Q1: What is the color of the precipitate formed by NiS when H₂S is passed in an ammoniacal medium?
Explanation: NiS forms a black precipitate when H₂S is passed in an ammoniacal medium.
Q2: Which of the following precipitates is pink in color?
Explanation: MnS forms a pink precipitate, while NiS and CoS are black, and ZnS is white.
Q3: When NiS, CoS, ZnS, and MnS are boiled with dilute HCl, which precipitates dissolve?
Explanation: ZnS and MnS dissolve in dilute HCl, forming their chloride salts (ZnCl₂ and MnCl₂), while NiS and CoS remain insoluble.
Q4: How are NiS and CoS dissolved after being insoluble in dilute HCl?
Explanation: NiS and CoS, being insoluble in dilute HCl, are dissolved using aqua regia, a mixture of HNO₃ and HCl in a 1:3 ratio.
Q5: What is the confirmatory test for Ni2+, and what color is observed?
Explanation: Ni2+ forms a red precipitate with dimethylglyoxime (DMG) in the presence of NH₄OH, confirming its presence.
Q6: What is the confirmatory test for Co2+, and what color is observed?
Explanation: Co2+ forms a deep blue color with NH₄SCN in acetone, confirming its presence.
Q7: What happens when MnCl₂ is treated with NaOH?
Explanation: MnCl₂ reacts with NaOH to form a white precipitate of Mn(OH)₂.
Q8: What happens when ZnCl₂ is treated with excess NaOH?
Explanation: ZnCl₂ initially forms Zn(OH)₂ with NaOH, but in excess NaOH, it dissolves to form the soluble complex Na₂[Zn(OH)₄].
Q9: What is the confirmatory color for Mn2+, and how is it achieved?
Explanation: Mn2+ is confirmed by oxidation to MnO₄⁻, which gives a purple color, typically using an oxidizing agent like HNO₃ or H₂O₂ in the presence of KMnO₄.
Q10: What is the confirmatory test for Zn2+, and what color is observed?
Explanation: Zn2+ is confirmed by passing H₂S in an ammoniacal medium, forming a white precipitate of ZnS.
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