JEE Advanced 2024 Inorganic Chemistry Principles of Qualitative Analysis Revision Notes

Introduction 

Qualitative Inorganic analysis deals with the identification of radicals present in salt.

• Cation derived from the base is termed as basic radical.

• Anion derived from acid is termed an acidic radical.

Example: $NaOH + HCl \to NaCl + {H_2}O$

Physical Properties of Salts:

Heating Effects on Various Salts

Dry Tests:

These texts give a clear indication of the presence of certain radicals.

Flame Test:

The flame test should not be performed in the presence of As, Sb, Bi, Sn and Pb as these radical form alloy with Pt, and wire may be spoiled.

Borax Bead Test:

• On heating Borax, the colorless glassy bead formed, which consists of sodium metaborate and boric anhydride.

$N{a_2}{B_4}{O_7}.10{H_2}O\xrightarrow{\Delta }N{a_2}{B_4}{O_7}\xrightarrow{\Delta }2NaB{O_2} + {B_2}{O_3}$

• Oxidising Flame: On heating with a colored salt, the glassy bead forms a colored metaborate.

$\mathrm{CuSO}_{4} \xrightarrow[]{\Delta} \mathrm{CuO}+\mathrm{SO}_{3}$

$\mathrm{CuO}+\mathrm{B}_{2} \mathrm{O}_{3} \xrightarrow[]{\Delta} \mathrm{Cu}\left(\mathrm{BO}_{2}\right)_{2} \text {, copper }(\mathrm{II}) \text { metaborate, blue }$

$\mathrm{Fe}_{2} \mathrm{O}_{3}+3 \mathrm{~B}_{2} \mathrm{O}_{3} \xrightarrow[]{\Delta} 2 \mathrm{Fe}\left(\mathrm{BO}_{2}\right)_{3} \text {, iron }(\mathrm{III}) \text { metaborate, yellow }$

$\mathrm{Cr}_{2} \mathrm{O}_{3}+3 \mathrm{~B}_{2} \mathrm{O}_{3} \xrightarrow[]{\Delta} 2 \mathrm{Cr}\left(\mathrm{BO}_{2}\right)_{3}, \text { chromium }(\text { III }) \text { metaborate, green }$

$\mathrm{CoO}+\mathrm{B}_{2} \mathrm{O}_{3} \xrightarrow[]{\Delta} \mathrm{Co}\left(\mathrm{BO}_{2}\right)_{2}, \text { cobalt }(\mathrm{II}) \text { metaborate, blue }$

• Reducing Atmosphere: Borax bead test can be carried out in the reducing atmosphere by using a charcoal cavity. The carbon background will act as reducing the atmosphere.

$\mathrm{CuO}+\mathrm{B}_{2} \mathrm{O}_{3} \rightarrow \mathrm{Cu}\left(\mathrm{BO}_{2}\right)_{2} \text {, blue }$

$2 \mathrm{Cu}\left(\mathrm{BO}_{2}\right)_{2}+\mathrm{C} \rightarrow 2 \mathrm{CuBO}_{2}(\text { white })+\mathrm{CO}+\mathrm{B}_{2} \mathrm{O}_{3}$

$2 \mathrm{CuBO}_{2}+\mathrm{C} \rightarrow 2 \mathrm{Cu}(\mathrm{red})+\mathrm{B}_{2} \mathrm{O}_{3}+\mathrm{CO}$

$\mathrm{FeO}+\mathrm{B}_{2} \mathrm{O}_{3} \rightarrow \mathrm{Fe}\left(\mathrm{BO}_{2}\right)_{2} \text {, green }$

Identification of Acidic Radicals (or) Anions

• Most of the salts are reacted with $dil.{H_2}S{O_4}$ (or) dil HCl and $Conc.{H_2}S{O_4}$are release characteristic gas with acidic radicals.

• But some anions are not decomposed either by $dil.{H_2}S{O_4}$ or $Conc.{H_2}S{O_4}$.

