Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
How Best to Maintain a Metal Bridge?
A grade 8-9 science (chemistry) module on
Rusting and Corrosion of Metals
Abstract
This set of activities allows students to consider factors which can be involved in
determining the best way to protect a metal (iron) bridge. In tackling this issue,
students are guided to realise that they need to be aware of the factors that cause
iron to rust and also that sacrificial metals can protect iron. The sacrificial metals can
be put in a series such that the metal s higher in the series protect those below from
corrosion (rusting). The decision making on which method to use to protect the bridge
involves the consideration of a range of social factors from the need to provide
employment to people, to ensuring maximum safety, to cost and also the bridge
being aesthetically suitable for the surroundings.
Sections included
1.
2.
3.
Student activities
(for students)
Teaching guide
Assessment
4.
Teacher notes
Describes the scenario in more detail and the
tasks the students should perform
Suggests a teaching approach
Gives suggested formative assessment
strategies
Gives student worksheets and information for
decision making
Acknowledgement
This module has been adapted from that developed under the PARSEL project (www.parsel.eu) as part of an EC
FP6 funded project (SAS6-CT-2006-042922-PARSEL) on
Popularity and Relevance of Science Education for scientific Literacy
1
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
Overall Objectives/Competencies: The students are expected to:
*
ability to use previous and acquired knowledge to decide how best to
protect an iron bridge;
*
ability to appreciate that ‘most appropriate’ can apply to a particular;
situation and can change if circumstances change;

ability to suggest experimental procedures for testing factors that are
necessary for rusting to occur;
*
ability to suggest suitable methods to protect iron from rusting;
*
ability to utilise information presented in tabular format;
*
ability to discuss meaningfully in groups;

understand the factors that are needed for iron to rust;

understand the corrosion process that may occur when two dissimilar
metals are put together.
Curriculum content: Rusting of iron, prevention of rusting, corrosion
Kind of activity: Devising and carrying out experiments related to rusting,
formulating the reactivity series from experimental outcomes, discuss ways to
prevent iron from rusting, selecting the most appropriate method to protect a metal
bridge.
Anticipated time: 8 lessons
This unique teaching-learning material is intended to guide the teacher towards
promoting students’ scientific literacy by recognising learning in 4 domains –
intellectual development, the process and nature of science, personal development
and social development.
Its uniqueness extends to an approach to science lessons which is designed to follow
a 3 stage model. For this the approach is intentionally from society to science and
attempts to specifically meet student learning needs.
This uniqueness is specifically exhibited by:
1.
a motivational, society-related and issue-based title (supported in the student
guide by a motivational, socio-scientific, real life scenario);
2.
forming a bridge from the scenario to the scientific learning to be undertaken;
3.
student-centred emphasis on scientific problem solving, encompassing the
learning of a range of educational and scientific goals;
4.
utilising the new science by including in socio-scientific decision making to
relate the science acquired to societal needs for responsible citizenship
2
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
How Best to Maintain a Metal Bridge?
Student Activities
Scenario
River
School
Metal
bridge
Housing
estate
The diagram shows a newly built housing estate (on the right) separated from the
school by a river. To gain access to the school a bridge has been built over the river.
As this is only a pedestrian access and it is estimated the bridge will only be needed
for 18-20 years (a new school will then be built on a different location), it has been
decided that the bridge should be constructed of iron.
But will the bridge last for 20 years ? How is it possible to ensure that it will last? And
which method is the most suitable to maintain the bridge ?
3
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
Your Tasks
From you previous school studies you are aware that iron is very strong building
materials, but that iron rusts.
In this exercise you are asked to:
1.
Participate in a brainstorming activity to indicate your knowledge of rusting and
to suggest factors affecting rusting.
2.
Complete the worksheet provided.
3.
Plan (in groups) a series of experiments to determine factors affecting the
rusting of iron.
4.
Carry out (in groups) the series of experiments to determine the factors
affecting rusting of iron.
5.
Write out the method for undertaking the experiments and the conclusions
reached.
Give a possible formula for rust.
6.
Suggest ways that iron can be protected so that the bridge can last a long
time;
7.
Experiment with wrapping iron with another metal to see if this can be a further
protection method and to describe the experimental findings;
8.
Make a decision about what form of protection, if any, is the most appropriate
for the iron bridge;
9.
Explain what is meant by most appropriate for these circumstances.
4
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
How Best to Maintain a Metal Bridge?
Teaching Guide
This decision making exercise is intended to reinforce previous knowledge on rusting.
It introduces through simple laboratory experiments, which students can plan (if the
students are unaware), the need for oxygen and water to be present for rusting to
occur. The exercise also allows students to explore the use of a sacrificial metal to
protect iron and includes theoretical understanding of reactions between dissimilar
metals (depending on the conceptual level required by the curriculum).
As a major aspect of the script, a decision making exercise is introduced. Students
are called upon to reflect on factors (besides scientific ideas) that need to be taken
into account in making a decision on the most appropriate way to protect a metal
bridge. This may range from doing nothing - the cheapest, to galvanising it - a
scientific answer. In between could be environmental, economic or societal solutions.
All are possibilities, but the difficulty is to decide which is the most appropriate and
then to explain the choice.
5
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
Lesson Learning Outcomes
Lesson 1
At the end of this lesson, students are expected to be able to:

