Estimation of Nitrogen by Dumas Method

Based on a method established by Jean-Baptiste Dumas in 1831, the Dumas method is an analytical method for quantitative measurement of nitrogen in a chemical material.

There are three processes to this method: combustion, reduction, separation, and detection.

Organic chemicals are heated to high temperatures and then burned in the presence of oxygen, resulting in carbon dioxide, water, and nitrogen oxides.

The gas mixture was run over hot copper in the reduction and separation stage to remove any oxygen and convert nitrogen oxides to nitrogen. Water and carbon dioxide are then removed from the sample using traps.

Dumas Method:

This approach is based on the fact that free nitrogen is produced when nitrogenous compounds are burned with cupric oxide in a CO2 environment. Thus

By travelling over a heated copper spiral, traces of nitrogen oxide, which can occur in some instances, are converted to elemental nitrogen.

The CO2  generator, combustion tube, and Schiff’s nitrometer are used in the Dumas technique.

CO2 generator: CO2 is produced in this procedure by heating magnetite or sodium bicarbonate in a hard glass tube, or by dilution HCl on marble in a kipps apparatus. After being dried by bubbling through Conc. H2SO4 , the gas is sent via the combustion tube.

Combustion Tube: The combustion tube is charged with

a) A roll of oxidised copper gauze to prevent back diffusion of combustion products and 

b) to heat the organic substance combined with CuO via radiation) a weighed amount of the organic substance mixed with excess CuO, 

c) a layer of course CuO packed in about 2/3 of the length of the tube and held in place by a loose asbestos plug on either side; this oxidises the organic vapours passing through it, and

d) a reduced copper spiral that converts any nitrogen oxides formed during combustion to nitrogen.

Schiff’s nitrometer: Nitrogen gas is produced by breakdown of a chemical in a combustion tube, and it is combined with a large amount of CO2 . When CO2 is absorbed by KOH and the nitrogen is collected in the top half of the graduated tube, it is quantified using a passing nitrometer.

Procedure:

To begin, the nitro meter’s tap is left open. To discharge the air in the combustion tube, CO2 is fed through it. When the potash solution fails to reach the top and is fully absorbed by the rising gas bubbles, it indicates that only CO2 is arriving and that all air has been evacuated from the combustion tube. After that, the nitrometer is filled with KOH solution by lowering the reservoir and closing the tap. The combustion tube in the furnace is now heated, and the temperature is progressively rising. The nitro metre catches the nitrogen that has been released from the chemical. When the combustion is finished, a high stream of CO2 is pumped through the device to remove any remaining nitrogen. After adjusting the reservoir such that the solution in it and the graduated tube are the same, the volume of gas collected is recorded. The temperature and air pressure are also recorded.

Calculations:

Weight of the substance taken

Volume of nitrogen

Room Temperature

Atmospheric Pressure of

Agueen tension at

room temperature of

Pressure of dry nitrogen of .

Let and be the pressure, Volume and temperature respectively of dry nitrogen at ,

Calculation of percentage of nitrogen. of at STP weigh of ,

of at S.T.P weigh

wg of Organic compound contain

of nitrogen,

Percentage of nitrogen =

Example Problem:

0.1688g when analyzed by the Dumas method yields 3.17ml of moist nitrogen measured at 14oC and 758 mm mercury pressure. Determine the % of N in the substance (Aqueous tension at 14oC = 12mm )

Solution:

Weight of Organic compound

Volume of moist nitrogen ,

Temperature ,

Pressure of Moist nitrogen

Aqueous tension at ,

of

The pressure of dry nitrogen

of Hg

Percentage of nitrogen,

Conclusion:

Historically, the Dumas technique of molecular weight measurement was employed to determine the molecular weight of an unknown material. The Dumas technique is suitable for determining the molecular weights of volatile organic liquids at room temperature.

The approach is named after the French scientist Jean Baptiste André Dumas, who devised the method. The approach was used by Dumas to calculate the vapour densities of elements (mercury, phosphorus, and sulphur) as well as inorganic compounds.

The molecular weight of a material is now determined using contemporary technologies such as mass spectrometry and elemental analysis.