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Question 31 — Shipwrecks, Corrosion and Conservation (25 marks) (a) (i) Identify ONE passivating metal - HSC - SSCE Chemistry - Question 31 - 2003 - Paper 1
Question 31
Question 31 — Shipwrecks, Corrosion and Conservation (25 marks) (a) (i) Identify ONE passivating metal. (ii) Account for the differences in corrosion of active and... show full transcript
Worked Solution & Example Answer:Question 31 — Shipwrecks, Corrosion and Conservation (25 marks) (a) (i) Identify ONE passivating metal - HSC - SSCE Chemistry - Question 31 - 2003 - Paper 1
Step 1
Step 2
Account for the differences in corrosion of active and passivating metals. Include a relevant balanced chemical equation in your answer.
Answer
Active metals, such as zinc, corrode easily because they readily lose electrons, while passivating metals, such as aluminum, form a protective oxide layer that inhibits further corrosion. The corrosion of zinc can be represented by the following balanced equation:
Step 3
Describe ONE precaution you took to minimise hazards, or to dispose of reactants and products safely.
Answer
One precaution I took was to place the copper sulfate solution in a secure container to prevent spills and avoid exposure to harmful chemicals while conducting the electrolysis experiment.
Step 4
Outline the procedure you used to show how ONE factor affects the rate of an electrolysis reaction.
Answer
To investigate one factor affecting the rate of electrolysis, I varied the concentration of the electrolyte. I set up the electrolysis apparatus with two electrodes placed in a beaker containing copper sulfate solution. I recorded the time taken for bubbles to form at the cathode at different concentrations, thereby observing how changes in concentration influence the rate of the reaction. A higher concentration typically resulted in a faster rate of gas evolution.
Step 5
Analyse how theories about corrosion at great ocean depth have changed since the recent discovery of extensive corrosion on wrecks such as the Titanic.
Answer
The understanding of corrosion at great ocean depths has evolved significantly. Initially, it was believed that the cold temperatures and high pressures would limit corrosion. However, recent findings show that the presence of sulfate-reducing bacteria accelerates corrosion processes by producing hydrogen sulfide, which can further corrode metal structures. This has led to a reassessment of how environmental factors contribute to the decay of shipwrecks, emphasizing biological factors along with chemical and physical conditions.
Step 7
Compare the effectiveness of these containers in limiting corrosion of steel fish hooks.
Answer
Among the three options — plastic, copper, and aluminum — plastic is the most effective container for limiting corrosion of steel fish hooks as it provides a non-reactive barrier. Copper can also be effective but may introduce electrochemical corrosion issues if moisture is present. Aluminum can form a protective oxide layer, similar to steel, but may not be as effective as plastic. Therefore, plastic is recommended for preventing rust and corrosion effectively.
Step 8
Assess how an understanding of electrolysis has contributed to the development of methods for cleaning and restoring marine artefacts.
Answer
An understanding of electrolysis has significantly impacted the restoration of marine artefacts. Techniques such as electrolysis are used to remove corrosion products from metal surfaces by reversing the corrosion process. By applying a controlled electric current through the artefact submerged in an electrolytic solution, rust can be stripped away, revealing the underlying metal. This method is preferred over mechanical cleaning because it minimizes physical damage to delicate artifacts, thereby preserving cultural heritage while allowing for effective restoration.