Which of the following complex is formed when A reacts with K4[Fe(CN)6] ?
A
Prussian blue
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B
Turnbull's blue
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C
Brown ring complex
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D
Sodium nitroprusside
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Solution
The correct option is B Prussian blue Option (A) is correct. Compound A will be Fe2(SO4)3. When A reacts with K4[Fe(CN)6] gives prussian blue color. Fe2(SO4)3Δ−→Fe2O3+3SO3(A) Reddish brown precipitate of ferric hydroxide dissolves in hydrochloric acid and ferric chloride is formed. Fe(OH)3+3HCl⟶FeCl3+3H2O When the solution containing ferric chloride is treated with potassium ferrocyanide solution a blue precipitate/colouration is obtained. The colour of the precipitate is Prussian blue. It is ferric ferro-cyanide. 4FeCl3+3K4[Fe(CN)6]⟶Fe4[Fe(CN)6]3+12KCl