Problem 149 - A Complete Resource Book in Chemistry for JEE Main

Question

Pick out the incorrect statement/s about noble gases. (1) 'He' cannot be used in preference to nitrogen \(\left(\mathrm{N}_{2}\right)\) to dilute the oxygen in the gas cyclinders used by divers. (2) 'He' is used in weather balloons and airships. (3) 'He' is used in cryoscopy to obtain the very low temperatures required for superconductivity and lasers. (4) 'Ar' is used in metallurgical processes. (a) 1 and 3 (b) 2 and 3 (c) 1 and 4 (d) 1 only

Step-by-Step Solution

Answer

(d) 1 only

Step 1: Understanding the Question

We are asked to identify the incorrect statements about noble gases. Each statement relates to a specific use case of noble gases like helium ('He') and argon ('Ar'). We will need to evaluate each statement for its accuracy.

Step 2: Analyzing Statement 1

Statement 1 suggests that helium cannot be used in preference to nitrogen to dilute oxygen in gas cylinders used by divers. However, helium is actually used in diving because it is less dense than nitrogen and reduces the risk of nitrogen narcosis. Thus, statement 1 is incorrect.

Step 3: Analyzing Statement 2

Statement 2 claims that helium is used in weather balloons and airships. This is correct because helium is lighter than air and non-flammable, making it ideal for these purposes.

Step 4: Analyzing Statement 3

Statement 3 mentions the use of helium in cryoscopy to achieve very low temperatures, as needed for superconductivity and lasers. Helium is indeed used for such purposes because it can remain in a liquid state at extremely low temperatures, reaching conditions necessary for superconductivity. Therefore, this statement is correct.

Step 5: Analyzing Statement 4

Statement 4 states that argon is used in metallurgical processes. This is true; argon is an inert gas used in welding and other metallurgical procedures to prevent unwanted chemical reactions.

Step 6: Conclusion

Based on our analysis, the only incorrect statement is statement 1, as helium can and is used instead of nitrogen for diving purposes.

Key Concepts

Helium Uses

Helium is a fascinating element with a variety of applications. Its most common use is in balloons, thanks to its lighter-than-air property. Helium's non-flammable nature has made it a popular choice over hydrogen when it comes to filling airships and weather balloons. This ensures safety while still providing the needed lift.

But helium isn't just for floating objects. It's also a crucial component in the medical and scientific fields. Helium's low boiling point makes it perfect for keeping ultra-low temperature environments, which is essential for applications like Magnetic Resonance Imaging (MRI) and in research settings where superconductivity is studied. By maintaining low temperatures, helium allows these processes to function effectively and safely.

Diving Gas Mixtures

Diving deep underwater is a unique experience, but it requires careful attention to the breathing gas mixture. Standard air, when compressed under high pressure, poses risks like nitrogen narcosis and oxygen toxicity. That's where helium comes in.

Helium is often used as a substitute for nitrogen in breathing gases for deep-sea divers. By creating a mixture such as "trimix" (helium, oxygen, and nitrogen) or "heliox" (helium and oxygen), divers can safely reach greater depths. Helium minimizes narcosis because it does not dissolve in tissues as easily as nitrogen. This reduces impairment, allowing divers to make clear decisions while submerged.

• Helium is less dense than nitrogen: makes breathing easier at depth.
• Heliox and trimix reduce the risk of decompression sickness.
• Reduces the narcotic effect experienced at depth due to nitrogen.

Cryoscopy

Cryoscopy is a technique that involves measuring the freezing point of substances. Helium plays a significant role in this field, especially when extremely low temperatures are required. Helium remains liquid at temperatures below extsuperscript{-269°C}, making it indispensable for such needs.

In fields like superconductivity and quantum computing, components need to be cooled to very low temperatures. Helium provides this cooling capability efficiently, thanks to its ability to remain in the liquid state under such conditions. This is vital for experiments and applications that require precise temperature control to function correctly.

Metallurgical Processes

Metallurgical processes involve transformations of metals that require an inert atmosphere to prevent reactions that could compromise structural integrity. This is where argon, another noble gas, becomes essential.

Argon is often used in welding and smelting processes. Its role is crucial in shielding the metal from oxygen and moisture in the air, preventing unwanted oxidation or contamination. Its inert nature makes it perfect for creating a protective environment around the welding arc or molten metal.

• Prevents oxidation: Maintains the quality of welds.
• Ensures precision: Critical for high-quality metallurgical outcomes.
• Cost-effective: Argon is abundant and therefore economical for industrial use.