Qualitative Analysis

Question 1

Test for Carbonate ion [CO3]2-

Answer 1

effervescence with the evolution of a colourless and odourless gas on
adding dil. H2SO4 to the solid salt. The gas turns lime water milky due to the formation of CaCO3.

Question 2

Test for Sulphide ion [S2–]

Answer 2

A piece of filter paper dipped in (CH3COO)2Pb solution turns black on exposure to the gas due to the formation of
PbS which is black in colour.

Question 3

Test for Sulphide ion [S2–]

Answer 3

Few drops of sodium nitroprusside solution in alkaline medium causes purple or violet colouration due to the formation of complex compound Na4[Fe(CN)5NOS]
confirms the presence of sulphide ion in the salt.

Question 4

Test for Sulphite ion [SO3]2-

Answer 4

On treatment with H2SO4 it produces SO2 gas.The gas turns potassium dichromate paper acidified with dil. H2SO4
,green [Cr]3+.

Question 5

Test for Sulphite ion [SO3]2-

Answer 5

produces a white precipitate of BaSO3 on addition of BaCl2 solution. precipitate on treatment with dilute HCl, dissolves. Evolved SO2 gas can be tested. It also decolourises acidified potassium permanganate
solution.

Question 6

Test for Nitrite ion [NO2]-

Answer 6

Addition of KI solution to
the salt solution followed by freshly prepared starch solution and
acidification with acetic acid produces blue colour.

Question 7

Test for Nitrite ion [NO2]-

Answer 7

Sulphanilic acid — 1-naphthylamine reagent test (Griss-Ilosvay test)
On adding sulphanilic acid and 1-naphthylamine reagent to the water
extract or acidified with acetic acid, a red azo-dye is formed.(Involves diazotisation)

Question 8

Test for Acetate ion [CH3COO]-

Answer 8

It gives a sweet smelling compound with ethanol.

Question 9

Test for Acetate ion [CH3COO]-

Answer 9

Acetate gives deep red colour on reaction with neutral ferric chloride
solution due to the formation of complex ion [Fe3(OH)2(CH3COO)6]+ which decomposes on
heating to give Iron (III) dihydroxyacetate [Fe(OH)2(CH3COO)] as brown red precipitate.

Question 10

Test for Chloride ion [Cl]-

Answer 10

Salt solution acidified with dilute HNO3 on addition of silver nitrate solution gives a curdy white precipitate soluble in NH4OH forming [Ag(NH3)2]Cl.

Question 11

Test for Chloride ion [Cl]-

Answer 11

Chromyl Chloride test: Salt is heated with solid acidified potassium dichromate to produce a gas CrO2Cl2. This gas is passed through NaOH. It reacts with (CH3COO)2Pb solution and gives a yellow precipitate of PbCrO4.

Question 12

Test for Chloride ion [Cl]-

Answer 12

Chromyl Chloride test: Salt is heated with solid acidified potassium dichromate to produce a gas CrO2Cl2.This gas is passed through NaOH. This mixture is acidified and treated with amyl alcohol and H2O2 to give a blue organic layer due to formation of CrO5.

Question 13

Test for Bromide ion [Br]-

Answer 13

Salt solution acidified with dilute HNO3 on addition of silver nitrate solution gives a pale yellow precipitate.

Question 14

Test for Bromide ion [Br]-

Answer 14

Salt is treated with CCl4 or CHCl3 and excess
of freshly prepared Cl- water dropwise. The appearance of an orange brown colouration in the
organic layer due to the dissolution of Br in it, confirms the presence of Br- ions.

Question 15

Test for Iodide ion I-

Answer 15

Salt is treated with CCl4 or CHCl3 and excess
of freshly prepared Cl- water dropwise. The appearance of an violet colouration in the
organic layer confirms the
presence of I- ions.

Question 16

Test for Iodide ion I-

Answer 16

Salt solution acidified with dilute HNO3 on addition of silver nitrate solution gives a yellow precipitate.

Question 17

Halogens + H2SO4

Answer 17

If on heating the salt with conc. H2SO4, coloured vapours with a pungent smell are evolved. Colour is intensified in presence of MnO2.

Question 18

Test for Nitrate ion [NO3]-

Answer 18

If on heating the salt with conc. H2SO4 with few copper turnings or
chips. Evolution of excess of brown fumes indicates
the presence of nitrate ions. The solution turns blue due to the formation
of copper sulphate.

Question 19

Test for Nitrate ion [NO3]-

Answer 19

Brown Ring Test: H2SO4 and freshly prepared FeSO4 solution along the sides
of the test tube is added dropwise so that it forms a layer on the top of the liquid. A dark brown ring is formed at the
junction of the two solutions due to the formation of [Fe(H2O)5(NO)]SO4.

Question 20

Test for Oxalate ion [C2O4]2-

Answer 20

Acidify with CH3COOH and add CaCl2 solution. A white precipitate of Ca(C2O4), insoluble in (NH4)2(C2O4) and H2C2O4 solution indicates the presence of oxalate ion.

Question 21

Test for Oxalate ion [C2O4]2-

Answer 21

Add dil. H2SO4 to it followed by dilute KMnO4 solution and warm. Pink colour of KMnO4 is disappears.

Question 22

Test of Sulphate ions [SO4]2-

Answer 22

Solution is acidified with
acetic acid on addition of barium chloride gives a white precipitate of
BaSO4 insoluble is all acids.

Question 23

Test of Sulphate ions [SO4]2-

Answer 23

Sulphate ions give white precipitate of lead sulphate when treated with lead acetate solution.

Question 24

Test for Phosphate ion [PO4]3-

Answer 24

Add conc. HNO3
and ammonium molybdate solution to the test solution containing phosphate ions and boil. A yellow colouration in solution or a canary yellow precipitate of ammonium-phosphomolybdate, (NH4)3[P (Mo3O10)4] is formed.

