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Difficulty: EasyNitrogen Gas, Nitrogen Cycle, and Oxides of Nitrogen

During the industrial separation of liquefied air to obtain pure nitrogen gas, nitrogen vaporizes at −196∘C-196^\circ\text{C} while oxygen remains in the liquid state at −183∘C-183^\circ\text{C}. Which of the following statements correctly explains why nitrogen distills over first?

  1. Nitrogen has a lower boiling point than oxygen, so it vaporizes at a lower temperature.Answer
  2. B
    Nitrogen has a higher boiling point than oxygen, causing it to evaporate before liquid oxygen.
  3. C
    Nitrogen diffuses faster than oxygen because it is less dense, forcing it out of the fractionating column first.
  4. D
    Nitrogen's boiling point appears lower only because negative Celsius temperatures convert inversely to the Kelvin scale.

Answer

Nitrogen has a lower boiling point than oxygen, so it vaporizes at a lower temperature.
Nitrogen has a lower boiling point (−196∘C-196^\circ\text{C} or 77 K77\text{ K}) than oxygen (−183∘C-183^\circ\text{C} or 90 K90\text{ K}). In fractional distillation, liquid mixtures are separated based on differences in boiling points, and the component with the lower boiling point boils off and distills over first.

Step-by-Step Solution

1
Compare the boiling point values on the Celsius and Kelvin temperature scales.
Nitrogen boils at −196∘C-196^\circ\text{C} (77 K77\text{ K}) while oxygen boils at −183∘C-183^\circ\text{C} (90 K90\text{ K}).
On the Celsius scale, −196-196 is smaller (lower) than −183-183.
2
Apply the physical principle of fractional distillation.
As liquefied air warms, nitrogen reaches its boiling point first and converts into gas.
The component with the lower boiling point always distills over first during fractional distillation.

Key Concept

Fractional Distillation of Liquid Air
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Topics

Nitrogen Gas, Nitrogen Cycle, and Oxides of Nitrogen

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