An inorganic salt is made up of two parts, i.e. cation (basic radical) and anion (acidic radical). The detection and identification of cations and anions in an inorganic salt or mixture of salts is known as qualitative analysis.
PRELIMINARY TESTS
Physical Appearance
It involves the examination of colour, smell, density etc. The salts of some transition elements have characteristic colours as mentioned in Table.
Radicals | Characteristic Colours |
---|---|
Cu2+, Ni2+ | Blue or bluish green |
Fe2+ | Light green |
Cr3+ | Dark green |
Fe3+ | Yellowish brown |
Co2+ | Pink violet |
Mn2+ | Light pink |
Dry Heating Test
It involves heating a small amount of the given sample of salt or mixture in a dry test tube. The identification can be done on the basis of below mentioned observations.
Gas Evolved
- Carbonates and some bicarbonates give CO2
CaCO3 → CaO + CO2↑
- Sulphates give SO2
SnSO4 → SnO2 + SO2↑
ZnSO4 → ZnO + SO2↑ - Hydrated chlorides give HCl
ZnCl2·6H2O → Zn(OH)Cl + HCl↑ + 5H2O
- Hydrated sulphides give H2S
BaS·2H2O → Ba(OH)2 + H2S↑
- Some nitrates give NO2
2Pb(NO3)2 → 2PbO + 4NO2↑ + O2↑
- Oxalates give mixture of (CO+CO2)
CaC2O4 → CaO + CO + CO2↑
Residues:
- Zinc salts give yellow residue when hot but changes to white when it is cold.
ZnCO3 → ZnO + CO2↑ (Residue)
- Hydrated copper sulphate gives white residue.
CuSO4·5H2O → CuSO4 + 5H2O
(Blue) → (White)
Flame Test
This test is performed with the paste of the given salt / mixture in conc. HCl. The paste is taken on a platinum wire and is heated in an oxidizing flame. The observation is mentioned in Table 2.
Cation | Colour of flame |
---|---|
Ca2+ | Brick red |
Sr2+ | Crimson red |
Ba2+ | Grassy green |
Cu2+ | Bluish |
K+ | Pale violet |
Na+ | Golden yellow |
Zn2+, Mn2+ | Green flashes |
Borax Bead Test
This test is applicable to only coloured salts. This is based on the fact that coloured cations form metaborates of specific colour.
Na2B4O7·10H2O → Na2B4O7 + 10H2O (Borax)
Na2B4O7 → 2NaBO2 + B2O3 (Glassy mass)
- Cr3+ forms green coloured metaborates.
Cr2(SO4)3 + 3B2O3 → 2Cr(BO2)3 + 3SO3 (Green)
- Co2+ ions form blue coloured bead.
CoSO4 + B2O3 → Co(BO2)2 + SO3 (Blue)
- Fe3+ ions form yellow coloured bead.
Fe2O3 + 3B2O3 → 3Fe(BO2)3 (Yellow)
Some metallic ions form different beads in oxidizing and reducing flames.
CuSO4 + B2O3 → Cu(BO2)2 + SO3 (Green - oxidizing flame)
Cu(BO2)2 + C → 2CuBO2 + B2O3 + CO (Colourless - reducing flame)
- Illustration 1: The gas that turns lime water milky is
(A) CO2
(B) SO2
(C) Both of the above
(D) None of the above
Solution: (C). Both CO2 and SO2 turns lime water [Ca(OH)2] milky due to formation of CaCO3 and CaSO3 respectively.
- Illustration 2: Composition of borax bead is
(A) B2O3 (B) Na2BO3 (C) Na2B4O7 (D) B2O3+NaBO2
Solution: (D). B2O3+NaBO2
- Illustration 3: Which compound is formed in borax bead test?
(A) Orthoborate
(B) Metaborate
(C) Double oxide
(D) Tetraborate
Solution: (B). Metaborate
Exercise 1
1) Flame test is not given by
(A) Be2+ (B) Ba2+ (C) Ca2+ (D) None of the above
2) Which of the following salt is colourless?
(A) CdCl2 (B) CuSO4·5H2O (C) MnSO4·7H2O (D) NiSO4·7H2O
3) In a mixture having nitrite and nitrate, nitrite can be destroyed by heating with
(A) Na2CO3 (B) urea (C) oxalic acid (D) NaCl
Exercise 2
A dark green bead in borax bead test indicates the presence of
(A) Cr3+ (B) Mn2+ (C) Co2+ (D) Ni2+
- Illustration 4: When copper (II) nitrate is strongly heated in a dry test tube, it is converted into
(A) Cu metal
(B) cupric oxide
(C) cuprous oxide
(D) cupric nitrate
Solution: (B). 2Cu(NO3)2 → 2CuO + 4NO2↑ + O2↑
IDENTIFICATION OF ACIDIC RADICALS
Dilute Acid Test
This test involves treatment of a given salt/mixture with dil. HCl or dil. H2SO4. It gives the indication of CO32–, SO32–, S2O32–, S2– and NO2– radicals.
Carbonate (CO32–) Gives colourless, odourless CO2 gas which turns lime water milky.
Na2CO3 + 2HCl → 2NaCl + CO2↑ + H2O
Ca(OH)2 + CO2 → CaCO3 + H2O (Lime water - Milkiness)
Sulphite (SO32–). Sulphites decompose to give colourless gas SO2 with smell of burning sulphur which turns K2Cr2O7 paper green.
Na2SO3 + H2SO4 → Na2SO4 + SO2↑ + H2O
K2Cr2O7 + H2SO4 + 3SO2 → Cr2(SO4)3 + K2SO4 + H2O (Green)
Thiosulphate (S2O32–) Reacts with dilute acids to produce SO2 gas along with the formation of yellow turbidity of sulphur.
Na2S2O3 + 2HCl → 2NaCl + SO2↑ + S↓ + H2O
Na2S2O3 + 2AgNO3 → Ag2S2O3 + 2NaNO3 (White)
Ag2S2O3 + H2O → Ag2S + H2SO4 (Black ppt.)
Sulphide (S2–) Sulphides are decomposed by dilute acids to give colourless gas (H2S) with rotten egg's smell.
Na2S + 2HCl → 2NaCl + H2S↑
(CH3COO)2Pb + H2S → PbS + 2CH3COOH (Black ppt.)
