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Analytical chemistry deals with qualitative and
quantitative analysis of substances.
Qualitative analysis : A salt consists of two parts
known as radicals. The positively charged part of a salt
(cation) which has been derived from a base is termed
as basic radical and the negatively charged part of salt
(anion) which has been derived from an acid is termed
as acidic radical. In qualitative inorganic analysis, the
given compound is analysed for the basic and acid
radicals ( i.e., the cations and the anions), that it
contains. For example zinc blende is analysed for the
2
Zn and
2
S ions that it contains.
Test for Different Gases
(1) Colourless gases
(i) Tests for CO 2 : It is colourless and odourless
gas. It gives white ppt. with lime water which dissolves
on passing excess of 2
CO.
Ca OH CO CaCO HO
Lime water Whiteppt
2
.
2 2 3
( )
Whiteppt Excess So le
CaCO CO HO Ca HCO
lub
2 2 32
.
3
( )
(ii) Test for CO : It is colourless and odourless
gas. It burns with a blue flame. 2 2
2 CO O 2 CO
(iii) Test for O 2 : It is colourless and odourless
gas. It rekindles a glowing splinter.
(iv) Tests for H 2
S : It is a colourless gas with a
smell of rotten eggs. It turns moist lead acetate paper
black.
Black
CH COO Pb HS CHCOOH PbS
3 2 2 3
(v) Tests for SO 2 : It is a colourless gas with a
suffocating odour of burning sulphur. It turns acidified
2 2 7
KCrO solution green.
SO KCrO HSO KSO Cr SO HO
Green
2 2 2 7 2 4 2 4 2 43 2
(vi) Tests for NH 3
: It is a colourless gas with a
characteristic ammonical smell. It gives white fumes of
NH Cl
4
with HCl ,
Whitefumes
NH HCl NH Cl
3 4
. With Nessler’s
reagents, it gives brown ppt.
K HgI NH KOH NH HgOHgI KI H O
Brown ppt
Nessler sreagent Iodine illons base
2
ofM '
3 2
'
2 4
( )
It gives deep blue colour with
4
CuSO solution,
Deep blue
CuSO NH CuNH SO
4 3 34 4
3
NH
dissolves in
water to give ,
4
NH OH
which being basic, turns red
litmus blue, NH HO NH OH
3 2 4
NH OH
4
(vii) Tests for HCl gas : It is colourless gas with a
pungent irritating smell. It turns moist blue litmus
paper red i.e., it is acidic in nature. It gives white ppt.
with
3
AgNO solution. This white ppt. is soluble in
4
NH OH
3
.
3
HCl AgNO AgCl HNO
Whiteppt
AgCl NH OH AgNH H O
2
Soluble
4 32
(viii) Test for CH COOH
3
vapours : These
vapours are colourless with a vinegar like smell.
Chemical Analysis
Chapter
(2) Coloured gases
(i) Tests for Cl 2
: It is a greenish yellow gas with
a pungent smell. In small quantity it appears almost
colourless. It bleaches a moist litmus paper,
Cl HO 2 HCl O
2 2
; Colour O Colourless. Blue
litmus paper first turns red and then becomes
colourless.
(ii) Tests for Br 2 : Brown vapours with a pungent
smell. It turns moist starch paper yellow.
(iii) Tests for I 2 : Violet vapours with a pungent
smell. It turns moist starch paper blue.
(iv) Tests for NO 2
: Brown coloured pungent
smelling gas. It turns moist starch KI paper blue
2 2 2
2 KI 2 NO 2 KNO I ;.
2
I Starch Bluecolour
It turns ferrous sulphate solution black,
FeSO NO H SO Fe SO FeSO NO HO
Black brown
4 2 2 4 2 43 4 2
Systematic Procedure for Qualitative
Analysis of Inorganic Salts
It involves the following steps : (1) Preliminary
tests (2) Wet tests for acid radicals and (3) Wet tests
for basic radicals.
(1) Preliminary tests
(i) Physical examination : It involves the study
of colour, smell, density etc.
Table : 21.1 Colour
Colour Salt
Black Oxides :
2 3 4
MnO , FeO , CuO , CoO ,
2 3
NiO
Sulphides :
Ag S , CuS , CuS , FeS , CoS , NiS
2 2
,
PbS , HgS ,
2 3
BiS
(blackish brown)
Blue Hydrated
4
CuSO , anhydrous
4
CoSO
Orange
2
KO
, some dichromate
2 2 7 2 3
( KCrO ), SbS
,
ferricyanides
Green Nickel salts, hydrated ferrous salts,
potassium permanganate ( )
4
KMnO , some
copper (II) salts
Brownish
yellow
SnS
Dark brown
2 2 2 3 4 3
PbO , AgO , CdO , FeO , CuCrO , FeCl
(but yellow in aq. solution)
Pale brown
3
MnCO
Light pink Hydrated manganese salts
Reddish pink Hydrated cobalt (II) salts
Red
2 3 4
HgI , PbO
Yellow CdS , PbI , AgBr , AgI
2
, chromates
(ii) Dry heating : Substance is heated in a dry test
tube.