• Hence acidic radicals have been classified into three groups, depending upon salt response to a reagent.
  
  

Group-I: Contains the radicals which are detected by $dil.{H_2}S{O_4}$(or) dil HCl. They are 

1. Carbonates$\left( {CO_3^{ - 2}} \right)$

2. Sulphite $\left( {SO_3^{ - 2}} \right)$

3. Sulphide $\left( {{S^{ - 2}}} \right)$

4. Nitrite $\left( {NO_2^{ - 1}} \right)$

5. Acetate $\left( {C{H_3}CO{O^{ - 1}}} \right)$
   
   

Group-II: Contains the radicals which are detected by $Conc.{H_2}S{O_4}$

1. Chloride $\left( {C{l^ - }} \right)$

2. Bromide $\left( {B{r^ - }} \right)$

3. Iodide $\left( {{I^ - }} \right)$

4. Nitrate $\left( {NO_3^ - } \right)$

5. Oxalate  $\left( {{C_2}O_4^{ - 2}} \right)$

Group-III: Contains the radicals which don’t give any characteristic gas with dilute and  $Conc.{H_2}S{O_4}$.

They are:

1. Sulphate $\left( {SO_4^{ - 2}} \right)$

2. Phosphate $\left( {PO_4^{ - 3}} \right)$

1. Reaction of $\left( {CO_3^{ - 2}} \right)$ ions:

i) With Dilute HCl: gives effervescence, due to the evolution of carbon dioxide.

The gas carbon dioxide turns lime water milky white ppt

$CO_3^{2 - } + 2H^+ {\text{ }} \to CO_2 + {H_2}O$ 

The gas gives turbidity with lime water and baryta water.

$\begin{array}{*{20}{l}}{C{O_2} + C{a^{2+}} + 2OH^- \to CaC{O_{3{\text{ }}}} + {H_2}O} \\{C{O_2} + B{a^{2+}} + 2OH^- \to BaC{O_{3}} + {H_2}O}\end{array}$ 

On prolonged passage of carbon dioxide in lime water, the turbidity sluggishly disappears due to the conformation of answerable hydrogen carbonate.

$CaCO_3 + C{O_2} + {H_2}O \to Ca{(HC{O_3})_2}$

ii) Barium Chloride or Calcium Chloride Solution: 

White ppt of barium or calcium carbonate is obtained, which is soluble in mineral acid.

$CO_3^{2 - } + B{a^{2 + }} \to BaC{O_3} \downarrow $

$CO_3^{2 - } + C{a^{2 + }} \to CaC{O_3} \downarrow $ 

The ppt is soluble in mineral acids and carbonic acid(soda water).

$BaC{O_3} \downarrow  + 2{H^ + } \to B{a^{2 + }} + C{O_2} \uparrow  + {H_2}O$

$BaC{O_3} \downarrow  + C{O_2} + {H_2}O \to B{a^{2 + }} + 2HCO_3^ - $

iii) Silver Nitrate Solution: 

White ppt of silver carbonate is obtained.

$CO_3^{2 - } + 2Ag^{ + } \to A{g_2}CO_3 $

The ppt so attained is soluble in nitric acid and in ammonia.

The ppt becomes brown on addition of excess reagent and the same may also be if the blend is boiled, due to the conformation of tableware oxide $A{g_2}CO_3  \to Ag{O } + C{O_2}$

2.   Sulphites $\left( {SO_3^{ - 2}} \right)$

i) Dilute HCl or Dilute ${H_2}S{O_4}$

decomposes with the evolution of sulfur dioxide

$SO_3^{2 - } + 2{H^ + } \to S{O_2} + {H_2}O$

The gas has a suffocating odor of burning sulfur.

ii) Acidified potassium dichromate solution: 

Turns sludge paper moistened with acidified potassium dichromate result, green due to the conformation of $C{r^{3 + }}$ions.

iii) Lime water: On passing the gas through lime water, a milky ppt is formed.

