1.

How many germs of K_(2)C_(7)O_(7) are required to oxidise 20.0g of Fe^(+) ion in FeSO_(4) "to" Fe^(3+) ions if the reaction is carried out in the acidic medium? Molar mass of K_(2)Cr_(2)O_(7) and FeSO_(4) are 294 and 152 respectively.

Answer»

6.45g
7.45g
8.45g
9.45g

Solution :Number of moles of `FeSO_(4)=((20g))/(152g mol^(-1))`
=0.132mol
Ionic equation for the OXIDATION reaction carried in the acidic medium may be WRITTEN as:
`Cr_(2)O_(7)^(2-)+6Fe^(2+)+14H^(+) to 2Cr^(3+)+6fe^(3+)+7H_(2)O`
6 mol. of `Fe^(2+) -= ` 1 mol of `K_(2)Cr_(2)O_(7)`
0.132 mol of `Fe^(2+)-=((1 mol))/((6 mol))xx(0.132 mol^(-1)`
= 0.022 mol . of `K_(2)Cr_(2)O_(7)`
MASS of `K_(2)Cr_(2)O_(7) = (0.022 mol) xx(294 g mol ^(-1))`
= 6.468 g.


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