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Chemistry Salt Analysis Scheme

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this the scheme for analysing a salt
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Chemistry Practical
Qualitative Analysis Scheme


There are two types of radicals in a salt which we have to analyze.
1. Anions: These are also known as acid radicals. These have negative charge on
them.
2. Cations: These are called basic radicals. These have positive charge on them.


Analysis of Anions


Group I
Dil. SULPHURIC ACID Group
It contains CO 2-
2-
-
3 , S2-, SO3 , and NO2 .
All these radicals evolve a gas with dil. H2SO4.
In the salt/mixture, add dil. H2SO4.
If there is effervescence, it is CO 2-
3 (Carbonate).
If there is a smell of burning Sulphur, it is SO 2-
3
(Sulphite).
If there is a smell of rotten egg, it is S2- (Sulphide).
If there are brown fumes evolving, it is NO -
2 (Nitrite).






Test for Carbonate (CO 2-
3 )

Preliminary Test: To the mixture, add dil. H2SO4. Brisk effervescence due to evolution of
CO
2-
2 gas indicates the presence of CO3 .

Confirmatory Test: Pass the evolved CO2 gas through lime water. If lime water turns milky
due to formation of CaCO
2-
3 indicates the presence of CO3
radical.
To the water extract of the salt, add few drops of MgSO
2-
4 solution, white ppt. confirms CO3 .
Caco3 + 2HCl → CaCl2 + CO2 + H2O
Ca(OH)2 + CO2 → CaCO3 + H2O


Test for Sulphide (S2-)

Preliminary Test: To the mixture, add dil. H2SO4. If there is a smell of rotten eggs (H2S
gas), it may be Sulphide S2-. Pass this gas through lead acetate paper. The paper will turn
black (due to formation of Lead Sulphide (PbS)).

Confirmatory Test: To 1 ml of Na2CO3/H2Oextract, add dil. Acetic acid and then a few
drops of lead acetate solution. Black ppt. confirms Sulphide (S2-).
To 1 ml of Na2CO3 extract, add alkaline solution of Sodium nitroprusside
[Na4{Fe(CN)5NOS}]. Purple or violet coloration appeared confirms Sulphide S2-.
Na2S + Pb(CH3COO)2 → PbS + 2CH3COONa
Na2S + Na2[Fe(CN)5NO] → Na4[Fe(CN)5NOS]


Test for Sulphite (SO 2-
3 )

Preliminary Test:
To the mixture, add dil. H2SO4. Gas with smell of burning Sulphur
evolves (SO2 gas). Pass the gas through dichromate paper, it will turn green.


Confirmatory Test: To 1 ml of Na2CO3/ H2O extract, add BaCl2 solution. White ppt. of
BaSO
2-
3 indicates SO3 . Dissolve this ppt. in dil. HCl (excess) and divide the solution in two
parts:-
To the first part, add KMnO4 solution, it will decolorize.
To the second part, add Bromine water, the brown colour of the Bromine water will
discharge.
Na2SO3 + BaCl2 → BaSO3 (ppt) + 2NaCl
(White)
Na2SO3 + H2SO4 → Na2SO4 + H2O + SO2
K2Cr2O7 + 4H2SO4 → K2SO4 + Cr2(SO4)3 + H2O + 3[O]


Test for Nitrite (NO -
2 )

Preliminary Test: To the mixture, add dil. H2SO4. If there are brown fumes of gas evolving
which turn starch iodide paper blue, it may be NO -
2 .

Confirmatory Test: To 1 ml of Na2CO3 extract, add excess of dil. Acetic acid or dil. H2SO4.
Boil the solution to expel CO2 gas. Or take water extarct add a pinch of solid KI and 1ml of
freshly prepared starch solution. Deep blue colouration confirms NO -
2 .

To aq. Solution add dilute acetic acid and ferrous sulphate solution. A black or dark brown
precipitate indicates nitrite.

To aq. Solution add a few drops of diphenyl amine. Deep blue colouration indicates nitrite.
2KI + 2H2SO4 + 2HNO3 → 2KHSO4 + I2 + 2NO + 2H2O
I2 Turns Starch paper Blue.





Group II
Conc. SULPHURIC ACID Group
It contains Cl-, Br-, NO -
3 , I-, (COO-)2 and CH3COO-.
All these tests do not give any test with dil. H2SO4.


Test for Chlorides (Cl-)

Preliminary Test: To the mixture, add conc. H2SO4. A colourless pungent gas (HCl) which
produces white fumes when blown across the mouth of the test tube indicates the presence of
Cl- anion. If we bring a glass rod dipped in NH3 solution near the mouth of the test tube,
dense white fumes arte formed.

Confirmatory Test: To 1 ml of Na2CO3 extract, add dil. HNO3 till effervescence due to
evolution of CO2 gas ceases, add some more acid and then 1 ml of AgNO3 solution. White
ppt. which is insoluble in HNO3 but soluble in NH4OH confirms Cl-.