The precipitate dissolves on prolonged passage of the gas, due to the conformation of hydrogen sulfite ions.

iv) Barium chloride or Strontium chloride solution: Gives white ppt. of barium or strontium sulfite.

3.   Sulphide $\left( {{S^{ - 2}}} \right)$

i) Dil. HCl or Dil. ${H_2}S{O_4}$: 

A colorless gas smelling of rotten eggs $\left( {{H_2}S} \right)$is evolved.

${S^{2 - }} + 2{H^ + } \to {H_2}S$

ii) The gas turns lead acetate paper black

iii) Silver nitrate solution: Black ppt. of silver sulfide insoluble in cold but soluble in hot dil nitric acid.

iv) Sodium Nitroprusside Solution: Turns sodium nitroprusside solution purple

$N{a_2}S{\text{ }} + {\text{ }}N{a_2}[Fe{\left( {CN} \right)_5}NO]{\text{ }} \to N{a_4}[Fe{\left( {CN} \right)_5}NOS]$ 

4.   Nitrites $(NO_2^ - )$

i)   Dil HCl and Dil. ${H_2}S{O_4}$ : Adding to solid nitrite in cold yields pale blue liquid (due to the presence of free nitrous acid $HN{O_2}$ or its anhydride ${N_2}{O_3}$ & the evolution of brown fumes of nitrogen dioxide, the latter being largely produced by a combination of nitric oxide with the oxygen of the air

ii)    Silver nitrate solution: White crystalline ppt. is obtained

iii) Turns acidified KI - starch paper blue

2KI + 2NO2 → 2KNO2 + I2 

Starch + I2 → Blue colour

5. Acetate  $({\mathbf{C}}{{\mathbf{H}}_{\mathbf{3}}}{\mathbf{CO}}{{\mathbf{O}}^ - })$ 

i) Dilute Sulphuric Acid: A smell of vinegar is observed.

$C{H_3}CO{O^ - } + {H^ + } \to {\text{ }}C{H_3}COOH$ 

The following test is performed with the aqueous salt solution.

ii) Iron (III) Chloride Solution: Gives deep - red coloration

3$C{H_3}COONa{\text{ }} + {\text{ }}FeC{l_3} \to {(C{H_3}COO)_3}Fe{\text{ }} + {\text{ }}3NaCl$ 

Brown color ppt forms

6. Thiosulphates 

i) Dil Hydrochloric acid: Gives sulphur & sulphur dioxide

ii) Silver nitrate solution: Gives white ppt. of silver thiosulphate.

The ppt. is unstable, turning dark on standing when silver sulphide is formed.

iii)   Lead acetate or Lead nitrate solution: Gives white ppt.

On boiling, it turns black due to the formation of PbS.

7. Chloride $\left( {C{l^ - }} \right)$

• Conc. ${H_2}S{O_4}$  : decomposes with the evolution of HCl.

$C{l^ - } + {\text{ }}{H_2}S{O_4} \to {\text{ }}HCl{\text{ }} + {\text{ }}HSO_4$- 

Gas so produced

(1) Turns blue litmus paper red

(2) Gives white fumes of NH4Cl when a glass rod moistened with ammonia solution is brought near the mouth of the test tube.

• Silver nitrate solution: White, curdy ppt. of AgCl insoluble in water & in dil .nitric acid, but soluble in dilute ammonia solution.

v)  Chromyl chloride test: When a salt containing chloride ion is heated with ${K_2}C{r_2}{O_7}$  and conc. ${H_2}S{O_4}$  orange-red fumes of chromyl chloride $(Cr{O_2}C{l_2})$ are formed.

${K_2}C{r_2}{O_7} + {\text{ }}4NaCl{\text{ }} + {\text{ }}6{H_2}S{O_4} \to {\text{ }}2KHS{O_4} + {\text{ }}4NaHS{O_4} + {\text{ }}2Cr{O_2}C{l_2}{\text{ }} + {\text{ }}3{H_2}O$ 

A sample of chlorine-containing salt is heated with conc $\mathrm{H}_{2} \mathrm{SO}_{4}$ in presence of $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$, deep red vapours of chromyl chloride are evolved.