Question 25

Confirmatory Tests for NH4+ ion

Answer 25

It is treated with hydrochloric acid to give ammonium chloride, which is visible as dense white fume. On passing the gas through Nessler’s reagent K2HgI4, a brown colouration or a precipitate of **HgO.Hg(NH2)I** is formed.

Question 26

Group 1 ions

Answer 26

Ag+, Pb2+, Hg22+

Question 27

Confirmatory Tests of Pb2+ ions

Answer 27

On adding potassium iodide **(KI)** solution, a **yellow precipitate** of lead iodide is obtained

Question 28

Confirmatory Tests of Pb2+ ions

Answer 28

On addition of potassium chromate (**K2CrO4**) solution a **yellow precipitate** of lead chromate is obtained.

Question 29

Confirmatory Tests of Pb2+ ions

Answer 29

A white precipitate of lead sulphate (**PbSO4**) is formed on addition of alcohol followed by dil. **H2SO4.**

Question 30

Group 2 ions

Answer 30

Pb2+, Cu2+, As3+

Question 31

Group 1 reagent

Answer 31

HCl

Question 32

Group 2 reagent

Answer 32

H2S+HCl

Question 33

Confirmatory Tests of Cu2+ ions

Answer 33

CuS dissolves in nitric acid due to the formation of copper nitrate. On **heating, sulphur** is **oxidised** to sulphate and **copper sulphate** is formed and the solution turns **blue**. A small amount of **NH4OH** **precipitates basic copper sulphate** which is soluble in excess of ammonium hydroxide due to the formation of **tetraamminecopper (II)** complex.

Question 34

Confirmatory Tests of Cu2+ ions

Answer 34

The blue solution on acidification with acetic acid and then adding **potassium ferrocyanide** [K4Fe(CN)6] solution gives a **chocolate colouration** due to the formation of **Cu2[Fe(CN)6].**

Question 35

Confirmatory Tests of As3+ ions

Answer 35

If group- II precipitate dissolves in **yellow ammonium sulphide** and the colour of the solution is yellow, this indicates the presence of As3+ ions. **Ammonium thioarsenide** formed on dissolution of As2S3 decomposes with dil. HCl, and **a yellow precipitate** of arsenic (V) sulphide is formed which dissolves in concentrated nitric acid on heating due to the formation of arsenic acid. On adding **ammonium molybdate **solution to the reaction mixture and heating, a **canary yellow precipitate** is formed.

Question 36

Group 3 ions

Answer 36

Al3+, Fe3+

Question 37

Confirmatory test of Al3+

Answer 37

When the solution containing Al3+ is treated with NaOH, a white gelatinous precipitate of Al(OH)3 is formed which is soluble in excess of NaOH. In the second test when blue litmus is added to the solution, a red colouration is obtained. On addition of NH4OH solution drop by drop the solution becomes alkaline and Al(OH)3 is precipitated. Al(OH)3 adsorbs blue colour from the solution and forms insoluble adsorption complex named ‘lake’. Thus a blue mass floating in the colourless solution is obtained. The test is therefore called lake test.

Question 38

Confirmatory test for Fe3+

Answer 38

When the solution containing ferric chloride is treated with potassium ferrocyanide solution a blue precipitate is obtained. The colour of the precipitate is Prussian blue Fe4[Fe(CN)6]3+

Question 39

Confirmatory test for Fe3+

Answer 39

(SCN)- solution. The appearance of a blood red colouration confirms the presence of Fe3+ ions [Fe(SCN)]2+

Question 40

Group 4 cations

Answer 40

Mn2+, Ni2+, Co2+, Zn2+

Question 41

Test for Zinc ion (Zn2+)

Answer 41

On addition of NaOH solution it gives a white precipitate of zinc hydroxide

Question 42

Test for Zinc ion (Zn2+)

Answer 42

When potassium ferrocyanide K4Fe(CN)6 solution is added to the solution a white or a bluish white precipitate of zinc ferrocyanide appears.

Question 43

Test for Manganese ion (Mn2+)

Answer 43

On addition of NaOH solution in excess, a white precipitate of Mn(OH)2 is formed which turns brown due to atmospheric oxidation into hydrated manganese dioxide MnO(OH).

Question 44

Test for Nickel ion (Ni2+)

Answer 44

After treatment with aqua regia nickel-chloride is obtained. When dimethyl glyoxime is added and made alkaline, by adding NH4OH solution, a brilliant red precipitate is obtained.

Question 45

Test for Cobalt ion (Co2+)

Answer 45

Cobalt sulphide dissolves in aqua regia. When the aqueous solution of the residue obtained a is treated with a strong solution of KNO2 a yellow precipitate of the complex of cobalt named potassium hexanitritocobaltate (III) K3[Co(NO2)6]

Question 46

Group 5 cations

Answer 46

Ca2+,Ba2+, Sr2+

Question 47

Test for Barium ion (Ba2+)

Answer 47

K2CrO4 solution gives a yellow precipitate of BaCrO4 when the solution in acetic acid is treated with it.

Question 48

Test for Strontium ion (Sr2+)

Answer 48

group precipitate in acetic acid gives a white precipitate of SrSO4 with (NH4)2SO4 solution on heating

Question 49

Test for Calcium ion (Ca2+)

Answer 49

Solution of the fifth group precipitate in acetic acid gives a white precipitate CaC2O4 with (NH4)2C2O4 solution.

Question 50

Group 6 cations

Answer 50

Mg2+

Question 51

Test for Magnesium ion (Mg2+)

Answer 51

When treated with ammonium hydrogen phosphate (NH4)2HPO4 white precipitate of Mg(NH4)PO4 is formed