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In qualitative analysis when H(2)S is pa...

In qualitative analysis when `H_(2)S` is passed through an aqueous solution of salt acidified with dil. HCL, a block precipitate is obtainned .On boiling the precipitate with dil. `HNO_(3)` it forms a solution of blue colour . Addition of excess of aqueous solution of ammonia to this solution given ....... .

A

deep blue precipitate of Cu `(OH)_(2)`

B

deep blue solution of `[Cu(NH_(3))_(4)]^(2+)`

C

deep blue solution of Cu `(NO_(3))_(2)`

D

deep blue solution of Cu `(OH)_(2)`. Cu `(ON_(3))_(2)`

Text Solution

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The correct Answer is:
B

In qualitative analysis when `H_(2)S` is passed through an aqueous sloution of salt acidified with dil . HCl a black ppt. of CuS is obtained .
`CuSO_(4)+H_(2)Soverset(dil. HCl)tounderset("blackppt")( CuS +)H_(2)SO_(4)`
On boiling CuS with dil. `HNO_(3)` it forms a blue coloured solution and the following reactions occur
`3CuS+8HNO_(3)to3Cu(NO_(3))_(2)+2NO+3S+4H_(2)O`
`S+2HNO_(3)toH_(2)SO_(4)+NO`
`2Cu^(2+)+SO_(4)^(2-)+2NH_(3)+2H_(2)OtoCu(OH)_(2)*CuSO_(4)+2NH_(4)OH`
`Cu(OH)_(2)*CuSO_(4)+8NH_(3)tounderset("Tetraammine copper"(||)("Deep blue solution"))(2[Cu(NH_(3))_(4)]SO_(4)+2OH^(-)+SO_(4)^(2-)`
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