Estimation of Nitrogen by Duma's Method

The nitrogen containing organic compound, when heated with copper oxide in an atmosphere of carbon dioxide, yields free nitrogen in addition to carbon dioxide and water.

C_xH_yN_z + (2x+y/2) CuO → x CO₂ + y/2 H₂O + z/2 N₂ + (2x+y/2) Cu

Traces of nitrogen oxides formed, if any, are reduced to nitrogen by passing the gaseous mixture over a heated copper gauze. The mixture of gases so produced is collected over an aqueous solution of potassium hydroxide which absorbs carbon dioxide.

Let the mass of organic compound = m g

Volume of nitrogen collected = V₁ mL

Room temperature = T₁ K

Volume of nitrogen at STP = (p₁V₁ x 273/(760 x T₁)

p₁ = Atmospheric pressure – Aqueous tension

22400 mL N₂ at STP weighs 28 g.

V ml of N₂ at STP weighs = (28 x V)/22400

Percentage of Nitrogen = (28 x V x 100)/(22400 x m)