Senior Secondary (HKDSE) · Chemistry

Corrosion, anodisation, social–environmental implications: Practice Questions

5 multiple-choice questions marked as you go, and 4 written questions with worked solutions. All on Corrosion, anodisation, social–environmental implications.

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Question 1

1 mark

When an aluminium object undergoes anodisation, which of the following substances is used as the electrolyte to provide the oxygen needed for the growth of the oxide layer?

Question 2

1 mark

Considering the socioeconomic implications of rusting, what is a primary reason why governments invest heavily in corrosion prevention for steel structures?

Question 3

1 mark

Which of the following statements regarding the corrosion of metals, their protection, and the associated socio-environmental implications is correct?

Question 4

1 mark

Which of the following methods protects an iron object from corrosion by applying a layer of a less reactive metal to its surface?

Question 5

1 mark

From a socioeconomic perspective, why is the corrosion of underground metallic pipelines a significant concern for society?

Question 6

2 marks

Explain why anodisation is used to protect aluminium products even though aluminium is a more reactive metal than iron.

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Question 7

5 marks

Evaluate the chemical advantage of anodisation over sacrificial protection for metallic structures where physical maintenance is restricted, and explain how the spontaneous reformation of the protective layer on aluminium contributes to the social-environmental goal of resource conservation compared to iron-based systems.

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Question 8

5 marks

When a steel hull of a ship is in contact with seawater, it can be protected from corrosion by attaching several blocks of zinc to it. Explain how this method prevents the steel hull from rusting.

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Question 9

8 marks

A steel pipeline used for transporting natural gas is buried in coastal soil that is both acidic and highly saline. Steel is primarily composed of iron.

(a) Explain how the presence of sodium chloride and acidic conditions in the soil accelerates the rusting of the iron pipeline. Provide the chemical half-equation for the reduction process that occurs specifically due to the presence of \(H^+(aq)\) ions in the acidic soil.

(b) In a laboratory simulation, a rust indicator containing \(K_3[Fe(CN)_6]\) and phenolphthalein is applied to a scratched section of the steel. Describe the colour changes observed at the scratch and in the surrounding area. Explain the chemical basis for each observation.

(c) Engineers are comparing sacrificial protection using magnesium blocks and tin-plating for this pipeline. Explain why magnesium provides effective protection even if the pipe is scratched, whereas tin-plating may actually accelerate corrosion under the same conditions. Refer to the relative positions of the metals in the electrochemical series.

(d) Discuss one social and one environmental implication of a major failure of this pipeline caused by corrosion.

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