This diagram shows the various layers of a pipe. Outline TWO reasons why this pipe would be resistant to corrosion. Iron corrodes differently under acidic and neutral conditions. (i) Write an equation to represent the process of rusting under neutral conditions. (ii) Explain why iron will corrode faster under acidic conditions than under neutral conditions. A wooden artefact was recovered from a shipwreck. After it was removed from the ocean, it was placed in a controlled environment. The water was changed weekly and the chloride ion concentration was monitored. After 10 weeks, the artefact was dried slowly in a controlled environment. The graph shows the chloride ion concentration in the tank in the first five weeks. (i) Account for the shape of this graph. (ii) Explain the possible effect on the artefact if it had been simply left to dry instead of undergoing the procedure described above. An investigation is to be set up in a school laboratory to determine the rate of corrosion of iron in different oxygen concentrations. (d) Identify the variables that need to be kept constant in this investigation. (e) Explain why a range of factors should be considered when using electrolysis to clean and stabilise a metal artefact.

SSCE HSC Chemistry Alcohols: This diagram shows the various l

This diagram shows the various layers of a pipe - HSC - SSCE Chemistry - Question 33 - 2060 - Paper 1

Question 33

This diagram shows the various layers of a pipe. Outline TWO reasons why this pipe would be resistant to corrosion. Iron corrodes differently under acidic and neut... show full transcript

Worked Solution & Example Answer:This diagram shows the various layers of a pipe - HSC - SSCE Chemistry - Question 33 - 2060 - Paper 1

Step 1

Outline TWO reasons why this pipe would be resistant to corrosion.

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Answer

The interior zinc coating acts as a sacrificial anode, protecting the steel from corrosion by corroding first before the steel can be affected.
The polymer and powder coatings provide a physical barrier to moisture and oxygen, which are necessary for the corrosion process to occur.

Step 2

Write an equation to represent the process of rusting under neutral conditions.

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Answer

The equation for the rusting of iron can be represented as:

$4Fe(s) + 3O_2(g) + 6H_2O(l) \rightarrow 4Fe(OH)_3(s)$

This indicates iron reacting with oxygen and water to form hydrated iron(III) oxide.

Step 3

Explain why iron will corrode faster under acidic conditions than under neutral conditions.

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Answer

In acidic environments, higher concentrations of hydrogen ions increase the rate of electron transfer in the corrosion process. The presence of a stronger oxidizing agent, such as hydrogen ions, accelerates the oxidation of iron compared to neutral conditions, where the reaction proceeds slowly.

Step 4

Account for the shape of this graph.

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Answer

The graph shows a series of increases and plateaus, indicating that chloride ion concentrations increase as the artefact absorbs ions from the water during soaking, followed by periods of stable concentration when the water is changed, allowing for the temporary removal of chloride ions.

Step 5

Explain the possible effect on the artefact if it had been simply left to dry instead of undergoing the procedure described above.

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Answer

If left to dry without controlled conditions, the artefact could suffer from uneven drying, leading to potential cracking or warping. Additionally, without managing the chloride ion concentration, residual salt could remain, which might contribute to further degradation of the wooden structure over time.

Step 6

Identify the variables that need to be kept constant in this investigation.

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Answer

The temperature of the environment in which the corrosion is measured.
The surface area of the iron samples being investigated.

Step 7

Explain why a range of factors should be considered when using electrolysis to clean and stabilise a metal artefact.

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Answer

Several factors play a critical role in the efficiency of electrolysis, such as:

The nature of the electrolyte used must not harm the metal and should facilitate effective cleaning.
The concentration of the electrolyte is important to control reactions and ensure that unwanted byproducts do not form.
The selection of electrodes is crucial; inappropriate materials may react in harmful ways, compromising the artefact.
Current settings must be monitored, as excessive current can produce rapid reactions that may damage the artefact.

This diagram shows the various layers of a pipe - HSC - SSCE Chemistry - Question 33 - 2060 - Paper 1

Worked Solution & Example Answer:This diagram shows the various layers of a pipe - HSC - SSCE Chemistry - Question 33 - 2060 - Paper 1

Outline TWO reasons why this pipe would be resistant to corrosion.

Write an equation to represent the process of rusting under neutral conditions.

Explain why iron will corrode faster under acidic conditions than under neutral conditions.

Account for the shape of this graph.

Explain the possible effect on the artefact if it had been simply left to dry instead of undergoing the procedure described above.

Identify the variables that need to be kept constant in this investigation.

Explain why a range of factors should be considered when using electrolysis to clean and stabilise a metal artefact.

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