Samantha Fraser
Kerrie Anne Shortland
Victor Roseverne
Edward Sze-Tu
Introduction
The electrochemistry option of the chemistry syllabus is taught in a very interesting context – the ocean and the effects of a saline environment.
The impact of such an environment can be investigated and analysed from observations on the reaction of corrosion for present day ships and the effects of corrosion on earlier iron ships which was determined by salvage efforts.
Therefore in this option we sahll look at the nature of corrosion and its prevention and at the ways of restoring corroded objects recovered from shipwrecks.
Whilst all steel structures (including those on land such as cars, machinery, bridges etc) are subject to corrosion, ships are more susceptible because of the corrosive atmosphere of the ocean. Being a solution of sodium chloride, the ocean is a strong electrolyte solution and so a good medium for the occurrence of redox reactions. Students will begin this option with a survey of the nature of ocean water.
Corrosion is an electrochemical process, that is, it involves the interaction of chemistry with electricity. In this option students will review the basic concepts of electrochemistry. This involves galvanic cells, the relative reactivity of metals and the use of standard electrode potentials. Electrolysis, which is often ised in restoring corroded artefacts recovered from shipwrecks, will also be considered.
Further, students will consider the corrosion of steel and its prevention. This will include discussion of galvanising and cathodic protection of steel structures.
Lastly students will discuss the restoration of recovered objects from shipwrecks. Several specific examples of restoration will be described to illustrate the chemistry involved.
In short the option Shipwrecks and Salvage consists of seven major parts:
9.6.1 – The chemical composition of the ocean infers its potential role as an electrolyte.
9.6.2 – Ships have been made of metals or alloys of metals.
9.6.3 – Electrochemical cells involve oxidation/reduction reactions.
9.6.4 – Iron and steel corrode quickly in a marine environment and must be protected.
9.6.6 – Predictions of slow corrosion at great depths were apparently incorrect.
This option is to be taught in thirty indicative hours, which we have broken up into individual lessons of one hour.
The prescribed focus areas of interest in this topic are:
The skills covered by this topic include:
The main problems teachers may encounter with this option is access to resource material. This is a reflection of the timing of this assignment. Fortunately, we were able to access textbooks available for the HSC 2001. However no laboratory manuals for the new syllabus are available until February 2001. We tried to locate information on practicals outlined in the syllabus using the internet but failed. Sample programmes have not yet been written by various teaching organisations for this option until 2001.
Text References
Web Sites
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9.6.1 The chemical composition of the ocean infers its potential role as an electrolyte. |
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Lesson |
Objectives (By the end of this lesson students should be able to) |
Outcomes (By the end of this lesson students should be able to) |
Content/Activities/Demonstrations |
Syllabus Outcomes |
Syllabus Links |
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1 |
Understand that sea water contains ions and these ions constitute current. |
Define an electrolyte. Recall that electricity is the flow of charges. Identify that the two sources of ions in sea water are from leaching by rainwater and hydrothermal vents in mid-ocean ridges. |
Students are to test the electrical conductivity of sea water using a basic electric circuit with ammeter and globe. Boil off the water to obtain salts. Teacher revises the water cycle with added emphasis on leaching through the soil on the board. Teacher also explains the addition of minerals through hydrothermal vents using a diagram on the board or if possible, with the aid of a prop. Students add Mg to copper sulfate, with the aid of equations teacher introduces the role of electrons in redox reactions. |
H6 H16 |
5.7.1a) 4.9.5a) 5.9.2a) |
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2 |
Appreciate the power of prediction methods in electrochemistry. |
Define the terms oxidation and reduction. Identify in a basic metal displacement reaction the oxidant and reductant. Write half equations for basic metal displacement reactions. Learn to predict the outcome of a metal displacement reaction given an activity series. |
Perform further experiments whereby students must predict the outcome of the reaction given an activity series. Oxidising acids are included to trick the students. Teacher presents reaction mechanisms on board. |
H6 H10 H12 H14 |
4.7.4, 4.7.6, 5.7.3 e) |
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3 |
Appreciate the work of past scientists in the field of electrochemistry. |
Summarise the contributions of Galvani, Davy, and Faraday in electrochemistry. |
Students are to present the work of either Galvani, Davy, Volta, or Faraday in groups. |
H3 H5 H6 H11 H13 H15 H16 |
PFA 4/5.1 |
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1 |
Consider the range of conditions under which the rusting of iron occurs. |
Perform a first hand investigation of the range of conditions in which rusting of iron occurs. Explain the process of rusting at the chemical level. |
Perform an investigation into the conditions required for rusting to occur. Demonstration of electrochemical cell to detect the flow of electrons during the corrosion of iron. |
H3 H5 H8 H11 H12 H13 H14 H15 |
5.7.3, 9.2.4 |
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2 & 3 |
To appreciate that steel and iron corrode at different rates and to understand why this occurs. |
Plan and perform a first hand investigation to compare the rate of corrosion of iron and steel. |
Plan & perform a first hand investigation to compare the rate of corrosion of pure iron and steel of known composition. |
