Question

Give the formula for a reagent which will:

a. dissolve SnS₂ but not HgS

b. dissolve Cu(OH)₂ but not Bi(OH)₃

c. form a precipitate with Cu²⁺ but not with Cd²⁺

d. form a precipitate with Bi³⁺ but not with Cd²⁺

e. form a precipitate with HgCl₂ but not with SnCl₂

Answer 1

a) SnS2 can be dissolved in NaOH(aq) or KOH(aq) but HgS can't be dissolved.

   NaOH can be used to separate the II group cations into copper(II) ion group and Arsenic(III) ion group.

   Hg^2+ belongs to copper (II) ion group and Sn^4+ belongs to Arsenic(III) ion group. Copper group sulfides are soluble in NaOH but arsenic group metal sulfides are not soluble.

b) Cu(OH)2 can dissolved in NH3(l) but Bi(OH)3 does not soluble. Because Cu(II) will form Cu(NH3)4^2+ complex which has deep blue color.

c) Cu2+ can form chocolate brown color precipitate with potassium ferrocyanide but Cd^2+ does not form precipitate with potassium ferrocyanide.

d) In concentrated ammonia solution only Bi^3+ can form precipitate but not Cd^2+

c) Potassium iodide can form precipitate with HgCl2 but not with SnCl2.