Table : 21.
Observation Result
(a) A gas or vapour is
evolved.
Compounds with water
of crystallisation
Vapour, evolved, test
with litmus paper.
Ammonium salts, acid
salts, and hydroxides.
(usually accompanied by
change of colour)
The vapour is alkaline. Ammonium salts.
The vapour is acidic. Readily decomposable
salts of strong acids.
Oxygen is evolved Nitrates,chlorates and
certain oxides.
Dinitrogen oxide Ammonium nitrate or
nitrate mixed with an
ammonium salt.
Dark-brown or reddish
fumes (oxides of
nitrogen), acidic in
reaction.
Nitrates and nitrites of
heavy metals.
2
CO is evolved, lime
water becomes turbid.
Carbonates or hydrogen
carbonates.
3
NH is evolved which
turns red litmus blue.
Ammonium salts.
2
SO is evolved, which
turns acidified
2 2 7
KCrO
green, decolourises
fuschin colour.
Sulphates and
thiosulphates.
HS
2
is evolved, turns
lead acetate paper black,
or cadmium acetate
yellow.
Hydrates, sulphides or
sulphides in the presence
of water.
2
Cl is evolved, yellowish Unstable chlorides e.g.,
copper chlorides in the
2 4 7
160
2
100
3 3
H BO HBO HBO
C C
o o
2 3
Red hot
BO
4
450
4 2
5
100
4 2
70
4 2
o
2 2
ZnSO. 7 HO ZnSO. 6 HO ZnSO. HO ZnSO
C
HO
C
HO
C
o o
(iii) Flame test
Characteristic flame colour : Certain metals and
their salts impart specific colours to Bunsen burner
flame.
(a) Pb imparts pale greenish colour to the flame.
(b) Cu and Cu salts impart blue or green colour to
the flame.
(c) Borates also impart green colour to the flame.
(d) Ba and its salts impart apple green colour to
the flame.
(e) Sr imparts crimson red colour to the flame.
(f) Ca imparts brick red colour to the flame.
(g) Na imparts yellow colour to the flame.
(h) K imparts pink-violet (Lilac) colour to the
flame.
(i) Li imparts crimson-red, Rb imparts violet and
Cs imparts violet colours to the flame.
(j) Livid- blue flame is given by As, Sb and Bi.
(iv ) Borax bead test : The transparent glassy
bead( ) 2 2 3
NaBO BO when heated with inorganic salt
and the colour produced gives some idea of cation
present in it.
Table : 21.
Colour of bead in
oxidising flame
Colour of bead in
reducing flame
Basic radical
present
Greenish when
hot, blue in cold.
Red and opaque Cu
Dark green in hot
and cold
Same Cr
Deep – blue Deep blue Co
Yellow when hot Green Fe
Violet in hot and
cold
Colourless Mn
Brown in cold Grey or black or
opaque
Ni
Microcosmic salt bead test : Microcosmic salt,
Na NH HPO HO
4 4 2
( ). 4 is also used to identify certain
cations just like borax. When microcosmic salt is
heated in a loop of platinum wire, a colourless
transparent bead of sodium metaphosphate is formed.
Na NH HPO HO NaNH HPO HO
4 4 2 4 4 2
Na NH HPO NaPO NH HO
4 4 3 3 2
Now
3
NaPO reacts with metallic oxides to give
coloured orthophosphates.
3 4
NaPO CuO NaCuPO
(Blue);
3 4
NaPO CoO NaCoPO
(Blue);
3 23 3 23
NaPO CrO NaPO. CrO
(Green)
(v) Charcoal cavity test
Table : 21.
(a) Compound fused in cavity directly
Nature and colour of
bead
Cation
Yellow, brittle bead
3
Bi
Yellow, soft bead which
marks on paper
2
Pb
White, brittle
3
Sb
White yellow when hot ZnO
White garlic odour
2 3
AsO
Brown CdO
Grey metallic particles
attracted by magnet
Fe , Ni , CO
Maleable beads Ag and Sn (White), Cu
(Red flakes)
(b) Compound mixed with
2 3
NaCO Crystalline
Salts,NaCl,KCl
Decrepitates
Sustance
, chlorates
2
3
Oxidisingagents like
deflagrates
Substance
NO NO
Substance infusible, perform test (a)
(vi) Cobalt Nitrate test
Table : 21.
