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Difficulty: MediumIndustrial Applications of Separation Methods

During the industrial separation of liquefied air by fractional distillation, the mixture is gradually warmed to separate its primary gas components. Given the boiling points of nitrogen (−196∘C-196^\circ\text{C}), argon (−186∘C-186^\circ\text{C}), and oxygen (−183∘C-183^\circ\text{C}), which of the following correctly indicates the sequence in which these gases boil off from first to last?

  1. Nitrogen, Argon, OxygenAnswer
  2. B
    Oxygen, Argon, Nitrogen
  3. C
    Nitrogen, Oxygen, Argon
  4. D
    Oxygen, Nitrogen, Argon

Answer

The gases distill off in the order of Nitrogen, Argon, and Oxygen.
During fractional distillation of liquid air, substances with lower boiling points vaporize first as the temperature rises. Because −196∘C-196^\circ\text{C} is lower than −186∘C-186^\circ\text{C}, which is in turn lower than −183∘C-183^\circ\text{C}, nitrogen distills off first, followed by argon, and finally oxygen.

Step-by-Step Solution

1
Compare the boiling points of the three gases given in the problem statement.
Nitrogen (−196∘C-196^\circ\text{C}), Argon (−186∘C-186^\circ\text{C}), and Oxygen (−183∘C-183^\circ\text{C}).
Lower boiling point values (more negative numbers) mean higher volatility.
2
Arrange the boiling points in order from lowest to highest.
−196∘C<−186∘C<−183∘C-196^\circ\text{C} < -186^\circ\text{C} < -183^\circ\text{C}.
As liquefied air warms up, the substance with the lowest boiling point reaches its boiling temperature first and vaporizes.
3
Match the arranged boiling points to their corresponding gases to determine distillation order.
Nitrogen boils off first, followed by Argon, and then Oxygen.
The fractional distillation column separates components in increasing order of boiling points.

Key Concept

Fractional Distillation of Liquefied Air
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Topics

Industrial Applications of Separation Methods