When air which contains the gases Oxygen, nitrogen, carbondioxide, water vapour and the rare gases, is passed…

Analysis of the Question

This question tests your knowledge of the composition of air and the chemical properties of specific reagents used to absorb gases. To solve this, we must track what happens to each component of air as it passes through the two chemical agents.

Concept Explanation

Air is a mixture of gases. To isolate specific components, we use "scrubbers" or chemical reagents that react with and remove specific gases:

1. Alkaline Pyrogallol: This is a strong reducing agent used specifically to absorb Oxygen ($O_2$). When air passes through it, all the oxygen is removed.
2. Quicklime (Calcium Oxide, $CaO$): This is a basic oxide. It is used to dry gases and absorb acidic gases. Specifically, it reacts with Carbon dioxide ($CO_2$) and Water vapour ($H_2O$).

Step-by-Step Solution

• Step 1: Identify the components of air. The air contains: Nitrogen ($N_2$), Oxygen ($O_2$), Carbon dioxide ($CO_2$), Water vapour ($H_2O$), and Rare gases (Noble gases like Argon, Neon, etc.).

• Step 2: Pass the air through Alkaline Pyrogallol. • The alkaline pyrogallol absorbs the Oxygen. • Remaining gases: Nitrogen, Carbon dioxide, Water vapour, and Rare gases.

• Step 3: Pass the remaining gases over Quicklime ($CaO$). • The quicklime absorbs the Carbon dioxide (an acidic oxide) and the Water vapour (drying agent). • Remaining gases: Nitrogen and the Rare gases.

Conclusion

After the oxygen, carbon dioxide, and water vapour have been removed by the respective reagents, only the chemically inert gases (Nitrogen and the Rare gases) remain.

Exam Tip

Remember the "Gas Scrubbing" sequence for air:

• KOH/NaOH solution: Removes $CO_2$.
• Alkaline Pyrogallol: Removes $O_2$.
• Conc. $H_2SO_4$ or Quicklime: Removes $H_2O$ (Water vapour).
• Nitrogen and Rare gases are generally unreactive under these conditions, so they pass through unaffected.