3.2.1 - Laboratory Activity: Effect of iron nails when in contact with other metals

Laboratory Activity 3.2.1: Effect of iron nails when in contact with other metals

Aim: To study the effect of other metals on the rusting of iron.
Problem statement: How is the rusting effect of iron when contact with other metals?
Hypothesis: If iron is in contact with more electropositive metals, the rusting process is slower.
Variable:

	»	Fixed variable : Iron nails
	»	Manipulated variable : Type of metals that in contact with iron nails
	»	Responding variable : Rate of rusting

Material: » Iron (Fe) nails » Magnesium (Mg) strip » Copper (Cu) strip » Hexacyanoferrate (III) » Phenolphthalein » Jelly solution

Apparatus: » Test tubes » Sand paper

Procedure:

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1. The following diagram shows the arrangement of apparatus of the experiment. 2. Sand paper is used to clean the iron nails, magnesium strip and copper strip. 3. Two of the nails are entwined with copper strip and magnesium strip respectively and place it in different test tube. 4. Take another clean nail and place it in another test tube. 5. Make a gelatin solution by mixing the gelatin with boiling water. 6. A few drops of hexacyanoferrate (III) is added into the gelatin solution. This will form a yellowish green colour solution. 7. A few drops of phenolphthalein is added. 8. The mixture of the gelatin solution is then poured into each test tubes and the whole set-up is left for a day.

Observation:

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Metal pair Blue colour intensity Degree of rusting Red colour intensity Fe Low A little rusted N/A Fe + Mg N/A None High Fe + Cu High Rusted heavily Low

Analysis:

	►	Iron – magnesium pair ○ Magnesium is more electropositive than iron. This means magnesium is more likely to lose electrons compare to iron. Mg(s) → Mg2+(aq) + 2e− ○ Magnesium acts as negative terminal (anode) because free electrons are produced here. ○ The iron nail acts as positive terminal (cathode) and the free electrons will flow towards the iron nail. Water and oxygen will take in electrons to form hydroxide. 2H2O(l) + O2(g) + 4e− → 4OH− ○ The present of OH− will change the colour of phenolphthalein to red, thus rusting of iron will not happen.
	►	Iron – copper pair ○ Iron is more electropositive than copper. This means iron is more likely to lose electrons compare to copper. Fe(s) → Fe2+(aq) + 2e− ○ The presence of Fe2+ ion causes the hexacyanoferrate (III) to change to blue colour. ○ Iron acts as negative terminal (anode) because free electrons are produced here. ○ Copper acts as positive terminal (cathode) and the free electrons will flow towards the copper strip. Water and oxygen will take in electrons to form hydroxide. 2H2O(l) + O2(g) + 4e− → 4OH− ○ Most of the hydroxide ions from water have been used to combine with iron(II) ion during the formation of rust. Thus, too few free OH− is available to change the colour of phenolphthalein to red.

Discussion:

	►	Hexacyanoferrate (III) solution is used to test the presence of Fe2+. If Fe2+ ions are present, dark blue colour will be formed.
	►	Phenolphthalein solution is used to detect the presence of OH−. If OH− ions are present, red colour will be formed.

Conclusion:

	►	Rusting will be faster when iron in contact with less electropositive metals.
	►	Rusting can be prevented when iron in contact with more electropositive metals

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