Na2S + Na4[Fe(CN)5NO] → Na4[Fe(CN)5NOS] (Sodium nitroprusside - Sodium sulphonitroprusside (violet))
Nitrite (NO2–) Nitrites react with dilute acids to give NO, a colourless gas which turns brown due to oxidation by air.
2NaNO2 + H2SO4 → Na2SO4 + 2HNO2
2HNO2 → NO↑ + H2O + NO2↑
2NO + O2 → 2NO2
FeSO4 + NO → FeSO4·NO or [Fe(H2O)5(NO)]SO4 (Brown ring)
Concentrated H2SO4 Test
This test involves heating of a given salt / mixture with conc. H2SO4. The test gives indication of Cl–, Br–, I–, NO3–, C2O42– radicals.
- Chloride (Cl–) Chlorides react with conc. H2SO4 to give colourless gas with pungent smell (HCl), which gives white dense fumes with NH4OH and white ppt. when passed through silver nitrate solution which is soluble in ammonia.
NaCl + H2SO4 → NaHSO4 + HCl↑
NH3 + HCl → NH4Cl (Fumes)
AgNO3 + HCl → AgCl + HNO3
AgCl + 2NH4OH → [Ag(NH3)2]Cl + 2H2O
- Chromyl chloride test: Chloride salt + K2Cr2O7 + conc. H2SO4 → Red vapours
4KCl + 6H2SO4 + K2Cr2O7 → 6KHSO4 + 2CrO2Cl2 + 3H2O (Red vapours)
CrO2Cl2 + 2NaOH → Na2CrO4 + 2NaCl + 2H2O (Yellow solution)
Na2CrO4 + (CH3COO)2Pb → PbCrO4 + 2CH3COONa (Yellow ppt.)
- Nitrate (NO3–) Nitrates are decomposed by conc. H2SO4 to form brown gas (NO2).
NaNO3 + H2SO4 → NaHSO4 + HNO3
4HNO3 → 4NO2↑ + 2H2O + O2↑
- Ring test: In salt solution add freshly prepared FeSO4 solution. Then add conc. H2SO4 along the sides of the test tube. A dark brown ring is formed at the junction of the two layers.
KNO3 + H2SO4 → KHSO4 + HNO3
6FeSO4 + 3H2SO4 + 2HNO3 → 3Fe2(SO4)3 + 4H2O + 2NO
FeSO4 + NO → FeSO4·NO (Brown ring - Nitrosoferrous sulphate)
The brown ring may also have composition [Fe(H2O)5NO]2+.
- Oxalate (C2O42–) On heating oxalates with conc. H2SO4, CO2 and CO gases are produced.
Na2C2O4 + H2SO4 → H2C2O4 + Na2SO4
H2C2O4 → CO2↑ + CO↑ + H2O
CO2 + Ca(OH)2 → CaCO3 + H2O (Lime water)
2KMnO4 + 3H2SO4 + H2C2O4 → K2SO4 + 2MnSO4 + 4H2O + 10CO2
- Bromide (Br–) Bromides are decomposed by conc. H2SO4 to give reddish brown vapours of Br2, which turn starch paper yellow.
KBr + H2SO4 → KHSO4 + HBr
2HBr + H2SO4 → Br2↑ + SO2↑ + 2H2O
Br2 + Starch → Yellow colour
- Iodide (I-): Iodides react with conc. H2SO4 to give violet vapours of iodine, which turn starch paper blue.
KI + H2SO4 → KHSO4 + HI
2HI + H2SO4 → SO2↑ + I2↑ + 2H2O
I2 + Starch → Blue
- Sulphate (SO42–): Salt solution + Lead acetate → White ppt. (soluble in ammonium acetate)
Na2SO4 + (CH3COO)2Pb → PbSO4 + 2CH3COONa
PbSO4 + 2CH3COONH4 → (CH3COO)2Pb + (NH4)2SO4 (soluble)
- Borate (BO33–): Take salt/mixture in a china dish. Add conc. H2SO4 and alcohol. Ignite the vapours. A green edged flame is obtained.
Na2B4O7 + H2SO4 + 4H2O → 4H3BO3 + Na2SO4
H3BO3 + 3C2H5OH → (C2H5)3BO3 + 3H2O (Ethyl borate - burns with green flame)
Illustration 5:
Reaction of K2Cr2O7 with NaCl and conc. H2SO4 gives
(A) CrCl3 (B) CrOCl2 (C) CrO2Cl2 (D) Cr2O3
Solution: (C). Chromyl chloride test.
Illustration 6:
Brown ring test is used to detect
(A) iodide (B) nitrate (C) iron (D) bromide
Solution: (B). NO3– is detected by brown ring test.
Exercise 3
1) A gas is obtained by addition of dilute H2SO4 to a mixture which turns lead acetate paper black. It is
(A) SO2
(B) CO2
(C) H2S
(D) NO2
2) A substance on treatment with dil. H2SO4 liberates a colourless gas which produces (i) turbidity with baryta water and (ii) turns acidified dichromate solution green. The reaction indicates the presence of
(A) CO32– (B) S2– (C) SO32– (D) NO2–
Illustration 7: Which of the following is not used as a preliminary test for detecting ions?
(A) Dilute H2SO4 test
(B) Charcoal cavity test
(C) Chromyl chloride test
(D) Flame test
Solution: (C). Chromyl chloride test is a confirmatory test for Cl– ion.
IDENTIFICATION OF BASIC RADICALS
Group I
Radicals: Ag+, Pb2+, Hg22+
- Group reagent: Dilute HCl
The radicals are precipitated in the form of their chlorides.
AgNO3 + HCl → AgCl + HNO3 (White ppt.)
Pb(NO3)2 + 2HCl → PbCl2 + 2HNO3 (White ppt.)
Hg2(NO3)2 + 2HCl → Hg2Cl2 + 2HNO3 (White ppt.)
White ppt. of PbCl2 is insoluble in cold water but dissolves in hot water. AgCl and Hg2Cl2 remain insoluble in hot water.
-
Test for Ag+ ions
The white ppt. of AgCl is soluble in NH4OH by forming a complex, while AgCl is again precipitated from the above solution by adding dil. HNO3.
