Verified Solution • 2025–26 Session moderate

QJEEM23Ch860c: JEE Main 2023 Chemistry - Class 12 JEEM23Ch860c Solution: When a solution of mixture having two inorganic salts was…

When a solution of mixture having two inorganic salts was treated with freshly prepared ferrous sulphate in acidic medium, a dark brown ring was formed whereas on treatment with neutral FeCl3\mathrm{FeCl}_{3} , it gave deep red colour which disppeared on boiling and a brown red ppt was formed. The mixture contains :

Multiple Choice Options

  • A SO 32−_3^{2-} & C 2_2 O 42−_4^{2-}
  • B CH3COO−& NO3−\mathrm{CH}_{3} \mathrm{COO}^{-} \& ~\mathrm{NO}_{3}^{-}
  • C C2O42−& NO3−\mathrm{C}_{2} \mathrm{O}_{4}{ }^{2-} \& ~\mathrm{NO}_{3}^{-}
  • D SO32−& CH3COO−\mathrm{SO}_{3}^{2-} \& ~\mathrm{CH}_{3} \mathrm{COO}^{-}

Step-by-Step Verified Solution

The mixture of salts gives a dark brown ring when treated with ferrous sulphate in acidic medium. This is a characteristic reaction of nitrate ions (NO 3−_3^- ). The brown ring is due to the formation of a complex between NO and Fe 2+^{2+} .

Additionally, the mixture gives a deep red color when treated with neutral ferric chloride (FeCl 3_3 ), which then disappears upon boiling to form a red-brown precipitate. This is a classic reaction of acetate ions (CH 3_3 COO −^- ) with Fe 3+^{3+} . Initially, the acetate ions form a complex with ferric ions, leading to the deep red color. Upon boiling, hydroxide ions displace some acetate ions in the complex, resulting in the red-brown precipitate.

Therefore, the mixture contains acetate (CH 3_3 COO −^- ) and nitrate (NO 3−_3^- ) ions.

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