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2021 O Level Chem P1 Q22 — Group 0 / Noble Gases Solution

Group 0 / Noble Gases 2021 O Level Pure Chemistry · Paper 1 · Q22

Question

Arc welding is a process which uses electricity to make high temperatures to melt two pieces of metal so that they can be joined. Argon is blown onto the surface where the molten metals are joining. Why is argon used?

AIt reacts with oxygen releasing heat which helps the metals to melt.
BIt gives off a lot of light to help the welder see what they are doing.
CIt is a good electrical conductor and so creates a high temperature.
DIt is an inert gas and so prevents the metals oxidising.

Correct answer: D

Video Solution

Explanation

Answer: D. Argon is a noble gas in Group 0 with a full outer electron shell, which makes it chemically inert. Blowing argon over the molten metal forms an inert blanket that pushes air away, stopping the hot metal from reacting with oxygen (being oxidised) or nitrogen during welding. This gives a clean, strong join.

Option A is wrong — argon does not react with oxygen, and certainly not to release heat. Option B is wrong — argon is colourless and gives off no light. Option C is wrong — argon is a poor conductor; the high temperature comes from the electric arc, not the gas.

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