Science - Teachers Sri Lanka

Competency 3.0 : Use chemical changes suitable to fulfil necessities of life
Competency level 3.6 :
Take steps to prevent metal corrosion
Activity 3.6 : Let us find ways to conserve metal by minimizing corrosion.
Time : 120 mts.
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Quality inputs : • Potassium fericyanide and Phenolpthalein
• Small quantity of freshly prepared FeSO 4
and NaOH
• 3 copies of artical on instructions for exploration in annex
3.6.1
• 3 work stations arranged according to instructions in annex
3.6.2
• Demy paper and pastel
Teaching learning
process : • Inquire about their precious knowledge on rusting of iron.
• Add to the freshly prepared FeSO4 solution a few drop of
potassium ferricyanide and a few drop of phenolpthalien to
NaOH solution and show the students.
• Lead a discussion highlighting the following points.
• Rusting is due to water and Oxygen reacting with Iron
• Acids and salts increase rusting where as bases retard
rusting.
• Initial reactions during rusting could be given as follows.
Fs (s)
Fe 2+ + 2e (Oxidation)
(aq)
2H 2
O (l)
+ O 2(g)
+ 4e 4OH - (reduction)
(aq)
• When Potassium fericyanide is added to a solution of Fe 2+
solution there is a deep blue colours.
• Potassium ferricyanide could be used as an indicator to
detect Fe 2+ ions in a medium.
• When Phenolphthalein is added to a solution containing
(OH) - there is a pink colour.
• Phenolphthalein could be used as an indicator to detect
(OH) - ions in a medium.
(15 mts.)
Step 3.6.2 : • Divide the class into four groups.
• Provide the groups with instrutiions for exploration, demy
papers and pastels.
• Assign the tasks and engage the groups in exploration.
• Prepare them to present their findings to the whole class
(60 mts)