0.6 g of a sample of pyrolusite was boiled with 200 " mL of " `(N)/(10)` oxalic acid and excess of dilute sulphuric acid. The liquid was filtered and the residue washed. The filtrate and washing were mixed and made up to 500 mL in a measuring flask. 100 " mL of " this solution required 50 " mL of " `(N)/(30)KMnO_4` solution. Calculate the percentage of `MnO_2` in the sample `(Mn=55)`.

Explanation

m" Eq of "excess of oxalic acid
`=32xx0.1 "in" 25 mL`
`=32xx0.1xx(250)/(25) "in" 250 mL`
`=32 mEq`
Total oxalic acid used `=50xx1=50mEq`
m" Eq of "oxalic acid used for `MnO_2=50-32=18`
m" Eq of "`MnO_2=18`
`=18xx10^(-3)xx(87)/(2)g` of `MnO_2`
`=0.783g`
`%of MnO_2=(0.783)/(1.6)xx100)=48.93%`
m" Eq of "`MnO_2= mEq` of `O_2`
m" Eq of "`O_2=18`
Weight of `O_2=18xx10^(-3)xx8=0.144g(1" Eq of "O_2=8g`
% of `O_2=(0.144)/(1.6)xx100=9%`