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Standard XII

Chemistry

Stereoisomerism

An aqueous bl...

Question

An aqueous blue coloured solution of transition metal sulphate reacts with H2S in acidic medium to give a black ppt. A which is insoluble in warm aqueous solution of KOH. The blue solution on treatment with KI in weakly acidic medium turns yellow and produces a white ppt B . Identify the transition metal ion.write the chemical reaction involved in the formation of A and B.

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Solution

The transition metal is cu2+ and the compound is cuso4.5h20 which desolves in water to give blue coloured solution due to presence of cu2+ ion.
On passing H2S acidic medium in the solution a black precipitate of CuS is obtained and it is not soluble in KOH.
CuSO4 + H2S ------------> CuS+H2SO4

On addition of KI solution it produce yellow coloured solution of CuI2 which will decompose to give a white precipitate of Cu2I2 and I2

CuSO4 + KI ---->CuI2 + k2SO4
2CuI2----> Cu2I2 + I2

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