Question

0.30g of an organic compound gave 50 cc of nitrogen collected at 300K and 715 mm pressure in Duma's method. Calculate the percentage of nitrogen in the compound.(Vapour pressure of water at 300K is 15 mm).

Answer 1

Mass of given organic compound = 0.30 g

We have to calculate the volume of nitrogen at N.T.P

Given:

${ V }_{ 1 }$ = 50 ml

${ P }_{ 1 }$ = 715 - 15 = 700 mm

${ T }_{ 1 }$ = 300 K

At NTP: ${ V }_{ 2 }\quad =\quad ?\\ \\{ P }_{ 2 }\quad =\quad 760\quad mm\\ \\{ T }_{ 2 }\quad =\quad 273\quad K\\ \\ \frac { { P }_{ 1 }{ V }_{ 1 } }{ { T }_{ 1 } } \quad =\quad \frac { { P }_{ 2 }{ V }_{ 2 } }{ { T }_{ 2 } } \\ \\{ V }_{ 2 }\quad =\quad \frac { { P }_{ 1 }{ V }_{ 1 }{ T }_{ 2 } }{ { T }_{ 1 }\quad \times \quad P_{ 2 } } \\ \\=\quad \frac { 700\quad \times \quad 50\quad \times \quad 273 }{ 300\quad \times \quad 760 } \quad \\ \\{ V }_{ 2 }\quad =\quad 41.90\quad ml$

Calculate the percentage of nitrogen:

22400 ml of nitrogen at N.T.P weight = 28 g

$41.90\quad ml\quad of\quad nitrogen\quad at\quad N.T.P\quad weighs\quad =\quad \frac { 28 }{ 22400 } \quad \times \quad 41.90\quad g\\ \\Percentage\quad of\quad nitrogen\quad =\quad \frac { 28 }{ 22400 } \quad \times \frac { 41.90 }{ 0.3 } \quad \times \quad 100\quad \quad =\quad 17.46$