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The mass of potassium dichromate crystal...

The mass of potassium dichromate crystal required to oxidise `750 cm^(3)` of `0.6` M Mohr's salt solution is `(molar mass=392)`

Text Solution

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Mohr's salt is `FeSO_(4).(NH_(4))_(2)SO_(4).6H_(2)O`
Only oxidizable part is `Fe^(2+)`
`[Fe^(2+) rarr Fe^(3+) + e]xx 6`
`Cr_(2)O_(7)^(2-) + 14H^(+) + 6e^(-) rarr 2Cr^(3+) + 7H_(2)O`
`6Fe^(2+) + Cr_(2)O_(7)^(2+) + 14H^(+) rarr 6Fe^(3+) + 2Cr^(3+) + 7H_(2)O`
Minimoles of `Fe^(2+) = 750 xx 0.6 = 450`
Moles of `Fe^(2+) = 450/1000 = 0.450 mol`
6 mol `Fe^(2+) = 1 "mol" Cr_(2)O_(7)^(2-)`
`:. 0.450 mol Fe^(2+) = 0.450/6 = 0.075 mol Cr_(2)O_(7)^(2-) = 0.075 xx 294 g = 22.05 g`
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