Chromyl Chloride Test: Take the mixture in a test tube and add solid K2Cr2O7 and heat it
with conc. H2SO4. Pass the evolved gas (CrO2CL2 - Chromyl Chloride) through NaOH
solution. The solution will turn yellow due to formation of Na2CrO4. Add acetic acid and lead
acetate to this yellow solution. A yellow ppt. of PbCrO4 confirms the presence of Cl- anion.
NaCl + AgNO3 → AgCl + NaNO3
(White ppt.)
AgCl + 2NH4OH → [Ag(NH3)2]Cl + 2H2O
Chromyl Chloride Test
4NaCl + K2Cr2O7 + 3H2SO4 → 2Na2SO4 + K2SO4 + 2CrO2Cl2 +
3H2O
CrO2Cl2 + 4NaOH → Na2CrO4 + 2H2O + 2NaCl
Na2CrO4 + Pb(CH3COO)2 → PbCrO4 + 2CH3COONa
(Yellow ppt.)

Test for Bromides (Br-)

Preliminary Test: To the mixture, add conc. H2SO4. Reddish brown gas (Br2 gas) evolves
which intensifies on addition of MnO2 to it.

Confirmatory Test: Take 1 ml of Na2CO3 extract and add dil. HNO3 followed by 1 ml of
AgNO3. Formation of yellow ppt. which is sparingly soluble in conc. NH4OH confirms Br-.

To 1 ml of NA2CO3 extract, add 1 ml of carbon tetrachloride CCl4 solution followed by conc.
HNO3 drop by drop. An orange coloured layer on CCL4 confirms Br- anion.
KBr + AgNO3 → KNO3 + AgBr
(Pale Yellow ppt.)
2KI + MnO2 + 3H2SO4 → 2KHSO4 + MnSO4 + 2H2O + I2


Test for Iodide (I-)

Preliminary Test: To the mixture, add conc. H2SO4. Violet vapours of Iodine (I2) which
intensifies on addition of MnO2 and if a starch paper is brought near the mouth of the test
tube, it will turn blue.

Confirmatory Test: To 1 ml of Na2CO3 extract, add dil. HNO3 and then AgNO3. Formation
of dark yellow ppt. confirms I-. These will be insoluble in HNO3 and NH4OH.

To 1 ml of Na2CO3 extract, add 1 ml of CCl4 solution. Now add conc. HNO3 to this solution
drop wise. A violet coloured layer in CCl4 confirms I-.
KI + AgNO3 → KNO3 +AgI
(Yellow ppt.)
2KI + MnO2 + 3H2SO4 →2KHSO4 + MnSO4 + 2H2O + I2




Test for Nitrate (NO -
3 )

Preliminary Test: To the mixture, add conc. H2SO4, brown gas (NO2) which intensifies due
to more NO2 formation on addition of copper turnings to the test tube indicates NO -
3 .

Confirmatory Test (Brown Ring Test): To 1 ml of water extract, add freshly prepared
FeSO4 solution. Pour conc. H2SO4 along the side of the test tube. A brown ring forms at the
junction of the two solutions.
To 1 ml of water extract, pour diphenyl-amine reagent (very carefully. Add 1 or 2 drops
while performing the test keeping it away from your face).
A blue ring will be formed at the junction of the two solutions.
2KNO3 + H2SO4 → K2SO4 + 2HNO3
Ring Test
KNO3 + H2SO4 → KHSO4 + HNO3
6FeSO4 + 3H2SO4 + 2HNO3 → 3Fe2(So4)3 + 4H2O + 2NO
FeSO4 + NO + 5H2O → [Fe(NO)(H2O)5]SO4



Test for Acetate (CH3COO-)

Preliminary Test:
Conc. H2SO4 when added to the salt gives brisk effervescence due to
evolution of CO2 with vinegar like smell due to the formation of CH3COOH.

Confirmatory Test: To 1 ml of water extract, add freshly prepared neutral FeCl3 solution.
Blood red colouration confirms the presence of acetate.

On the palm of your hand, take the salt, add oxalic acid (a pinch) to it and a few drops of
water, and rub it. Vinegar like smell confirms acetate.
(COOH)2 + 2CH3COONa → (COONa)2 + 2CH3COOH
Ferric Chloride Test
3CH3COONa + FeCl3 → Fe(CH3COO)2 + 3 NaCl

Fe(CH3COO)3 + 2H2O → Fe(CH3COO)(OH)2 + 2CH3COOH
(Reddish Brown ppt.)


Test for Oxalate (C
2-
2O4 )

Preliminary Test: On adding conc. H2SO4, there will be brisk effervescence due to evolution
of CO2 gas.

