Q.

In Dumas’ method for estimation of nitrogen 0.4 g 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 is

(Given: Aqueous tension at 300 K = 15 mm Hg)                     [2025]

1 15.71%  
2 20.95%  
3 17.46%  
4 7.85%  

Ans.

(1)

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

PN2=(715-15)mmHg=700mmHg=700760atm

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

Moles of nitrogen (nN2)=PN2VN2RT =700760×0.060.0821×300

Mass of nitrogen (WN2)=nN2× molar mass of nitrogen

=700760×0.060.0821×300×28 g

Mass percentage of nitrogen

=WN2Mass of organic compound×100

=700760×0.06×280.0821×300×0.4×100=15.71%