State that iron rusts

Suggest ways to investigate the factors that cause iron to rust
Lesson 2
At the end of this lesson, students are expected to be able to:

Undertake and understand experiments that can be performed to show
the factors that cause iron to rust
Lesson 3
At the end of this lesson, students are expected to be able to:

Explain why oxygen and water are needed for iron to rust

Suggest a formula for rust
Lesson 4
At the end of this lesson, students are expected to be able to :

Suggest experimental procedures to determine the sacrificial metal
when two metals are put together

Predict the likely outcome when metals are put together in an
atmosphere that prvides both oxygen and water.
Lesson 5
At the end of the is lesson, students are expected to be able to

Identify the reactivity series

Justify the decision as to the best way to protect a metal bridge.
Lesson 6
At the end of this lesson, students are expected to be able to

Suggest ways to rate sacrificial metals and hence forms a series
Lesson 7
At the end of this lesson, students are expected to be able to:

Identify the reactivity series
Lesson 8
At the end of this lesson, students are expected to be able to

Justify the decision as to the best way to protect a metal bridge.
6
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
Suggested Teaching Strategy
The guidelines are given in 4 parts – (1) previous knowledge (2) planning for the
investigation (3) student experimentation and (4) post experimental follow-up.
Part (1) – obtaining students’ conception about factors affecting rusting (5 minutes)
Lesson 1
The teacher can
 Write the word ‘rust’ in a box in the middle of the black(white)board
 Initiate a brainstorming session with students obtaining their ideas about rusting
and, in particular, the conditions necessary for rusting to occur (as usual in
brainstorming the teach access all student answers irrespective of whether they
are, or are not appropriate or conceptually correct)
 Write the students ideas from brainstorming on the black(white) board linked to
the term rust using appropriate connecting words
Part (2) - gaining evidence - testing ideas of factors affecting rusting (approx 20
minutes but may be much longer depending on students’ prior knowledge and
previous practice in planning experiments)
Lesson 1
The teacher can
 Guide students to explore the summary of ideas on the blackboard to determine
potential factors affecting rusting
 Establish that air(oxygen) and water could be factors necessary for rusting
(students may suggest others as well)
 Introduce the scientific research question ‘how can we find out what factors affect
rusting?’
 All students (in groups) to come up with possible procedures to investigate
whether the factors identified influence rusting
 Go around the groups during the planning exercise advising as necessary, until
student groups have completed their work or they have stopped because of
insufficient guidance.
 (assuming time is sufficient) Select good ideas from the different groups (in a
whole class situation) – the groups are selected by the teachers based on the
teacher’s prior knowledge gained from interacting with the groups in the group
work session.
 (assuming time is still sufficient) Guide, based on the group submissions (or lack
thereof) the experimental procedure to solve the problem posed by the question
Part (3) – experimentation (1 lesson)
7
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
Lesson 2
The teacher can
 Ensure student groups are
o aware of the purpose of the experimentation
o know what apparatus, chemicals they need
o are conversant with safety procedures
 Allow students to prepare for the experimental work and put forward their
hypotheses
 Allow students to set up the experiments which will then be left until next lesson
to observe the outcomes
 (if time permits) Instruct students, individually, to describe the procedure they
followed in their notebooks under the research question (the title) and to include
their predictions of the likely outcome.
Part (4) – post experimental follow-up (10-15 minutes – more if students write the
report at this time)
Lesson 3
The teacher can:
 Allow students to examine their experimental outcomes and determine whether
their predictions were, or were not correct
 Discuss, using a whole class question and answer, whether all outcomes were
the same for each group and the meaning attached to the outcomes
 Ensure the students can conclude form their experiments (it is expected the
conclusion will be that air(oxygen) and water are necessary for rusting)
 Request students to write down in their books their suggested formula for rust (go
around the class to check whether students have sufficient background to
complete this task which requires transference of understanding from one
situation to another.
 Guide the whole class, by question and answer plus teacher input as needed, to
a suggested formula (satisfactory for the whole class) (a suitable response here
could be FeO.H2O unless students are familiar with oxidation numbers when
Fe2O3.H2O is expected)
 Explain to the class that rust is thus a complex substance and not a simple oxide
 (if not already undertaken) Students write a report of their experiment explaining
the procedure followed and whether their predictions were correct (if report was
written earlier, then this part is now added). They can make the appropriate
conclusion and give a suggested formula for rust.
8
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
Part (5) introducing sacrificial metals
Lesson 4
 Point out that some metals react more quickly in air or water and demonstrate the
action of sodium on water compared with magnesium (where the magnesium
needs the water heated and turn into stream to give a fast reaction.
 Suggest that metals more reactive that iron could react rather than the iron and
thus offer a form of protection
 Guide the students to suggest how experiments where one metal is a sacrificial
metal can be carried out. It is expected that with appropriate guidance the
students will suggest wrapping one metal with another.
Part (6) – conducting experiments on sacrificial metals
Lesson 4
The teacher can:
 The teacher can then suggest that it is appropriate to take iron nails and to test
whether a metal can be sacrificial by wrapping the nail with strips of (a) copper,
(b) zinc, (c) magnesium, (d) aluminium (other metals are possible).
 Provide worksheets for the students so that they can set up the experiments in
petri dishes using salt water, add a drop of potassium hexacyanoferrate(II)
solution [K4Fe(CN)6] which will turn blue if the iron rusts and then leave the
dishes without lids until the next lesson.
Part (7)
- interpreting and concluding for the experiment
Lesson 5
The teacher can:
 Allow the students to observe the outcomes from the experiments and make
conclusions
 Expect the students to realise that copper cannot act as a sacrificial metal
whereas the others can (aluminium has a coating of oxide and the metal is
heavily protected by this and may not protect the iron)
 This illustrates that zinc and magnesium can act as sacrificial metals as they are
more reactive than iron
 Guide students to explain what is happening
Part (8) - developing the reactivity series
Lesson 6
The teacher can:
9
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science