$\mathrm{NaCl}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{NaHSO}_{4}+\mathrm{HCl}$

$\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}+2 \mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow 2 \mathrm{KHSO}_{4}+2 \mathrm{CrO}_{3}+\mathrm{H}_{2} \mathrm{O}$

$\mathrm{CrO}_{3}+2 \mathrm{HCl} \rightarrow \mathrm{CrO}_{2} \mathrm{Cl}_{2}+\mathrm{H}_{2} \mathrm{O}$

                            Chromyl chloride

                             (deep red vapour)

When these vapours are passed through a NaOH solution, the solution becomes yellow due to the formation of sodium chromate.

$\mathrm{CrO}_{2} \mathrm{Cl}_{2}+4 \mathrm{NaOH} \rightarrow \mathrm{Na}_{2} \mathrm{CrO}_{4}+2 \mathrm{NaCl}+2 \mathrm{H}_{2} \mathrm{O}$

The yellow solution is neutralized with acetic acid and on the addition of lead acetate gives a yellow precipitate of lead chromate.

$\mathrm{Na}_{2} \mathrm{CrO}_{4}+\mathrm{Pb}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2} \rightarrow \mathrm{PbCrO}_{4}+2 \mathrm{CH}_{3} \mathrm{COONa}$

8.   Bromide $({\mathbf{B}}{{\mathbf{r}}^ - })$ 

• Conc. ${H_2}S{O_4}$  : Gives reddish-brown vapors of bromine accompanying the hydrogen bromide.

• Manganese dioxide and conc. sulphuric acid: When a mix of solid bromide, $Mn{O_2}$, and conc.${H_2}S{O_4}$ is heated reddish-brown vapors of bromine are evolved.

The following tests are performed with the aqueous salt solution.

• Silver nitrate solution: Pale yellow ppt. of silver bromide is obtained. This ppt. is sparingly soluble in dil but readily soluble in conc. ammonia solution and insoluble in dil. $HN{O_3}$

• Lead acetate solution: White crystalline ppt. of lead bromide which is soluble in boiling water.                   

9.   Iodide $\left( {{I^ - }} \right)$

• Conc. ${H_2}S{O_4}$ : Gives violet vapors of iodine

• Silver nitrate solution: Yellow ppt. of silver iodide AgI, very slightly soluble in conc. ammonia solution and insoluble in dil nitric acid.

10.  Nitrate $\left( {NO_3^ - } \right)$

• Conc ${H_2}S{O_4}$  : Gives reddish-brown vapors of nitrogen dioxide

• Brown ring test: When freshly saturated solution of iron (II) sulfate is added to nitrate solution and conc. H2SO4 is poured slowly down the side of the test - tube, a brown ring is obtained.

On shaking and warming the mix, the brown color disappears, nitric oxide is evolved and a yellow solution of Iron(III) ions remains.

11. Test for Oxalate ion [C2O24 – ]

CaCl2 + Na2C2O4 → CaC2O4 (White precipitate) + 2NaCl

12. Sulfate $({\mathbf{S}}{{\mathbf{O}}_{\mathbf{4}}}^{{\mathbf{2}} - })$ 

i)     Barium chloride solution: White ppt. of barium sulfate $BaS{O_4}$ insoluble in warm dil. hydrochloric acid and in dilute nitric acid but moderately soluble in boiling, conc. hydrochloric acid.

ii)    Lead acetate solution: Gives white ppt forms

Na2SO4 + (CH3COO)2Pb → PbSO4(white ppt) + 2CH3COONa

13. Test for Phosphate ion [PO3 4 –]

Na2HPO4 + 12 (NH4 )2 MoO4 + 23 HNO3 → (NH4 )3 [P (Mo3O10) 4 ] (Canary yellow precipitate) + 2NaNO3 + 21NH4NO3 + 12H2O

Test for Cations:

