Question

In dumas method for the estimation of nitrogen 0.30gm if the organic comp .gave 50ml of N2 collected at 300k and 715 mm pressure calculate % composition of N in the compound (Aqous tension at 300k is 15mm

Answer 1

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

mass of the subs.= .30g.

vol. of N2 = 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.

P1 V1 /T1   =  P2 V2 / T2

700 x 50/ 300  = 760 x V2 / 273

= 41.9 cm3 .

c. CONVERT THE VOLUME AT STP INTO MASS .

222400cm3 of N2 at STP weighs 28 g.

41.9 cm3 would weigh

28 x 41.9  / 22400    g.

d. % of N2.

mass of N2 at STP  / Mass of the substance taken x 100.

28 x 41.9  x 100  / 22400  x 0.3      =  17.46