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Difficulty: MediumNoble Gases: Isolation, Electronic Structure, and Uses

During the industrial isolation of noble gases from liquid air, argon is collected in a fraction between nitrogen and oxygen. What physical property explains why argon distills over after nitrogen but before oxygen?

  1. Argon has a higher boiling point than nitrogen but a lower boiling point than oxygen.Answer
  2. B
    Argon has a lower boiling point than nitrogen but a higher boiling point than oxygen.
  3. C
    Argon has a higher vapor density than oxygen but a lower vapor density than nitrogen.
  4. D
    Argon has a lower molar mass than nitrogen but a higher molar mass than oxygen.

Answer

Argon has a higher boiling point than nitrogen but a lower boiling point than oxygen.
Fractional distillation of liquefied air separates gases according to their boiling points. Nitrogen distills first at −196 ∘C-196\ ^{\circ}\text{C} (77 K77\text{ K}), argon distills next at −186 ∘C-186\ ^{\circ}\text{C} (87 K87\text{ K}), and oxygen distills last at −183 ∘C-183\ ^{\circ}\text{C} (90 K90\text{ K}). Therefore, argon distills over after nitrogen but before oxygen because its boiling point is higher than that of nitrogen and lower than that of oxygen.

Step-by-Step Solution

1
Identify the separation principle of liquid air distillation.
Components of liquid air are separated based on differences in their boiling points during fractional distillation.
Fractional distillation separates liquids with different boiling points as the liquid mixture is warmed.
2
Compare the boiling points of nitrogen, argon, and oxygen.
Nitrogen boils at −196 ∘C-196\ ^{\circ}\text{C}, argon boils at −186 ∘C-186\ ^{\circ}\text{C}, and oxygen boils at −183 ∘C-183\ ^{\circ}\text{C}.
Lower boiling point components boil and distill off first as vapor.
3
Deduce the sequence of distillation for argon.
Since −196 ∘C<−186 ∘C<−183 ∘C-196\ ^{\circ}\text{C} < -186\ ^{\circ}\text{C} < -183\ ^{\circ}\text{C}, nitrogen distills off first, followed by argon, while oxygen remains liquid longest.
Argon distills after nitrogen because its boiling point is higher than nitrogen's, and before oxygen because its boiling point is lower than oxygen's.

Key Concept

Isolation of noble gases from liquid air by fractional distillation
Estimated Time:1m 0s
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Topics

Noble Gases: Isolation, Electronic Structure, and Uses

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