Which of the following Group I cations forms a white chloride precipitate with dilute , which unique — Qualitative and Quantitative Analysis Chemistry Question
Question
Which of the following Group I cations forms a white chloride precipitate with dilute $HCl$, which uniquely undergoes a disproportionation reaction to turn completely black upon the addition of aqueous ammonia?
Answer: C
💡 Solution & Explanation
$Hg_2Cl_2$ (calomel) is a white precipitate. When treated with $NH_4OH$, it undergoes disproportionation to form finely divided elemental mercury ($Hg$, black) and mercury(II) amidochloride ($Hg(NH_2)Cl$, white). The overall mixture appears black.
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