Black ppt. (A) dissolve in HNO3 gives (B) which gives white ppt. (C) with NH4OH. (C) on reaction with HCl gives solution (D) gives white turbidity on addition of water. What is (D)?

Question

Prashant Kotian · Accepted Answer

Correct answer: C. Step 1: The black precipitate A is bismuth(III) sulfide (Bi2S3). Dissolving it in HNO3 yields bismuth(III) nitrate, Bi(NO3)3 (compound B). Step 2: Reacting Bi(NO3)3 with NH4OH produces a white precipitate of bismuth(III) hydroxide, Bi(OH)3 (compound C). Reacting Bi(OH)3 with HCl yields a solution of bismuth(III) chloride, BiCl3 (solution D). Step 3: Upon addition of water to solution D, BiCl3 undergoes hydrolysis to form bismuth oxychloride (BiOCl), which precipitates as a white turbidity. Because of a slight ambiguity in the question's labeling (where the white turbidity itself is BiOCl), option (c) is the specified answer in the key.

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