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Explain Dumas method of estimation of nitrogen. |
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Answer» Solution :Dumas method Principle: This method is based on the fact that nitrogeneous compound when heated with cupric oxide in an atmosphere of `CO_(2)` yields free nitrogen. `C_(x)H_(y)N_(z)+(2x+(1)/(2)) CuO rarr x CO_(2)+(y)/(2)H_(2)O+(z)/(2)N_(2)+(2x+(y)/(2))Cu` Traces of nitrogen are reduced to elemental nitrogen by passing over heated copper spiral. Description of the apparatus,  `CO_(2)` Generator: `CO_(2)` needed in this process is prepared by heating magnetite or sodium bicarbonate contained in a hard glass tube (or) by the action of dil. HCl on MARBLE in a kipps apparatus. The gas is passed through the combustion tube after dried by bubbling through cone. `H_(2)SO_(4)` . Combustion tube: The combustion tube is heated in a furnace is charged with (a) A roll of oxidised copper gauze to prevent the BACK diffusion of products of combustion and to heat the organic substance mixed with CuO by radiation (b) a weighed amount of organic substance mixed with excess of CuO (c) a layer of CuO packed in about `2 // 3` length of the tube and KEPT in position by loose asbestos PLUG on either side and (d) a reduced copper spiral which reduces any oxides of nitrogen formed during combustion of nitrogen. Schiff.s nitromete: The nitrogen gas obtained by the decomposition of the substance in the combustion tube is mixed with considerable excess of `CO_(2)` . It is estimated by passing nitro mater when `CO_(2)` is absorbed by KOH and the nitrogen gas gets collected in the upper part of the graduated tube. Calculation: Weight of the substance taken = Wg Volume of nitrogen= `V_(1)` L Room temperature = `T_(1)` K Atmospheric pressure =P mm Hg Aqueous tension at room temperature =`P^(.)` mm of Hg `:. "Pressure of dry nitrogen"=P-P^(.)= P_(1)^(.) mm Hg` `P_(0)` , `V_(0)` and `T_(0)` be the pressure, volume and temperature respectively of dry nitrogen at S.T.P. Then, `(P_(0)V_(0))/(T_(0))=(P_(1)V_(1))/(T_(1))` `:. V_(0)=(P_(1)V_(1))/(T_(1)) xx (T_(0))/(P_(0))` `:. V_(0)=(P_(1)V_(1))/(T_(1)) xx (273 K)/(760 mm Hg)` 22.4 L of `N_(2)` at STP weigh 28 g of `N_(2)` `:. V_(0)L "of" `N_(2)` "at STP weigh" (28)/(22.4) xx V_(0)` W g of organic compound contain `(28)/(22.4) xx V_(0) "g of" N_(2)` `:. "100 g of organic contain" (28)/(22.4) xx (V_(0))/(w) xx 100="% of Nitrogen"` |
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