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Principles of Qualitative Analysis appeared 7 times across 3 years — 0.8% of Chemistry. This question is from Identification of Anions and Gases.

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On passing a gas, 'X', through Nessler's reagent, a brown precipitate is obtained. The gas 'X' is

Solution & Explanation

Related Formula
2K₂[HgI₄] + NH₃ + 3KOH arrow HgO (NH₂)I + 7KI + 2H₂O
Core Logic

Nessler's reagent (K₂[HgI₄] in alkaline solution) reacts explicitly with ammonia gas (NH₃) or ammonium ions to create an insoluble iodide of Millon's base (HgO (NH₂)I). This characteristic complex showcases a signature brown structural coloration.

Step 1: Finalization

Thus, the unknown tracking gas 'X' is uniquely identified as ammonia (NH₃).

Pattern Recognition

Ammonia detection relies directly upon alkaline potassium tetraiodomercurate(II) resulting in brown Millon's base precipitations.

Chapter Mix

Class 12 Chemistry: Principles of Qualitative Analysis

More Principles of Qualitative Analysis Previous-Year Questions — Page 2

Q64 jee_main_2024_31_jan_morning Precipitate Colors
The compound that is white in color is
  • A. ammonium sulphide
  • B. lead sulphate
  • C. lead iodide
  • D. ammonium arsinomolybdate

Solution

Core Logic

Analyzing the colors of the given salts: Lead sulphate (PbSO₄) is white. Ammonium sulphide ((NH₄)₂S) is soluble/colorless in solution. Lead iodide (PbI₂) is bright yellow. Ammonium arsinomolybdate is yellow.

Chapter Mix

Class 12 Chemistry: Salt Analysis

Q81 jee_main_2024_31_jan_morning Anion Identification
Molar mass of the salt from NaBr, NaNO₃, KI and CaF₂ which does not evolve coloured vapours on heating with concentrated H₂SO₄ is ________ g mol⁻¹. (Molar mass in g mol⁻¹: Na: 23, N: 14, K: 39, O: 16, Br: 80, I: 127, F: 19, Ca: 40)
Numerical Answer. Answer: 78 to 78

Solution

Step 1: Analyzing the reactions with Concentrated H2SO4

NaBr conc. H₂SO₄ Br₂ (Reddish-brown vapour evolves) NaNO₃ conc. H₂SO₄ NO₂ (Brown vapour evolves) KI conc. H₂SO₄ I₂ (Violet vapour evolves) CaF₂ conc. H₂SO₄ HF (Colorless vapour evolves)

Thus, CaF₂ does not evolve colored vapours.

Step 2: Calculating Molar Mass

Molar mass of CaF₂: Ca = 40

F₂ = 2 × 19 = 38 Molar mass = 40 + 38 = 78 g/mol
Chapter Mix

Class 12 Chemistry: Salt Analysis

Rankbit System
JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%) | JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%)