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

Statement (1) is incorrect, so option (d) is correct.

Step 1: Understanding the Role of Helium in Diving

Helium has a lower solubility in blood than nitrogen and is used to dilute oxygen in gas cylinders for deep-sea divers. It's preferred because it reduces the risk of nitrogen narcosis. Therefore, statement (1) suggesting that helium cannot be used in preference to nitrogen is incorrect.

Step 2: Examining Helium's Use in Weather Balloons and Airships

Helium is non-flammable and lighter than air, making it ideal for filling weather balloons and airships. Thus, statement (2) is correct.

Step 3: Investigating Helium's Use in Cryoscopy

Helium, especially in its liquid form, is utilized in cryogenics to reach extremely low temperatures necessary for superconductivity. Consequently, statement (3) is correct.

Step 4: Exploring Argon's Use in Metallurgical Processes

Argon is an inert gas and is commonly used in metallurgical processes to provide an oxygen-free environment. Statement (4) correctly states argon's application in metallurgy.

Step 5: Summarizing the Incorrect Statements

After examining all statements, the incorrect statement is (1) about helium not being used in preference to nitrogen. This makes option (d) the correct choice.

Key Concepts

Helium Usage

Helium is a noble gas that finds a wide array of applications due to its unique properties. It is colorless, odorless, non-toxic, and has a very low density, making it lighter than air. This combination makes helium particularly useful in applications where a lightweight, non-reactive gas is required.
For example:

• Helium is used in weather balloons and airships as it allows them to float and travel seamlessly through the air without the risk of combustion, unlike hydrogen.
• Helium's low solubility is also critical in medical applications, such as MRI machines, to cool the superconducting magnets they use.

Helium's properties continually expand its use in various fields, be it scientific, medical, or industrial.

Gas Mixtures for Divers

Deep-sea diving requires carefully curated gas mixtures to ensure the safety and well-being of divers. The challenge is to prevent conditions like nitrogen narcosis and decompression sickness, which can occur due to breathing high-pressure nitrogen while underwater.
To mitigate this, divers use gas mixtures like heliox or trimix. Heliox is a blend of helium and oxygen, offering several advantages:

• Helium is less soluble in blood compared to nitrogen, which decreases the likelihood of developing nitrogen narcosis.
• This property allows divers to safely venture to greater depths without the associated risks of using regular air.

Trimix, which consists of helium, oxygen, and nitrogen, allows for even deeper dives by reducing the concentration of oxygen and nitrogen proportionally. Helium not only improves safety but also enhances divers’ performance by reducing breathing resistance under high pressure.

Cryogenics

Cryogenics is the science of producing and managing extremely low temperatures, and helium plays a vital role in this field. Due to its boiling point at around -269°C, liquid helium is one of the coldest substances on Earth. In practical applications:

• Liquid helium is used to achieve the superconducting temperatures required in MRI machines and scientific instruments, which need to operate with minimal electrical resistance.
• It's instrumental in experiments that study the properties of atoms and molecules at temperatures close to absolute zero.

These uses demonstrate helium’s crucial role within the world of cryogenics, enabling groundbreaking research and essential medical technologies.

Inert Gases in Metallurgy

In metallurgy, inert gases are crucial during various processes where reactivity with atmospheric elements must be minimized. Argon, another noble gas, is particularly well-suited for these tasks as it does not react with metals at high temperatures. When used in metallurgy:

• Argon provides a protective atmosphere during processes like welding to prevent oxidation or contamination of the weld by air.
• It's also used in refining processes to remove impurities from molten metals, ensuring a purer final product.

Thanks to its inertness, argon helps achieve high-quality results in metal fabrication and processing, further illustrating the value of noble gases in industrial settings.