Colour Composition Result
Blue residue
2 3
CoO. AlO Al
Green residue
CoO. ZnO ZnO
Pink dirty
residue
CoO. MgO MgO
Blue residue 4
NaCoPO
3
4
PO in
absence of Al.
(2) Wet tests for acid radicals : Salt or mixture
is treated with dil. 2 4
HSO and also with conc.
2 4
HSO
separately and by observing the types of gases evolved.
Confirmatory tests of anions are performed.
Table : 21.7 Observations with Dilute
2 4
HSO
Observations Acid Radical Confirmatory test
Brisk effervescence with
evolution of colourless and
odourless gas.
2
3
CO (carbonate)
Gas turns lime water milky but milkyness disappears on passing gas
inexcess,
2 3 2 4 2 4 2 2
Na CO HSO NaSO HO CO
Ca OH CO CaCO HO
2
milky
2 3
lime water
2
soluble
3 2 2 32
CaCO HO CO Ca ( HCO )
Brown fumes
2
NO (Nitrite)
Add KI and starch solution blue colour
3 2 4 2 4 2
2 NaNO HSO NaSO 2 HNO ;
HNO NO
2
(colourless);
2 2
2 NO O (air) 2 NO (brown)
2 4 2 2 4 2 2
2 KI HSO 2 NHO KSO 2 HO 2 NO I
2
I
starch
blue colour
Smell of rotten eggs
H S
2
( smell) on heating
2
S (sulphide)
Gas turn lead acetate paper black
Sodium carbonate extract
( SE )+ sodium nitroprusside – purple colour,
2 2 4 2 2 4
Na S HSO HS NaSO
H S CHCOO Pb PbS CHCOOH
3
(black)
2 3 2
sodiumnitroprusside (purple)
[ ( ) ] [ ( ) ]
2 2 5 4 5
Na S Na FeCN NO Na FeCN NOS
Colourless gas with pungent
smell of burning sulphur
2
3
SO (sulphite) Gas turns acidified
2 2 7
KCrO solution green [different from ]
2
3
CO since
gas also turns lime water milky
2 3 2 4 2 4 2 2
Na SO HSO NaSO HO SO
Cr O SO H Cr SO HO
2
(green)
2
4
3
2
2
2 7
(milky)
2 2 3
Ca ( OH ) SO CaSO
Solution gives smell of
vinegar
CH COO
3
(acetate)
Aq. Solution + neutral
3
FeCl blood red colour
3 CH COONa FeCl Fe ( CHCOO ) 3 NaCl
(red)
3 3
neutral
3 3
White or yellowish white
turbidity on warming
2
2 3
SO
(thiosulphate)
Aq. Solution +
3
AgNO white ppt. changing to black (viii) on warming
,
3
white ppt.
2 2 3 3 2 2 3
Na SO 2 AgNO AgSO 2 NaNO
black ppt.
2 2 3 2 2 2 4
Ag SO HO AgS HSO
Table : 21.8 Observation with concentrated
2 4
HSO
Observation Acid Radical Confiramatory Test
Colourless pungent gas
giving white fumes with
Cl (chloride)
Add
2
MnO in the same test tube and heat–pale green
2
Cl gas (i)
tube. A dark brown ring of
2
4
2
2 5
[ Fe ( HO ) NO ] SO at the
interface between the two liquids is formed.
3 2 4 4 3
2 NaNO HSO 2 NaHSO 2 HNO ;
3 4 2 4
2 HNO 6 FeSO 3 HSO
Fe SO NO HO
2 43 2
Fe HO SO NO FeHO NO SO HO
2
2
4
2
2 6 4 2 5
[ ( )] [ ( ) ]
Oxalate :
2 2 4 2 4 2 4 2 2
Na CO HSO NaSO HO CO CO
CO burns with blue flame and
2
CO
turns lime
water milky.
(ix) C O MnO H CO Mn HO
2
colourless
2
2
(violet)
4
2
2 4
(x) CaCl NaCO CaCO 2 NaCl
white ppt.
2 2 4 2 4
2 2
CaCO
decolourises acidified. 4
KMnO
Specific test in solution
(i) Sulphate : S.E. add dil. (to decompose
2
3
CO until reaction ceases). Add
2
BaCl
solution. White
ppt. insoluble in conc. 3
HNO ,
BaCl NaSO BaSO 2 NaCl
white ppt.
