1.

50 cm^(3) of 0.04 M K_2Cr_2O_7 in acidic medium oxidizes a sample of H_2S gas to sulphur. Volume of 0.03M KMnO_4 required to oxidize the same amount of H_2S gas to sulphur, in acidic medium is

Answer»

`60cm^(3)`
`80cm^(3)`
`90cm^(3)`
`120cm^(3)`

SOLUTION :`K_(2)Cr_(2)O_(7)` and `KMnO_(4)` both are good oxidizing agents in acidic medium. The reaction is as follows :
`Cr_(2)O_(7)^(2-) + 14H^(+)+6e^(-) rarr 2Cr^(3+)+7H_(2)O`
`MnO_(7)^(2-)+8H^(+)+5e^(-) rarr MN^(2+)+4H_(2)O`
Normality of `Cr_(2)O_(7)^(2-)=` MOLARITY `xx` no. of ELECTRONS involved
`= 0.04xx6= 0.24` N
Normality of `MnO_(4)^(-)=` Molarity `xx` no. of electrons involved
`=0.03xx5= 0.15` N
`underset((K_(2)Cr_(2)O_(7)))(N_(1)V_(1))= underset((KMnO_(4)))(N_(2)V_(2))`
`rArr0.24xx50=0.15xxV_(2)`
`V_(2)=(0.24xx50)/(0.15)=80cm^(3)`


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