Group I $({\mathbf{P}}{{\mathbf{b}}^{{\mathbf{2}} + }},{\text{ }}{\mathbf{A}}{{\mathbf{g}}^ + },{\text{ }}{\mathbf{H}}{{\mathbf{g}}^ + })$ 

• $PbC{l_2}$  gives a yellow ppt. with ${K_2}Cr{O_4}.$  The ppt. is insoluble in acetic acid but soluble in NaOH

$PbC{l_2} + {\text{ }}2KI{\text{ }} \to Pb{I_2}{\text{ }} + {\text{ }}2KCl$

$PbC{l_2} + {\text{ }}2KI{\text{ }}\left( {excess} \right){\text{ }} \to {\text{ }}{K_2}[Pb{I_4}]$ 

• AgCl is soluble in NH4OH forming a complex while $H{g_2}C{l_2}$  forms a black ppt. with $N{H_4}OH$ .

2.    Group II A  

• $C{u^{ + 2}}$  ions in solution give deep blue color with an excess of $N{H_4}OH$ $C{u^{ + 2}} + {\text{ }}4N{H_4}OH{\text{ }} \to {[Cu{(N{H_3})_{4}}]^{ + 2}} + {\text{ }}4{H_2}O$ 

$C{u^{ + 2}}$  ions give a chocolate precipitate with ${K_4}Fe{\left( {CN} \right)_6}.$ 

$2C{u^{ + 2}} + {\text{ }}{K_4}Fe{\left( {CN} \right)_6} \to C{u_2}[Fe{\left( {CN} \right)_6}]{\text{ }} + {\text{ }}4{K^ + }$ 

• For Pb2+

3PbS + 8HNO3 → 3Pb (NO3)2 + 2NO + 4H2O + 3S 

Pb(NO3 )2 + H2SO4 → PbSO4 + 2HNO3

White precipitate of lead sulphate appears in the above reaction. For further confirmation.

PbSO₄ + 4CH₃COONH₄ → (NH₄)₂ [Pb (CH₃COO)₄ ] + (NH₄)₃SO₄ 

(NH4)₂ [Pb(CH₃COO)4 ] + K2CrO₄ → PbCrO₄ + 2CH₃COOK + 2(NH₄)₂SO₄

The Colour of PbCrO₄ is yellow which confirms the presence of Pb²⁺.

3.   Group II B 

• $A{s^{ + 3}}$ ions in solution give a yellow precipitate with ammonium molybdate and$HN{O_3}$  on heating.

${H_3}As{O_4} + 12{(N{H_4})_2}Mo{O_4} + 21HN{O_3} \to {\text{ }}{(N{H_4})_3}AsM{o_{12}}{O_{40}} + {\text{ }}21N{H_4}N{O_3} + {\text{ }}12{H_2}O$ 

4.    Group III A

• White precipitate of $Al{\left( {OH} \right)_3}$ is soluble in NaOH

• $Al{\left( {OH} \right)_3} + {\text{ }}NaOH \to NaAl{O_2} + {\text{ }}2{H_2}O$ 

• $Fe{\left( {OH} \right)_3}$ is insoluble in NaOH

• Brown precipitate of $Fe{\left( {OH} \right)_3}$ is dissolved in HCl and addition of KCNS to this solution gives   blood red color.

• Also on the addition of K₄Fe(CN)₆ to this solution, a Prussian blue color is obtained.

$FeC{l_3} + {\text{ }}3{K_4}Fe{\left( {CN} \right)_6} \to {\text{ }}F{e_4}{[Fe{\left( {CN} \right)_6}]_3} + {\text{ }}12KCl$ 

5.   Group IV $({\mathbf{N}}{{\mathbf{i}}^{{\mathbf{2}} + }},{\text{ }}{\mathbf{C}}{{\mathbf{o}}^{{\mathbf{2}} + }},{\text{ }}{\mathbf{M}}{{\mathbf{n}}^{{\mathbf{2}} + }},{\text{ }}{\mathbf{Z}}{{\mathbf{n}}^{ + {\mathbf{2}}}})$ 

• $N{i^{ + 2}}$ after conversion into NiCl₂ forms a red ppt with dimethyl glyoxime.

