`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 0.03 `M KMnO_4` required to oxidize the same amount of `H_2S` gas to sulphur, in acidic medium is

Options

A. `60cm^(3)`
B. `80cm^(3)`
C. `90cm^(3)`
D. `120cm^(3)`

Answer

B

Explanation

`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)`