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InterviewSolution
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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. |
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Answer» Correct Answer - `59.4%` `MnO_(2)` present in pyrolusite oxidises ferrous ammonium sulphate into ferric ammonium sulphate, i.e., `Fe^(2+) to Fe^(3+)`. Unreacted ferrous ammonium sulphate is estimated by potassium dichromate solution. `MnO_(2)+2Fe^(2+)+4H^(+) to Mn^(2+) +2H_(2)O+2Fe^(3+)` `Cr_(2)O_(7)^(2-)+6Fe^(2+) +14H^(+) to 2Cr^(3+)+7H_(2)O+6Fe^(3+)` 50 mL diluted ferrous ammonium sulphate solution `=10 mL " of" 0.1 N K_(2)Cr_(2)O_(7)` 500 mL diluted ferrous ammonium sulphate solution `=10xx10 mL " of" 0.1 N K_(2)Cr_(2)O_(7)` =100 mL of 0.1 N FeAS `=(0.1xx392)/(1000)xx100=3.92 g` Used FeAS=(20-3.92)=16.08 g `MnO_(2)` present in pyrolusite `=(87)/(392xx2)xx16.08=1.784 g` Percentage of pure `MnO_(2)=(1.784)/(3.0)xx100=59.4 %` |
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