Experiment on HOW RUSTING CAN BE PREVENTED BY USING SACRIFICIAL METHOD.

Experiment onHOW RUSTING CAN BE PREVENTED BY USING SACRIFICIAL METHOD

• Introduction………………………………1

• How does rusting occurs?………………...2

• How rusting can be prevented……………3

• What is a sacrificial metal?………………4

• Our experiment on preventing iron from rusting using sacrificial metal……………5

CONTENT PAGE

INTRODUCTION

In this experiment, we are doing a practical on preventing iron rusting using sacrificial metal. This sacrificial metal protects the iron from rusting. This method is mostly used in car manufacturers factory to prevent cars from rusting. We are using zinc as the sacrificial metal in the experiment.

• The surface of a piece of iron is never smooth. There are many small holes into which water can flow. When iron is in contact with water containing oxygen, rust forms. The iron atoms lose electrons to become iron (II) ions:

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

• The electrons are transferred to the oxygen and water molecules which form hydroxide ions:

½ O2(g)+H2O(l)+2e- 2OH- (aq)

• The complete equation is obtained by adding the two half –equation:

Fe(s)+ ½ O2(g)+H2O (l) Fe2+ (aq)+ 2OH–(aq)

i.e. Fe (OH)2 iron (II) hydroxide

How Does Rusting Occurs?

The iron(II) ions Fe2+ are oxidized to iron (III) ions Fe3+ by the oxygen:2Fe2+(aq)+ ½ O2 (g) + H2O (l) 2Fe3+(aq) + 2OH–(aq)

Iron(III) ions react with hydroxide ions to give iron(III) hydroxide:

Fe3+ (aq) + 3OH– (aq) Fe (OH)3 (s)

On standing, this changes into hydrated iron(III) oxide, which is rust (Fe2 O3 .x H2O).

What is a Sacrificial Metal?

Maybe some of you may be wondering, what is sacrificial metal? Well, it is a special metal that is used to coat the iron to prevent it from rusting. As what we have mentioned, these special metals are mostly used on car manufacturing or even other purposes such as preventing underground pipe from rusting, preventing iron pipes from rusting, stainless steel.

How Rusting Can Be Prevented?

Rusting is a serious problem. It has been calculated that over one- fifth of the iron produced is used to replace that lost by corrosion. Chemists have done a lot of work to try to reduce this loss. They found that applying protective layer is one of the good way. Painting it with oil or grease will be a good way although it is not really successful as the grease or the paint will come off easily or the iron may damp when painted.

Another method is using tin plating that is mostly used for can food, using galvanizing (zinc plating), which we are doing on. Zinc is a good sacrificial metal because it is not easily attacked by air or water. Thus, it prevents iron from rusting even if the surface is broken. This is because zinc is higher in the electrochemical series than iron.

How Rusting Can Be Prevented?

Another method is using sacrificial corrosion. It is whereby iron is connected to blocks of metals that are higher in the electrochemical series. Two examples are: bags of magnesium are placed in holes in the ground connected to a pipe by a conductor and sides of ships are attached to blocks of zinc.

How Rusting Can Be Prevented?

Experimental Set-Up

Iron nail

Zinc foil

Agar with phenolphthalein and potassium

hexacyanoferrate (III)Experiment 1 Experiment 2

Experimental Set-Up

Positive terminal

Positive terminal

Negative terminal

Negative terminal

Agar with phenolphthalein and potassium

hexacyanoferrate (III)

Zinc foil

Iron nail Iron nail

Experiment 3 Experiment 4

Materials Needed for Experiment

• 5grams of yellow agar• 7.5grams of NaCl• Four iron nails• Two zinc foils• Phenolphthalein• potassium

ferriycanide K3Fe(CN)6

• Hydrocholric acid• 400ml beaker• One stirring rod• Bunsen burner• Two petri dishes• Two 9V batteries with

alligator clips

Our Experiment

• Add 7.5g of sodium chloride to 250 ml of distilled water in a 400 ml beaker. Heat this to boiling. Turn off the Bunsen Burner and add 5g of agar slowly with constant stirring.

