PBL 1 - Corrosion of Iron

Group 2Andiko PrasetyantoDanestyan Arif PradanaIndira Zahra ZafiraTrizi Afrianza

Date of submission: October 1st 2014

I. Introduction Iron is a relatively abundant element in the universe. It is found in the sun and many types of stars in considerable quantity. Iron nuclei are very stable. Iron is a vital constituent of plant and animal life, and is the key component of hemoglobin.The pure metal is not often encountered in commerce, but is usually alloyed with carbon or other metals. The pure metal is very reactive chemically, and rapidly corrodes, especially in moist air or at elevated temperatures. Any car owner knows this. Iron metal is a silvery, lustrous metal which has important magnetic properties.

II. Theory of Fundamental Principles

A. Chemical and Physical Properties of IronIron Basic Facts:Symbol:FeAtomic Number:26Atomic Weight:55.847 Element Classification:Transition MetalCAS Number:7439-89-6Iron Periodic Table LocationGroup:8Period:4Block:dIron Electron ConfigurationShort Form: [Ar]3d64s2Long Form: 1s22s22p63s23p63d64s2Shell Structure:2 8 14 2Iron DiscoveryDiscovery Date:Ancient TimesName:Iron derives its name from the Anglo-Saxon 'iren'. The element symbol, Fe, was shortened from the Latin word 'ferrum' meaning 'firmness'.History:Ancient Egyptian iron objects have been dated to around 3500 B.C. These objects also contain approximately 8% nickel showing the iron may have originally been part of a meteorite. The "Iron Age" began around 1500 B.C. when the Hittites of Asia Minor began to smelt iron ore and make iron tools.Iron Physical DataStateat room temperature (300 K): SolidAppearance:malleable, ductile, silvery metalDensity:7.870 g/cc (25 C)Density at Melting Point:6.98 g/ccSpecific Gravity: 7.874 (20 C)Melting Point:1811 KBoiling Point:3133.35 KCritical Point:9250 K at 8750 barHeat of Fusion:14.9 kJ/molHeat of Vaporization:351 kJ/molMolar Heat Capacity:25.1 J/molKSpecific Heat:0.443 J/gK (at 20 C)Iron Bonding: Metallic BondingIron Atomic DataOxidation States(Bold most common):+6, +5, +4,+3,+2, +1, 0, -1, and -2Electronegativity:1.96 (for oxidation state +3) and 1.83 (for oxidation state +2)Electron Affinity:14.564 kJ/molAtomic Radius:1.26 Atomic Volume:7.1 cc/molIonic Radius:64 (+3e) and 74 (+2e)Covalent Radius:1.24 FirstIonization Energy:762.465 kJ/molSecond Ionization Energy:1561.874 kJ/molThird Ionization Energy:2957.466 kJ/molIron Nuclear DataNumber ofisotopes:14 isotopes are known. Naturally occuring iron is made up of four isotopes.Natural Isotopes and %abundance:54Fe (5.845),56Fe (91.754),57Fe (2.119) and58Fe (0.282)Iron Crystal DataLattice Structure:Body-Centered CubicLattice Constant:2.870 Debye Temperature:460.00 K

B. Ionization energies and electron affinityTheelectron affinityof iron is 15.7 kJ mol-1. Electron affinity is defined as the change as the change in energy of a neutral atom when an electron is added to the atom to form a negative ion, the neutral atoms likelihood of gaining an electron.

Theionization energy is the quantity of energy that an isolated gaseous atom in the ground electronic state must absorb to discharge an electron resulting in cation.

C. Extraction of Iron from Iron Ore using Blast FurnaceIron is extracted from iron ore in a huge container called a blast furnace. Iron ores such ashaematitecontain iron oxide. The most commonly used iron ores are haematite,Fe2O3, and magnetite, Fe3O4. The oxygen must be removed from the iron oxide to leave the iron behind.

The heat sourceThe air blown into the bottom of the furnace is heated using the hot waste gases from the top. Heat energy is valuable, and it is important not to waste any.The coke (essentially impure carbon) burns in the blast of hot air to form carbon dioxide - a strongly exothermic reaction. This reaction is the main source of heat in the furnace.

The reduction of the oreAt the high temperature at the bottom of the furnace, carbon dioxide reacts with carbon to produce carbon monoxide.

It is the carbon monoxide which is the main reducing agent in the furnace.

In the hotter parts of the furnace, the carbon itself also acts as a reducing agent. Notice that at these temperatures, the other product of the reaction is carbon monoxide, not carbon dioxide.

The temperature of the furnace is hot enough to melt the iron which trickles down to the bottom where it can be tapped off.

The function of the limestoneIron ore isn't pure iron oxide - it also contains an assortment of rocky material. This wouldn't melt at the temperature of the furnace, and would eventually clog it up. The limestone is added to convert this intoslagwhich melts and runs to the bottom.The heat of the furnace decomposes the limestone to give calcium oxide.