H3 H5 H8 H11 H12 H13 H14 H15 |
5.7.3, 8.3.1, 9.2.4 |
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4 |
Recognise that the main metals used in building ships are iron and steel. Also understand that the steel varies in composition. Understand that the physical properties of an alloy differ from those of its constituent components. |
Identify that iron and steel are used in building ships. Memorise the composition of steel and explain how the percent compositions of steel affects its properties. |
Presentation of information to the class. Web and literature research on the composition of steel. Research historical developments in the design and construction of ocean going vessels over the last 150 years. Focus on the metals they used and why they used them. Students perform a hands on soldering activity. |
H3 H5 |
8.3.1 |
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5 |
Consider the differences in the corrosion of active and passivating metals. |
Recall the conditions under which rusting occurs and describe the differences in the corrosion of active and passivating metals. |
Performing an investigation of the corrosion of iron nails and compare it to aluminium. Determine what is occuring at the chemical level. Use the teaching strategy of predict, observe, and explain. |
H3 H5 H8 H13 H14 H15 |
5.7.3 |
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9.6.3 Electrochemical cells involve oxidation/reduction reactions. |
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1 |
Understand that voltage of a galvanic cell is dependant upon the activities of the substances in use. The further they are apart in the activity series the higher the voltage produced. |
Define the terms galvanic cell and electrolytic cell. Construct their own galvanic cell given materials. |
Teacher demonstrates to class how to set up an Mg/Mg2+//Cu/Cu2+ galvanic cell with voltmeter or light globe attached. They repeat the activity with Zn and Cu and then Sn and Cu. Students note down brightness of globe and/or the reading on the voltmeter in each case. Class discusses results and activity series is brought up in discussion. |
H3 H6 H13 H15 H16 |
4.7.4, 4.7.6, 5.7.3 e), 5.7.1 c) |
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2 |
To use the standard reduction potential tables correctly. To gain a general understanding of how a battery works. |
Write half equations. Predict the voltage of a cell using table of standard reduction potentials. Define the terms anode and cathode. |
For an Fe/Ag galvanic cell students try to predict the voltage produced. Teacher does calculations using standard reduction potentials they setup experiment and obtain reading. Table of standard potentials is introduced and teacher explains how to write half reactions, then obtain the correct voltage. Teacher performs lots of examples on the board. |
H3 H6 H10 H13 H15 H16 |
No prior experience. |
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3 |
To understand why with the use of a voltage electrolysis occurs. |
Define the process of electrolysis. Write the correct half reactions at each electrode. Describe the process of galvanising. |
By using the cell used in previous lesson, teacher connects battery to it and reverses galvanic processes. Students perform same experiment, observe, and give their thoughts on what is occurring. Teacher explains significance of standard electrode potentials in determining the required battery voltage. Classroom discussion on applications of electrolysis in industry such as galvanising. |
H3 H6 H10 H13 H15 H16 |
4.7.4, 4.7.6, 5.7.3 e), 5.7.1 c) |
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4 |
Appreciate the differences between electrolytic and galvanic cells. Acknowledge that the nature of the electrolytes, concentration, and type of electrode can affect the result of an electrolytic cell. |
List the differences between galvanic and electrolytic cells. |
Comparison of galvanic versus electrolytic cells. Teacher performs a demonstration of the effects of changing the electrolytes, concentration, and the electrodes for an electrolytic cell. Students note down results. |
H3 H6 H10 H13 H15 H16 |
4.7.4, 4.7.6, 5.7.3 e), 5.7.1 c) |
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5 |
Understand how Faraday's First Law is derived. |
Outline the effects of changing the concentration, and nature of an electrolyte, and also electrode in electrolysis. State Faraday's first law of electrolysis. |
Class investigates why these results occurred with help of teacher. Teacher then sets up Faraday's electrolysis experiment and using Q=It students compare the amount of charge passed through to the mass of copper deposited on the electrode. Then class draws graph of results on board then Faraday's First Law is introduced or determined. |
H3 H6 H10 H13 H15 H16 |
4.7.4, 4.7.6, 5.7.3 e), 5.7.1 c) |
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9.6.4 Iron and steel corrode quickly in a marine environment and must be protected. |
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1 |
Understand ways of preventing rust formation particularly on hulls of ships. |
Identify the ways in which a metal hull may be protected including development of surface alloys, corrosion of resistant metals, new paints. Provide a historical account of the design & construction of ocean going vessels with a focus on metals used. |
Identify data, gather and process information from secondary sources to trace the historical developments in the design and construction of ocean going vessels with a focus on metals. |
H3 H5 |
8.3.1, 8.2.3, 9.2.1 |
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2 & 3 |
Understand that metals corrode at different rates. |
Predict the metal which corrodes when two metals form an electrochemical cell using a list of standard electrode potentials. |
Identify data, choose equipment, plan & perform a first hand investigation to compare the corrosion rate in a suitable electrolyte, of a variety of metals including modern alloys to identify those best suited for marine vessels. |
H8 H11 H12 H13 H14 H15 |