Guide students to suggest further experiments to determine the actual series for
all the metals (in this case it is probably better to consider comparable rates of
reactions with water and between metal (and metal oxide)
Part (9) Empirical derivation of the reactivity series
Lesson 7
The teacher can:
 Provide worksheets for the students to undertake experiments to determine the
reactivity series for the following metals – copper, lead, zinc, magnesium,
sodium,
 Allow student to undertake the experiments and try to derive the series
 Discuss the experimental outcomes with the students
 Provide a sheet giving the reactivity series for a range of metals and including
hydrogen (and carbon?)
Part (10) Decide the best way to protect the metal bridge
Lesson 8
The teacher can:
 Ask the students to use their knowledge and decide on the best way to protect
the bridge.
 Through discussion, narrow down the possibilities of protecting the iron (from
those originally suggested in the brainstorming and now extended, perhaps,
with the use of sacrificial metals) to a manageable 3 or 4. Here the teacher
may need to inject ideas. One important point needed at this stage is that the
bridge should last for 18-20 years and that if the bridge is allowed to rust (i.e.
no action is taken), the bridge will need replacing after 6 years. Nevertheless
this could be a viable option, although safety considerations may eliminate this
because it can never be certain that the bridge will rust at an even rate each
year and that weather conditions do not promote accelerated rusting.
 The teacher also gives out additional information for the students to consider
(see teacher notes)
 Allow the students to make a decision and to justify this.
 In their groups, students are then asked to consider which method is the most
appropriate for maintaining this important right-of-way ? It is important for the
teacher to go around the groups and determine whether the students have a
clear grasp of the problem and are considering a wide range of possibilities
(there is a strong tendency, especially with weaker students to consider the
science answer and possibly the economic answers only). If necessary it is
appropriate to stop the group discussion after 5-10 minutes to here the
possible solutions. Where choices are very different, this by itself may
stimulate further discussion in the groups and encourage greater in-depth
10
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
thinking. If choices are very similar (usually because the range of options students
have considered is low), then the teachers will need to inject other considerations
e.g. the aesthetic aspect - that it is important what the bridge looks like), societal
factors (the need to provide unskilled employment opportunities because of mass
unemployment) or simply asking the students to consider the use of metal within
the society and to reflect on how this is actually being protected (it is inappropriate
for students to put forward unrealistic decisions).
 Following the group discussion, the teacher needs to ask each group to
present their choice and its reasons. This can then lead to a general
discussion session to see if consensus can be obtained for the whole class (if
this is not possible, it is worth reminding the class that in a real community,
ways need to be found to overcome such a situation otherwise it could lead to
violent confrontation. It is necessary to understand the points of views of
others and this is only possible by considering all aspects of a problem).
 Make comments on the students’ decisions as appropriate.
11
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
Achieving the competences
The educational competencies to be achieved are expected to be met as follows :
Competences
to be achieved by:
1. Ability to use previous and
students’ utilising knowledge gained about, and
acquired
knowledge
to
ways to prevent iron from rusting, are consolidated
decide how best to protect an
through group discussions in which students
iron bridge.
determine how best to maintain a metal bridge.
2. Ability to appreciate that
student appreciating that besides economic and
‘most appropriate’ can apply
scientific factors, there could be societal factors
to a particular situation and
(employment needed as many persons out-of-work),
can change if circumstances
business factors (finding the money to do the work
change.
and hence interest repayments), or environmental
factors. An aesthetic consideration may be also
important. Students should be aware that the factors
are not constant - this changes with circumstances.
3. Ability to identify suitable
students selecting suitable processes to protect iron
methods to protect iron from
from rusting are tested in class. They take the
rusting.
results of the brainstorming exercise and then
eliminate methods that would be inappropriate (in
this case a concrete bridge would not be appropriate
because, being on soft soil, it would need extensive
foundations to take the much greater weight).
4. Ability to utilise information
students interpreting the data presented in the
presented in tabular format.
tables.
5.
Ability to discuss
students discussing ‘most appropriate‘ through
meaningfully in groups.
groupwork to realise that the ‘most appropriate’ is
not an absolute answer, but dependent on choice
and circumstances.
6.
Ability
to
suggest
students detailing experimental plans to show that
procedures for testing factors
air(oxygen) and water are necessary for rusting.
that could influence rusting.
7. Understand the factors that
students offering explanations for the experimental
are needed for iron to rust.
results which show both air (oxygen) and water are
needed for rusting.
8. Understand the corrosion students explaining that zinc and other metals e.g.
process that may occur when magnesium are able to protect iron from rusting by
two dissimilar metals are put preferentially corroding themselves. Students
together.
appreciating that other metals e.g. copper do not
protect iron but enhances the rusting process.
12
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
How Best to Maintain a Metal Bridge?
Suggested Assessment Strategies
An assessment of achievement of the objectives can be by formative methods and
summative methods. As written records are requested, summative assessment