2 4 4
(ii) Borate : lgnite the mixture containing borate,
conc.
2 4
HSO
. And ethanol in a china-dish with a
burning splinter – green edged flame of ethyl borate.
3 3 2 4
(conc.)
3 3 2 4
2 Na BO 3 HSO 2 HBO 3 NaSO ;
H BO CHOH CHO B HO
ethanol
2
(volatile)
burns withgreenflame
3 3 2 5 2 5 3
In presence of
2
Cu , perform this test in a test
tube since
2
Cu salts are not volatile.
(iii)
3
S. E. HNO ammonium molybdate solution.
Heat, yellow crystalline ppt. confirms
3 4 42 4 3
NaPO 12 ( NH ) MoO 24 HNO
NH PO MoO NH NO NaNO HO
3 4 3 3 2
y ellowppt.
4 3 4
Arsenic also gives this test. Hence presence of
phosphate should also be checked after group II.
(iv) Fluoride : Sand +salt ( )
F +conc. ;
2 4
HSO
heat and bring a water wetted rod in contact with
vapours at the mouth of the test tube. A white deposit
on the rod shows the presence to
F
NaF HSO NaHSO HF
2 4 4
SiO HF SiF HO
2 4 2
4 2
white
4 2 2 6 4 4
3 SiF 4 HO 2 HSiF HSiO
(3) Wet tests for basic radicals : Analysis of Basic Radicals
Table : 21.
Group Basic radicals Group reagent Ppt. as Explanation
I
2 2
2
Ag , Hg (I), Pb
dil HCl Chloride
2 2 2
AgClHgCl PbCl
SP
K values of chlorides are low,
hence precipitated. Others have
higher
SP
K
values hence not
precipitated.
II
2 2 2
Cu , Cd , Pb ,
2
Hg (II),
3 3
Bi , As ,
3 2
Sb , Sn
HS
2
gas in
presence of dil.
HCl
Sulphides
2 3
CuS , AsS etc.)
SP
K
values of sulphides are low
hence precipitated by low[ ]
2
S
ion. HCl
(with common
H ion)
decreases ionization of HS
2
which gives low[ ]
2
S. Hence II
group is precipitated. Others
with higher
SP
K values not
precipitated.
III
3 3 3
Al , Cr , Fe
NH OH
4
in
presence of
NH Cl
4
Hydroxide,
3
Al ( OH )
etc.
SP
K values of
3
Al ( OH ) etc. are
low. NH Cl
4
(with common
4
NH
ion) decreases ionization of
NH OH
4
giving low[ ]
OH. Hence
group III is precipitated.
IV
2 2 2 2
Zn , Ni , Mn , Co
HS
2
in
ammonical
medium
Sulphides ( ZnS
etc.)
SP
K values of sulphides of
group IV are high hence
precipitation takes place in
higher [ ]
2
S. Basic medium
increases ionization of HS
2
increasing [ ]
2
S hence
precipitation of group IV.
V
2 2 2
Ca , Ba , Sr
NH CO NHCl
4 2 3 4
Carbonates (
3
CaCO
etc.)
SP
K values of carbonate are less
than that of group VI ( )
2
Mg
hence precipitation before
2
Mg.
VI
Mg ,( Na , K
2
also
included)
4 2 4
NH OH NaHPO
(only for
2
Mg )
White ppt.
4
MgHPO
(Zero)
4
NH
- – Tested independently from original
solution.
Chemical reactions involved in the tests of basic
radicals
Group I : When dil. HCl is added to original
solution, insoluble chlorides of lead, silver mercurous
mercury are precipitated.
3 2 2 3
Pb ( NH ) 2 HCl PbCl 2 HNO ;
3 3
AgNO HCl AgCl HNO
3 2 2 3
Hg ( NO ) 2 HCl HgCl 2 HNO
Pb
2+
(lead)
(i)
2
PbCl is soluble in hot water and on cooling
white crystals are again formed.
(ii) The solution of
2
PbCl gives a yellow
precipitate with potassium chromate solution which is
insoluble in acetic acid but soluble in sodium
hydroxide.
PbCl KCrO PbCrO 2 KCl
yellow ppt.
2 2 4 4
PbCrO NaOH NaPbO NaCrO HO
4 2 2 2 4 2
4 2
(iii) The solution of
2
PbCl forms a yellow
precipitate with potassium iodide solution.
PbCl 2 KI PbI 2 KCl
Yellow ppt.
