In DUMAS method for estimation of nitrogen, 0.3g of an organic compound gave 50ml diatomic nitrogen. The gas was collected at 300K and 715mm of Hg pressure. Calculate the percentage of diatomic nitrogen in the compound.

a. we know that aqueous tension of water at 300 K is 15mm.

mass of the subs.= .30g.

vol. of N_{2} = 50 ml.

room temp = 300 K.

VAPOUR PRESSURE OF WATER AT 300 K = 15 mm

actual pressure (dry gas ) = 715-15 = 700 mm Hg.

b. CONVERT THE VOL. AT EXPERIMENTAL CONDITIONS TO VOL AT STP.

P_{1}V_{1}/T_{1} = P_{2}V_{2} / T_{2}

700 x 50/ 300 = 760 x V_{2} / 273

= 41.9 cm^{3} .

c. CONVERT THE VOLUME AT STP INTO MASS .

222400cm^{3} of N_{2} at STP weighs 28 g.

41.9 cm^{3} would weigh

28 x 41.9 / 22400 g.

d. % of N_{2}.

mass of N_{2} at STP / Mass of the substance taken x 100.

28 x 41.9 x 100 / 22400 x 0.3 = 17.46