Chromium(III) hydroxide is highly insoluble in distilled water but dissolves rea

Question

Chromium(III) hydroxide is highly insoluble in distilled water but dissolves readily in either acidic or basic solution. Briefly explain why the compound can dissolve in acidic or in basic but not in neutral solution. Write appropriate equations to support your answer. Explain how dissolving the Group IV carbonate precipitate with 6M CH_3COOH, followed by the addition of extra acetic add, establishes a buffer with a pH of approximately 5. A solution contains either Cr^3+ or Ni^2+ ion. Describe a reaction with a single reagent that will identify which ion is present. The addition of S^2-ion to Fe(OH)_2(s) results in the formation of FeS(s). Explain why the addition of S^2- ion to Cr(OH)_3(s) does not result in the formation of Cr_2S_3(s).

Explanation / Answer

1.The solubility product (Ksp) of Cromium(III) hydroxide is very less in water ( 6.3×10thpower -31 ) so it is highly insoluble in disdilled water , but due to amphoteric nature Cromium(III)hydroxide react both with acid and base forming soluble salt and complex respectively

Cr(OH)3 ---

- >Cr3- + 3OH-

< ----

Cr(OH)3 + 3HCl ---- > CrCl3 + 3 H2O

Cr(OH)3 + NaOH ---'--- > Na[Cr(OH)4]

3. If hydrogen sulphide is passed through the solution then Ni2+ is present black precipitate of NiS will form but Cr3+ will not form the Sulphide

Ni2+ S2- --------- > NiS (precipitate )

2. Dissolving Carbonate precipitate by acetic acid giving the salt of acetic acid.Compination of a weak acid and its salt act as a buffer solution.

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