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When air which contains the gases: oxygen, nitrogen…

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When air which contains the gases: oxygen, nitrogen, carbon dioxide, water vapor and the rare gases, is passed through alkaline pyrogallol and then over quicklime, the only gases left are:

A. nitrogen and carbon dioxide

B. the rare gases

C. nitrogen and oxygen

D. nitrogen and the rare gases




The alkaline pyrogallol will absorb oxygen out of the air, and the quicklime will firstly react with the water vapor to form lime water, this lime water will absorb carbon dioxide out of the air.

The only gasses left will be: nitrogen and rare gasses.

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Now for the right answer to the above question:

  1. Option A is incorrect. the carbon dioxide will be absorbed by the lime water formed when the water vapor reacts with the quick lime.
  2. Option B is incorrect. rare gasses will not be the only gasses left, nitrogen too will be left.
  3. C is incorrect. alkaline pyrogallol is very sensitive to oxygen, it will readily remove the oxygen component of air.
  4. D is the correct answer.


You may please note these/this:

  • Alkaline pyrogallol has a very strong affinity with oxygen, it will remove it from the air mixture.
  • Quicklime also has a strong affinity with water, it will react with it to form slaked lime which will turn milky after absorbing carbon dioxide.

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/ culled from 2017 JAMB-UTME Chemistry question 31 /

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