based on post session marking is possible for some objectives. Formative
assessment, however, can occur at all stages of the development of the script and be
use to determine student achievement of all objectives.
The assessment needs to relate to the learning outcomes put forward. It determines
whether the students have achieved the intended learning. As there are 4 learning
outcomes, then 4 separate marks are possible (they can, of course, be combined).
1.
Identify factors affecting the rusting of iron (please note: the learning outcome
is not concern with the ‘rate of rusting’ – that is another area of learning)
This will be shown during the initial brainstorming and reinforced by the
experiments to be undertaken, although the final identification may not occur
until the evidence has been collected after the experiment. The conclusion
written by students will confirm whether this learning outcome has been
achieved.
2.
Plan a series of experiments to identify factors affecting rusting.
The achievement of this learning outcome will be shown by the completing of
parts 3 and 4 of the student worksheet.
3.
Explain factors found to affect the rusting of iron.
This will also be indicated by the conclusion made after the experimentation.
13
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
4.
Deduce a possible formula or structure for rust
This is determined from the classwork undertaken by the students individually
at the end of the discussion.
Part A
Assessment based on Skills Attained
Formative assessment strategies
Able to award a social value grade (competencies 1 and 2)
The teacher listens to the discussions of the various groups,
x
Not able to make a meaningful contribution to the discussions on the best
method to maintain a metal bridge. Unable to make a choice other than based
on economic grounds i.e. cheapest.
√
Able to participate in the discussion and recognise that a choice can be made
on
scientific as well as economic grounds. Can consider other factors e.g.
environmental or social, but only when given guidance by the teacher.
√√
Able to play a significant role in the discussions and reflect on the viewpoints
from which a discussion could be made. Able to select an appropriate choice
based on social as well a environmental, economic and scientific grounds.
Appreciates any disparity that may occur between the best choice and actual
practice within society.
Able to award a scientific method grade (competencies 3 and 4)
The teacher listens to the discussions of the various groups and reviews the
experimental plans for determining facts for rusting to occur. The teacher asks
questions for clarity where appropriate
x
Not able to comprehend the data presented in the tables. Able to use little of
previous scientific knowledge in suggesting ways to prevent rusting. Not able
to develop experimental plans.
√
Able to interpret the data in the tables and determine the various costs. Able
to plan a suitable experiment to show that both air (oxygen) and water are
needed for rusting to occur, but may not set up a control of variables.
√√
Able to interpret the data and understand how the figures in the tables were
derived. Able to plan the experiment with due attention to the controlling of
variables and the use of appropriate.
14
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
Able to award a personal skills grade (competencies 5 and 6)
The teacher observes the group during the discussions
x
Does not take part in the discussion or show interest in the topic. Does
not help the group towards a decision. Ability to communicate scientifically is
not illustrated.
√
Able to participate in the discussion, helping the group to eliminate non helpful
choices from those put forward during the brainstorming session. Able to
communicate within the group to derive a 'best method' using suitable
scientific language. Able to present to others, if points reinforced by the
teacher.
√√
Eager to participate and to help others to join in. Leads the group to make
choices ensuring all members of the group are permitted to contribute. Able to
communicate both within the group and as a presentation in clear and
scientific language.
Able to award a science concepts grade (competencies 7 and 8)
The teacher observes the various groups during the discussions. The teacher asks
questions for clarity of understanding where appropriate
x
Not able to eliminate inappropriate choices put forward during brainstorming
on scientific grounds. Does not understand the rusting process.
√
Able to eliminate inappropriate choices from the brainstorming session.
Understands the rusting process in terms of oxidation of iron in the presence
of air and water and that this can be prevented by eliminating water or air and
by setting up a metal couple using a more reactive metal.
√√
In addition are able to recognise that the some metals although suitable from
the reactivity series point of view, are not usable on the basis of cost,
too reactive, or in the case of metals such as aluminium, protected by an
oxide layer.
Summative assessment
Able to award a science method grade (competencies 3 and 4)
The teacher can assess written records of students on the experimental planning of
an experiment to determine factors necessary for rusting to occur
x
Written record poor. Unable to plan the experiment.
√
Written record complete. An experiment is described to determine the factors
necessary for rusting with suitable conclusions.
√√
Very clear and detailed written record explaining the factors necessary for
rusting pointing out how variables can be controlled for a fair result.
15
Project funded within the EC FP7 Programme: 5.2.2.1 – SiS-2010-2.2.1
Grant Agreement No.:266589
Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
Able to award a science concept grade (competencies 7 and 8)
The teacher can assess the written record interpreting an experiment in which two
dissimilar metals are put together
x
Unable to interpret the findings from the experiment.
√
The written record interprets the experimental findings showing that iron is
more reactive than copper and thus rusts in the presence of copper, but that
iron is less reactive than zinc and magnesium and does not rust when in
contact with these metals.
√√
A very clear interpretation of the experimental findings showing that, in the