2 2
(iv) White precipitate of lead sulphate is formed
with dilute. 2 4
HSO The precipitate is soluble in
ammonium acetate, PbCl HSO PbSO 2 HCl 2 2 4 4
4 3 4 3 2 42 4
PbSO 2 CHCOONH Pb ( CHCOO ) ( NH ) SO
Ag
+
(silver)
(i) AgCl dissolves in ammonium hydroxide,
chloride
Diammine silver(I)
4 32 2
AgCl 2 NHOH Ag ( NH ) Cl 2 HO
(ii) On adding dilute
3
HNO to the above solution,
white precipitate is again obtained
Whiteppt.
( ) 2 2
3 2 3 4 3
Ag NH Cl HNO AgCl NH NO
(iii) On adding KI to the complex solution, yellow
precipitate is obtained.
3 2 3
Ag ( NH ) Cl KI AgI KCl 2 NH
Hg
2
2
(mercurous)
(i)
2 2
HgCl turns black with NH OH
4
Hg Cl NHOH Hg HgNH Cl NHCl HO
4 2
Black
2 2 4 2
(ii) The black residue dissolves in aqua-regia
forming mercuric chloride.
3 HCl HNO NOCl 2 HO 2 Cl
3 2
2 2 2
2 Hg ( NH ) Cl 6 Cl 2 HgCl 4 HCl N
2
Hg 2 Cl HgCl
(iii) The solution of
2
HgCl forms white or slate-
coloured precipitate with stannous chloride.
4
white ppt.
2 2 2 2
2 HgCl SnCl HgCl SnCl
4
Greyppt.
2 2 2
Hg Cl SnCl 2 Hg SnCl
(iv) The solution of
2
HgCl with copper turning
forms a grey deposit.
NH AsO MoO NHNO HO
3 4 3 2
Yellow ppt.
4 3 4
Sn
2+
or Sn
4+
(tin) : Solution of sulphide in
concentrated HCl is reduced with iron fillings or
granulated zinc.
White ppt.
2 4 2
SnS 4 HCl SnCl 2 HS
4
Grey
4 2
SnCl Fe SnCl FeCl
2
HgCl solution is added to above solution which
gives first a white precipitate that turns to grey.
Whiteppt.
2 2 2 4
HgCl SnCl HgCl SnCl
Grey
2
2 2 2 4
Hg Cl SnCl Hg SnCl
Sb
2+
(antimony) : Filtrate of sulphide in
concentrated HCl is divided into two parts.
Part I : On dilution with excess of water, a white
precipitate of antimony oxychloride is obtained.
Whiteppt.
3 2
SbCl HO SbOCl 2 HCl
Part II : HS
2
is circulated. Orange precipitate is
formed, 2 SbCl 3 HS SbS 6 HCl
Orange ppt.
3 2 2 3
Group III : Hydroxides are precipitated on
addition of excess of ammonium hydroxide in presence
of ammonium chloride.
AlCl NHOH AlOH NHCl
4
Gelatinous ppt.
3 4 3
CrCl NHOH CrOH NHCl
4
Green ppt.
3 4 3
FeCl NHOH FeOH NHCl
4
Brownish redppt.
3 4 3
Fe
3+
(iron) : The brownish red precipitate
dissolves in dilute HCl. The solution is divided into two
parts.
Part I : [ ( )]
4 6
K FeCN solution is added which forms
deep blue solution or precipitate.
Fe OH HCl FeCl HO
3 3 2
4 FeCl 3 K [ Fe ( CN )] Fe [ Fe ( CN )] 12 KCl
Prussian blue
3 4 6 4 63
Part II : Addition of potassium thiocyanate
solution gives a blood red colouration.
FeCl 3 KCNS Fe ( CNS ) 3 KCl
Blood redcolour
3 3
Cr
3+
(chromium) : The green precipitate is fused
with fusion mixture( ). 2 3 3
Na CO KNO The fused product
is extracted with water or the precipitate is heated
with NaOH
and bromine water.
3 2 3
2 Cr ( OH ) 3 KNO 2 NaCO
Na CrO KNO CO HO
2 4 2 2 2
or NaOH Br NaBrO NaBr HO
2 4 2
NaBrO NaBr [ O ]
2 ( ) 4 3 [ ]
3
Cr OH NaOH O NaCrO HO
4 2
The solution thus obtained contains sodium
chromate. The solution is acidified with acetic acid and
treated with lead acetate solution. A yellow precipitate
appears.
Na CrO PbCHCOO PbCrO CHCOONa
3
Yellow ppt.
2 4 3 2 4
Al
3+
(aluminium) : The gelatinous precipitate
dissolves in NaOH , Al OH NaOH NaAlO HO
2
Soluble
3 2
( ) 2
The solution is boiled with ammonium chloride
when
3
Al ( OH ) is again formed.
