Chemistry - Salt Analysis Question with Solution | TestHub
A mixture contains a Reddish Brown metallic oxide (A) and a yellow crystalline salt (B). When the mixture is treated with dilute sulphuric acid, it yields a clear acidic filtrate along with a yellow insoluble residue (B). The filtrate is oxidised with excess hydrogen peroxide, and the solution is subsequently boiled to expel the excess peroxide, cooled, and then divided into two equal portions.
(C). The first portion, on treatment with aqueous potassium ferrocyanide solution , produces a blue precipitate
• The second portion, on addition of ammonium thiocyanate ,develops a blood-red coloration.
The insoluble residue (B) is found to be :
• Insoluble in excess aqueous ammonia ,
• But readily soluble in potassium cyanide solution as well as in sodium thiosulphate solution.
Furthermore, the sodium extract of the original mixture, when treated with chlorine water, yields a brown solution. On shaking this solution with chloroform, the organic layer turns violet.
Substance a dissolved in HCl and a coloured solution is prepared. Calculate number of reagents that can convert this solution green.
Tin(II) chloride, Potassium iodide, Hydroxylamine, Hydrochloride, Hydrazine sulphate, Ascorbic acid, Zinc metal, Cadmium metal, Hydrogen sulphide, Sulphurdioxide, Concentrated nitric acid, Hydrogen peroxide, Concentrated hydrochloric acid with Potassium chlorate, Aquaregia, Potassium permanganate, Potassium dichromate, Cerium(IV) sulphate in acid solution .
Answer:
Solution:
Reddish-brown oxide is A = Fe₂O₃.
After dissolving in HCl, the solution contains Fe³⁺ ions.
A blue precipitate with potassium ferrocyanide and a blood-red colour with SCN- confirm Fe³⁺.
The green color corresponds to Fe²⁺, so we count reagents that reduce Fe³⁺→ Fe2+
Reducing reagents are:
KI
Hydroxylamine hydrochloride
Hydrazine sulfate
Ascorbic acid
Zinc metal
Cadmium metal
H2S
Total reducing reagents = 7.
Oxidizing agents like KMnO₄, K₂Cr₂O₇, HNO₃, H₂O₂, Ce4+ etc., do not produce a green Fe²⁺ solution.
Hence, the final answer is 7.