9.2.4 |
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4 & 5 |
Students will understand cathodic protection both in the form of sacrificial and charged inert electrodes and its applications. |
Outline the process of cathodic protection, describing examples of its use in both marine and terrestrial environments. Describe the process of cathodic protection in selected examples in terms of oxidation/reduction chemistry involved. Gather and process information to identify applications of cathodic protection and use available evidence to identify the reasons for their use and the chemistry involved. |
Discussion, library research, presentation and report writing. |
H3 H5 H13 H14 |
9.2.4 |
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6 |
To develop an understanding of the effectiveness of metal protective methods. |
Perform a first hand investigation to compare the effectiveness of alternate protection used to coat a metal such as iron and how these methods prevent corrosion. |
Compare the corrosion rate of an unprotected metal with a variety of metals that have been protected in some form. Describe at the chemical level what is occuring in each circumstance. |
H3 H5 H8 H11 H12 H13 H14 H15 |
5.7.3, 9.2.4 |
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1 |
To understand that concentrations of gas differ in the atmosphere and ocean. Recognise that temperature and pressure may affect the solubility of gases and salts. |
Identify the gases normally dissolved in the oceans and state the nature of their concentrations in both the oceans and atmosphere. Outline the effect of temperature and pressure on the solubility of gases and salts. |
Teacher led discussion involving video segments and worksheet exercises. Possibly look at performing a practical investigation of one of those parameters for example gas solubility according to temperature or solubility of a salt with varying temperature. |
H3 H5 H11 H12 H13 H14 H15 |
8.4.4 |
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2 & 3 |
To understand that the solubility of gases varies with pressure. In addition recognise that corrosion varies according to temperature variations and temperature and salt concentrations. |
Compare and explain how the solubility of selected gases vary at increasing depths of the ocean. |
Teacher led discussion. Perform a first hand investigation to compare and describe the rate of corrosion of materials in different oxygen concentrations, temperatures, and salt concentrations. Modify a corrosion experiment from texts. To determine the concentration of oxygen in the water using the procedure from Senior Chemistry practical manual. |
H3 H5 H8 H11 H12 H13 H14 H15 |
8.4.4 |
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4 |
To appreciate how temperature and the depth of the ocean affect the rate of corrosion in metals. |
Use available evidence to predict the rate of decomposition of a metal ship wreck at great depths in the ocean. Ie. Low temperature, low oxygen and give reasons for the predictions made. |
Teacher led discussion. Worksheet exercises. |
M5 |
5.7.3 |
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9.6.6 Predictions of slow corrosion at great depths were apparently incorrect. |
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1 |
Understand how certain anaerobic bacteria are able to corrode iron. |
Students will explain that shipwrecks at great depths are not corroded by electrochemical reactions but rather by anaerobic bacteria. |
Teacher led discussion. Titanic documentary video. |
H3 H5 |
4.8.3 a) |
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2 |
Understand that certain anaerobic bacteria are able to corrode iron by redusing sulafte to sulfide and hydroxide. |
Students will describe the bacteria as a sulfur reducing species whose wastes produce acidic environments around deep wrecks. |
Teacher led discussion. Worksheet activities. |
H5 H8 |
5.7.3 d) 4.7.6 b) 8.3.1 |
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3 & 4 |
Understand the effect of pH on the rate of corrosion. |
Students will explain that acidic environments accelerate corrosion in non-passivating metals. Students will perform a first hand investigation to compare and describe the rate of corrosion of materials in different acidic and neutral solutions. |
Practical activity "the corrosion of iron". |
H8 H11 H13 |
9.3.3 |
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1 |
Understand that changes occur to objects that have been submerged in sea water for a long time. |
Explain that artefacts from long submerged wrecks will be saturated with dissolved chlorides and sulfates. Describe the processes that occur when a saturated solution evaporates and relate this to the potential damage to dying artefacts. |
Teacher led discussion. Library research & web site search and activity. |
H16 |
4.7..6 b) |
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2 |
Appreciate how electrolysis can be used to restore corroded objects made from certain metals. |
Identify the use of electrolysis as means of removing salt and as a means of cleaning and stabilising strong metal artefacts. Students will identify appropriate electrolytic treatment of cholride saturated artefact to remove salt. |
Worksheets. Practical from Foundations of Chemistry pg 421. |
H3 H11 H13 H14 H15 |
9.2.4 |
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3 |
Understand how to remove soluble salts and encrusted carbonates from recovered artefacts. |
Discuss the range of chemical procedures which can be used to clean, preserve, and stabilise artefacts from wrecks and where possible provide an example of ach procedure. |
Library research. Poster presentation. |
H3 H5 |
9.3.3 8.3.2 |
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4 |
Understand that salt saturated artefacts may change in appearance as drying occurs. |
Students will model the evaporation of water from salt saturated wooden, leather, and textile artefacts and describe the change in the artefact as it drys. |
Practical - modelling the evaporation of water explained in the outcomes section. |
H15 H12 |
4.7.5 d) |