2 4 2 3 3
NaAlO NHCl HO Al ( OH ) NaCl NH
Group IV : On passing HS
2
through the filtrate of
the third group, sulphides of fourth group are
precipitated. NiS and CoS are black and insoluble in
concentrated HCl while MnS (buff coloured), ZnS
(colourless) are soluble in conc. HCl.
Zn
2+
(zinc) : The sulphide dissolves in HCl.
ZnS HCl ZnCl HS
2 2
When the solution is treated with NaOH , first a
white precipitate appears which dissolves in excess of
NaOH
ZnCl 2 NaOH Zn ( OH ) 2 NaCl
White ppt.
2 2
Zn OH NaOH NaZnO HO
2
(Soluble)
2 2 2
On passing HS
2
, white precipitate of zinc
sulphide is formed
Na ZnO HS ZnS 2 NaOH
White ppt.
2 2 2
Mn
2+
(manganese) : Manganese sulphide
dissolves in HCl MnS HCl MnCl HS
2 2
On heating the solution with NaOH and
2
Br -
water, manganese dissolve gets precipitated.
MnCl 2 NaOH Mn ( OH ) 2 NaCl
2 2
Mn OH O MnOHO
2 2 2
The precipitate is treated with excess of nitric
acid and
2
PbO or
3 4
PbO (red lead). The contents are
heated. The formation of permanganic acid imparts
pink colour to the supernatant liquid.
2 3 32
2 MnO 4 HNO 2 Mn ( NO )
2 2
2 H O O
3 2 3 4 3
2 Mn ( NO ) 5 PbO 26 HNO
Permanganic acid(pink)
4 32 2
2 HMnO 15 Pb (NO) 12 HO
The above test fails in presence of HCl.
Ni
2+
(nickel) and Co
2+
(cobalt)
The black precipitate is dissolved in aqua- regia.
NiS HCl HNO NiCl NO S HO
3 2 2
3 6 2 2 2 3 2
CoS HCl HNO CoCl NO S HO
3 2 2
The solution is evaporated to dryness and residue
extracted with dilute HCl. It is divided into three parts.
Part I : Add NHOH
4
(excess) and dimethyl
glyoxime. A rosy red precipitate appears, if nickel is
present,
NHOH
CH C NOH
CH C NOH
NiCl
4
3
3
2
NHCl HO
C CH
C CH
OH
N
N
O
Ni
O
N
N
OH
CH C
CH C
4 2
3
3
3
3
Part II : Add CHCOOH
3
in excess and.
2
KNO The
appearance of yellow precipite confirms the presence
of cobalt.
2 3 3 2
KNO CHCOOH CHCOOK HNO
CoCl 2 KNO Co ( NO ) 2 KCl
2 2 22
Co NO HNO CoNO NO HO
2 2 2 23 2
( ) 3 [ ( )]
2 3 2 3 26
Co NO KNO K CoNO
Part III : Solution containing either nickel or
cobalt is treated with
3
NaHCO
and bromine water.
Appearance of apple green colour is observed, the
solution is heated when black precipited is formed,
which shows the presence of nickel,
CoCl 2 NaHCO Co ( HCO ) 2 NaCl
2 3 32
3 2 3 4 33 2 2
Co ( HCO ) 4 NaHCO NaCo ( CO ) 3 HO 3 CO
Br HO 2 HBr O
2 2
2 Na Co ( CO ) HO O 2 NaCo ( CO ) 2 NaOH
(Green colouratio n)
sod. cobalticarbonate
4 33 2 3 33
2 3 3 2 2
NiCl 2 NaHCO NiCO 2 NaCl HO CO
2 [ ] 2
2
(Black)
3 2 3
NiCO O NiO CO
Group V : Ammonium carbonate precipitates V
group radicals in the form of carbonates are soluble in
acetic acid.
BaCO CHCOOH CHCOO Ba CO HO
3 3 3 2 2 2
SrCO CHCOOH CHCOO Sr CO HO
3 3 3 2 2 2
CaCO CHCOOH CHCOO Ca CO HO
3 3 3 2 2 2
Ba
2+
(barium) : Barium chromate is insoluble and
precipitated by the addition of potassium chromate
solution,
Ba CHCOO KCrO BaCrO CHCOOK
3 2 2 4 4 3
Sr
2+
(Strontium) : Strontium sulphate is
insoluble and precipitated by the addition of
ammonium sulphate solution,
3 4
White ppt.
3 2 42 4 4
Sr ( CHCOO ) ( NH ) SO SrSO 2 CHCOONH
Ca
2+
(calcium) : Calcium oxalate is insoluble and
precipitated by the addition of ammonium oxalate.