AgCl + 2NH4OH → [Ag(NH3)2]Cl + 2H2O (Diammine silver(I) chloride)
[Ag(NH3)2]Cl + 2HNO3 → AgCl + 2NH4NO3 (White ppt.)
- Test for Pb2+ ions
To the hot solution of PbCl2, add K2CrO4 solution. A yellow precipitate of PbCrO4 is formed which is insoluble in AcOH but soluble in NaOH.
Pb2+ + K2CrO4 → PbCrO4 + 2K+ (Yellow ppt.)
PbCl2 (aq) + 2KI(aq) → 2KCl + PbI2 (Yellow ppt.)
PbI2 + 2KI(excess) → K2[PbI4] (Complex - soluble)
- Test for Hg22+ ions
The white ppt. of Hg2Cl2 turns black on treating with NH4OH.
Hg2Cl2 + 2NH4OH → Hg + Hg(NH2)Cl + NH4Cl + 2H2O (Black)
The black ppt. is dissolved in aqua regia:
3HCl + HNO3 → NOCl + 2H2O + 2[Cl]
2Hg(NH2)Cl + 6[Cl] → 2HgCl2 + 4HCl + N2
Hg + 2[Cl] → HgCl2
SnCl2 + 2HgCl2 → SnCl4 + Hg2Cl2 (White ppt.)
SnCl2 + Hg2Cl2 → SnCl4 + 2Hg (Black)
Group II
- Group II A: Hg2+, Pb2+, Bi3+, Cu2+, Cd2+ (Insoluble in yellow ammonium sulphide)
- Group II B: As3+, Sb3+, Sn2+, Sn4+ (Soluble in yellow ammonium sulphide)
- Group reagent: H2S in acidic medium
The radicals of group II are precipitated as their sulphides.
Sulphide | Colour |
---|---|
HgS | Black |
PbS | Black |
Bi2S3 | Brown black |
CuS | Black |
CdS | Yellow |
As2S3 | Yellow |
Sb2S3 | Orange |
SnS2 | Yellow |
SnS | Brown |
Group II B sulphides dissolve in ordinary ammonium sulphide with the exception of SnS. Except HgS, all the sulphides of group II A become soluble in 50% HNO3. HgS dissolves in aqua regia. Copper and Cadmium are separated with the help of KCN.
-
Test for Hg2+ ions
HgS is dissolved in aqua regia and the solution is tested by SnCl2.
3HgS + 2HNO3 + 6HCl → 3HgCl2 + 3S + 2NO + 4H2O
2HgCl2 + SnCl2 → Hg2Cl2 + SnCl4 (White ppt.)
Hg2Cl2 + SnCl2 → 2Hg + SnCl4 (Grey)
-
Test for As3+ ions
The yellow ppt. of As2S3 is insoluble in conc. HCl but dissolves in conc. HNO3. To this solution ammonium molybdate is added, a yellow precipitate is formed.
As2S3 + 10HNO3 → 2H3AsO4 + 10NO + 2H2O + S (boil) (Yellow ppt. - Arsenic acid)
H3AsO4 + 12(NH4)2MoO4 + 21HNO3 → (NH4)3AsO4·12MoO3 + 21NH4NO3 + 12H2O (Yellow ppt. - Ammonium arsenomolybdate)
-
Test for Sb3+ ions
The orange ppt. of Sb2S3 is soluble in conc. HCl. This solution on dilution with water forms a white turbidity.
Sb2S3 + 6HCl → 2SbCl3 + 3H2S (Orange ppt.)
SbCl3 + H2O → 2SbOCl + 2HCl (White turbidity - Antimony oxychloride)
-
Test for Sn2+ ions
The brownish ppt. of SnS is soluble in conc. HCl to give SnCl2. It is tested by HgCl2.
SnS + 2HCl → SnCl2 + H2S
SnCl2 + 2HgCl2 → SnCl4 + Hg2Cl2 (White ppt.)
SnCl2 + Hg2Cl2 → SnCl4 + 2Hg (Grey ppt.)
-
Test for Pb2+ ions
The black ppt. of PbS is dissolved in 50% HNO3. The resulting solution gives a white ppt. on treating with dil. H2SO4.
3PbS + HNO3 → 3Pb(NO3)2 + NO + S + 4H2O (Solution)
Pb(NO3)2 + H2SO4 → PbSO4 + 2HNO3 (White ppt.)
-
Test for Bi3+ ions
The black ppt. of Bi2S3 is dissolved in 50% HNO3. The resulting solution gives white ppt. with NH4OH.
Bi(NO3)3 + 3NH4OH → Bi(OH)3 + 3NH4NO3 (White ppt.)
Bi(OH)3 + 3HCl → BiCl3 + 3H2O
BiCl3 + H2O → BiOCl + 2HCl (Bismuth oxychloride - White ppt.)
2BiCl3 + 3Na2SnO2 + 6NaOH → 3Na2SnO3 + 2Bi + 6NaCl + 3H2O (Black - Sodium stannate/Sodium stannite)
-
Test for Cu2+ ions
The black ppt. of CuS is dissolved in 50% HNO3. To the solution so formed, add K4[Fe(CN)6], forms chocolate ppt.
3CuS + 8HNO3 → 3Cu(NO3)2 + 4H2O + 3S + 2NO
Cu(NO3)2 + K4[Fe(CN)6] → 4KNO3 + Cu2[Fe(CN)6] (Chocolate ppt. - Copper hexacyanoferrate(II))
Cu(NO3)2 + 2NH3 → [Cu(NH3)4]2+ + 2HNO3 (Blue colouration)
-
Test for Cd2+ ions
The yellow ppt. of CdS is dissolved in 50% HNO3. To the resulting solution NH4OH is added slowly, a white ppt. is formed which dissolves in excess of NH4OH.
3CdS + 8HNO3 → 3Cd(NO3)2 + 4H2O + 3NO + 3S
Cd(NO3)2 + 2NH4OH → 2NH4NO3 + Cd(OH)2 (White ppt.)
Cd(OH)2 + 2NH4OH → 2NH4NO3 + [Cd(NH3)4](NO3)2 + 4H2O (Soluble)
[Cd(NH3)4](NO3)2 + H2S → CdS + 2NH4NO3 + 2NH3 (Yellow ppt.)