Confirmatory Test: To 1 ml of Na2CO3 extract, add dil. HNO3 (excess). Boil and add
NH4OH in excess. Boil to expel NH3. Cool and add equal volume of CaCl2 solution. White
ppt. of calcium oxalate will be formed. Then add dil. H2SO4 and heat it. Then add 3-4 drops
of KMnO4 solution. Pink colour of KMnO4 will be discharged. It confirms oxalate.
(NH4)2C2O4 + CaCl2 → CaC2O4 + 2NH4Cl
(White ppt.)


Independent Group
It contains SO 2-
3-
4 , PO4 .


Test for Sulphate (SO 2-
4 )

Preliminary Test:
To 1 ml of Na2CO3 extract, add dil. HCl and BaCl2 solution. White ppt.
which is insoluble in HNO
2-
3 confirms SO4 .

Confirmatory Test: To 1-2 ml of Na2CO3 extract, add dil. CH3COOH. Boil it and then add 1
ml of lead acetate solution. White ppt. which is soluble in excess of hot ammonium acetate
solution confirms sulphate.


Na2SO4 + BaCl2 → BaSO4 + 2NaCl
(White ppt.)
Lead Acetate Test
Na

2SO4 + Pb(CH3COO)2
PbSO4 + 2CH3COONa


Test for Phosphate (PO 3-
4 )

Ammonium Molybedate Test: To 2- 3 ml of NA2CO3 extract, add dil. HNO3 in excess.
Then add 1 ml of conc. HNO3 and a pinch of solid ammonium molybedate into it. Yellow
ppt. of ammonium phosphomolybedate confirms PO 3-
4
in the mixture.
K3PO4 + 3(NH4)2MoO4 → 2(NH4)3PO4 + 3K2MoO4







Cation Analysis


ZERO GROUP
No Specific Group Reagent.

NH +
4 (NH3)











(Pungent Gas)

Ist GROUP

Dil. HCl




Pb2+ (PbCl2)











(White ppt.)


IInd GROUP
H2S Gas In Presence Of Dil. HCl
Cu2+ & Cd2+











(CuS Black ppt)











(CdS Yellow ppt)

IIIrd GROUP

NH4OH In Presence Of NH4Cl
Fe3+ & Al3+











Fe(OH)3 Brown











Al(OH)3 White

IVth GROUP

H2S Gas In Presence Of NH4Cl
Ni2+, Co2+,




And NH4OH




Zn2+, Mn2+











(NiS, CoS, ZnS,











MnS)

Vth GROUP

NH4Cl, NH4OH And (NH4)2CO3
Ca2+, Sr2+, Ba2+











(CaCO3, SrCO3,











BaCO3 White)

VIth GROUP

No Specific Group Reagent.

Mg2+ (MgCl2)











(White ppt)


Analysis of Zero Group (NH +
4 )

Preliminary Test:
To the mixture of, add NaOH solution. Evolution of NH3 gas indicates
NH +
4 radical. Then gently warm the solution and bring a glass rod dipped in HCl near the
mouth of the test tube. White dense fumes appear at the mouth of the test tube.

NH +
4 + OH- → NH3 + H2O
NH3 + HCl → NH4Cl

Confirmatory Test: To the salt solution, add NaOH solution. Gently warm it and then add
Nesseler’s reagent. Reddish brown ppt. confirms NH +
4 .


2K
O → NH
2HgI4 + 4NH3 + H2
2.HgO.HgI + 4KI + 3NH4I


Analysis of Group I (Pb2+)

Preliminary Test: Prepare O.S. (It can be prepared by adding H2O/ dil. HCl/ conc. HCl) Add
dil. HCl to O.S. If there is a white ppt. it indicates presence of Pb2+, which is precipitated as
PbCl2.

Pb2+ (aq) + 2 Cl-(aq) → PbCl2 (s)

Confirmatory Test: Dissolve the ppt. in hot water and divide the solution in 2 parts:-
To the 1st part, add potassium chromate solution. A yellow ppt. soluble in NaOH
confirms Pb2+.

Pb2+ (aq) + CrO 2-
4 (aq) → PbCrO4 (s) Yellow

To the 2nd part, add KI solution. Orange yellow ppt. is obtained.

Pb2+ (aq) + 2I- (aq)→ PbI2 (s) Orange


Analysis of Group II (Cu2+, Cd2+, Pb2+, Hg2+, As3+)

Take filtrate of Group I. (If 1st group is absent, directly take O.S.). Add dil. HCl to it. Warm it
and then pass H2S gas through it. If there is a black ppt., it is Cu2+, if the ppt. is yellow, it is
Cd2+.

Analysis of Cu2+: Dissolve the black ppt. in 50% conc. HNO3. Heat it and divide the
solution in two parts.
To the 1st part, add NH4OH solution in excess. Deep blue colouration confirms Cu2+.

3CuS + 8HNO3 (aq) → 3Cu(NO3)2 + 2NO + 4H2O + 3S
(Black ppt.)

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