Question

Identify one anionic radical in the given inorganic salt ``M$_3$'' by performing dry and wet tests.

Hint:

Do screening with acid tests first, then run only the relevant confirmatory test. For halides: AgNO$_3$ colour + NH$_3$ solubility pattern is decisive. For sulphite vs sulphate: Ba$^{2+}$ test + acid solubility separates them. Handle conc. H$_2$SO$_4$ and NO$_x$ fumes in a fume hood.

Answer 1

Aim.  
To detect one acidic radical (anion) present in the sample "M3" using standard preliminary (dry) and confirmatory (wet) tests. 

Apparatus & Reagents (as needed). 
Test tubes, glass rod, dropper, corked test tube for brown–ring, watch glass, lead acetate paper, blue/red litmus, lime water (Ca(OH)2), freshly prepared FeSO4 solution, BaCl2 solution, dil. & conc. H2SO4, AgNO3, dil. NH3, chlorine water, starch–KI paper, KMnO4/acid, etc. 

Step 1: Preliminary (physical) check. 
Note colour/odour/texture. (Most anion tests are independent of this, but note any vinegar smell ⇒ acetate, rotten‐egg odour on moistening ⇒ sulphide hints.) 

Step 2: Dry tests (on solid or with conc. acid). 
(A) Action of dilute H2SO4 on a pinch of salt. Observe the gas. 
 

Observation	Inference (possible anion)
Brisk effervescence; gas turns lime water milky, extinguishes flame	CO3^2- (carbonate)
Pungent gas with smell of burning sulphur; acidified dichromate paper turns green / moist blue litmus turns red then bleached	SO3^2- (sulphite) → SO2
Rotten‐egg smell; blackening of moist lead acetate paper	S^2- (sulphide) → H2S
Vinegar smell on warming	CH3COO^- (acetate)
Brown fumes appear only on adding Cu turnings too	NO2 from NO^-/NO3^- (nitrite/nitrate screening)

(B) Action of conc. H2SO4 (cautiously). 
 

Observation	Inference
Dense white fumes (HCl) that fume with NH3	Cl^-
Reddish–brown vapours (Br2)	Br^-
Violet vapours/black deposit (I2)	I^-
No obvious change (screen out SO4^2-, PO4^3- etc.)	Test by wet method

Step 3: Wet (confirmatory) tests on aqueous extract. 
Prepare an aqueous extract of "M3" (boil gently with distilled water, cool, filter). Perform appropriate tests guided by Step 2. Use at most one confirmatory set and record the matching result. 

(i) Halides (Cl^-, Br^-, I^-) — AgNO3 test: 
To 2 mL extract add dil. HNO3, then AgNO3. Note precipitate and its behaviour with NH3. 
 

Observation	Inference
White ppt. → dissolves in dil. NH3	Cl^- (AgCl)
Pale cream ppt. → dissolves only in conc. NH3	Br^- (AgBr)
Yellow ppt. → insoluble in NH3	I^- (AgI)

(ii) Sulphate (SO4^2-): Add dil. HCl then BaCl2. White heavy ppt. that is insoluble in acids ⇒ BaSO4 confirms SO4^2-. 
(iii) Sulphite (SO3^2-): Acidify extract and add acidified KMnO4 (or dichromate). Decolourisation with smell of SO2 confirms SO3^2-. Also gives white ppt. with BaCl2 soluble in dil. HCl (BaSO3). 
(iv) Carbonate (CO3^2-): Add dil. acid; pass gas through lime water ⇒ milky CaCO3 which clears on excess CO2 (due to Ca(HCO3)2) confirms CO3^2-. 
(v) Nitrate (NO3^-) — Brown‐ring test: 
To 2 mL extract add freshly prepared FeSO4, then carefully add conc. H2SO4 down the side to form two layers. A brown ring at the junction ⇒ NO3^-. 
(vi) Nitrite (NO2^-): Acidify a portion and add freshly prepared starch–KI paper: blue colour (via I2) confirms NO2^-. Also, with dil. H2SO4 and Cu turnings ⇒ brown fumes of NO2. 
(vii) Phosphate (PO4^3-): Acidify with HNO3, warm, then add ammonium molybdate and heat gently: canary yellow ppt. of ammonium phosphomolybdate confirms PO4^3-. 
(viii) Acetate (CH3COO^-): Warm the solid/extract with conc. H2SO4 + ethanol: fruity odour of ethyl acetate; or heat with conc. H2SO4 alone: vinegar smell (acetic acid). 

Step 4: Inference and Report. 
Match your observations from Step 2 with confirmatory evidence from Step 3 and write: 
Anion present in "M3": ______________________ (write the confirmed radical).