This is an endothermic reaction, absorbing heat from the furnace. It is therefore important not to add too much limestone because it would otherwise cool the furnace.Calcium oxide is a basic oxide and reacts with acidic oxides such as silicon dioxide present in the rock. Calcium oxide reacts with silicon dioxide to give calcium silicate.

The calcium silicate melts and runs down through the furnace to form a layer on top of the molten iron. It can be tapped off from time to time as slag.Slag is used in road making and as "slag cement" - a final ground slag which can be used in cement, often mixed with Portland cement.

Cast ironThe molten iron from the bottom of the furnace can be used as cast iron.Cast iron is very runny when it is molten and doesn't shrink much when it solidifies. It is therefore ideal for making castings - hence its name. However, it is very impure, containing about 4% of carbon. This carbon makes it very hard, but also very brittle. If you hit it hard, it tends to shatter rather than bend or dent.Cast iron is used for things like manhole covers, guttering and drainpipes, cylinder blocks in car engines, Aga-type cookers, and very expensive and very heavy cookware.

D. Uses of IronIron is vital to plant and animal life. Iron is the active part of the hemoglobin molecule our bodies use to transport oxygen from the lungs to the rest of the body. Iron metal is widely alloyed with other metals and carbon for a multiple commercial uses. Pig iron is an alloy containing about 3-5% carbon, with varying quantities of Si, S, P, and Mn. Pig iron is brittle, hard, and fairly fusible and is used to produce other iron alloys, including steel. Wrought iron contains only a few tenths of a percent of carbon and is malleable, tough, and less fusible than pig iron. Wrought iron typically has a fibrous structure. Carbon steel is an iron alloy with carbon and small amounts of S, Si, Mn, and P. Alloy steels are carbon steels that contain additives such as chromium, nickel, vanadium, etc. Iron is the least expensive, most abundant, and most used of all metals.E. Chemical Reactions of IronReaction of Iron with airIron metal reacts in moist air by oxidation to give a hydrated iron oxide. This does not protect the iron surface to further reaction since it flakes off, exposing more iron metal to oxidation. This process is called rusting and is familiar to any car owner. Finely divided iron powder is pyrophoric, making it a fire risk.On heating with oxygen, O2, the result is formation of the iron oxides Fe2O3and Fe3O4.4Fe(s) + 3O2(g) 2Fe2O3(s)3Fe(s) + 2O2(g) Fe3O4(s)Reaction of Iron with HalogensIron reacts with excess of the halogens F2, Cl2, and Br2, to form ferric, that is, Fe(III), halides.2Fe(s) + 3F2(g) 2FeF3(s) (white)2Fe(s) + 3Cl2(g) 2FeCl3(s) (dark brown)2Fe(s) + 3Br2(l) 2FeBr3(s) (reddish brown)This reaction is not very successful for iodine because of thermodynamic problems. The iron(III) is too oxidizing and the iodide is too reducing. The direct reaction between iron metal and iodine can be used to prepare iron (II) iodide, FeI2.Fe(s) + I2(s) FeI2(s) (grey)

Reaction of Iron with AcidsIron metal dissolves readily in dilute sulphuric acid in the absence of oxygen to form solutions containing the aquated Fe(II) ion together with hydrogen gas, H2. In practice, the Fe(II) is present as the complex ion [Fe(OH2)6]2+.Fe(s) + H2SO4(aq) Fe2+(aq) + SO42-(aq) + H2(g)If oxygen is present, some of the Fe(II) oxidizes to Fe(III).The strongly oxidizing concentrated nitric acid, HNO3, reacts on th surface of iron and passivates the surface.

Iron Reaction with WaterIron does not clearly alter in pure water or in dry air, but when both water and oxygen are present (moist air), iron corrodes. Its silvery colour changes to a reddish-brown, because hydrated oxides are formed. Dissolved electrolytes accelerate the reaction mechanism, which is as follows:4 Fe + 3 O2 + 6 H2O -> 4 Fe3+ + 12 OH- -> 4 Fe(OH)3 or 4 FeO(OH) + 4 H2O

Usually the oxide layer does not protect iron from further corrosion, but is removed so more metal oxides can be formed. Electrolytes are mostly iron (II) sulphate, which forms during corrosion by atmospheric SO2. In sea regions atmospheric salt particles may play an important role in this process.Iron (II) hydroxide often precipitates in natural waters.

F. Corrosion of IronWhen iron metal is exposed to oxygen and water, a familiar result is observed-rust. The rusting process consists of several steps. In the first step, iron is oxidized to iron(II) ions, Fe2+, and oxygen from the air is reduced to hydroxide ions, OH-. This oxidation-reduction reaction takes place via two separate but simultaneous half-reactions (Equations 1 and 2).

