Quantitative Analysis - Nitrogen by Dumas Method Problem

Description:

Problem

0.30 g of an organic compound gave 30 cm³ of moist nitrogen gas at 290 K and 745 mm pressure. Calculate the percentage of nitrogen using Dumas method. (given, aqueous tension at 290 K = 12.7 mm).

Solution:

Given, mass of the substance = 0.30 g

Pressure, P₁ = 745 − 12.7 mm = 732.3 mm

Step I: To reduce the nitrogen to STP,

P₁V₁

/

T₁

=

P₂V₂

/

T₂

V₂ =

P₁V₁ x 273

/

760 x T₁

=

732.3 mm x 30 cm³ x 273 K

/

290K x 760 mm

= 27.2 cm³

Step II:  To calculate percentage of nitrogen,

22400 cm³ N₂ at STP weighs = 28 g

27.2cm³ N₂ in the given organic compound weighs =

28 x 27.2

/

22400

= 0.034 g

Percentage of N₂ =

28 x V_N2(STP) x 100

/

22400 x m

=

28 x 27.2 x 100

/

22400 x 0.30

= 11.33%