• Co2+ ion forms a yellow ppt in the following reaction.

CoCl₂ + 7KNO₂ + 2CH₃COOH → K₃ [Co(NO₂) 6] + 2KCl + 2CH₃COOK + NO + H₂O

• $Z{n^{ + 2}}$ ions in solution give a white precipitate with NaOH, which dissolves in excess of NaOH.

• Mn2+ ions in solution give a pink precipitate with NaOH turning black or brown on heating.

6. Group V $({\mathbf{B}}{{\mathbf{a}}^{{\mathbf{2}} + }},{\text{ }}{\mathbf{S}}{{\mathbf{r}}^{{\mathbf{2}} + }},{\text{ }}{\mathbf{C}}{{\mathbf{a}}^{{\mathbf{2}} + }})$ 

• $B{a^{ + 2}}$ ions in solution give yellow precipitate with ${K_2}Cr{O_4}$ 

$B{a^{ + 2}} + {\text{ }}{K_2}Cr{O_4} \to {\text{ }}BaCr{O_4}{\text{ }} + {\text{ }}2{K^ + }$ 

• $S{r^{ + 2}}$ ions give a white precipitate with ${(N{H_4})_2}S{O_4}$.

• $C{a^{ + 2}}$ ions give a white precipitate with ${(N{H_4})_2}{C_2}{O_4}$ only.

7.   Group VI 

For Mg2+, white ppt of Magnesium ammonium phosphate forms as shown in below reaction.

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

8.  Group 0

NH4+ ion can be formed by the following reaction sequence.

(NH₄)₂SO₄ + 2NaOH → Na₂ SO4 + 2NH₃ + 2H₂O 

NH₃ + HCl → NH₄Cl(white)

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

Importance of Inorganic Chemistry Principles of Qualitative Analysis

The qualitative analysis of a substance helps in the determination of the physical and chemical properties of a compound, element, or ion. There are different types of qualitative analysis methods that are covered in this chapter.

This chapter will introduce how different extracts are formulated and then analyzed to understand the qualitative features of compounds. These techniques can also be used in the analysis of organic compounds.

It will describe how different methods are used for analysing and confirming the presence of particular elements, ions, functional groups, and compounds. Sodium extract is one such method. The inorganic salts are also analyzed using their various qualitative features such as crystal structure, colour, precipitation, etc.

There are other means of testing various compounds to check their activities such as heating, flame test, etc. JEE Advanced Inorganic Chemistry Principles of Qualitative Analysis will explain how different cations and anions behave in such tests.

This chapter is extremely important for the students who are preparing to appear in the JEE Advanced exam. The fundamental principles of this chapter will guide students to determine elements, anions, cations, functional groups, and compounds. They will also guide us to find out the results of different types of qualitative reactions.

Benefits of Vedantu’s Principles of Qualitative Analysis Notes PDF

• These revision notes are compiled with the sole aim to simplify the crucial concept of inorganic chemistry. These concepts have multiple applications in Chemistry.

• These notes are prepared in such a way that students can utilize these notes to learn how to answer questions related to chemical tests, and reactions, and how to determine the subsequent results.

• These revision notes will enable students to prepare this chapter for the JEE Advanced exam.

• They can resolve all doubts on their own using these notes. Such notes will help them strengthen their foundation by offering a consolidated study resource on this chapter. 

Download Principles of Qualitative Analysis JEE Advanced Notes Free PDF

The PDF of Principles of Qualitative Analysis revision notes is available on Vedantu for free download. Students can refer to these notes and prepare this chapter effectively for the exam. These notes cover all topics given in the chapter in detail, thus, students can quickly revise the chapter with the help of these revision notes before their exam and answer all questions asked from this chapter.

Important Related Links for JEE Main and JEE Advanced