Group III
- Radicals: Cr3+, Fe3+, Al3+
- Group reagent: NH4OH in the presence of NH4Cl
The radicals are precipitated as their respective hydroxides.
Hydroxide | Colour |
---|---|
Al(OH)3 | Gelatinous white |
Fe(OH)3 | Reddish brown |
Cr(OH)3 | Green |
-
Test for Al3+ ions
The white gelatinous ppt. of Al(OH)3 is soluble in NaOH due to formation of sodium metaaluminate. Fe(OH)3 and Cr(OH)3 are insoluble in NaOH.
Al(OH)3 + NaOH → NaAlO2 (aq) + 2H2O
Al(OH)3 + 3HCl → AlCl3 + 3H2O (Soluble - blue litmus)
AlCl3 + 3NH4OH → 3NH4Cl + Al(OH)3 (Blue colour is adsorbed and float in colourless solution)
-
Test for Fe3+ ions
The reddish brown precipitate of Fe(OH)3 is dissolved in HCl. The solution gives an intense blue colour with K4[Fe(CN)6] and blood red colour with KCNS.
Fe(OH)3 + 3HCl → FeCl3 + 3H2O
4FeCl3 + 3K4[Fe(CN)6] → Fe4[Fe(CN)6]3 + 12KCl (Ferric ferrocyanide - Blue colour)
FeCl3 + 3KCNS → Fe(CNS)3 + 3KCl (Blood red colouration - Ferric thiocyanate)
-
Test for Cr3+ ions
The green ppt. of Cr(OH)3 is dissolved in NaOH in the presence of H2O2 and the resulting solution is neutralized with CH3COOH then treated with lead acetate.
Cr(OH)3 + 4NaOH + 3H2O2 → 2Na2CrO4 + 8H2O (Yellow)
Na2CrO4 + (CH3COO)2Pb → PbCrO4 + 2CH3COONa (Yellow ppt)
Group IV
- Radicals: Co2+, Ni2+, Mn2+, Zn2+
- Group reagent: H2S in alkaline medium
The radicals are precipitated as their respective sulphides.
Sulphide | Colour |
---|---|
CoS | Black |
NiS | Black |
MnS | Flesh colour |
ZnS | Dirty white |
-
Test for Co2+ ions
The black ppt. of CoS is dissolved in aqua regia.
3CoS + 6HCl + 2HNO3 → 3CoCl2 + 2NO + 3S + 4H2O
Now, add CH3COOH in excess and KNO2, yellow ppt. is formed.
KNO2 + CH3COOH → CH3COOK + HNO2
CoCl2 + 2KNO2 → Co(NO2)2 + 2KCl
Co(NO2)2 + 2HNO2 → Co(NO2)3 + NO + H2O
Co(NO2)3 + 3KNO2 → K3[Co(NO2)6] (Yellow ppt.)
-
Test for Ni2+ ions
The black ppt. of NiS is dissolved in aqua regia.
3NiS + 6HCl + 2HNO3 → 3NiCl2 + 2NO + 3S + 4H2O
Now, add NH4OH in excess and dimethyl glyoxime, a rosy red precipitate appears.
-
Tests for Mn2+ ions
The flesh coloured ppt. of MnS is dissolved in dil HCl. On adding NaOH to this solution, a ppt. is formed which does not dissolve in excess of NaOH.
MnS + 2HCl → MnCl2 + H2S
MnCl2 + 2NaOH → Mn(OH)2 (Buff ppt. insoluble in NaOH)
-
Tests for Zn2+ ions
The white ppt. of ZnS is dissolved in dil. HCl.
ZnS + 2HCl → ZnCl2 + H2S
The resulting solution is treated with NaOH, white ppt. of Zn(OH)2 appears which dissolved in excess of NaOH.
ZnCl2 + 2NaOH → 2NaCl + Zn(OH)2 (White ppt.)
Zn(OH)2 + 2NaOH → Na2ZnO2 + 2H2O (Sodium zincate - Soluble)
Na2ZnO2 + H2S(g) → 2NaOH + ZnS (White ppt.)
Group V
- Radicals: Ba2+, Sr2+, Ca2+
- Group reagent: (NH4)2CO3 in the presence of NH4OH and NH4Cl
The radicals are precipitated as their respective carbonates (all white ppt.).
-
Tests for Ba2+ ions
The white ppt. of BaCO3 is dissolved in CH3COOH and the solution is treated with potassium chromate, a yellow ppt. is formed.
BaCO3 + 2CH3COOH → (CH3COO)2Ba + H2O + CO2 (White ppt.)
(CH3COO)2Ba + K2CrO4 → 2CH3COOK + BaCrO4 (Yellow ppt. - insoluble in acetic acid)
-
Tests for Sr2+ ions
The white ppt. of SrCO3 is dissolved in acetic acid and the solution is treated with ammonium sulphate, a white ppt. of SrSO4 is formed.
SrCO3 + 2CH3COOH → (CH3COO)2Sr + H2O + CO2
(CH3COO)2Sr + (NH4)2SO4 → 2CH3COONH4 + SrSO4 (White ppt.)
-
Tests for Ca2+ ions
The white ppt. of CaCO3 is dissolved in acetic acid. To this solution ammonium oxalate is added, a white ppt. of calcium oxalate is formed.
CaCO3 + 2CH3COOH → (CH3COO)2Ca + H2O + CO2 (white)
(CH3COO)2Ca + (NH4)2C2O4 → 2CH3COONH4 + CaC2O4 (White ppt. - insoluble in acetic acid)
Group VI
- Radicals: Mg2+, Na+, K+
- Group reagent: There is no common group reagent.
-
Tests for Mg2+ ions
Filtrate of group V + NH4OH + Na2HPO4 → White ppt.
MgCl2 + NH4OH + Na2HPO4 → Mg(NH4)PO4 + 2NaCl + H2O (White ppt.)
-
Tests for K+ ions
To the salt solution add sodium cobaltinitrite, yellow ppt. is formed.
Na3[Co(NO2)6] + 3KCl → 3NaCl + K3[Co(NO2)6] (Potassium cobaltinitrite - Yellow ppt.)
