1.6 g of pyrolusite ore was treted with 50 " mL of " 1.0 N oxalic acid and some sulphuric acid. The oxalic acid left undecomposed was raised to 250 mL in a flask. 25 " mL of " this solution, when titrated with 0.1 N `KMnO_4` required 32 " mL of " this solution. Find out the percentage of pure `MnO_2` and also the percentage of available oxygen from `MnO_2`.

Explanation

`25xm^(3)" of oxalic acid left required "KMnO_(4)=32cm^(3)" of 0.1 M"`
`therefore 250 cm^(3)" of the oxalic acid required "KMnO_(4) = 320 cm^(3)" of 0.1 N = 32 cm"^(3) " of 1 N"`
`therefore" Oxalic acid used up pyrolusite "=(50-32)cm^(3)" of 1 N "=18cm^(3)" of 1 N"`
`18cm^(3)" fo 1 N oxalic acid = 18 millieq. of oxalic acid"`
It must have reacted with equivalent amount of `MnO_(2)" of pyrolusite"`
`"Eq. wt. of "MnO_(2)=(55+32)/(2)=(87)/(2)=43.5`
`therefore" 18 millieq. Of oxalic acid = 18 millieq. of "MnO_(2)=(18)/(1000)xx43.5g=0.783g`
`therefore" "%" of pure "MnO_(2)" in pyrolusite "=(0.783)/(1.6)xx100=48.9%`