presence of a suitable conducting medium, two dissimilar metals will sent up a
reactivity cell and that the more reactive metal will corrode. The reactivity
decreases from magnesium and zinc to iron and copper is less react that iron.
Part B
Assessment by Lesson
Lesson 1
Dimension
1
Answers questions
2
Plans anvestigation
Criteria for evaluation
The student:
Recognise that iron rusts and able to suggest
what this means.
Puts forward suggestions on ways to investigate
the factors that cause iron to rust.
Creates an appropriate experimental plan to the
level of detail required by the teacher.
Mark/grade given
(x,√,√√)
Puts forward an appropriate
prediction/hypothesis.
Develops an appropriate procedure (including
apparatus/chemicals required and safety
procedures required) and indicates variables to
control.
Lesson 2
Dimension
Criteria for evaluation
The student:
Mark/grade given
(x,√,√√)
16
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Supporting and coordinating actions on innovative methods in science education: teacher
training on inquiry based teaching methods on a large scale in Europe
Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
1
Functioning in the
group during
experimentation
2
Performing the
investigation or
experiment
Lesson 3
Dimension
Contributes to the group discussion during the
inquiry phases (raising questions, planning an
investigation/ experiment, putting forward
hypotheses/predictions, analyzing data, drawing
conclusions, making justified decisions).
Cooperates with others in a group and fully
participates in the work of the group.
Illustrates leadership skills – guiding the group by
thinking creatively and helping those needing
assistance (cognitive or psychomotor);
summarising outcomes.
Shows tolerance with, and gives encouragement
to, the group members.
Understands the objectives of the
investigation/experimental work and knows which
tests and measurements to perform.
Performs the investigation/experiment according
to the instructions/plan created.
Uses lab tools and the measurement equipment
in a safe and appropriate manner.
Behaves in a safe manner with respect to
him/herself and to others.
Maintains an orderly and clean work table.
Criteria for evaluation
The student:
1
Interpret
findings Interprets data collected in a justifiable manner.
and
make Explains why the experiments show that oxygen
conclusions
and water are necessary for rusting.
2
Answers questions
Lesson 4
Dimension
1
Suggest
experimental
procedure
Mark/grade given
(x,√,√√)
Suggest what rust might be.
Able to indicate why the suggestion given was
put forward.
Criteria for evaluation
Mark/grade given
The student:
(x,√,√√)
Puts forward an appropriate experimental
procedure to determine the sacrificial metal when
two metals are put together.
17
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Supporting and coordinating actions on innovative methods in science education: teacher
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Puts forward an appropriate
prediction/hypothesis.
Lesson 5
Dimension
1
2
Criteria for evaluation
Mark/grade given
The student:
(x,√,√√)
Draws appropriate conclusions from the
Put forward a
experimental data
reactivity series
Puts forward a series based on the evidence
obtained
Scientific or socio- Illustrates creative thinking/procedures in
scientific reasoning
putting forward suggestions on which to base
the decision
Gives a justified socio-scientific decision on the
best way to protect the metal bridge, giving
special attention to scientific components.
Lesson 6
Criteria for evaluation
The student:
Dimension
1
2
4
Mark/grade given
(x,√,√√)
Record experimental
data collected
Makes and Records observations/data
collected appropriately (in terms of numbers of
observations deemed acceptable/accuracy
recorded/errors given)
Interpret or calculate Interprets data collected in a justifiable manner
from data collected including the use of appropriate graphs, tables
and
making and symbols
conclusions
Draws appropriate conclusions related to the
research/scientific question
Examine charts.
Able to provide graphical representation as
required
Able to present graphical representations of a
suitable size and in suitable detail
Able to provide full and appropriate headings
for diagrams, figures, tables
Lesson 7
Dimension
Criteria for evaluation
The student:
Mark/grade given
(x,√,√√)
18
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1
Scientific or socio- Participates in the discussion on the most
scientific reasoning
appropriate way to maintain the metal bridge.
Gives a justified socio-scientific decision to an
issue or concern, correctly highlighting the
scientific component
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Professional Reflection-Oriented Focus on Inquiry-based Learning and Education through Science
Part C
Assessment based on Teacher Strategy
Assessment Tool based on the Teacher's Marking of Written Material
Dimension
1
2
3
Criteria for evaluation
The student:
Mark/grade
given (x,√,√√)
Writes a plan or report Puts forward an appropriate research/ scientific
of an investigation
question and/or knows the purpose of the
investigation and experiments.
Creates an appropriate investigation to
determine the factors affecting rusting and the
manner in which to determine which metal is
the sacrificial metal..
Puts forward an appropriate prediction/
hypotheses
Develops an appropriate procedure (including
apparatus/chemicals required and safety
procedures required) and indicates variables to
control
Record experimental Makes
and
Records
observations/data
data collected
collected appropriately (in terms of numbers of
observations deemed acceptable/accuracy
recorded/errors given)
Interpret or calculate Interprets data collected in a justifiable manner
from data collected
including the use of appropriate graphs, tables
and making
and symbols
conclusions
Draws appropriate conclusions related to the
research/scientific question
4
Answers questions
Provides correct written answers to questions
given orally or in written format
Provides answers in sufficient detail especially
when called upon to give an opinion or decision
5
Scientific or socioscientific reasoning
Illustrates creative thinking/procedures in
suggesting the may to protect the bridge
Gives a justified socio-scientific decision as to
the best way to protect the bridge, correctly
