When a salt is treated with sodium hydroxide solution it gives gas X. On passing gas X through reagent Y a brown coloured precipitate is formed. X and Y respectively, are:

Solution & Explanation

### Related Formula mathrmNH_4^+ + mathrmOH^- rightarrow mathrmNH_3uparrow + mathrmH_2mathrmO ### Core Logic 1. Treating an ammonium salt (containing mathrmNH_4^+) with mathrmNaOH releases Ammonia gas (mathrmX = mathrmNH_3): mathrmNH_4^+ + mathrmOH^- rightarrow mathrmNH_3uparrow + mathrmH_2mathrmO 2. Passing ammonia gas through Nessler's reagent (mathrmY = mathrmK_2[mathrmHgI_4] + mathrmKOH) produces a distinct brown precipitate (known as iodide of Millon's base): 2[mathrmHgI_4]^2- + mathrmNH_3 + 3mathrmOH^- rightarrow mathrmHgO cdot mathrmHg(NH_2)I downarrow (textbrown) + 7mathrmI^- + 2mathrmH_2mathrmO Hence, mathrmX is mathrmNH_3 and mathrmY is mathrmK_2mathrmHgI_4 + mathrmKOH. ### Pattern Recognition Classic confirmatory test for ammonium ion: heating with alkaline solutions yields mathrmNH_3 gas, which always produces a brown precipitate with alkaline Nessler's reagent. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Qualitative Salt Analysis Class 12 Chemistry: p-Block Elements

Reference Study Guides

Qualitative Salt Analysis

More Qualitative Salt Analysis Previous-Year Questions — Page 2

Q81 jee_main_2024_31_jan_morning Anion Identification
Molar mass of the salt from NaBr, NaNO_3, KI and CaF_2 which does not evolve coloured vapours on heating with concentrated H_2SO_4 is ________ textg mol^-1. (Molar mass in textg 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 xrightarrowtextconc. H_2SO_4 Br_2 (Reddish-brown vapour evolves) NaNO_3 xrightarrowtextconc. H_2SO_4 NO_2 (Brown vapour evolves) KI xrightarrowtextconc. H_2SO_4 I_2 (Violet vapour evolves) CaF_2 xrightarrowtextconc. H_2SO_4 HF (Colorless vapour evolves) Thus, CaF_2 does not evolve colored vapours. ### Step 2: Calculating Molar Mass Molar mass of CaF_2: Ca = 40 F_2 = 2 times 19 = 38 textMolar mass = 40 + 38 = 78 text g/mol ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Chemistry: Salt Analysis
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