Q.

In Dumas’ method for estimation of nitrogen, 0.5 gram of an organic compound gave 60 mL of nitrogen collected at 300 K temperature and 715 mm Hg pressure. The percentage composition of nitrogen in the compound (Aqueous tension at 300 K = 15 mm Hg) is             [2025]

1 1.257  
2 20.87  
3 18.67  
4 12.57  

Ans.

(4)

Pressure of nitrogen (PN2) = Total pressure - aqueous tension

=(715-15)mmHg=700mmHg=700760atm

Volume of nitrogen (VN2) = 60 mL = 0.06 L

nN2=PN2VN2RT=700×0.06760×0.0821×300=2.24×10-3mol

Mass of nitrogen = nN2×molar mass of N2

=2.24×10-3×28 g=0.06282 g

Percentage of nitrogen in organic compound:

=Mass of nitrogenMass of organic compound×100

=0.062820.5×10012.57%