H_(2)S is passed into one dm^(3) of a solution containing 0.1 mole of Zn^(2+) and 0.01 mole of Cu^(2+) till the sulphide ion concentration reaches 8.1xx10^(-19) moles .Which one of the following statements is true? [K_(sp) of ZnS and CuS are 3xx10^(-22) and 8xx10^(-36) respectively]

H_(2)S is passed into one dm^(3) of a solution containing 0.1 mole of

1.	H_(2)S is passed into one dm^(3) of a solution containing 0.1 mole of Zn^(2+) and 0.01 mole of Cu^(2+) till the sulphide ion concentration reaches 8.1xx10^(-19) moles .Which one of the following statements is true? [K_(sp) of ZnS and CuS are 3xx10^(-22) and 8xx10^(-36) respectively]
Answer» Only ZnS precipitates Both CuS and ZnS precipitate Only CuS precipitates No precipitation occurs Solution :Precipitation occures only when ionic product exceeds the VALUE of solubility product. 1`dm^(3)` of a solution containing 0.1 mole of `Zn^(2+)` 0.01 mole of `Cu^(2+)`and `8.1xx10^(-19)` mole of `S^(2+)` .Let Ionic product of ZnS=`[Zn^(2+)][S^(2-)]` `=0.1xx8.1xx10^(-19)=8.1xx10^(-20)` `K_(sp)` of ZnS`=3xx10^(-22)` `therefore` Ionic product`gtK_(sp)` Both ZnS and CuS have less `K_(sp)` values than their respective ionic products so ZnS and CuS both precipitates.