-
Tests for Na+ ions
To the salt solution add potassium pyroantimonate, a ppt. of sodium pyroantimonate is formed.
2Na+ + K2H2Sb2O7 → 2K+ + Na2H2Sb2O7 (Milkiness or ppt.)
Zero Group
Test for NH4+ ions: All ammonium salts on heating with NaOH solution liberate ammonia gas.
(NH4)2SO4 + 2NaOH → Na2SO4 + 2H2O + 2NH3↑
Aqueous solution of ammonium salt when treated with Nessler's reagent gives brown ppt.
Illustration 8: Three separate samples of aqueous solution of (X) gave following results. One formed white ppt. with excess of ammonia solution, one formed white precipitate with dil. NaCl solution and one formed a black precipitate with H2S. The salt could be
(A) AgNO3
(B) Pb(NO3)2
(C) Hg(NO3)2
(D) MnSO4
Solution: (B)
Pb(NO3)2 + 2NH4OH → Pb(OH)2 + 2NH4NO3 (White ppt.)
Pb(NO3)2 + 2NaCl → PbCl2 + 2NaNO3 (White ppt.)
Pb(NO3)2 + H2S → PbS + 2HNO3 (White ppt.)
- Exercise 4: The brown ring test for nitrate employs
(A) barium chloride (B) ferrous sulphate (C) nitric acid (D) none of the above
- Exercise 5: Which one among the following pair of ions cannot be separated by H2S in dilute HCl?
(A) Bi3+, Sn4+ (B) Al3+, Hg2+ (C) Zn2+, Cu2+ (D) Ni2+, Cu2+
Illustration 9: When a substance (A) reacts with water it produces a combustible gas (B) and a solution of substance (C) in water. When another substance (D) reacts with this solution of (C) it also produces the same gas (B) on warming but (D) can produce gas (B) on reaction with dilute sulphuric acid at room temperature. (A) imparts a deep golden yellow colour to a smokeless flame of Bunsen burner. (A), (B), (C) and (D) are
(A) Na, H2, NaOH, Zn
(B) K, H2, KOH, Al
(C) Ca, H2, Ca(OH)2, Sn
(D) CaC2, C2H2, Ca(OH)2, Fe
Solution: (A)
2Na + 2H2O → 2NaOH + H2↑ (A→C+B)
Zn + 2H2O → Na2ZnO2 + H2↑ (D→B)
Illustration 10: A red solid is insoluble in water. However, it becomes soluble if some KI is added to water. Heating red solid in a test tube produces violet coloured fumes and droplets of metal appear on the cooler parts of test tube. The red solid is
(A) (NH4)2Cr2O7 (B) HgI2 (C) HgO (D) Pb3O4
Solution: (B). HgI2 is scarlet red compound insoluble in water.
HgI2 + 2KI → K2[HgI4] (Soluble)
HgI2 Heat→ Hg + I2 (Droplet - violet vapour)
CHAPTER AT A GLANCE
- Salts of Hg2+, Pb2+, Ba2+ are heavy whereas salts containing carbonate are generally light and fluffy.
- Salts like Zn(NO3)2, MgCl2, ZnCl2 absorb moisture and attain paste like appearance are deliquescent.
- Salts like Pb(NO3)2, Ba(NO3)2 decrepitate, i.e. they produce crackling sound. These salts have mother liquor trapped in crystal structures. During heating when crystal structure crumbles, it produces crackling sound.
- Some salts such as alums, phosphates, borates swell up due to evaporation of water of crystallization.
- During the flame test, the purpose of making paste in conc. HCl is to convert the salt into its respective chlorides which are relatively volatile.
- Bi2(CO3)3 and BaCO3 are not easily decomposed by dil. H2SO4. This is because Bi2(SO4)3 and BaSO4 thus formed are insoluble in water.
- PbCO3 reacts slowly both with dil. HCl as well as dil. H2SO4. This is because PbCl2 and PbSO4 thus formed are insoluble in cold water.
- Chlorides of mercury owing to little ionization do not respond to chromyl chloride test.
- The flame test should be avoided in case of As, Sb, Sn, Pb and Bi salts since they corrode the platinum wire.
- Deliquescent salts: Chlorides of Al, Zn, Cd, Mg or nitrate of Zn absorb moisture from atmosphere to such an extent that finally get dissolved in it and form solution.
- An asbestos fibre can be safely used in place of platinum wire for performing flame test. Glass rod should never be used as it gives a golden yellow persistent colour due to sodium present in it.
- Sulphides of Hg2+, Pb2+, Co2+, Ni2+, Sb2+, Sn2+ are decomposed with dil. H2SO4 only if a pinch of Zn dust is added to the reaction mixture.
Zn + H2SO4 → ZnSO4 + 2[H]
HgS + 2[H] → Hg + H2S
ANSWER TO EXERCISES
Exercise 1: 1) A 2) A 3) B
Exercise 2: A
Exercise 3: 1) C 2) C
Exercise 4: B
Exercise 5: A
Solved Examples
1. When K₂Cr₂O₇ crystals are heated with conc. HCl, the gas evolved is
(A) O₂ (B) Cl₂ (C) CrO₂Cl₂ (D) HCl
Solution: (C). CrO₂Cl₂
2. Microcosmic salt is
(A) Na(NH₄)HPO₄·4H₂O (B) Na(NH₄)·H₂O
(C) Na(NH₃)HPO₄·4H₂O (D) K(NH₄)HPO₄·2H₂O
Solution: (A). Na(NH₄)HPO₄·4H₂O
3. Which among the following is most soluble in water?
(A) Mg(OH)₂ (B) Sr(OH)₂ (C) Ca(OH)₂ (D) Ba(OH)₂
Solution: (B). Among the hydroxides of group II, the solubility increases down the group.
4. Which of the following sulphide has lowest solubility product?
(A) FeS (B) MnS (C) PbS (D) ZnS
Solution: (C).
5. A Chloride is insoluble in cold water but dissolves appreciably in hot water. When placed on platinum wire in Bunsen flame, no distinctive colour is noticed. The cation would be
(A) Mg²⁺ (B) Ba²⁺ (C) Pb²⁺ (D) Ca²⁺
Solution: (C). PbCl₂ is insoluble in cold water but soluble in hot water.
