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Equation for Rusting of Iron

You must have seen rusted water pipeline on roadsides. Do you observe green color copper pipes or red color iron pipes? The silvery color of iron turns to reddish-brown due to formation of hydrated oxide which is known as rust and the process is called as rusting. Rusting takes place in contact with water, oxygen and other atmospheric impurities. 

Rusting of iron involve a series of reaction. When metal surface comes in contact with water, the dissolved oxygen reacts with metal like iron causing the formation of iron oxides. The metal surface acts as a electrolytic cell in which water drop acts as cathode and metal surface acts as anode. Oxidation at anode produce metal ion , which dissolve in water to form metal oxide There are several processes which prevent the corrosion or minimise the rate of reaction. 

Anodization, plating, painting of anti-corrosive substances or coating of corrosion inhibitors used to prevent corrosion on metal surface. Let’s discuss the process in brief. If we left a piece of bare iron outside where it is exposed to moisture, it will rust very quickly. The rate of corrosion increases in salt water. It is an electro chemical process in which a water droplet severs as a voltaic cell when it comes in contact with the metal and oxidizing it. 

Just imagine a water droplet on the metal surface. In this process, metal supplies electrons at the edge of the droplet and reduces the atmospheric oxygen. The inner side of the water droplet serves as the anode in this process. The reaction of oxidation of metal atoms can be written as given below;
Fe(s) Fe2+(aq) + 2e-

Now these electrons move from metallic iron to the outside of the droplet and react with oxygen and water to form hydroxide ions;

O2(g) + 2H2O(l) + 4e- 4OH-(aq)

These hydroxide ions move inward the metal surface and again react with metal ions to form iron (II) hydroxide which is precipitated on the metal surface.
Fe2+(aq) + 2OH-(aq) Fe(OH)2(s)

Overall the formation of rusting is a redox reaction and involves the conversion of metal to metal oxide. The complete equation for rusting of iron is as given below;
4Fe(OH)2(s) + O2(g)   2Fe2O3 • H2O(s) + 2H2O(l)

Since it is an electrochemical process, therefore the unprotected iron can easily rust in the presence of air and water. However there are several protection methods to prevent this process such as use of magnesium rod with iron pipes protect the corrosion of iron because Mg is more reactive metal compare to Fe. Because of this Mg forms oxides and use O2 and H2O present in the surroundings and prevent Fe surface.

This method is called as cathodic protection or sacrificial protection. Corrosion of some metals prevents further corrosion such as formation of aluminium oxide over aluminium metal surface prevent further corrosion as the oxide layer serves as a barrier for metal surface. Similar oxide layer can be observed over silver surface in jewellery and utensil. The green colour of copper utensils is due to oxides of copper. This process cannot observe in less reactive metals such as gold or platinum.

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Question:Rusting Iron: 4Fe + 3O2 = 2Fe2O3 If you have a 1.50 mol sample of iron, how many moles of Fe2O3 will there be after the iron has rusted completely?

Answers:No, No, No. The rusting of iron REQUIRES water. The formula for the most common form of rust is FeO(OH). 4Fe(s) + 3O2(g) + 2H2O(l) --> 4FeO(OH)(s) You have the equation for the "combustion" of iron. 4Fe + 3O2 = 2Fe2O3 Because the mole ratio (as given by the balanced chemical equation) is 4:2 (2:1), 1.50 mol of Fe will produce half as many moles of Fe2O3, 0.750 mol Fe2O3. 1.50 mol Fe x (1 mol Fe2O3 / 2 mol Fe) = 0.750 mol Fe2O3

Question:and how do you represent them in a word equation ? Pleasee helpp as soon as possiblee :)

Answers:Rusting of iron EXPLANATION OF THE RUSTING OF IRON When iron rusts a spontaneous redox reaction occurs, between the oxygen and iron. If water is added the rusting occurs more rapidly. Iron (s) + Oxygen(g)----------> Iron (III) oxide(s) When water is added to iron, an electrochemical cell is created that has a distinct anode and cathode. If an iron nail is placed in agar or gel in which ferric cyanide ions and phenolphthalein indicator have been placed, the ends of the nail turn blue and the middle of the nail turns red. The blue colour is caused by ferricyanide indicator reaction with the iron ions, and the red colour (pink) is due to reaction between hydroxide ions and phenolphthalein. How are these ions produced. At one spot on the nail (the Anodic site of our electrochemical cell) Iron loses electrons (is oxidized) to form iron (II) ions. Fe (s) ------> Fe2+ (aq) + 2e- At another spot on the nail the oxygen in the air combines with water and forms hydroxide ions. 1/2 O2 (g) + H2O (l) + 2e- --------> 2OH- (aq) In the presence of oxygen the iron further oxidizes at the anode (loses electrons) to become iron (III) ions. Fe 2+ (aq) ------> Fe3+ (aq) + e- The iron (III) ions and the hydroxide combine to form rust ( flaky brown substance) . 2 Fe 3+ (aq) + 6OH- (aq) -----> Fe2O3 (s) + 3 H2O (l) Notice that water is required for the reaction at the cathode but produced in the overall reaction. It therefore is acting like a homogeneous catalyst, to speed up the rusting of iron. In essence the water and oxygen make it easier for iron to rust. As with an electrochemical cells the electrons flow from the anode to the cathode. Oxygen and water are both need to speed the rusting process in metals.

Question:Hey! I am working on corrosion in chem at the moment. I don't quite follow how salt speeds up the rate of corrosion iron... I figure there is some large significance since the nails i had in a higher salinity lost more weight then those in a lower salinity... I am just not sure what it is. Help please!

Answers:When metals rust, it forms metal oxides. But by definition, Catalyst Speeds up the process of the Rxn but does not get used up. However as you can see in the equation below, Oxygen is consumed with metal to for metal oxide. Therefore Oxygen CAN'T be a catalyst. It is a reactant. Fe + O2 ---> Fe2O3 The Correct answer is SALT. (Sodium in NaCl for an example) Rust is the process of metal oxidizing into metal oxide. The oxidation needs a transfer medium to occur, such as water. Salt in the water speeds up the oxidation process by acting as a catalyst. The salt is never used up and the problem with salt is that even when water is gone, it remains and wait to restart the forming of rust once more moisture is present. This is why metals rust much easily in salty areas such as beaches and cold states where they use salt to melt the icy roads.


Answers:Yes it is a chemical reaction. It is the reaction of iron with oxygen in the presence of water in what is known as oxidation. When something is oxidized, it loses electrons to what is known as a reducing agent. In this case, oxygen is the reducing agent and it is essentially stealing electrons from the iron.

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