CHM-DSM-251 Unit 1: Qualitative Inorganic Analysis

Course Code: CHM-DSM-251

Paper Name: Practical (Inorganic, Organic and Physical Chemistry)

Section Marks: 25 Marks

1. Introduction to Qualitative Analysis
2. Preliminary Tests
3. Identification of Anions
4. Identification of Cations (Group Analysis)
5. Exam Focus: Tips and Viva Questions

1. Introduction to Qualitative Analysis

Qualitative inorganic analysis involves the identification of the constituent particles (ions) present in an inorganic salt or mixture. For this paper, the focus is on mixtures containing 2 anions and 2 cations without interfering radicals.

2. Preliminary Tests

Before deep wet tests, physical observations provide crucial clues about the ions present.

Color: Blue (Copper), Light Green (Ferrous), Pink (Manganese), Dark Brown (Ferric).
Solubility: Testing if the salt dissolves in water or dilute acids helps in preparing the "Original Solution" (O.S.).
Dry Heating Test: Heating the salt in a dry test tube may release gases or cause color changes (e.g., crackling sound for Lead Nitrate).

3. Identification of Anions

Anions are generally tested by treating the salt with acids to observe the evolution of characteristic gases.

Group I Anions (Dilute H2SO4 Group)

Carbonate (CO3²⁻): Brisk effervescence of CO2 gas that turns lime water milky.
Sulphide (S²⁻): Smell of rotten eggs (H2S gas).
Nitrite (NO2⁻): Pungent reddish-brown fumes of NO2.

Group II Anions (Concentrated H2SO4 Group)

Chloride (Cl⁻): Pungent white fumes of HCl; confirmed by the Chromyl Chloride Test.
Bromide (Br⁻): Reddish-brown fumes of Br2.
Nitrate (NO3⁻): Brown fumes enhanced by adding copper turnings; confirmed by the Brown Ring Test.

4. Identification of Cations (Group Analysis)

Cations are identified systematically by separating them into groups based on their solubility products.

Group	Group Reagent	Common Cations
Group I	Dilute HCl	Pb²⁺, Ag⁺
Group II	H2S gas in presence of HCl	Cu²⁺, As³⁺
Group III	NH4OH + NH4Cl	Fe³⁺, Al³⁺
Group IV	H2S gas in presence of NH4OH	Zn²⁺, Mn²⁺
Group V	(NH4)2CO3 + NH4Cl	Ba²⁺, Ca²⁺, Sr²⁺
Group VI	Na2HPO4	Mg²⁺

5. Exam Focus: Tips and Viva Questions

Practical Exam Tips:

Original Solution: Ensure your O.S. is perfectly clear before proceeding to group analysis.
Washing: Always wash the precipitates obtained in each group before testing them to avoid contamination from previous groups.
Common Ion Effect: Remember that NH4Cl is added before NH4OH in Group III to suppress OH⁻ concentration.

Frequently Asked Questions

Q: Why is HCl added before H2S in Group II?
A: To suppress the ionization of H2S (common ion effect), ensuring that only cations with very low solubility products precipitate.

Q: What is the group reagent for Group V?
A: Ammonium carbonate [(NH4)2CO3] in the presence of NH4Cl and NH4OH.

Q: What are interfering radicals?
A: Anions like Oxalate or Phosphate that interfere with cation precipitation; however, these are not included in your current syllabus.