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P Block Elements question

2007 · Shift 1 · Q14
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P Block Elements question

2007 · Shift 1 · Q14

JEE AdvancedChemistryP Block ElementsMCQ+3 / −1
The noble gases have closed-shell electronic configuration and are monoatomic gases under normal conditions. The low boiling points of the lighter noble gases are due to weak dispersion forces between the atoms and the absence of other interatomic interactions. The direct reaction of xenon with fluorine leads to a series of compounds with oxidation numbers +2, +4 and +6. XeF 4{}_44​ reacts violently with water to give XeO 3{}_33​. The compounds of xenon exhibit rich stereochemistry and their geometries can be deduced considering the total number of electron pairs in the valence shell.Argon is used in arc welding because of its
  1. A
    low reactivity with metal
  2. B
    ability to lower the melting point of metal
  3. C
    flammability
  4. D
    high calorific value
View written solutionFree

Correct answer: A

Step-by-step Derivation:

  1. Analyze the process: The question asks for the reason Argon (Ar) is used in arc welding. Arc welding is a process that uses an electric arc to create extremely high temperatures to melt and join metals.

  2. Identify the challenge in arc welding: At the very high temperatures involved in arc welding, the molten metal is highly reactive. It can easily react with gases present in the atmosphere, particularly oxygen (O2O_2O2​) and nitrogen (N2N_2N2​).

  3. Consequences of atmospheric reactions:

    • Reaction with oxygen leads to the formation of metal oxides, a process called oxidation. This can result in a weak, porous, and brittle weld.
    • Reaction with nitrogen can form metal nitrides, which can also compromise the strength and ductility of the weld. To obtain a strong and high-quality weld, the molten metal pool must be protected from these atmospheric gases.

  4. Role of a shielding gas: A shielding gas is used to create a protective, inert atmosphere around the weld pool. This gas displaces the ambient air (containing O2O_2O2​ and N2N_2N2​), thereby preventing the molten metal from reacting with them.

  5. Properties of Argon: Argon is a noble gas. Noble gases are characterized by their stable, closed-shell electronic configuration (a full valence shell). This makes them chemically inert or having very low reactivity. Argon is also readily available and cost-effective compared to other noble gases like Helium for many applications.

  6. Evaluating the options:

    • A: low reactivity with metal: Because Argon is a noble gas, it is chemically inert. It does not react with the molten metal even at the extreme temperatures of the welding arc. This property makes it an ideal shielding gas to protect the weld from atmospheric contamination. This statement is correct.
    • B: ability to lower the melting point of metal: A shielding gas does not significantly alter the melting point of the metal being welded. This is not the function or property of Argon in this context. This statement is incorrect.
    • C: flammability: Argon is non-flammable. Using a flammable gas in a high-temperature process like welding would be extremely hazardous. This statement is incorrect.
    • D: high calorific value: Calorific value relates to the heat produced by combustion. Argon is non-combustible and thus has a calorific value of zero. Gases with high calorific value are used as fuels (e.g., in gas welding), not as inert shields. This statement is incorrect.

  7. Conclusion: The primary reason for using Argon in arc welding is its chemical inertness, which means it has very low reactivity with the hot, molten metal. This protects the weld and ensures its quality and strength.

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