3 4
White ppt.
3 2 42 2 4 2 4
Ca ( CHCOO ) ( NH ) CO CaCO 2 CHCOONH
Group VI : In the filtrate of V group, some
quantity of ammonium oxalate is added as to remove
Ba , Ca and Sr completely from the solution. The clear
solution is concentrated and made alkaline with
4
NHOH Disodium hydrogen phosphate is now added, a
white precipitate is formed.
MgCl NaHPO NHOH
2 2 4 4
(Whiteppt.)
Megnesium ammoniumphosphate
4 4 2
Mg ( NH ) PO 2 NaCl HO
Zero group NH
4
(ammonium) : The substance
(salt or mixture) when heated with NaOH solution
evolves ammonia.
NH Cl NaOH NaCl NH HO
4 3 2
When a rod dipped in HCl is brought on the mouth
of the test tube, white fumes of ammonium chloride are
formed,
White fumes
3 4
NH HCl NHCl
used as an indicator in the titrations of strong acids
against strong and weak alkalies. As no indicator gives
correct results in the titrations of weak acids against
weak bases, such titrations are performed by some
other methods (physical methods).
(2) Oxidation reduction titrations : The
titrations based on oxidation-reduction reactions are
called redox titrations. The chemical reactions proceed
with transfer of electrons (simultaneous loss or gain of
electrons) among the reacting ions in aqueous
solutions. Sometimes these titrations are named after
the reagent used, as:
(i) Permanganate titrations : These are titrations
in which potassium permanganate is used as an
oxidising agent in acidic medium. The medium is
maintained by the use of dilute sulphuric acid.
Potassium permanganate acts as a self-indicator. The
potential equation, when potassium permanganate acts
as an oxidising agent, is :
2 3 2 3 5 [ ]
4 2 4 2 4 4 2
KMnO HSO KSO MnSO HO O
or
MnO H e Mn HO
2
2
4
8 5 4
Before the end point, the solution remains
colourless (when 4
KMnO solution is taken in burette)
but after the equivalence point only one extra drop of
4
KMnO solution imparts pink colour, i.e., appearance of
pink colour indicates the end point. Potassium
permanganate is used for the estimation of ferrous
salts, oxalic acid, oxalates, hydrogen peroxide, etc. The
solution of potassium permanganate is always first
standardised before its use.
(ii) Dichromate titrations : These are titrations
in which, potassium dichromate is used as an oxidising
agent in acidic medium. The medium is maintained
acidic by the use of dilute sulphuric acid. The potential
equation is
4 ( ) 4 3 [ ]
2 2 7 2 4 2 4 2 43 2
K CrO HSO KSO Cr SO HO O
or Cr O H e Cr HO
2
2 3
2 7
14 6 2 7
The solution of potassium dichromate can be
directly used for titrations. It is mainly used for the
estimation of ferrous salts and iodides. In the titration
of 2 2 7
KCrO versus ferrous salt either an external
indicator (potassium ferricyanide) or an internal
indicator (diphenyl amine) can be used.
(iii) Iodimetric and iodometric titrations : The
reduction of free iodine to iodide ions and oxidation of
iodide ions to free iodine occurs in these titrations.
I 2 e 2 I
2
(reduction)
2 I I 2 e
2
(oxidation)
These are divided into two types :
(a) Iodimetric titrations : These are the titrations
in which free iodine is used. As it is difficult to prepare
the solution of iodine (volatile and less soluble in
water), it is dissolved in potassium iodide solution.
Potassium tri-iodide
2 3
KI I KI
This solution is first standardised before use.
With the standard solution of
2
I. Substances such as
sulphite, thiosulphate, arsenite, etc., are estimated.
(b) Iodometric titrations : In iodometric titrations,
an oxidising agent is allowed to react in neutral
medium or in acidic medium, with excess of potassium
iodide to liberate free iodine.
KI oxidising agent
2
I
Free iodine is titrated against a standard reducing
agent usually with sodium thiosulphate. Halogens,
oxyhalogens, dichromates, cupric ion, peroxides, etc.,
can be estimated by this method.
2 22 3 2 4 6
I NaSO 2 NaI NaSO
4 22 2 4 2
2 CuSO 4 KI CuI 2 KSO I
2 2 7 2 4
KCrO 6 KI 7 HSO
2 43 2 4 2 2
Cr ( SO ) 4 KSO 7 HO 3 I
In iodimetric and iodometric titrations, starch
solution is used as an indicator. Starch solution gives
blue or violet colour with free iodine. At the end point
the blue or violet colour disappears when iodine is
completely changed to iodide.
