Qualitative Analysis - Problem 8

Description:

Problem − Which among the following statement(s) is/are true? Justify.

a) CCl₄ gives white precipitate with AgNO₃ resulting in positive silver nitrate test.

b) Nitrobenzene and benzoic acid can be separated through extraction by using ether and NaHCO₃.

c) KOH is used to absorb CO₂ evolved during estimation of carbon in organic compound.

d) The correct formula of Prussian blue complex is Fe₄[Fe(CN)₆]₃.

Solution

a) CCL₄ gives white precipitate with AgNO₃resulting in positive silver nitrate test…. (False!!)

• CCL₄ is a covalent compound and does not ionize.

• Thus, due to the absence of any free Cl^- ions in the solution, the AgNO₃ does not result in the formation of white precipitate of AgCl.

b) Nitrobenzene and benzoic acid can be separated through extraction by using ether and NaHCO₃…… (True!!)

• When a mixture of nitrobenzene and benzoic acid are shaken with a  dilute solution of NaHCO₃ and ether, the nitrobenzene moves to the ether layer due to increased solubility in organic solvent, while benzoic acid reacts with basic NaHCO₃ to form water-soluble salt which goes into the aqueous layer.

• Distillation of the organic solvent layer gives nitrobenzene.

• The aqueous layer when treated with dil.HCl,  benzoic acid gets precipitated, which is collected after filtration.

c) KOH is used to absorb CO₂ evolved during estimation of carbon in organic compound…. (True!!)

• Answer − CO₂ is slightly acidic in nature such that it reacts with basic KOH to give K₂CO₃ according to the reaction.

• 2KOH + CO₂ → K₂CO₃ + H₂O

d) The correct formula of  Prussian blue complex (ferri ferrocyanide) which is iron(III)hexacyanoferrate(II) is Fe₄[Fe(CN)₆]₃ …. (True!!)