highlighting the scientific component
20
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Assessment Tool based on the Teacher's Observations
Dimension
Criteria for evaluation
The student:
1
Functioning in the
group during
experimentation or
discussion
2
Performing the
investigation or
experiment
3
Presenting the
investigation or
experiment orally
Contributes to the group discussion during the
inquiry phases (raising questions, planning
investigation/experiment,
putting
forward
hypotheses/predictions, analyzing data, drawing
conclusions, making justified decisions).
Cooperates with others in a group and fully
participates in the work of the group.
Illustrates leadership skills – guiding the group by
thinking creatively and helping those needing
assistance
(cognitive
or
psychomotor);
summarising outcomes.
Shows tolerance with, and gives encouragement
to, the group members.
Understands
the
objectives
of
the
investigation/experimental work and knows which
tests and measurements to perform.
Performs the investigation/experiment according
to the instructions/plan created.
Uses lab tools and the measurement equipment
in a safe and appropriate manner.
Behaves in a safe manner with respect to
him/herself and to others.
Maintains an orderly and clean work table.
Presents the activity in a clear and practical
manner with justified decisions.
Presents
by illustrating
knowledge
and
understanding of the subject.
Uses precise and appropriate scientific terms and
language.
Presents with clarity and confidence using an
audible voice.
Mark/grade
given (x,√,√√)
21
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Assessment Tool based on the Teacher's Oral Questioning
Dimension
1
2
3
Criteria for evaluation
The student:
Questions to
Answers questions at an appropriate cognitive
individuals in a
level using appropriate scientific language
Whole Class setting Shows interest and a willingness to answer
Willing and able to challenge/support answers by
others, as appropriate
Questions to the
Able to explain the work of the group and the
group
actions undertaken by each member
Understands and can explain the science
involved using appropriate language
Willing to support other members in the group in
giving answers when required
Thinks in a creative manner, exhibits vision and
can make justified decisions
Questions to
Able to explain the work of the group and actions
individuals in the
taken by each member
group
Understands the purpose of the work and shows
knowledge and understanding of the subject
using appropriate scientific language
Can exhibit non-verbal activity (demonstrate) in
response to the teacher’s questions, as
appropriate
Mark/grade
given (x,√,√√)
22
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How Best to Maintain a Metal Bridge?
Teacher Notes
Student Worksheet on the Rusting of Iron
This worksheet is guiding you to seek answers to 2 research questions:
1.
What are the factors which I predict affect the rusting of iron?
2.
How can I gain evidence about whether the factors I predict affect the rusting
of iron do in fact affect the rusting of iron ?
Carefully read each section and provide suitable answers within the boxes.
1.
One procedure to gain evidence for factors necessary for the rusting of iron
is to eliminate one possible factor at a time and see the outcome. How can
you do this in the case of iron ?
1
Factor (possibly
affecting rusting) to
eliminate
Air
2
Water
3
Carbon dioxide
4
(Others)
Suggested method by which this factor can be
eliminated
23
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2.
Explain whether you think a control experiment is required. And if you think
a control experiment is needed, how will you set this up?
I think a control experiment (is/ is not) needed
3
Give you predicted observations, after some days, for each experiment you
set up.
1
Factor (possibly
affecting rusting) to
be eliminated
Air
2
Water
3
Carbon dioxide
Predicted observation
4
4.
State what you actually did in your experiments.
Indicate the apparatus you used (a labelled diagram may be helpful for this)
The procedure you followed in each experiment
(DO THIS ON THE SEPARATE SHEET PROVIDED)
5.
Write a conclusion to your series of experiments by answering the question
‘What factors are needed for the rusting of iron’?
6.
Give your suggested formula for rust.
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SEPARATE SHEET
State what you did in your experiments.
You can use well labelled diagrams to illustrate the apparatus and chemicals used,
but you must also describe what you did.
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Student Worksheet on Protecting Iron using another metal
This worksheet is to guide you to seek answers to 2 research questions:
1.
Can other metals be used to protect iron and stop the iron form rusting? If so,
what type of metals ?
2.
How can we set up the experiment to determine whether other metals can be
used to protect iron? And can we explain the observations made ?
Guidelines for question 1
For this experiment, the following metals (besides iron nails) are provided
a)
magnesium
b)
zinc
c)
copper
Are you able to predict what might happen in the case of each metal ?
Or more precisely, what do you predict we will observe ?
And importantly do we predict the observations will be the same with each metal
combination?
Guidelines for question 2
Wrap each strip, separately, tightly around an iron nail. This ensures the two metals
are in contact with each other.
But what do we do now? Will placing the metals in the classroom be sufficient ?
Suggest a way in which the metals are in the best conditions for ‘rusting’.
I suggest (to ensure good conditions for rusting) that the nails wrapped with another
metal are placed …..
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Observations
Record you observation in the table below:
Metal
combination
(use
symbols for
the metals)
Observation
metal 1
with
Observation
metal 2
with
1
2
3
Explanation
My explanation for my observations is as follows:
Combination 1
Combination 2
Combination 3
Conclusion
Magnesium can/cannot prevent iron from rusting.
Zinc can/cannot prevent iron form rusting
Copper can/cannot prevent iron form rusting
I therefore conclude …..
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Possibilities for protecting the bridge
I
