Minggu, 18 April 2010



1.1 Background

Various goods made of metal, shaped, molded, so that eventually become such a desired shape. After completion of the necessary stages, completion (finishing). Finishing it all kinds, there are just so smooth and shiny polished, can also be coated with other metals to change its nature, can be recorded or varnished, glazed ceramic or enamel, there is also a substrate coating of the derivative itself.

In addition to the metals needed for easy experience corrosion, also serves a decorative finishing. Corrosion is a redox reaction between a metal with various substances in environment compounds that produce undesirable. In everyday language is called perkaratan corrosion. The most common example is the corrosion of iron corrosion. Iron also with the use of chemical properties. Metal can also be protected from corrosion by using protective electrodes. Other protection methods can be performed with the potential to change the object by using the protective electrodes.

Corrosion prevention is one of the important problems in science and modern technology. This experiment focused on the corrosion of iron because these metals are used very widely and corrosion of metals is a major problem.

Due to the large metal properties that can inhibit, or even accelerate corrosion precisely, we perform this experiment.

1.2 Experiment Objectives
1.2.1 Purpose Experiment

The purpose of this experiment is to study the corrosion of iron, with or without contact with some metals, like Cu, Zn, and Al.

1.2.2 Experiment objectives

The purpose of this experiment was to determine the metal which increases the corrosion of iron and inhibit corrosion.

1.3 Principle Experiment

Observed on iron corrosion by comparing the iron that is not coated with other metals are coated with iron, Zn, Cu, and Al with the aid of PP indicator that produces a pink color that shows the scene of the reduction and K 3 Fe (CN) 6 which produces a blue color show where the occurrence of oxidation reactions.


Oxygen is one corrotant that cause corrosion. Corrosion by oxygen occurs because there are differences in oxygen concentration (cell concentration difference). If there is no difference in oxygen concentration, according to the theory of corrosion will not occur, but in practice it is highly unlikely because oxygen is everywhere. The basic processes of metal corrosion is very simple atoms containing metals react in solution or form a cluster of positively charged ions, which can corrode due to oxidation. When the elements affected by corrosion of the steel construction resulted in decreased strength of these elements and other elements disrupted as interconnected, so in the long run could jeopardize the building collapsed (Migas Indonesia Online, December 22, 2009).

Factors that influence the corrosion can be divided into two, namely that derived from the material itself and the environment. Factor of the materials include material purity, material structure, crystal shape, trace elements contained in the material, mixing techniques and materials. The factors of the environment include air pollution levels, temperature, humidity, presence of chemical substances which are corrosive and so forth . Corrosive materials (which can cause corrosion) is comprised of acidic, alkaline and salt, either in the form of inorganic compounds or organic. Evaporation and release of corrosive substances into the air can accelerate the corrosion process. Indoor air that is too acidic or alkaline can memeprcepat corrosion process of electronic equipment in the room. Flour, hydrogen fluoride and its compounds known as corrosive materials. The air becomes too acidic and with terlarutnya corrosive acid gases in the air. This certainly sour air that can interact with anything, including trace components in electronic equipment. If that happens, then the corrosion process can not be avoided anymore (Akhadi, 2000).

In the event of corrosion, metal oxidation, while oxygen (air) is reduced. Rust is generally in the form of metal oxide or carbonate. The chemical formula of iron rust is Fe 2 O 3. NH 2 O, a solid substance of brown-red. Corrosion is an electrochemical process. In the corrosion of iron, certain parts of the metal acts as an anode, where oxidation of iron.

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

The electrons liberated in the anode flow to other parts of the metal that acts as a cathode, where oxygen is reduced.

O 2 (g) + 4H + (aq) + 4e - 2H 2 O (l)


O 2 (g) + 2H 2 O (l) + 4e - 4OH - (aq)

Iron ions (II) was formed at the next anode oxidized form of iron (III) which then formed the hydrated oxide compound,, namely iron rust. About what portion of the metal that acts as an anode and the parts which act as cathode, depending on various factors such as impurities, or the difference in density of the metal. Corrosion can also be interpreted as attacks that damage the metal because the metal reacts with a chemical or electrochemical environment. There is another definition that says that corrosion is the reverse of the process of extraction of metals from mineral ores. For instance, an iron ore minerals in the wild is in the form of a compound of iron oxide or iron sulfide, when extracted and processed, will produce steel used for making steel or steel alloys. During use, the steel will react with the environment that causes corrosion (back to compounds of iron oxide) (Wikipedia, March 7, 2010).

