`MnO_(2)` on ignition converts into `Mn_(3)O_(4)`. A sample of pyrolusite having 75% `MnO_(2)`, 20% inert impurities and rest water is ignited in air to constant mass. What is the percentage of Mn in the ignited sample ?

Options

A. `24.6%`
B. `37%`
C. `55.24%`
D. `74.05%`

Answer

C

Explanation

Let mass of sample is x g, mass of `MnO_(2)` is 0.75 xg
moles of `MnO_(2)=(0.75 x)/(87)`
mass of `Mn = (0.75 x)/(87) xxx 55 = 0.474x`
 `3MnO_(2) to Mn_(3)O_(4)+O_(2)`
mass of `Mn_(3)O_(4)` produced
`=(0.75 x)/(87) xx (1)/(3) xx 229=0.658 x g`
Total mass of residue=0.658x + 0.2 x (mass of impurities)
% of Mn in residue `= (0.474x)/(0.858x) xx 100 = 55.24`