Do nothing. The bridge will rust and will need replacing after 6 years.
II
Once the bridge is built, give the bridge 2 costs of paint. As the painting is
affected by weather, it is predicted that repainting will be necessary every 3
years.
III
Once the bridge is erected, carefully remove all signs of rust by sandblasting
and then applying a primer paint and 2 coats of ordinary paint. It is predicted
this will last for 6 years and the process will need to be repeated.
IV
Before the bridge is erected, sandblast and galvanise the metal. It is predicted
the bridge will last for at least 20 years without further attention.
Supporting data that may be useful
Costs at 2007 prices (in US$)
Metal for the bridge
Construction cost
Paint for the bridge
Sandblasting charge
Galvanising cost + labour
=
=
=
=
=
80000
10000
6000
4000
21000
Cost of the scrap metal
Cost of labour for painting
Cost of labour for sandblasting
Interest payments on loans
=
=
=
=
2000
1000
1000
7%
Calculations
A. Cost (in US$ x 1000) of maintaining the bridge, with time, for each of the four
possibilities
Option
Initial cost
After 3 yrs
After 6 yrs
After 9 yrs
After 12 yrs
After 15 yrs
1
90
90
178
178
266
266
2
97
104
111
118
125
132
3
102
102
114
114
126
126
4
123
123
123
123
123
123
28
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B. Costs (in US$ x 1000) if the initial cost is borrowed, and interest repayments are
made yearly
Initial cost
After 3 yrs
After 6 yrs
After 9 yrs
After 12 yrs
15 yrs
90
108
196
214
338
356
97
124
151
178
205
232
102
123
156
177
210
231
123
149
175
201
227
253
Corrosion
Corrosion occurs in the presence of moisture. For example when iron is exposed to
moist air, it reacts with oxygen to form rust,
The amount of water complexed with the iron (III) oxide (ferric oxide) varies as
indicated by the letter "X". The amount of water present also determines the color of
rust, which may vary from black to yellow to orange brown. The formation of rust is a
very complex process which is thought to begin with the oxidation of iron to ferrous
(iron "+2") ions.
Fe -------> Fe+2 + 2 eBoth water and oxygen are required for the next sequence of reactions. The iron (+2)
ions are further oxidized to form ferric ions (iron "+3") ions.
Fe+2 ------------> Fe+3 + 1 eThe electrons provided from both oxidation steps are used to reduce oxygen as
shown.
O2 (g) + 2 H2O + 4e- ------> 4 OHThe ferric ions then combine with oxygen to form ferric oxide [iron (III) oxide] which is
then hydrated with varying amounts of water. The overall equation for the rust
formation may be written as :
iron as illustrated below. This is possible because the electrons produced via the
initial oxidation of iron can be conducted through the metal and the iron ions can
diffuse through the water layer to another point on the metal surface where oxygen is
available. This process results in an electrochemical cell in which iron serves as the
anode, oxygen gas as the cathode, and the aqueous solution of ions serving as a
"salt bridge" as shown below.
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The involvement of water accounts for the fact that rusting occurs much more rapidly
in moist conditions as compared to a dry environment such as a desert. Many other
factors affect the rate of corrosion. For example the presence of salt greatly
enhances the rusting of metals. This is due to the fact that the dissolved salt
increases the conductivity of the aqueous solution formed at the surface of the metal
and enhances the rate of electrochemical corrosion. This is one reason why iron or
steel tend to corrode much more quickly when exposed to salt (such as that used to
melt snow or ice on roads) or moist salty air near the ocean.
Resistance to corrosion
Gold nuggets do not corrode, even on a geological time scale.
The materials most resistant to corrosion are those for which corrosion is
thermodynamically unfavorable. Any corrosion products of gold or platinum tend to
decompose spontaneously into pure metal, which is why these elements can be
found in metallic form on Earth, and is a large part of their intrinsic value. More
common "base" metals can only be protected by more temporary means.
Some metals have naturally slow reaction kinetics, even though their corrosion is
thermodynamically favorable. These include such metals as zinc, magnesium, and
cadmium. While corrosion of these metals is continuous and ongoing, it happens at
an acceptably slow rate. An extreme example is graphite, which releases large
amounts of energy upon oxidation, but has such slow kinetics that it is effectively
immune to electrochemical corrosion under normal conditions.
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Passivation
Given the right conditions, a thin film of corrosion products can form on a metal's
surface spontaneously, acting as a barrier to further oxidation. When this layer stops
growing at less than a micrometre thick under the conditions that a material will be
used in, the phenomenon is known as passivation (rust, for example, usually grows
to be much thicker, and so is not considered passivation, because this mixed
oxidized layer is not protective). While this effect is in some sense a property of the
material, it serves as an indirect kinetic barrier: the reaction is often quite rapid unless
and until an impermeable layer forms. Passivation in air and water at moderate pH is
seen in such materials as aluminium, stainless steel, titanium, and silicon.
These conditions required for passivation are specific to the material. Some
conditions that inhibit passivation include: high pH for aluminum, low pH or the
presence of chloride ions for stainless steel, high temperature for titanium (in which
case the oxide dissolves into the metal, rather than the electrolyte) and fluoride ions
for silicon. On the other hand, sometimes unusual conditions can bring on
passivation in materials that are normally unprotected, as the alkaline environment of
concrete does for steel rebar. Exposure to a liquid metal such as mercury or hot
solder can often circumvent passivation mechanisms.
Applied coatings
Plating, painting, and the application of enamel are the most common anti-corrosion
treatments. They work by providing a barrier of corrosion-resistant material between