Unprotected surfaces of low-alloy steels and aluminum alloys are subject to Trust forms of chemical or electrochemical attack Known collectively as corrosion. Electrochemical corrosion involves oxygen Generally, an electrolyte and electron transfer, converting the metal to a metallic compound. When combined with the fatigue it is a significant contributor to aging airframe. Stainless steels are not immune to Some forms of corrosion. When two dissimilar metals or alloys are in close contact in the presence of an electrolyte, a galvanic cell formed in Which May be spontaneous electrochemical corrosion occurs. Oxidation occurs at the more active metal (the anode) and electrons flow from the anode to the less active metal (the cathode). The anodic metal corrodes the cathodic metal but not May. In a galvanic couple, aluminum alloys are anodic to most other metals (see the Following galvanic series table) so additional must Steps taken to separate the two metals - by using a corrosion inhibiting compound (Brandon, 2010).

Unprotected steel surfaces of low alloy and aluminum alloy subjected some form of chemical or electrochemical corrosion, known as an attack. Electrochemical corrosion generally involves oxygen, electrolyte and electron transfer, change of metal with metal compounds. When combined with fatigue is a significant contributor to the aging airframe. Stainless steel is not immune to some forms of corrosion. When two different metals or alloys in close contact in the presence of an electrolyte, galvanic cell may be formed in which the electrochemical corrosion appeared spontaneously. Oxidation occurs in a more active metal (anode) and electrons flow from the anode to the less active metal (cathode). Corrosion of metal anodic cathodic metal but not impossible. In some galvanic, aluminum alloy anodic to most other metals (see table below galvanic series) so that additional steps must be taken to separate the two metals - using corrosion inhibiting compound (Brandon, 2010).

Because the immobilization reagent containing fenolptalin changing to pink with the existence of OH -, the color pink in the gel indicates the place where reduction occurs. In all cases, because reduksinya same reaction, the color pink will be observed. Ferisianida Gel also contains potassium (potassium hexacyanoferrate (III)), K 3 Fe (CN) 6, which changed to blue with Fe 2 +:

K + (aq) 2 + + Fe (aq) + Fe (CN) 6 3 + Kfe [Fe (CN) 6] (p)

The blue color in the gel indicates the place where the Fe is oxidized - if the site exists (Taba et al, 2010).

In the manufacture of metal-metal objects, an object made of metal or metal-metal aliase often overlaid with a thin layer of another metal. This is generally done to protect against corrosion and to be more interesting. One way is by electrolysis meyepuh. It will be plated cathode, and a thick piece of metal used as anode penyepuh. Both electrodes were immersed into a salt solution of metal plate and connected with a source of direct current (Keenan, 1980).

There are two types of electrodes:
Anode. In galvanic cells, anode is where oxidation, negative charge is caused by a spontaneous chemical reaction, electrons are released by these electrodes. In the electrolysis cell, an external voltage source is obtained from outside, so that the positively charged anode, when linked to the cathode. Thus, negatively charged ions to flow into the anode to oxidize.
Cathodes are electrodes where the reduction of various chemical substances. In galvanic cells, cathode is positively charged when connected to the anode. Positively charged ions to flow into the electrode is to be reduced by electrons coming from the anode. In the electrolytic cell, the cathode is negatively charged electrode. Posisitf charged ions (cations) flowing into the electrode is to be reduced. Thus, the galvanic cell, electrons move from anode to cathode in the external circuit (Dogra and Dogra, 1990).


3.1 Experimental Equipment

The tools used in these experiments are a test tube, tube rack, 250 mL beaker, Cu foil, foil Al, Zn foil, wire netting, measuring pipette, tweezers, three legs, Bunsen, wire netting, hammers, and nails.

3.2 Experimental Materials

The materials used in this experiment is to include K 3 Fe (CN) 6, NaCl, H 2 SO 4 2 M, an indicator of PP, agar-agar, sandpaper, and the tissue roll.

3.3 Experimental Procedure

Heated approximately 100 mL of water into a glass cup, 250 mL, until boiling.
Added 0.5 g gelatin in water and heated while stirring until slightly melted.
5 g NaCl added to a solution of the heat, then stir.
Added 2 mL and 1 mL PP indicator K 3 Fe (CN) 6 0.1 M, stirred with a good solution and heating was stopped. Taken up to a warm solution before use.
4th placed iron nail in a test tube containing H 2 SO 4 2 M for some time.
Boiling water in a glass cup, 250 mL, acid didekantasi of nails, washed with water and carefully put the nails into hot water. Nails removed at the time required using clean tweezers.
Tubes labeled 1-4. In tube 1 is inserted clean nails. In preparation for each tube 2-4, it should be remembered that the piece of metal used must be attached firmly on the nail.
Cu foil with a hole cut nails and clean nails inserted through one hole. Done the same thing on the Zn foil and Cu foil. Each test tube is inserted in the 2-4.
Indicator gel is poured into each tube until all the nails covered with gel.
Tube placed 1-4 in the tube rack. Colored areas were observed that appeared in the gel.


