QUALITATIVE ANALYSIS
( SALT ANALYSIS )
Salt is made up of one cation & one anion. When a salt is dissolved in water,
it ionizes into cation ( basic radical ) & anion ( acidic radical )
In Qualitative analysis, all the cations are classified into seven groups according
to the Ksp values ( increasing order of Ksp from first to sixth group ) of their salts which precipitate during the salt analysis.
GROUP
|
CATIONS
|
GROUP REAGENT
|
PRECIPITATE
|
ZERO GROUP
|
NH4+
|
No group reagent as Ammonium salts do not get precipitated easily.
|
----------
|
FIRST GROUP
|
Pb2+
|
Dil. HCl
|
PbCl2 ( white )
|
SECOND GROUP
|
Cu2+
As3+
|
Dil. HCl + H2S
|
CuS ( black )
As2S3 (Yellow )
|
THIRD GROUP
|
Fe3+
Al3+
|
NH4Cl + NH4OH
|
Fe(OH)3
( reddish brown)
Al(OH)3(Gelatinous White )
|
FOURTH GROUP
|
Zn2+
Ni2+
Co2+
Mn2+
|
NH4Cl + NH4OH + H2S
|
ZnS ( Greyish white)
NiS ( Black )
CoS ( Black)
MnS ( Light pink or buff )
|
FIFTH GROUP
|
Ba2+
Sr2+
Ca2+
|
NH4Cl + NH4OH+ (NH4)2CO3
|
BaCO3 ( White)
SrCO3 ( White)
CaCO3 ( White)
|
SIXTH GROUP
|
Mg2+
|
No group reagent
|
-------------
|
GROUP
|
ANIONS
|
Dilute H2SO4
|
CO32- , SO32- , S2- , NO2-
|
Concentrated H2SO4
|
Cl- , Br- , I- , NO3- , CH3COO-
|
SO42- & PO43- are tested independently as their salts are not easily attacked by mineral acids.
The systematic procedure involved in the qualitative analysis of salt involves the three categories of the tests :
PHYSICAL TEST
EXPERIMENT
|
OBSERVATION
|
INFERENCE
|
COLOUR :
Note the colour of the given salt.
|
White
Blue
Reddish orange
Light pink
|
NH4+ , Pb2+ , As3+ , Al3+ , Zn2+ , Ca 2+ , Sr2+ , Ba2+ , Mg2+ may be present.
Cu2+ may be present.
Fe3+ may be present.
Co2+ , Mn2+ may be present.
|
ODOUR or SMELL :
Take a pinch of salt in a watch glass ,add few drops of water & note the smell of the salt.
|
Smell of Ammonia gas
Smell of rotten eggs
Smell of vinegar
|
NH4+ may be present.
S2- may be present.
CH3COO- may be present.
|
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