(3) Precipitation titrations : The titrations which
are based on the formation of insoluble precipitates,
when the solutions of two reacting substances are
brought in contact with each other, are called
precipitation titrations. For example, when a solution
of silver nitrate is added to a solution of sodium
chloride or a solution of ammonium thiocyanate, a
white precipitate of silver chloride or silver
thiocyanate is formed.
3 3
AgNO NaCl AgCl NaNO
3 4 4 3
AgNO NHCNS AgCNS NHNO
Such titrations involving silver nitrate are called
argentometric titrations.
(4) Complexometric titrations : A titration, in
which an undissociated complex is formed at the
equivalence point, is called complexometric titration.
These titrations are superior to precipitation titrations
as there is no error due to co-precipitation.
2
2
Hg 2 SCN Hg ( SCN )
2 [ ( )]
2
Ag CN AgCN
EDTA (ethylenediamine tetra-acetic acid) is a
useful reagent which forms complexes with metals. In
the form of disodium salt, it is used to estimate
2
Ca
and
2
Mg ions in presence of eriochrome black- T as an
indicator.
Equivalent masses of acids and bases :
Equivalent masses of some acids and bases are given in
the following table
Table : 21.
Acid Basicity Mol. Mass Eq. Mass
HCl 1 36.
1
- 5
HNO
3
1
63
H
2
SO
4
2
98
CH 3 COOH 1 60
1
60
H
2
C
2
O
4
. 2 H
2
O 2 126
2
126
H
3
PO
4
3
98
H 3 PO 3 2 82
2
82
H
3
PO
2
1
66
Table : 21.
Alkali Acidity Mol. Mass Eq. Mass
NaOH 1 40
1
40
KOH 1 56
1
56
Ca(OH) 2
2
74
NH 4 OH 1 35
1
35
Calculations of Volumetric analysis
The following points should be kept in mind while
making calculations of volumetric exercises.
(i) 1 g equivalent mass of a substance reacts
completely with 1 g equivalent mass of any other
substance. 1 g equivalent mass of a substance means
equivalent mass of the substance in grams. For
example,
1 g equivalent mass of NaOH 40 g of NaOH
1 g equivalent mass of H SO 49 g
2 4
of
2 4
HSO
1 g equivalent mass of
4
KMnO
in acidic medium
31. 6 g of
4
KMnO
1 g equivalent mass of hydrated oxalic acid
63 g of hydrated oxalic acid
Note : Equivalent mass is a variable quantity and
depends on the reaction in which the substance takes
part. The nature of the reaction should be known
before writing the gram equivalent mass of the
substance. For example in the reactions.
2 NaCl 2 HSO 2 NaHSO 2 HCl
2 4 4
…..(i)
2 NaCl HSO NaSO 2 HCl
2 4 2 4
…..(ii)
The value of g
equivalent mass of
2 4
HSO
in
reaction (i) is 98 g and in reaction (ii) 49 g.
(ii) Number of g equivalents
Equivalentmassof thesubstance
Massof the substancein g
Number of g moles
M olecularmassof thesubstance
M ass of thesubstancein g
- 4
Volumeinlitresof thesubstanceatN.T.P.
(only for
gases)
Number of milli-equivalent
Equivalentmass
Mass in 1000
g
Number of milli-moles
M olecularmass
M ass in 1000
g
(iii) Molarity
No.oflitresof thesolution
No.ofmolesof thesolute
m V
w
Molarity molecular mass = strength of the
solution ( g / L )No. of moles of the solute = Molarity
No. of litres of solution Mass of the solute in g ( w )
molarity No. of litres of solution mol. mass of
solute
Normality
No.oflitresof thesolution
No. of g equivalentof thesolute
E V
w
Normality equivalent mass = strength of the
solution ( g/L )
No. of equivalents of the solute = Normality
No.
of litres of solution
Mass of the solute in g ( w ) Normality No. of
litres of solution Eq. mass of the solute
Molarity
Normality
Equivalentmass
Molecular mass
n
Normality n Molarity
(iv) Normality equation : When solutions A and
B react completely.
A A B B
N V N V
Normality of A
volume of A
Normality of B
volume of B
or
A B
V
B
B
V
A
A
Eq.mass
Strength
Eq.mass
Strength
Eq.wt.ofmetaloxide
Eq.wt.ofmetalhydroxide
wt,ofmetaloxide
Wt. ofmetalhydroxide
2
Eq.wt.ofmetal Eq.wt of
Eq.wtofmetal Eq.wtof
O
OH
