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3.0 g of pyrolusite ore were treated with 20 g of pure ferrous ammonium sulphate (Mol.mass =392 " g mol"^(-1)) and dilute H_(2)SO_(4). After the reaction, the solution was diluted to 500 mL. 50 mL of diluted solution required 10 mL of 0.1 N K_(2)Cr_(2)O_(7) solution. Calculate the % of pure MnO_(2) in pyrolusite.

Answer» <html><body><p><br/></p>Solution :`MnO_(2)` present in pyrolusite oxidises ferrous ammonium <a href="https://interviewquestions.tuteehub.com/tag/sulphate-1234306" style="font-weight:bold;" target="_blank" title="Click to know more about SULPHATE">SULPHATE</a> into ferric ammonium sulphate, i.e., `Fe^(2+) to Fe^(3+)`. <br/> Unreacted ferrous ammonium sulphate is estimated by potassium dichromate solution. <br/> `MnO_(2)+2Fe^(2+)+4H^(+) to Mn^(2+) +2H_(2)O+2Fe^(3+)` <br/> `Cr_(2)O_(7)^(2-)+6Fe^(2+) +14H^(+) to 2Cr^(3+)+7H_(2)O+6Fe^(3+)` <br/> 50 mL <a href="https://interviewquestions.tuteehub.com/tag/diluted-7675406" style="font-weight:bold;" target="_blank" title="Click to know more about DILUTED">DILUTED</a> ferrous ammonium sulphate solution <br/> `=<a href="https://interviewquestions.tuteehub.com/tag/10-261113" style="font-weight:bold;" target="_blank" title="Click to know more about 10">10</a> mL " of" 0.1 <a href="https://interviewquestions.tuteehub.com/tag/n-568463" style="font-weight:bold;" target="_blank" title="Click to know more about N">N</a> K_(2)Cr_(2)O_(7)` <br/> 500 mL diluted ferrous ammonium sulphate solution <br/> `=10xx10 mL " of" 0.1 N K_(2)Cr_(2)O_(7)` <br/> =100 mL of 0.1 N <a href="https://interviewquestions.tuteehub.com/tag/feas-3629986" style="font-weight:bold;" target="_blank" title="Click to know more about FEAS">FEAS</a> <br/> `=(0.1xx392)/(1000)xx100=3.92 g` <br/> Used FeAS=(20-3.92)=16.08 g <br/> `MnO_(2)` present in pyrolusite `=(87)/(392xx2)xx16.08=1.784 g` <br/> Percentage of pure `MnO_(2)=(1.784)/(3.0)xx100=59.4 %`</body></html>


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