Experiment : 5

Aim: To analyze inorganic salt for acid radicals.

CATIONS: Pb2+,Hg2+,Cu2+,Cd2+, Ag+, Fe2+, Fe3+, Al3+, Zn2+, Mn2+, Co2+, Sr2+, Ba2+,Mg2+, NH4+

ANIONS: CO32-, S2-, SO32-, SO42-, NO2-, NO3-, Cl-, Br-, PO43-, CH3COO-

Preliminary Tests

1. Note the state (amorphous or crystalline) and color of salt.

2. Test the solubility of the salt in the following solutions:

i. Water (cold and hot)

ii. Dilute HCl (cold and hot)

iii. Dilute HNO3(cold and hot)

____________________________________________________________________________________________________

IDENTIFICATION OF ACID RADICALS (ANIONS)

This part is the classified into three groups:

FIRST GROUP OF ACID RADICALS

The acid radicals involved in this group are carbonate (CO32-), Sulphide (S2-), Sulphite(SO32-),
Thiosulphate (S2O32-) and nitrite(NO2-). The group reagent is dilute H2SO4acid.

EXPERIMENT OBSERVATION INFERENCE

Salt + dil. H2SO4 effervescence or evolution of gases 1stgroup of acid
radicals is present.
(a) Colorless, odorless gas turns lime water milky The acid radical may
be CO32-or HCO3-
(b) Colorless with rotten eggs smell and turnslead Sulphide(S2-)
acetate paper black. confirmed.
(c) Colorless gas with suffocating smell. Heat and SO32- confirmed.
pass the gas through acidified K2Cr2O7solution. The
solution turns green
(d) Colorless gas followed by brown gas and it turns NO2- confirmed.
starch iodide paper blue
(e) Colorless gas with the smell of vinegar. The acid radical may
be CH3COO-
Chemical reactions involved in dilute H2SO4 acid test:

Test for Carbonate ion (CO3-2):

Na2CO3 + H2SO4→Na2SO4 + H2O +CO2↑

Ca(OH)2 + CO2→CaCO3 + H2O

Test for Sulphide ion [S-2 ]

Na2S + H2SO4 →Na2SO4 + H2S↑

(CH3COO)2Pb + H2S →PbS↓ + 2CH3COONa
black

Test for Sulphite ion [SO23–]

K2Cr2O7 + H2SO4 + 3SO2→K2SO4 + Cr2(SO4)3 + H2O

Chromium(III) sulphate (green)

Test for Nitrite ion [NO2- ]

NO2– + CH3COOH →HNO2 + CH3COO–

2HNO2 + 2KI + 2CH3COOH →2CH3COOK + 2H2O + 2NO + I2
I2 + Starch →Blue complex

Test for Acetate ion [CH3COO–]

2 CH3COONa + H2SO4→Na2SO4 + 2 CH3COOH

CH3COOH + C2H5OH →CH3COOC2H5 + H2O
Ethyl acetate (fruity odour)

Tests to distinguish between CO32-and HCO3-

EXPERIMENT OBSERVATION INFERENCE

Salt + water, boil and pass the gasthrough (a) Lime water does not turn CO32- confirmed
lime water milky.
(b) Lime water turns milky. HCO3- confirmed.

*Like CO2 sulphur dioxide also turns lime water milky. But CO2 is odourless gas and SO2 has a characteristic smell.
 Confirmation test for Acetate

EXPERIMENT OBSERVATION INFERENCE

Salt solution + Neutral FeCl3 sol. Appearance of blood red Acetate confirmed
colour.

6 CH3COO– + 3Fe3+ + 2H2O →[Fe3(OH)2(CH3COO)6]+ + 2H+

[Fe3(OH)2(CH3COO)6]+ + 4H2O →3[Fe(OH)2(CH3COO)] + 3CH3COOH + H+
Iron(III)dihydroxyacetate (Brown-red ppt)

SECOND GROUP OF ACID RADICALS

The acid radicals involved in this group are Cl-, Br-and NO3-. The group reagent is conc.
sulphuric acid (H2SO4).

EXPERIMENT OBSERVATION INFERENCE

Salt +Conc. H2SO4 and Effervescence with colorless or colored gases 2ndgroup Acid
heatif necessary radical is present
(a) Colorless gas with a pungent smell and Acid radical may
gives dense white fumes when a glass rod be Cl-
dipped in ammonium hydroxide (NH4OH) is
exposed.
(b) Brown gas Acid radical may
be Br-
(c)Violet vapours Acid radical may
be I-
(d) Light brown gas and brown gas with Acid radical may
pieces of copper turnings and the solution be NO3-
turns blue in the test tube.

