If an our sample containing `Mn` is treated with `50 mL` of `0.2750 M Na_(2)C_(2)O_(4)` and the unreacted `Na_(2)C_(2)O_(4)` required `18.28 mL` of `0.1232 M KMnO_(4)` in acidic medium, the number of moles of `Mn` in the ore is

Options

A. (a)`1.38xx10^(-2)`
B. (b)`1.49xx10^(-3)`
C. (c )`1.15xx10^(-2)`
D. (d)`8.12xx10^(-3)`

Answer

D

Explanation

Ore of Mn is `MnO_(2) ("pyrolusite")`.
`2e^(-)+MnO_(2) rarr Mn^(2+)`
`(x-4) rarr x=+2(x=4-2=2)`
`E_(w)` of `MnO_(2)=M_(w)/2`
Excess of `C_(2)O_(4)^(2-)=18.28xx0.1232xx5 mEq` of `MnO_(4)^(-)`
or `=11.26 mEq of C_(2)O_(4)^(2-)`
`Total C_(2)O_(4)^(2-)=50xx0.2750xx2 mEq=27.5 mEq`
Reacted `C_(2)O_(4)^(2-)=27.5-11.26=16.24=16.24 mEq of C_(2)O_(4)^(2-)`
`or =16.24 mEq of MnO_(2)=16.24xx10^(-3) eq of MnO_(2)`
Moles of `MnO_(2)=(16.24xx10^(-3))/2=8.12xx10^(-3) mol`