSO4 solution. Conc. H2SO4 is added along the sides of the test tube without shaking.

 Brown ring is formed at the junction of the two liquids.

This is due to the formation of the following comples

[Fe(H2O)5NO]

Penta aquo nitroso ferrus(II) Complex ion

(Nitroso ferrous sulphate)

 Presence of NO3 - Confirmed
  Conf. of CH3COO-.
  1. The extract is acidified with dil HNO3 boiled and neutralised with NH4OH followed by FeCl3
  1. Ester test. The extract is treated with ethyl alcohol and a drop of Conc. H2SO4 and warmed. The solution is now added to a large quantity of water. 
  1. Red colour turning brown on boiling.

    2.  

     
     
     
     
     
     

  2. Pleasant fruity smell.
 		 a) Presence of CH3COO-
 
 
 
 
 

b) Presence of CH3COO- Confirmed.
  Confirmation of PO43-.

The extract is treated with dil. HNO3 and excess of AgNO3 . NH4OH is now added through the sides of the test tube.

 Yellow ring is formed at the neutral junction. Presence of PO43-.
  Confirmation of S2-.

The extract is treated with dilute acetic acid and Lead Acetate

 Black precipitate Presence of S2-

 

Tests For Cations


 
Zero NH4+ NaOH and Nessler’s Reagent Brown Precipitate
I Group Pb2+ Salt Solution and dil. HCl White Precpitate
II Group Pb2+

Cu2+

Cd2+

 Salt Solution , dil HCl and H2S Black Precipitate

Black Precipitate

Yellow Precipitate
III Group Al3+

Fe3+

Mn2+

 Salt solution is treated with NH4Cl solid followed by NH4OH Gelatinous White ppt.

Gelatinous Brown ppt.

White turning Brown on standing.
IV Group Mn2+

Zn2+

Ni2+

 Salt solution is treated with NH4Cl solid followed NH4OH and H2S. Buff or Pale pink ppt

Dull white ppt

Black ppt
V Group Ba2+

Sr2+

Ca2+

 Salt solutions is treated with NH4Cl followed byNH4OH and (NH4)2CO3 White ppt

White ppt

White ppt
VI Group Mg2+ Salt solutions is treated with NH4Cl followed byNH4OH and (NH4)2HPO4 White ppt
Preparation of Original Solution .

The mixture should be dissolved in an suitable solvent. The choice of solvents can have the following sequence.1.Cold Water, 2. Warm water, 3. Dilute HCl, 4. Concentrated HCl, 5. Dilute HNO3, 6. Concentrated HNO3, and 6. Aquaregia. The solution prepared by dissolving the mixture in the solvent is referred to a the original solution or O.S. 
 
 
EXPERIMENT
OBSERVATION
INFERENCE
0 Group      
  Shake the aqueous mixture solution well with NaOH and note the odour. Smell of Ammonia NH3 Presence of NH4+ indicated
  To one ml of Nesslers (K2[HgI4]) reagent add aqueous mixture solution Brown precipitate of Mercuric Amido Iodide (NH2.HgO.HgI) is obtained. NH4+ Confirmed
I Group      
  A) White Precipitate.

Dissolve the above precipitate in hot water and perform the following tests

 The white ppt. of PbCl2 is soluble in hot water

Pb2+ + 2Cl-® PbCl2

 Pb2+ may be present
  (i) Treat a part of the above solution with K2CrO4 solution Yellow precipitate due to the formation of PbCrO4.

Pb2+ + CrO4® PbCrO4.

 Pb2+ Present
  (ii) To another part of group one solution add KI solution Yellow precipitate due to the formation of PbI2 which is soluble in hot water reappears as golden spangles on cooling

Pb2+ + I-® PbI2

 Pb2+ Confirmed
II Group      
  Black Precipitate.(NiS). Dissolve the group II black residue in dil HNO3 and perform the following tests.
  1. Solution is blue
  2. Solution is Colourless
  1. Cu2+
  2. Pb2+
  a) If the solution is blue perform the following tests.

(i) Add NH4OH drop wise until it is in excess. 

 Blue precipitate is formed which dissolves in excess of the reagent.

Cu2+ + 2OH-® Cu(OH)2

Cu(OH)2 + 4NH4OH ® [Cu(NH3)4](OH)2 + 4H2O.

 Cu2+
  (ii) Acidify the second portion with acetic acid and add potassium Ferrocyanide. Reddish brown precipitate is obtained.

2Cu2+ + [Fe(CN)6]4-® Cu2[Fe(CN)6]

 Cu2+
  b) If the solution is colour less perform the following tests.

(i) Add KI to one part of the above solution.

 Yellow precipitate due to the formation of PbI2 which is soluble in hot water reappears as golden spangles on cooling.

