`A` sample is a mixture of Mohr's salts and `(NH_(4))_(2)SO_(4). A 0.5 g ` sample on treatment with excess of `BaCl_(2)` solution gave `0.75 g BaSO_(4)`. Determine percentage composition of the salt mixture. What weight of `Fe_(2)O_(3)` would be obtained if `0.2 g` of the sample were ignited in air?

Answer

`18.77mg`

Explanation

Let the sample contain `x g` Mohr's salt `[FeSO_(4)(NH_(4))_(2)SO_(4).6H_(2)O]`
`=(x)/(392)xx2xx(0.5-x)/(132)=(0.75)/(233)`
Solving `x=0.23g` implies Mohr's salt `=(0.23)/(0.50)xx100=46%,(NH_(4))_(2)SO_(4)=54%`
Also moles of `Fe` in `0.2g` sample `=(x)/(392)xx(0.2)/(0.5)=2.347xx10^(-4)`
implies mass of `Fe_(2)O_(3)` obtained on ignition of `0.2` sample `=(2.347xx10^(-4))/(2)xx160=18.77mg`