Analytical ChemistryHard

Question

Which of the following statements is/are correct ?

Options

A.An aqueous solution of Co(II) thiocyanate (10% freshly prepared) and mercuric nitrate solution taken in equal volumes on stirring the wall of the vessel with a glass rod produce deep-blue precipitate.
B.White precipitate of Al(OH)3 is soluble in sodium hydroxide as well as in ammonia solution.
C.Green precipitate of Cr(OH)3 readily dissolves in excess of sodium hydroxide forming a green solution.
D.Chromium (III) salts give green coloured borax bead in both oxidising and reducing flame.

Solution

(A) Hg2+ + Co2+ + 4SCN- → Co[Hg(SCN)4] ↑ (deep blue)
(B) Soluble in NaOH forming [Al(OH)4]-, not in NH3 (aq)
(C) Cr(OH)3 ↑ (green) + OH- ⇋ [Cr(OH)4]- (green solution)
(D) Correct statement.

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