Confirmation test for Chloride

EXPERIMENT OBSERVATION INFERENCE

(a) Chromyl Chloride test: Salt + few Red vapours are
K2Cr2O7 crystals + conc. H2SO4 and heat. obtained.
Chloride
The solution turns confirmed
yellow.
(b) Pass the vapors through the test tube
which contains NaOH solution. Yellow ppt. is formed
 (c) To this yellow solution, add
diluteCH3COOH and lead acetate solution.

Silver Nitrate test: Salt solution +AgNO3 solution + White ppt. is formed Chloride
dilute HNO3 which is soluble in confirmed.
NH4OH.

Test for Chloride ion [Cl ]

–

Chromyl – Chloride test:

4NaCl + K2Cr2O7 + 6H2SO4→2KHSO4 + 2CrO2Cl2 + 4NaHSO4 + 3H2O

(Chromylchloride)
CrO2Cl2 + 4NaOH →Na2CrO4 + 2NaCl + 2H2O
(CH3COO)2Pb + Na2CrO4→PbCrO4↓ + 2CH3COONa
Lead chromate
(Yellow precipitate)
(a) Silver Nitrate test:
NaCl + AgNO3→NaNO3+ AgCl↓
Silver chloride (White precipitate)

Confirmation test for Bromide

EXPERIMENT OBSERVATION INFERENCE

(b)Silver Nitrate test: Salt solution + AgNO3 A light yellow ppt. Bromide confirmed.
solution + dilute HNO3 slightly soluble in
NH4OH is obtained

Test for Bromide ion (Br–)

(a) NaBr + AgNO3→NaNO3 + AgBr↓

(Silver bromide) pale yellow ppt

Confirmation test for Iodide

EXPERIMENT OBSERVATION INFERENCE

Silver Nitrate test: Salt solution + AgNO3solution + A yellow ppt. Iodide confirmed.
dilute HNO3 insoluble in NH4OH

Test for Iodide ion (I–)

NaI + AgNO3→AgI ↓ + NaNO3
silver iodide(Yellow precipitate)
 Confirmation test for Nitrate

EXPERIMENT OBSERVATION INFERENCE

Brown ring test: Strong solution of the substance + A brown ring is Nitrate confirmed
2-3 drops of conc. H2SO4, and cool. Add freshly formed at the
prepared FeSO4 solution along the sides of the test junction of
tube. twoliquids.

Test for Nitrate ion [NO3- ]

NaNO3 + H2SO4→NaHSO4 + HNO3

6 FeSO4 + 3H2SO4 + 2HNO3→3Fe2 (SO4)3 + 4H2O + 2NO
FeSO4 + NO + 5 H2O →[Fe(NO)(H2O)5]SO4
Nitroso ferrous sulphate(Brown)

THIRD GROUP OF ACID RADICALS

The basic radicals involved in this group are SO42-and PO43-.

EXPERIMENT OBSERVATION INFERENCE

Test for sulphate: Aqueous solution of A white ppt. insoluble Sulphate (SO42-) confirmed
salt + dil. HCl + BaCl2solution. in diluteHCl is obtained

Test of Sulphate ions [SO42–]

Na2SO4 + BaCl2→ BaSO4↓ + 2NaCl

Barium sulphate
(White precipitate)
 Experiment: 6

Aim: To analyze inorganic salt for basic radicals.

Basic radicals are classified into six groups. They are mentioned as below:

GROUP RADICALS GROUP REAGENTS

zero NH4+ none

I Pb2+ Dilute Hydrochloric acid (HCl)
II Pb2+, Cu2+, As3+ Dilute HCl + H2S gas.
III Al3+,Fe3+ NH4Cl (s) + NH4OH
IV Zn2+, Mn2+, Co2+, Ni2+ NH4Cl (s) + NH4OH + H2S gas
V Ca2+, Sr2+, Ba2+ NH4Cl(s) + NH4OH + (NH4)2CO3
VI Mg2+ none

Wet Tests for Identification of Cations

The cations indicated by the preliminary tests given above are confirmed bysystematic analysis
given below.The first essential step is to prepare a clear and transparent solution of thesalt.
This is called original solution. It is prepared as follows:

Preparation of Original Solution (O.S.)

To prepare the original solution, following steps are followed one after the otherin a systematic
order. In case the salt does not dissolve in a particular solventeven on heating, try the next
solvent.