Pb2+ + 2I-® PbI2

 Pb2+ Confirmed
  (ii)Add K2CrO4 to another part of the solution Yellow precipitate due to the formation of PbCrO4

Pb2+ + CrO42-® PbCrO4 

 Pb2+ Confirmed
 
  1. Yellow precipitate (CdS)
Boil the yellow precipitate with yellow ammonium sulphide and divide into two parts .		   Presence of Cd2+
  (i) One part of the residue is dissolved in dil HNO3 and ammonium hydroxide is added drop wise. White Precipitate soluble in excess. Presence ofCd2+
  (ii) To the Second part of the above solution pass H2S. Yellow precipitate. Presence ofCd2+ Confirmed.
III Group      
 
  1. Gelatinous white ppt. of Al(OH)3.
Dissolve the white gelatinous precipitate by boiling with NaOH solution and divide it into two parts.		    
  (i) To the first part add NH4Cl and boil White precipitate Al3+ present
  (ii) To the second part add dil. HCl ,litmus solution and excess of NH4OH A blue lake Presence of Al3+ confirmed.
  Ash test: Group III residue + 3 drops of conc. HNO3 + 3 drops of Cobalt nitrate. Dip a rolled filter paper in this solution and burn in the flame A Blue tinted ash is obtained.

2Al(OH)3 ® Al2O3 + 3H2O.

2 Al2O3 + 2Co(NO)3 ® 2CoO.Al2O3 + 4NO2 + O2

 Presence of Al3+ confirmed.
  B) Gelatinous brown ppt. Fe(OH)3. Dissolve the ppt. in dil HCl and divide it into two parts.    
  (i) To one part of the above precipitate add Potassium Ferrocyanide solution. A blue (Prussian blue) coloured solution or precipitate is formed.

Fe3++ 3 [Fe(CN)6]4-® Fe4[Fe(CN)6]3

 Presence of Fe3+ indicated.
  (ii) To the second part add Potassium thiocyanide. Blood red coloration

Fe3+ + 3CNS-® Fe(CNS)3

 Presence of Fe3+ confirmed.
IV Group      
  A) Black precipitate. (NiS)

Conformation for Ni2+ Dissolve the black precipitate in dil. HCl add NH4Cl and NH4OH and divide into two parts:

   Presence of Ni2+
  (i) To the first part add Dimethyl Glyoxime Rose Red Precipitate. Presence of Ni2+ Confirmed.
  (ii) Through the second part pass H2S gas.  A black precipitate is formed Presence of Ni2+ Confirmed.
  B)DullWhite precipitate.

Conformation for Zn2+ Dissolve the white ppt. in dilute HCl, to this solution NaOH is first added in drops then in excess until the ppt. dissolves.

    
  (i) To one part add Acetic acid and potassium Ferrocyanide. White precipitate is formed.

Zn2+ + [Fe(CN)6]4-® Zn2[Fe(CN)6]

 Presence of Zn2+ confirmed.
  (ii) Pass H2S and filter White precipitate is formed Presence of Zn2+ confirmed.
  Ash test: Group IV residue + 3 drops of conc. HNO3 + 3 drops of Cobalt nitrate. Dip a rolled filter paper in this solution and burn it in the non luminous part of the flame. Green tinted ash is formed. Presence of Zn2+ confirmed 
  C) Conformation of Mn2+. Buff precipitate is heated with PbO2 and conc. HNO3 and dilute with water.  The supernatent liquid turns pink due to the formation of permanganic acid.

2Mn(NO3)2 + 5PbO + 6HNO3 ® 5Pb(NO3)2 + 2HMnO4 + 2H2O

 Presence of Mn2+ is confirmed. 
V Group      
  White precipitate:

Dissolve the group V precipitate in minimum quantity of Acetic acid and divide into three parts. Keep aside a part of the group precipitate for Flame test.

    
 
  1. To one part of the above soln. Add K2CrO4 .
 A Yellow precipitate is formed.

Ba2+ + CrO42-® BaCrO4

 Presence of Ba2+ Ba2+ confirmed.
 
  • To the second part add CaSO4 and boil.
    		•  A White precipitate is formed.

    Sr2+ + SO42-® SrSO4

    		 Presence of Sr2+ confirmed
     
  • To the third part add Ammonium Oxalate
    		•  A White precipitate is formed.

    Ca2+ + C2O42-® Ca C2O4

    		 Presence of Ca2+ confirmed
      Flame test:

    The group V residue is treated with conc. HCl and a Nichrome / Platinum wire dipped in the above solution is shown into the non luminous part of the flame. 

    		 a) Apple Green flame

    b) Crimson Flame 

    c) Brick Red Flame 

    		 a) Ba2+ Confirmed

    b) Sr 2+ confirmed

    c) Ca 2+ confirmed
    VI Group      
      White Crystalline ppt.

    Group VI ppt. is dissolved in minimum quantity of dil HNO3 and few drops of conc. HNO3 and Cobalt Nitrate are added. A rolled filter paper is dipped in the above solution and burned in the non luminous part of the flame.

    		 A pink tinted ash is obtained. Presence of Mg2+ is confirmed.
      Magneson reagent test: 

    The group VI residue is dissolved in dil. HCl to this a few drops of Magneson reagent is added followed by NaOH.

    		 A blue precipitate is formed. Presence of Mg2+ is confirmed.