6. CrO₃ dissolves in aqueous NaOH to give
(A) CrO₄²⁻ (B) Cr₂O₇²⁻ (C) Cr(OH)₃ (D) Cr₂(OH)₂
Solution: (A). CrO₃ + 2NaOH → Na₂CrO₄ + H₂O
7. Which of the following is soluble in yellow ammonium sulphide?
(A) CuS (B) CdS (C) SnS (D) PbS
Solution: (C). Among these, SnS is soluble in yellow ammonium sulphide.
[Image: Test tubes showing colored precipitates of different sulphides and a hot wire flame test for chlorides]
8. Which of the following compound gives a red precipitate with AgNO₃?
(A) KI (B) K₂CrO₄ (C) NaBr (D) NaNO₃
Solution: (B). 2AgNO₃ + K₂CrO₄ → Ag₂CrO₄↓ (Red ppt) + 2KNO₃
9. The metal ion which is precipitated when H₂S is passed through the solution which has been acidified with HCl is
(A) Zn²⁺ (B) Ni²⁺ (C) Cd²⁺ (D) Mn²⁺
Solution: (C). Cd²⁺ is in group II A, which is precipitated as CdS in HCl medium.
10. Correct formula of the complex formed in the brown ring test for nitrates is
(A) FeSO₄·NO (B) [Fe(H₂O)₅NO]²⁺ (C) [Fe(H₂O)₄(NO)⁺] (D) [Fe(H₂O)₅NO]³⁺
Solution: (B). Brown ring test for nitrates is due to the formation of [Fe(H₂O)₅NO]²⁺ complex ion.
Assignment Problems
- Which is the hottest part of the flame?
(A) Blue zone
(B) Zone of partial combustion
(C) Zone of complete combustion
(D) Zone of no combustion
- Soda extract is prepared by
(A) fusing soda and mixture, and then extracting with water
(B) dissolving NaHCO₃ and mixture in dilute HCl
(C) boiling Na₂CO₃ and mixture in dilute HCl
(D) boiling Na₂CO₃ and mixture in distilled water
- A precipitate of calcium oxalate will not dissolve in.
(A) acetic acid
(B) HCl
(C) HNO₃
(D) aqua regia
- In the test for iodine, when I₂ is treated with sodium thiosulphate (Na₂S₂O₃) the reaction occurs as, I₂ + 2Na₂S₂O₃ → 2NaI + P. The product ‘P’ is
(A) Na₂S₄O₆
(B) Na₂SO₄
(C) Na₂S
(D) Na₃ISO₄
- When borax is heated on a platinum wire, it forms a glass like bead which is made up of
(A) sodium tetraborate
(B) sodium metaborate
(C) sodium metaborate and boric anhydride
(D) boric anhydride and sodium tetraborate
- Chromyl chloride vapours are dissolved in water and acetic acid and lead acetate solution is added, then
(A) the solution will remain colourless
(B) the solution will become dark green
(C) a yellow solution will be obtained
(D) a yellow precipitate will be obtained
- Which of the following nitrates on strong heating leaves the metal as the residue?
(A) AgNO₃
(B) Pb(NO₃)₂
(C) Cu(NO₃)₂
(D) Al(NO₃)₃
- A mixture on heating with MnO₂ and conc. H₂SO₄ gives brown vapour of
(A) HBr
(B) Br₂
(C) NO
(D) NO₂
- K₂CrO₄ is used to identify
(A) Cu²⁺
(B) Ba²⁺
(C) Ag⁺
(D) Ca²⁺
- On mixing two colourless gases a deep brown gas is formed. The two gases are
(A) N₂O and NO
(B) NO₂ and O₂
(C) NO and O₂
(D) HCl + NH₃
- Which of the following gives blood red colour with KCNS?
(A) Ca²⁺
(B) Fe³⁺
(C) Al³⁺
(D) Zn²⁺
- H₂S on passing through ammonium solution gives white ppt. of
(A) CoS
(B) NiS
(C) MnS
(D) ZnS
- The carbonate of which of the following cation is insoluble in water
(A) Na⁺
(B) K⁺
(C) NH₄⁺
(D) Ca²⁺
- AgCl dissolves in ammonia solution and forms
(A) Ag⁺, NH₄⁺ and Cl⁻
(B) Ag(NH₃)⁺ and Cl⁻
(C) Ag₂(NH₃)₂⁺ and Cl⁻
(D) Ag(NH₃)₂⁺ and Cl⁻
- Colour of KMnO₄ is decolourized without evolution of any gas. The radical present may be
(A) SO₄²⁻
(B) SO₃²⁻
(C) Sn²⁺
(D) both (B) and (C)
Answers to Assignment Problems
1. C
2. D
3. A
4. A
5. C
6. D
7. A
8. B
9. B
10. C
11. B
12. D
13. D
14. D
15. D
Frequently Asked Questions
What are the 5 qualitative analysis methods?
While there are many different approaches to qualitative analysis, five methods are widely recognized and commonly used across various fields for their distinct focus and application. Understanding these can help you choose the right approach for your research question.
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Thematic Analysis: This is one of the most foundational and flexible methods. The primary goal is to identify, analyze, and report patterns (or "themes") within a dataset. A researcher would comb through interview transcripts, survey responses, or other texts, systematically coding for recurring ideas and then grouping these codes into broader, interpretive themes. For example, a UX researcher analyzing user feedback on a new app might identify themes like "intuitive navigation," "slow loading times," and "desire for more customization." It's an excellent method for understanding the key aspects of people's experiences or views on a topic.
-
Content Analysis: This method involves systematically categorizing words, phrases, or concepts within textual, visual, or audio data. It can be both qualitative (interpreting meanings) and quantitative (counting frequencies). In a qualitative context, a brand might use content analysis to examine the tone and key topics in news articles about their company to understand their public image. It's less about deep interpretation and more about systematically summarizing the content.
-
Narrative Analysis: This approach centers on analyzing the stories people tell. Researchers examine the structure of a narrative, the language used, and how the story is constructed to understand how individuals make sense of their experiences and convey their perspectives. For example, a case worker might analyze the life stories of at-risk youth to understand the sequence of events and turning points that shaped their current situation. It's powerful for capturing rich, personal, and chronological accounts.
