What is Dumas Method | Chemistry | Extraclass.com

Summary

The Dumas method, developed by Jean-Baptiste Dumas in 1831, is a technique for determining the nitrogen content in organic compounds. The process involves heating the compound with cupric oxide in a carbon dioxide atmosphere, releasing nitrogen gas. The collected gas is measured and its volume is adjusted to standard conditions. Through a series of calculations using the molar concept, the nitrogen percentage in the compound is determined. The video explains the method step by step, demonstrating its application with an example calculation that results in 11.33% nitrogen content in the sample.

Takeaways

• 😀 Dumas' method for nitrogen determination was developed by Jean-Baptiste Dumas in 1831.
• 😀 The method involves heating a nitrogen-containing organic compound with cupric oxide in a carbon dioxide atmosphere.
• 😀 The carbon and hydrogen in the compound are oxidized to carbon dioxide and water, while nitrogen is liberated as free nitrogen gas.
• 😀 Any nitrogen oxides formed during the reaction are reduced back to nitrogen gas by heated copper.
• 😀 The resulting mixture of gases (CO₂, H₂O, and N₂) is collected over an aqueous potassium hydroxide solution.
• 😀 Nitrogen gas is the only component that is not absorbed by the solution, allowing it to be measured.
• 😀 The volume of nitrogen gas collected is used to calculate the percentage of nitrogen in the organic compound.
• 😀 Key variables include the mass of the organic compound, the volume of nitrogen gas, atmospheric pressure, temperature, and water vapor pressure.
• 😀 The volume of nitrogen at experimental conditions is corrected to standard conditions (STP) using the combined gas law equation.
• 😀 The percentage of nitrogen is calculated based on the volume of nitrogen gas obtained, the molar volume of nitrogen, and the mass of the organic compound.

Q & A

Who developed the Dumas method for nitrogen determination?

The Dumas method for nitrogen determination was developed by Jean-Baptiste Dumas in 1831.

What is the basic principle behind the Dumas method?

In the Dumas method, a nitrogen-containing organic compound is heated with cupric oxide in an atmosphere of carbon dioxide. The carbon and hydrogen are oxidized to carbon dioxide and water, while nitrogen is released as a gas.

How are nitrogen oxides handled during the Dumas method?

Any nitrogen oxides produced during the process are reduced back to free nitrogen using heated copper.

What is the role of potassium hydroxide in the Dumas method?

Potassium hydroxide absorbs all gases except nitrogen, allowing for the collection and measurement of nitrogen gas.

How is the percentage of nitrogen in the compound calculated in the Dumas method?

The percentage of nitrogen is calculated by measuring the volume of nitrogen gas collected, correcting it to standard temperature and pressure (STP), and then applying the formula: (Weight of nitrogen / Weight of organic compound) * 100.

What is the significance of standard temperature and pressure (STP) in the Dumas method?

STP conditions allow for the accurate comparison and calculation of gas volumes, ensuring consistency in determining the nitrogen content, as gas volumes are influenced by temperature and pressure.

In the example given in the script, what is the measured volume of nitrogen gas?

In the example, the measured volume of nitrogen gas is 30 cm³.

What is the equation used to calculate the volume of nitrogen gas at STP?

The volume of nitrogen gas at STP is calculated using the equation: V2 = (P - p) * V * 273 / (760 * T), where P is atmospheric pressure, p is vapor pressure, V is the measured volume, and T is room temperature.

How is the weight of nitrogen gas determined from its volume at STP?

The weight of nitrogen gas at STP is determined by using the molar volume of nitrogen (22,400 cm³ = 28 grams), and applying the ratio of the volume of nitrogen gas to the molar volume.

What was the percentage of nitrogen in the given organic compound in the example?

The percentage of nitrogen in the organic compound was calculated to be 11.33% based on the volume of nitrogen gas collected and the mass of the compound.