BY : NUR ATIQAH BINTI M. HANAPIAHCLASS : 5 ARIF

TEACHER : MRS AMMY CYNTHIA ACHAN

[F5] CHAPTER 3 : OXIDATION AND REDUCTION[F5] CHAPTER 3 : OXIDATION AND REDUCTION

• How do different types of metals in contact with iron affect the How do different types of metals in contact with iron affect the rusting of ironrusting of iron

• A more electropositive metal will prevent iron from rusting.A more electropositive metal will prevent iron from rusting.

A less electropositive metal will increase the rate of rusting.A less electropositive metal will increase the rate of rusting.

• To investigate the effect of other metals on the rusting of iron

• Manipulated variable : Different types of metals• Responding variable : The presence of blue

colouration/rusting of iron• Controlled variable : Iron nails, hot jelly solution

• Test tubes and test tube rack

• Iron nails, magnesium ribbon, copper strip, zinc strip, tin strip, hot jelly solution, potassium hexacyanoferrate(III) solution, phenolphtalein indicator and sandpaper.

1. Five iron nails, magnesium ribbon, copper strip, zinc strip and tin strip are cleaned with sandpaper.

2. A clean iron nail is placed in test tube labelled A.3. The other four iron nails are wrapped with magnesium ribbon,

copper strip, zinc strip and tin strip respectively and placed in test tubes labelled B, C, D and E.

4. A hot jelly solution is prepared. A few drops of potassium hexacyanoferrate(II) solution and phenolphtalein are added to the hot jelly solution.

5. The mixture is stirred and the poured into each test tubes to completely cover all the four iron nails.

6. The test tubes are kept in a test tube rack and set aside for two days.

7. Any changes of the colour of the solution each test tube are observed and recorded

Test tube

Pair of metals

Intensity of the blue colour in

the solution

Intensity of the pink colour in

the solution

inference

A Fe only low noneIron(II) ions present. Iron nail

undergoes rusting.

B Fe+Zn none HighIron(II) ions absent. No rusting

occurs. Hydroxide ions are present.

C Fe+Cu Very high NoneVery high concentration of iron(II)

ions presence. Iron nail rusts at the highest rate

D Fe+Mg None Very highIron(II) ions is not present. No rusting

occurs. A lot of hyroxide ions present.

E Fe+Sn high noneA lot of iron(II) ions present. Iron nail

undergoes rusting faster than iron nail in test tube A.

1. The more electropositive metals prevent rusting of iron.

2. The less electropositive metals increase the rate of rusting

3. The hypothesis is accepted.

1. Potassium hexacyanoferrate(III) solution is added to detect the presence of iron(II) ions Fe2+. When iron ions presence, a dark blue colour produced. The more iron(II) ions formed, the higher the intensity of the dark blue colour produced.

2. Phenolphtalein is added to detect the presence of hydroxide ions, OH-. The presence of hydroxide ions, OH- increases the alkalinity of the solution and gives pink colour to the solution.

3. Jelly solution is used to enable us to see the blue and pink colour in the solution because it is transparent and it slows down the diffusion process.

• Test tube A is used as a control to compare the effect of other metals on the rusting of iron.

• In the presence of water and oxygen, iron nail rust a little. The iron is oxidised to iron(II) ions.

Fe(S) Fe2+(aq) + 2e-

The presence of iron(II) ions, Fe2+ give dark blue precipitate with potassium hexacyanoferrate(III) solution.

• The oxygen in the solution together with the water is reduced to hydroxide ions, OH-.

• The hydroxide ions, OH- formed combined with iron(II) ions to form iron(II) hydroxide, Fe(OH)2 during the rusting pprocess. Therefore, the phenolphtalein does not produce pink colour.

• In test tube B and D, zinc and magnesium are more electropositive than iron. They act as negative terminal (anode) and iron as the positive terminal ( cathode)

• Zinc is oxidised to zinc ion, Zn2+ by donating electrons Zn(s) Zn2+( aq) + 2e-

• Magnesium is oxidised to magnesium ion, Mg2+ by donating electrons.Mg(s) Mg2+(aq) + 2e-

• The electrons flow to iron which acts as the positive terminal (cathode)and received by oxygen in the solution. The oxygen in the solution together with thewater is rduced to hydroxide ions, OH-.

O2(g) + 2H2O(l) + 4e- 4OH-(aq) The presence of the hydroxide ions, OH- gives pink colour with

phenolphtalein.• The corrosion of magnesium is faster than the corrosion of zinc because

magnesium is more elctropositive than zinc. Test tube D produce higher intensity of pink colour compared to test tube B.

• Copper and tin are less electropositive than iron. Iron acts as negative terminal (anode) while they act as positive terminal (cathode).

• Iron is oxidised to iron(II) ion, Fe2+ by donating electrons.

Fe(s) Fe2+(aq) + 2e-• The presence of iron(II) ions, Fe2+ give dark blue precipitate with potassium

hexacyanoferrate(III) solution.• The electrons flow to copper and tin and received by oxygen. Oxygen and water

reducec to hyroxide ions, OH-.

O2(g) + 2H2O(l) + 4e- 4OH-(aq)• Hydroxide ions combined with iron(II) ios forming iron(II) hydroxide during

rusting. Phenolphtalein does not produce pink colour.• Rate of rusting in test tube C and E are higher than in test tube A because the

presence of copper and tin with different electropositivity which speed up the rusting process (oxidation of iron) . Hence, the intensity of blue colour in test tube C and E are higher than A.

• Comparing the intensity of blue colour in C and E, C has higher intensity as copper is less electropositive than tin. Rate of rusting in C is higher and more iron(II) ions produced give higher intensity of dark blue colour with potassium hexacyanoferrate(III) solution.