• After the agar has been dissolved, add 5 to 10 drops of the 0.1M potassium ferricyanide solution and 5 drops of 0.1% phenolphthalein solution.

Our Experiment

• While the agar mixture is cooling in the beaker. Obtain four nails that have been soaked in 3 M HCl to remove any zinc coating. After that, wrapped two of the iron nails with zinc foil. Prepare two petri dishes. Put one iron nail and one nail with zinc foil wrapped in each dish.

Our Experiment

• Prepare two 9V batteries. Clip one iron nail to the +v.e terminal and one nail wrapped with zinc foil to the –v.e terminal with alligator clips. The other dish is iron nail to the –v.e terminal and one nail wrapped with zinc foil to the +v.e terminal.

Our Experiment

• Pour the agar mixture into the petri dishes to a depth of a little less than a centimeter and allow it to cool.

Our Experiment

Experiment Results

• Experiment Observations- The agar around the nail

connected to the positive terminal turned blue.

- After five minutes, the agar around the same nail turned brown.

- The agar around the nail with zinc foil, which is connected to the negative terminal, turned pink and no further reaction is observed.

Explanations- the iron nail connected to

the positive terminal will act as the anode, The rate of oxidation is sped up because the iron atoms lost the electrons more readily.

Anode: Fe(s) Fe2+(aq) + 2e-

- The electrons are transferred to the negative terminal, the cathode, to form hydroxide ions with the oxygen and water molecules

Experiment Results

Cathode: ½ O2(g) + H2O(l) + 2e- 2OH- (aq)- The hydroxide ions formed at the cathode are

basic. Therefore, the phenolphthalein in the agar was observed to turn pink.

- The iron(II) ions formed at the anode initially reacted with the potassium hexacyanoferrate(III) to give the blue colour. When the iron(III) ions were further oxidized to iron(III) ions, the brown colour observed as a result of the reaction between iron(III) ions and potassium hexacyanoferrate(III).

Experiment Results

Observations- The agar around the nail with zinc foil connected to

the positive terminal did not show any reaction initially.

- After sometime, the agar was observed to turn blue slowly and then turned brown.

- The agar around the nail connected to the negative terminal turned pink and no further reaction is observed.

Experiment Results

Explanations- Initially, the iron nail with the zinc foil at the

anode did not show any reactions because the zinc atoms are oxidized to zinc ions. The iron atoms are not oxidized.

Anode: Zn(s) Zn2+(aq) + 2e-

- The electrons are transferred to the negative terminal, the cathode, to form hydroxide ions with the oxygen and water molecules.

Experiment Results

Cathode: ½ O2(g) + H2O(l) + 2e- 2OH-(aq)

-The hydroxide ions formed at the cathode are basic. Therefore the agar around the nail was observed to turn pink.

-After sometime, when most of the zinc foil has been oxidized, iron atoms are then oxidized to iron(II) ions. Therefore, the agar around the nail with zinc foil is observed to turn blue.

-The iron(II) ions are further oxidized to iron(III) ions and the agar around the nail with zinc foil is observed to turn blue.

-The iron(II) ions are further oxidized to iron(III) ions and the agar around the nail is observed to turn brown.

Experiment Results

Anode: Fe(s) Fe2+(aq) + 2e-

blue solution with Fe(N)63-

Fe2+(aq) Fe3+(aq) + e-

brown solution with Fe(N)63-

Experiment Results

SOURCES

• “Chemistry” Fifth Edition By Raymond Chang

• “A-level chemistry” Second Edition By E.N.Ramsden

• “chemistry A New Approach” Third Edition By Rex Heyworth

• Http://www.hwscience.com/smarsden/unit 13.corros.pdf

THE END

Done By:

Teo Qing Xiang (39)

Choi Chung Wo (28)

Anderson Yong (25)

Guo Yao Yao (8)