An underground steel pipeline in Saudi Arabia is protected from corrosion by connecting it to buried magnesium blocks. After several years, the magnesium blocks need to be replaced. What is the correct explanation for this observation?

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Question

An underground steel pipeline in Saudi Arabia is protected from corrosion by connecting it to buried magnesium blocks. After several years, the magnesium blocks need to be replaced. What is the correct explanation for this observation?

Accepted Answer

The magnesium has been oxidised instead of the iron, providing sacrificial protection. — Award 1 mark for understanding that magnesium is more reactive than iron and corrodes preferentially, protecting the steel pipeline. A is incorrect — while magnesium may react with water, this is not the primary protection mechanism. C is incorrect — the magnesium does not coat the pipeline. D is incorrect — magnesium does not absorb oxygen in this way.

Answer

The magnesium has absorbed all the oxygen from the surrounding soil.

Answer

The magnesium has formed a protective coating on the surface of the pipeline.

Answer

The magnesium has reacted with water in the soil to form magnesium hydroxide.

Answer

The magnesium has been oxidised instead of the iron, providing sacrificial protection.

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