-
Grounded Theory: This is a more complex method where the objective is to generate a new theory that is "grounded" in the data itself. Rather than starting with a pre-existing hypothesis, the researcher builds a theory from the ground up through a rigorous process of simultaneous data collection and analysis. An organizational psychologist might use grounded theory to develop a new model of employee burnout by interviewing dozens of professionals across different industries and identifying the core processes that lead to it.
-
Discourse Analysis: This method focuses on the analysis of language beyond the sentence level. It explores how language is used in real-life social contexts and the power dynamics it reflects. A researcher might use discourse analysis to study doctor-patient conversations to understand how communication styles affect patient compliance and understanding. It’s not just about what is said, but how it is said and the social implications of that language.
Qualitative analysis is an investigative process focused on understanding the 'why' and 'how' behind human behavior, experiences, and perceptions. Unlike its quantitative counterpart, which deals with numbers and statistics, qualitative analysis dives into non-numerical data to uncover rich, contextual insights. This data can take many forms, including text from interviews or open-ended survey responses, audio recordings from focus groups, videos of user interactions, and images or documents. The core goal isn't to measure or count but to interpret meaning, identify patterns, and construct a narrative from the data collected. It’s an exploratory approach that seeks to understand concepts, opinions, or experiences in-depth. For instance, if a company sees a drop in sales (a quantitative finding), they might use qualitative analysis like conducting in-depth interviews with former customers to understand the reasons behind that drop. They're not looking for a number; they're looking for stories, feelings, and motivations, such as "the new user interface is confusing" or "the customer service felt impersonal." This process is inherently interpretive, meaning the researcher's role is crucial in sifting through the data, connecting ideas, and developing themes that explain the phenomenon being studied. It provides the rich context and human story that numbers alone often cannot capture.
The process of qualitative analysis involves systematically organizing, examining, and interpreting this unstructured data to make sense of it. Researchers often begin by transcribing interviews or organizing field notes. They then immerse themselves in the data, reading and re-reading it to become deeply familiar with the content. The next crucial step is coding, where the researcher identifies key concepts, ideas, or phrases and assigns them a label or 'code'. For example, in analyzing customer complaints, codes might include "long wait times," "unhelpful staff," or "website glitch." As the researcher continues to code the data, they begin to group related codes into broader categories and, ultimately, into overarching themes. These themes are the foundational pillars of the final analysis, representing the significant, recurring patterns of meaning within the data set. The final result is a deep, nuanced understanding of the research topic, grounded directly in the expressed words and actions of the participants. This method is invaluable in fields like marketing, user experience (UX) research, sociology, and healthcare for developing a profound understanding of complex human-centered issues.
Qualitative analysis encompasses a variety of methods, each designed to interpret non-numerical data from a different angle. A prominent example is thematic analysis, where researchers meticulously examine data from interviews or focus groups to identify recurring themes or patterns. For instance, a healthcare provider might use thematic analysis on patient testimonials to uncover common themes in their experience, such as "communication with nurses," "clarity of treatment information," and "hospital atmosphere." This helps the organization understand what aspects of care are most significant to patients. Another powerful method is content analysis, which is used to systematically categorize and interpret textual, visual, or audio data.
A marketing team could apply content analysis to social media comments about a new product launch. They would categorize comments by sentiment (positive, negative, neutral) and topic (e.g., packaging, price, performance) to gauge public reception and pinpoint specific areas for improvement, moving beyond a simple count of mentions to understand the substance of the conversation. This provides actionable intelligence directly from the customer's voice.
Another key example is narrative analysis, which focuses on the stories people tell. This method examines the structure, content, and context of narratives to understand how individuals make sense of their experiences. A brand researcher might use narrative analysis to study customer journey stories, piecing together how a person first became aware of a product, what their decision-making process was like, and how they integrated it into their life. This provides a holistic view of the customer relationship. Furthermore, grounded theory is a unique approach where the goal is to develop a new theory based entirely on the data collected. A sociologist studying remote work culture might use grounded theory to analyze interviews with employees and managers, gradually building a theoretical model that explains how trust and productivity are established in a virtual environment. Finally, discourse analysis examines how language is used in social contexts.
For example, a political analyst might use discourse analysis to study a politician's speeches to understand how they use specific words and rhetorical strategies to build rapport with voters and frame policy issues. Each of these methods offers a different lens through which to understand the complex tapestry of human experience.
Qualitative and quantitative analysis are two distinct but complementary approaches to research and data interpretation that help us understand the world in different ways. The fundamental difference lies in the type of data they use and the questions they aim to answer. Quantitative analysis is all about numbers, measurements, and statistical relationships. It focuses on the 'what,' 'how many,' and 'how often.' This approach uses structured data, such as survey ratings, sales figures, or website clicks, to test hypotheses, identify correlations, and make predictions. For example, a quantitative study might analyze survey data from 1,000 customers to determine that 75% are satisfied with a service or that there is a statistical correlation between customer age and purchasing frequency. The goal is to produce objective, generalizable results that can be represented with charts and graphs. It is confirmatory in nature, seeking to measure and validate known variables.
On the other hand, qualitative analysis explores the 'why' and 'how' behind the numbers. It deals with unstructured, non-numerical data like interview transcripts, open-ended feedback, observation notes, and social media comments. The focus is on gaining a deep, contextual understanding of human behavior, motivations, and experiences. Instead of asking "how many," it asks "why?" or "in what way?" For example, following the quantitative finding that customer satisfaction is at 75%, a qualitative analysis would involve conducting in-depth interviews with a small group of both satisfied and dissatisfied customers to understand the specific reasons for their feelings. You might uncover stories about exceptional service or frustrating website experiences that explain the satisfaction scores. Qualitative analysis is exploratory, seeking to uncover new ideas, themes, and perspectives. While quantitative analysis provides the broad overview and statistical proof, qualitative analysis delivers the depth, nuance, and human story that brings the data to life. Often, the most powerful insights come from using both methods together in a mixed-methods approach to get a complete picture.
While there are many different approaches to qualitative analysis, five methods are widely recognized and commonly used across various fields for their distinct focus and application. Understanding these can help you choose the right approach for your research question.