the damaging environment and the (often cheaper, tougher, and/or easier-toprocess) structural material. Aside from cosmetic and manufacturing issues, there
are tradeoffs in mechanical flexibility versus resistance to abrasion and high
temperature. Platings usually fail only in small sections, and if the plating is more
noble than the substrate (for example, chromium on steel), a galvanic couple will
cause any exposed area to corrode much more rapidly than an unplated surface
would. For this reason, it is often wise to plate with a more active metal such as zinc
or cadmium.
Reactive coatings
If the environment is controlled (especially in recirculating systems), corrosion
inhibitors can often be added to it. These form an electrically insulating and/or
chemically impermeable coating on exposed metal surfaces, to suppress
electrochemical reactions. Such methods obviously make the system less sensitive
to scratches or defects in the coating, since extra inhibitors can be made available
wherever metal becomes exposed. Chemicals that inhibit corrosion include some of
the salts in hard water (Roman water systems are famous for their mineral deposits),
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chromates, phosphates, and a wide range of specially-designed chemicals that
resemble surfactants (i.e. long-chain organic molecules with ionic end groups).
Anodization
Aluminium alloys often undergo a surface treatment. Electrochemical conditions in
the bath are carefully adjusted so that uniform pores several nanometers wide
appear in the metal's oxide film. These pores allow the oxide to grow much thicker
than passivating conditions would allow. At the end of the treatment, the pores are
allowed to seal, forming a harder-than-usual surface layer. If this coating is
scratched, normal passivation processes take over to protect the damaged area.
Cathodic protection
Cathodic protection (CP) is a technique to control the corrosion of a metal surface by
making that surface the cathode of an electrochemical cell.
It is a method used to protect metal structures from corrosion. Cathodic protection
systems are most commonly used to protect steel, water, and fuel pipelines and
tanks; steel pier piles, ships, and offshore oil platforms.
For effective CP, the potential of the steel surface is polarized (pushed) more
negative until the metal surface has a uniform potential. With a uniform potential, the
driving force for the corrosion reaction is halted. For galvanic CP systems, the anode
material corrodes under the influence of the steel, and eventually it must be replaced.
The polarization is caused by the current flow from the anode to the cathode, driven
by the difference in electrochemical potential between the anode and the cathode.
For larger structures, galvanic anodes cannot economically deliver enough current to
provide complete protection. Impressed Current Cathodic Protection (ICCP) systems
use anodes connected to a DC power source (a cathodic protection rectifier). Anodes
for ICCP systems are tubular and solid rod shapes of various specialized materials.
These include high silicon cast iron, graphite, mixed metal oxide or platinum coated
titanium or niobium coated rod and wires.
Galvanic corrosion
Galvanic corrosion occurs when two different metals electrically contact each other
and are immersed in an electrolyte. In order for galvanic corrosion to occur, an
electrically conductive path and an ionically conductive path are necessary. This
effects a galvanic couple where the more active metal corrodes at an accelerated
rate and the more noble metal corrodes at a retarded rate. When immersed, neither
metal would normally corrode as quickly without the electrically conductive
connection (usually via a wire or direct contact). Galvanic corrosion is often utilised in
sacrificial anodes. What type of metal(s) to use is readily determined by following the
32
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galvanic series. For example, zinc is often used as a sacrificial anode for steel
structures, such as pipelines or docked naval ships. Galvanic corrosion is of major
interest to the marine industry and also anywhere water can contact pipes or metal
structures.
Factors such as relative size of anode (smaller is generally less desirable), types of
metal, and operating conditions (temperature, humidity, salinity, &c.) will affect
galvanic corrosion. The surface area ratio of the anode and cathode will directly
affect the corrosion rates of the materials.
Microbial corrosion
Microbial corrosion, or bacterial corrosion, is a corrosion caused or promoted by
microorganisms, usually chemo-autotrophs. It can apply to both metals and nonmetallic materials, in both the presence and lack of oxygen. Sulphate-reducing
bacteria are common in lack of oxygen; they produce hydrogen sulphide, causing
sulphide stress cracking. In presence of oxygen, some bacteria directly oxidize iron to
iron oxides and hydroxides, other bacteria oxidize sulphur and produce sulphuric acid
causing biogenic sulphide corrosion. Concentration cells can form in the deposits of
corrosion products, causing and enhancing galvanic corrosion.
High temperature corrosion
High temperature corrosion is chemical deterioration of a material (typically a metal)
under very high temperature conditions. This non-galvanic form of corrosion can
occur when a metal is subject to a high temperature atmosphere containing oxygen,
sulphur or other compounds capable of oxidising (or assisting the oxidation of) the
material concerned. For example, materials used in aerospace, power generation
and even in car engines have to resist sustained periods at high temperature in
which they may be exposed to an atmosphere containing potentially highly corrosive
products of combustion.
The products of high temperature corrosion can potentially be turned to the
advantage of the engineer. The formation of oxides on stainless steels, for example,
can provide a protective layer preventing further atmospheric attack, allowing for a
material to be used for sustained periods at both room and high temperature in
hostile conditions. Such high temperature corrosion products in the form of
compacted oxide layer glazes have also been shown to prevent or reduce wear
during high temperature sliding contact of metallic (or metallic and ceramic) surfaces.
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