A sample of pynolusite (MnO_(2)) weights 0.5 gm. To this solutioin 0.594 gm As_(2)O_(3) and a dilute acid are added. After the reaction has stopped As^(+3) is AS_(2)O_(3) is titrated with 45 mlof M/50 KMn_(4) solution. Calculate the percentage of MnO_(2) in pyrolusite.

A sample of pynolusite (MnO_(2)) weights 0.5 gm. To this solutioin 0.5

1.	A sample of pynolusite (MnO_(2)) weights 0.5 gm. To this solutioin 0.594 gm As_(2)O_(3) and a dilute acid are added. After the reaction has stopped As^(+3) is AS_(2)O_(3) is titrated with 45 mlof M/50 KMn_(4) solution. Calculate the percentage of MnO_(2) in pyrolusite.
Answer» `65.25%` `68%` `67.3%` `66.6%` Solution :`MnO_(2)+As_(2)O_(3)rarrMn^(+2)+AsO_(4)^(-3)` For excess of `As_(2)O_(3)`, we have `As_(2)O_(3)+MnO_(4)^(-)rarrMn^(+2)+AsO_(4)^(-3)` Npw `As_(2)O_(3)` getting oxidized to `AsO_(4)^(-3)`, the half reaction is `As_(2)O_(3)+5H_(2)Orarr2As+10H^(+)+4e^(-)` for 1MOL of `As_(2)O_(3)`, No. of `e^(-)s=4`, So, eq. wt of `Al_(2)O_(3)=198//4` M.eq of `As_(2)O_(3)=(0.594)/(198//4)xx1000=12` Me eq of excess of `As_(2)O_(3)` = M.eq of `KMnO_(4)` `=45=((1)/(50)xx5)=4.5` The other half reaction is `MnO_(4)^(-)+5e^(-)+8H^(+)rarrMn^(2)+4H_(2)O` M.eq of `As_(2)O_(3)` used for `MnO_(2)=12-4.5=7.5` `therefore` wt implies `(W)/(87//2)xx1000=7.5impliesW=0.326gm` `%MnO_(2)=(0.326)/(0.5)xx100=65.25%`