The following solvents are tried:

1. Take a little amount of the salt in a clean boiling tube and add a few mL of distilled water and
shake it. If the salt does not dissolved, heat the contentof the boiling tube till the salt
completely dissolves.
2. If the salt is insoluble in water as detailed above, take fresh salt in a cleanboiling tube and add
a few mL of dil.HCl to it. If the salt is insoluble incold, heat the boiling tube till the salt is
completely dissolved.
3. If the salt does not dissolve either in water or in dilute HCl even on heating,try to dissolve it
in a few mL of conc. HCl by heating.
4. If salt does not dissolve in conc. HCl, then dissolve it in dilute nitric acid.
5. If salt does not dissolve even in nitric acid then a mixture of conc. HCl andconc. HNO 3 in the
ratio 3:1 is tried. This mixture is called aqua-regia. A saltnot soluble in aqua-regia is
considered to be an insoluble salt

ZERO GROUP OF BASIC RADICALS

Test for NH4+ Radicals: This test is carried out before starting the analysis for the basic radicals.

EXPERIMENT OBSERVATION INFERENCEE

(a) Salt + NaOH solution and heat it. Colorless gas with a pungent smell NH4+may be
Expose a glass rod dipped in conc. HCl is obtained. Dense white fumes and present in the
to the gas and moist red litmus paper. moist red litmus paper turns blue salt
(b) Original solution + Nesseler’s Brown solution or ppt. obtained NH4+confirmed.
reagent.

(NH4)2SO4 + 2NaOH →Na2SO4 + 2NH3 + 2H2O

NH3 + HCl→NH4Cl

2K2HgI4 + NH3 + 3KOH →HgO.Hg(NH2)I + 7KI + 2H2O

Basic mercury (II)
amido-iodine(Brown precipitate)

FIRST GROUP OF BASIC RADICALS

The basic radicals of this group are Pb2+& Ag+. The group reagent is dilute HCl.

EXPERIMENT OBSERVATION INFERENCEE

(1) Original solution + Dilute HCl White ppt. is formed. May be Pb2+
Filter and add water to ppt. and
heat.
(a) ppt. dissolves in hot water. May be Pb2+

(2) Original solution + Potassium (a) A yellow ppt. is formed Pb2+ confirmed
Chromate
(3) Original solution + KI solution A yellow ppt. soluble in hot water, on Pb2+ confirmed
ppt. obtained + water and heat it cooling reappears as golden yellow.
PbCl2 + 2KI →PbI2 + 2KCl
Yellow precipitate

PbCl2 + K2CrO4→PbCrO4 + 2KCl

Lead chromate
(Yellow precipitate)
 SECOND GROUP OF BASIC RADICALS

The basic radicals of this group are May be Pb2+, Hg2+, Cu2+ & Cd2+.The group reagent is dilute
HCl+ H2S gas.

EXPERIMENT OBSERVATION INFERENCEE

Original solution + dilute A black ppt. is observed. Pb2+, As3+ and Cu2+may be
HCl+ H2S gas. present

The identification of Pb2+, As3+ and Cu2+ is as follows:

EXPERIMENT OBSERVATION INFERENCEE

(a) Original solution + Potassium A yellow ppt. is observed Pb2+ confirmed
Chromate

(b) Original solution + NH4OH A bluish white ppt. soluble in excess Cu2+may be
of NH4OH is observed which gives present
deep blue solution.
(c) Original solution + dil. acetic acid A Chocolate red ppt. is observed Cu2+ confirmed
+ Potassium ferrocyanide
solution

Test for Lead ion (Pb2+)

Pb2+ + CrO42–→PbCrO4
Lead chromate
Pb2+ + 2I–→PbI2
Lead iodide(Yellow precipitate)

Test for Copper ion (Cu2+)

2Cu2++ SO42-+2NH3+2H2O →Cu(OH)2.CuSO4+ 2NH3

Cu(OH)2.CuSO4 + 8NH3→2 [Cu(NH3)4]SO4 + 2OH– + SO42-
Tetraamminecopper (II)sulphate (Deep blue)

[Cu(NH3)4] SO4 + 4CH3COOH →CuSO4 + 4CH3COONH4

2CuSO4 + K4[Fe(CN)6] →Cu2[Fe(CN)6] ↓+ 2K2SO4
(Chocolate brown precipitate)
 THIRD GROUP OF BASIC RADICALS

The basic radicals of this group are Al3+and Fe3+.The group reagent is NH4Cl + NH4OH

EXPERIMENT OBSERVATION INFERENCE

(1) Original solution + (a) A white gelatinous ppt. is obtained May be Al3+
NH4Cl(s) + NH4OH in excess (c) A reddish brown ppt. is obtained May be Fe3+
(2) Original solution + NaOH (a) White gelatinous ppt. soluble in excess of The basic radical
solution NaOH is obtained which gives a colorless sol. is Al3+
(b) Dirty green ppt. insoluble in excess of The basic radical
NaOH is Fe2+
(c) Reddish brown ppt. insoluble in excess The basic radical
of NaOH is Fe3+
(3) Clear solution of 2(a) + The white gelatinous ppt. reappears Al3+ confirmed
solid NH4Cl and heat
(4) Original solution + (a) The pink colour of KMnO4is not Fe3+confirmed.
acidified KMnO4Solution discharged.
which is added drop wise.