-
Thematic Analysis: This is one of the most foundational and flexible methods. The primary goal is to identify, analyze, and report patterns (or "themes") within a dataset. A researcher would comb through interview transcripts, survey responses, or other texts, systematically coding for recurring ideas and then grouping these codes into broader, interpretive themes. For example, a UX researcher analyzing user feedback on a new app might identify themes like "intuitive navigation," "slow loading times," and "desire for more customization." It's an excellent method for understanding the key aspects of people's experiences or views on a topic.
-
Content Analysis: This method involves systematically categorizing words, phrases, or concepts within textual, visual, or audio data. It can be both qualitative (interpreting meanings) and quantitative (counting frequencies). In a qualitative context, a brand might use content analysis to examine the tone and key topics in news articles about their company to understand their public image. It's less about deep interpretation and more about systematically summarizing the content.
-
Narrative Analysis: This approach centers on analyzing the stories people tell. Researchers examine the structure of a narrative, the language used, and how the story is constructed to understand how individuals make sense of their experiences and convey their perspectives. For example, a case worker might analyze the life stories of at-risk youth to understand the sequence of events and turning points that shaped their current situation. It's powerful for capturing rich, personal, and chronological accounts.
-
Grounded Theory: This is a more complex method where the objective is to generate a new theory that is "grounded" in the data itself. Rather than starting with a pre-existing hypothesis, the researcher builds a theory from the ground up through a rigorous process of simultaneous data collection and analysis. An organizational psychologist might use grounded theory to develop a new model of employee burnout by interviewing dozens of professionals across different industries and identifying the core processes that lead to it.
-
Discourse Analysis: This method focuses on the analysis of language beyond the sentence level. It explores how language is used in real-life social contexts and the power dynamics it reflects. A researcher might use discourse analysis to study doctor-patient conversations to understand how communication styles affect patient compliance and understanding. It’s not just about what is said, but how it is said and the social implications of that language.
Qualitative research is a broad field that uses many different methods to gather in-depth, non-numerical data. These methods are designed to explore and understand the complexity of human experiences from the participants' perspective. Here are ten common examples of qualitative research designs and approaches:
-
One-on-One Interviews: A researcher engages in a detailed conversation with a single participant, using open-ended questions to explore their thoughts, feelings, and experiences on a specific topic.
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Focus Groups: A small, curated group of participants (typically 6-10 people) are brought together to discuss a particular subject under the guidance of a facilitator. This method is excellent for observing group dynamics and shared opinions.
-
Ethnographic Research: This immersive method involves the researcher observing and/or interacting with participants in their real-life environment over an extended period. The goal is to gain a deep, holistic understanding of a community's culture, behaviors, and social dynamics.
-
Case Study Research: This involves an in-depth, detailed examination of a single case, which could be an individual, a group, an organization, or an event. The goal is to understand a complex issue by studying a specific real-world example in great detail.
-
Phenomenological Research: This approach focuses on understanding the "lived experience" of individuals concerning a particular phenomenon. Researchers aim to describe and interpret what an experience is like from the viewpoint of those who have lived it, such as the experience of being a first-time parent.
-
Grounded Theory Studies: As a research design, this involves collecting data (often through interviews) with the explicit goal of developing a new theory or conceptual model that is derived directly from that data.
-
Historical Research: This method involves collecting and analyzing data from historical sources, such as documents, records, and artifacts, to understand past events and their impact on the present.
-
Participant Observation: A variation of ethnography where the researcher becomes an active participant in the group or community they are studying to gain an insider's perspective on their behaviors and motivations.
-
Discourse/Conversation Analysis: This research focuses on analyzing naturally occurring language and conversation. Researchers study the structure, patterns, and functions of talk and text to understand how people use language to construct meaning and social order.
-
Record Keeping/Document Analysis: This involves using existing documents as a source of data. A researcher might analyze meeting minutes, company reports, letters, or public records to gain insights into an organization or social phenomenon without direct interaction.
Analyzing qualitative data is an iterative and interpretive process that transforms raw text, audio, or video into meaningful findings. While it's less rigid than statistical analysis, it requires a systematic approach to ensure credibility. The process can generally be broken down into six key steps.
Step 1: Prepare and Organize Your Data The first step is to get your data into a workable format. This almost always involves transcribing audio or video recordings into written text. It’s crucial that these transcriptions are accurate and detailed, often including pauses or emotional cues. Once transcribed, organize your data files logically (e.g., by participant or date) and make backups. This foundational step ensures you can easily access and work with your information.
Step 2: Review and Explore the Data Before you start formal analysis, you need to immerse yourself in the data. Read through all your transcripts or notes several times. The goal here is to get a holistic sense of the content. What are your initial impressions? Are there any striking phrases or ideas that jump out? This initial exploration helps you become deeply familiar with the dataset and start thinking about potential patterns without yet imposing a rigid structure.
Step-3: Develop an Initial Coding System This is the core of the analysis. Coding involves reading through the data line-by-line and assigning short labels (codes) to chunks of text that represent a specific idea, concept, or piece of information. For example, in an interview about remote work, a sentence like "I miss the spontaneous chats by the coffee machine" might be coded as "loss of informal social interaction." You can start with a pre-defined set of codes (deductive approach) or develop codes as you go (inductive approach).
Step 4: Apply the Codes to Your Data Systematically go through your entire dataset and apply your codes wherever relevant text appears. This is a meticulous process. As you go, you will likely refine your coding system, merging similar codes, splitting broad ones, or creating new ones. The goal is to have a consistently applied set of codes that accurately represents the content of your data. Many researchers use Qualitative Data Analysis Software (QDAS) to help manage this process.
Step 5: Identify Themes and Patterns Once all your data is coded, you can start to see the bigger picture. In this step, you group related codes together to form broader themes. A theme is a significant pattern of meaning in the data that helps answer your research question. For example, codes like "loss of informal social interaction," "feelings of isolation," and "difficulty collaborating" might be grouped under the overarching theme of "Challenges of Remote Connection."
Step 6: Interpret and Present the Findings The final step is to weave your themes into a coherent narrative. You need to explain what your themes mean, how they relate to each other, and what they tell you about your research topic. Support your interpretations with compelling, anonymous quotes from the data to give voice to your participants and demonstrate that your findings are grounded in their experiences. The final output could be a report, a presentation, or a detailed persona that tells the story you've uncovered