How many grams of potassium dichromate are required to oxidise 20.0 g of `Fe^(2+)` in `FeSO_(4)` to `Fe^(3+)` if the reaction is carried out in an acidic medium ? (Molar mass of `K_(2)Cr_(21)O_(7)` and `FeSO_(4))` are 294 and 152 respectively

Answer

`6.45`

Explanation

`Kr_(2)Cr_(2)O_(7)+4H_(2)SO_(4)rarrK_(2)SO_(4)+Cr_(2)(SO_(4))_(3)+4H_(2)O+3[O]`
`2FeSO_(4)+H_(2)SO_(4)+OrarrFe_(2)(SO_(4))_(3)+H_(2)Oxx3`
balanced redox reaction
`K_(2)Cr_(2)O_(7)+6FeSO_(4)+7H_(2)SO_(4)rarrK_(2)SO_(4)+Cr_(2)(SO_(4))_(3)+3Fe_(2)(SO_(4))_(3)+7H_(2)O`
It is evident from balanced equation that 6 moles of `FeSO_(4)=1` mole of `K_(2)Cr_(2)O_(7)`
`therefore` 20 g of `FeSO_(4)` will require `K_(2)Cr_(2)O_(7)`
`=(294)/(6xx152)xx20=6.45 g`