Test for Aluminium ions (Al3+ )

AlCl3 + 3NaOH→Al(OH)3 ↓+ 3NaCl

Al(OH)3 + NaOH→NaAlO2 ↓+ 2H2O
White gelatinousprecipitate

FOURTH GROUP OF BASIC RADICALS

The basic radicals of this group are Zn2+, Mn2+, Co2+& Ni2+.The group reagent is NH4Cl +
NH4OHand H2S (g)

EXPERIMENT OBSERVATION INFERENCE

(1) Original solution + NH4Cl(s)+ (a) a white ppt. is obtained May be Zn2+,
NH4OH in excess + H2S(g) Mn2+or Co2+

(b) Buff or pale pink or flash May be Mn2+

colored ppt. soluble in dilute HCl is
obtained.
(2) Original solution + NaOH solution (a) The white ppt. is soluble in Zn2+ confirmed
 excess of NaOH giving a colorless
solution.
b)The white ppt. insoluble in Mn2+ confirmed
excess of NaOH but turns brown
(3)Dissolve the 1(a) in aqua-regia,
evaporate to dryness, add 1 ml of
distilled water and divide the resultant
product into two parts.

Part (1) + 1 ml amyl alcohol + 100 mg

solid NH4SCN & stir it. A blue colour in alcohol layer Co2+confirmed

Part (2) + 5 drops dimethyl glyoxime A pink ppt. Ni2+ confirmed

reagent + NH4OH.

Test for Zinc ion (Zn2+ )

ZnS + 2HCl →ZnCl2 + H2S

ZnCl2 + 2NaOH →Zn(OH)2 + 2NaCl
Zn(OH)2 + 2NaOH →Na2ZnO2 + 2H2O

Test for Manganese ion (Mn2+ )

MnS + 2HCl →MnCl2 + H2S

MnCl2 + 2NaOH →Mn(OH)2 + 2NaCl
(White precipitate)
Mn(OH)2 + [O] →MnO(OH)2
(Brown colour)

Test for Nickel ion (Ni2+)

3NiS + 2HNO3 + 6HCI →3NiCl2 + 2NO + 3S + 4H2O

Test for Cobalt ion (Co2+)

CoS + HNO3 + 3HCl →CoCl2 + NOCl + S + 2H2O

CoCl2 + 7KNO2 + 2CH3COOH →K3 [Co(NO2)6] + 2KCl + 2CH3COOK + NO + H2O
Potassium
hexanitritocobaltate(III)
(Yellow precipitate)
 FIFTH GROUP OF BASIC RADICALS

EXPERIMENT OBSERVATION INFERENCE

Original solution + Potassium Chromate A yellow ppt. Ba2+confirmed.
To O.S. add ammonium sulphate solution. Heat and scratch A White ppt. Sr2+confirmed
the sides of the test tube with a glass rod and cool.
To O.S. add ammonium oxalate solution and shake well. A white ppt Ca2+confirmed

Test for Barium ion (Ba2+ )

BaCO3 + 2CH3COOH →(CH3COO)2Ba + H2O + CO2

(CH3COO)2Ba + K2CrO4→BaCrO4 + 2CH3COOK
Barium chromate(yellow precipitate )

Test for Strontium ion (Sr2+ )

SrCO3 + 2CH3COOH →(CH3COO)2Sr + H2O + CO2

(CH3COO)2Sr + (NH4)2SO4→SrSO4 + 2CH3COONH4
Strontium
sulphate(White precipitate)

Test for Calcium ion (Ca2+ )

CaCO3 + 2CH3COOH →(CH3COO)2Ca + H2O + CO2

(CH3COO)2Ca + (NH4)2C2O4→(COO)2Ca + 2CH3COONH4
(White precipitate)

SIXTH GROUP OF BASIC RADICALS

EXPERIMENT OBSERVATION INFERENCE

Original solution + excess NH4OH + ammonium hydrogen A white ppt. Mg2+ confirmed.
phosphate

Test for Magnesium ion (Mg2+ )

Mg2+ + Na2HPO4→Mg(NH4)PO4 + NH4OH + 2Na+ + H2O

(White precipitate)

*Some times precipitate of magnesium ammonium phosphate appear s after some time. So
warm the solution and scratch the sides of test tube after adding sodium hydrogenPhosphate
solution.