356 " mg of " an alloy of Zn and Cd is precipitated as ZnS and CdS by `H_(2)S`. The mixed precipitate sulphur. The filterate is acidified and the divalent `Fe^(2+)` reqruied 1.6 millimoles of `KMnO_(4)` Find the percentage of Cd in the alloy. `(Cd=112,Zn=65.4)`

Explanation

`ZnS+Fe_(2)(SO_(4))_(3)toZnSO_(4)+2FeSO_(4)+S`
`CdS+Fe_(2)(SO_(4))_(3)toCdSO_(4)+2FeSO_(4)+S`
`m" Eq of "KMnO_(4)=1.6xx5`
`=8 m" Eq of "FeSO_(4)`
`=8 m" Eq of "ZnS and CdS`
`=8 m" Eq of "Zn and Cd`
Let m" Eq of "`Cd=x and m" Eq of "Zn=(8-x)`
Weight of `Cd=x xx(112)/(2)=56x`
Weight of `Zn=(8-x)xx(65.4)/(2)`
Total weight of Zn and Cd in ally
`56x+(8-x)xx(65.4)/(2)=356`
`x=4.05 xx10^(-3)xx56=0.2268g=226.8g`
`% of Cd=(226.8xx100)/(356)=63.7%`