4.1 Result

4.2 Discussion

In this experiment, we will compare the corrosion processes on coated metal nails that are not coated with metal such as aluminum (Al), copper (Cu) and zinc (Zn).

Important materials used in this experiment is agar-agar, NaCl, K 3 Fe (CN) 6 and fenoftalen indicator and distilled water used in the manufacture of the gel. Where the addition of gel on the nail will cause the occurrence of redox reactions. While nail material serves as the main ingredient that will be observed due to the corrosion process will occur, and sheet metal Al, Cu, Zn coated nails are used fatherly. NaCl salt bridge serves as a substitute, while the indicator serves as reduction of PP and K 3 Fe (CN) 6 functions as oxidation. In this experiment, also performed a useful warm fatherly accelerating solubility in particular on agar. Made solution should be stirred, with the goal of keeping the gel that was not jelling. The sulfuric acid (H 2 SO 4) functioning used to stimulate corrosion. Acid decantation done to clean the nail from the nature of acidity.

In this experiment, we heat the water to 100 mL in 250 mL beaker until boiling. Sementera we weigh 1 gram of agar-agar and 3 grams of NaCl. Gelatin which had been weighed we enter into the water while heated, then the solution is stirred until the gelatin dissolve, then added 3 grams of sodium chloride in the solution to such heat, stirring until the solution became homogeneous, then into the solution were added 3 mL K 3 Fe (CN) 6 and 2 mL of solution fenoftalen indicators. Where known K 3 Fe (CN) 6 is the solution of the yellow and translucent colored fenoftalen indicators. Thus, by the addition of K 3 Fe (CN) 6 and the indicator solution fenoftalen yellowish green.

Meanwhile, put 4 pieces of nails, iron nails used must be clean, where the first nail is not coated with metal, both coated with a metal nail Al, the third nail coated with Zn metal, and the fourth nail coated with copper metal. The four pins are inserted into the beaker which already contain 50 mL of 2 M sulfuric acid for 5 minutes. This is done because the H 2 SO 4 can accelerate corrosion. Where corrosion can occur at pH 3-4, followed by four nails are soaked in hot water that had been simmer, with the intention to eliminate the acidity properties of the nail.

After a few moments, the four pins are placed in a test tube. Then the gel that was created is inserted into a test tube containing the fourth nail, to cover all the nails, after a few moments later, each of these spikes we observe.

In this experiment, the results of the first observation of note on nails that are not coated with any part of the nail tip is blue, the second spike (which is coated with Al), the head of the pink nails, nail the third (which is coated with zinc) the head and the tip of a nail pink lempengannya while blue, while in the fourth nails are coated with a Cu head and the tip of the nail lempengannya blue and pink. This shows that the material is able to slow the corrosion of Al. Nails are coated with Al may be experiencing corrosion, but may be due to the Al-coated nails too quickly removed from the gel, so did not get to experience corrosion. Because the gel must first peel the new Al can penetrate the nail.

According to theory is known that Al and Zn are metals that can protect the steel from corrosion. This is because Al and Zn have a standard electrode potential more negative than iron, we can see in the voltaic series "Li K Ba Sr Ca Na Mg Al Mn Zn Cr Fe Cd Co Ni Sn Pb Sb Bi H Cu Hg Ag Pt Au" so that Al and Zn is oxidized. While Cu is a metal that can accelerate corrosion, because copper is only able to protect themselves.


5.1 Conclusion

From the experiments have been conducted, we can conclude that the metals that can inhibit the corrosion of the metal is aluminum and zinc, while the metal is to accelerate the corrosion of copper.

5.2 Suggestions
5.2.1 Experiment

Should be used in this experiment, other metals tested except iron for praktikan thereby increasing knowledge, and can expand the horizon for praktiakan.

5.2.2 Assistant

Keep the attitude in guiding your student.


Akhadi, Mukhlis., 2000, Electronics, Online Electronics, Electro Indonesia.

Brandon, John., Metal Corrosion, January 10, 2010.

Dogra, SK, and Dogra, S., 1990, Physical and Chemical Problems, Penenrbit University of Indonesia, Jakarta.

Keenan, C, W., Kleinfelter, DC and Wood JH, 1980, Chemistry for Universities, grants, Jakarta.

Migas Indonesia Online., Corrosion, 23 November 2009.

Taba, P., and Paulina, St., 2006, Practical Guide of Physical Chemistry, Physical Chemistry Laboratory Science, State UH, Makassar.

Simple., Corrosion, 04 April 2010.

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