TargetIIT

1)excess KCN is added to cupric salt and H2S is passed through the solution. no black CuS is precipitated because Cu is present in the solution as
a)[Cu(CN)6][p]4-[/p]
B)[Cu(CN)4][p]3-[/p]
C)[Cu(CN)4][p]2-[/p]
D)NONE.

2)Co[p]3+[/p] forms a complex with F[p]-[/p] ion. the complex had a magnetic moment of 4.8BM. the hybridisation and geometry of the complex would be?

the answer is B..I read it in JD LEE that the compound given in B is soluble...

but govind i t have read it somewhere in ncert that Cu is more stable in +2 oxidation state than in +1 oxidation state........so shouldnt the answer be C?

@saket wat u have read is right... Cu[p]2+[/p] is more stable than Cu[p]+[/p]..and that's becsuse of the greater hydration energy released in case of Cu[p]2+[/p] ..but here in this case we have [Cu(CN)[ss]4[/ss]][p]2-[/p] and [Cu(CN)[ss]4[/ss]][p]3-[/p] ...more hydration energy will be released in case of [Cu(CN)[ss]4[/ss]][p]3-[/p]..that may be the reason but i am not sure abt it...

Another example Au exists in +1 and +3 oxidation states..and +3 oxidation state is more stable..but wen Au forms complex with CN[p]-[/p] (U may have read abt the complex in metallurgy chapter in the NCERT under the topic leaching and extraction of gold and silver) ..it exists in +1 oxidation state..

PS: Sometimes in inorganic it happens when u think logically u may get the wrong answer..but u shudnt feel disheartened...u shud learn frrom the mistake....coz inorganic chemistry is all abt learning and practicing more and more questions...

thanks man.......