Oxidation half-reaction: Fe(s) Fe2+(aq) + 2e- Equation 1

Reduction half-reaction: O2(g) + 2H2O(l) + 4e- 4OH-(aq)Equation 2

Combining the oxidation and reduction half-reactions gives the balanced chemical equation for the overall reaction of iron, oxygen, and water (Equation 3). Notice that two iron atoms are oxidized for every oxygen molecule that is reduced-the number of electrons gained by one oxygen molecule is equal to the number of electrons given up by two iron atoms.

2Fe(s) + O2(g) + 2H2O(1) 2Fe2+(aq) + 4OH-(aq) Equation 3

Fe2+and OH- ions may combine to form solid iron(II) hydroxide, Fe(OH)2 (Equation 4). This is almost never observed, however, because iron(II) hydroxide reacts further with oxygen and water to form hydrated iron(III) oxide, Fe2O3nH2O, the flaky, reddish-brown solid known as rust (Equation 5).

Fe2+(aq) + 2OH-(aq) Fe(OH)2(s)Equation 4

4Fe(OH)2(s) + O2(g) + xH2O(I) 2Fe2O3(x+4)H2O(s) Rust Equation 5

G. Prevention of IronOnce rusting is started, the iron continues to corrode because rust is permeable to air and water. The interior metallic iron beneath the rust layer again gets in touch of air and water, and therefore, rust forms again Prevention:We abundantly use iron and steel products, and this is why prevention of rust has become a major economic activities. Barrier ProtectionA barrier film can be introduced between the iron and atmospheric oxygen and moisture. A barrier protection can be achieved by painting the surface or by coating the surface with a very thin film of grease or oil or by electroplating iron with metal such as copper, nickel and chromium etc.

Sacrificial ProtectionIn this method, iron surface is covered with a layer of more active metal such as zinc. Zn loses e in preference to iron and prevents the rusting of iron. The process by which iron is protected by Zinc is called galvanization. Zinc, aluminum and magnesium powder dissolved in paints are also effective to protect iron from rust.

Use of Anti-rust solutionsThe alkaline chromate and alkaline phosphate act as anti-rust solutions. When iron objects are dipped into strongly alkaline solution of sodium phosphate, a protective insoluble iron phosphate film is formed. The film prevent the object to be rusted.Cathodic Protection Still another way to protect against corrosion is to confer a continual negative electrical charge on a metal. This method is referred to as cathodic protection. Cathodic protection replicates the effects of a sacrificial coating but with a more active metal. The source of negative charge is usually an external direct-current power supply. Cathodic protection is used to protect underground fuel tanks and pipelines, among other things.

Passivation Passivation is a process through which a thin film of corrosion products builds on a metal surface to serve as a barrier against oxidation. The formation of a passivation layer is affected by environmental pH, temperature, and chemical conditions. Anodization Anodization is another surface treatment that protects against corrosion. The metal to be protected is bathed in a specific substance, and electrochemical conditions are adjusted such that uniform pores several nanometers wide appear in the metal's oxide film. These pores allow an oxide film thicker than a passivation layer to build up. The resultant protective layer is very hard and very resilient.

Mixed Inhibitors Mixed inhibitors work by reducing both the cathodic and anodic reactions. They are typically film forming compounds that cause the formation of precipitates on the surface blocking both anodic and cathodic sites indirectly. Hard water that is high in calcium and magnesium isless corrosive than soft water because of the tendency of the salts in the hard water to precipitate on the surface of the metal forming a protective film.

Volatile Corrosion Inhibitors

Volatile Corrosion Inhibitors (VCI), also called Vapor Phase Inhibitors (VPI), are compounds transported in a closed environment to the site of corrosion by volatilization from a source. Inboilers, volatile basic compounds, such as morpholine or hydrazine.When these inhibitors come in contact with the metal surface, the vapor of these salts condenses and is hydrolyzed by any moisture to liberate protective ions. It is desirable, for an efficient VCI, to provide inhibiton rapidly while lasting for long periods. Both qualities depend on the volatility of these compounds; fast action wanting high volatility while enduring protection requires low volatility.

H. Calculation of Iron Rusting

Consider the rusting of oxygen:

Suppose we have a brand new iron nail and find that it has a mass of 43.6 g. We let it rust away in air. If the entire nail rusts away, what will be the mass of the rust (Fe2O3)? We can solve this problem in one of two ways:Method I:Step 1Determine moles of iron:

Step 2Convert from moles of iron to moles of rust:

Step 3Convert from moles of rust to mass of rust:

Method 2:Steps 1-3 above can be accomplished in one overall calculation by treating the problem like a dimensional analysis problem:

III. Questions

Assignments I1.Why Iron is located in transition metals? Because Iron is one of the metals that have partially filled d-sublevel orbitals.2.How is the valence electrons in Iron configured and how does it affect bonding formation? Irons configuration is [Ar] 3d6 4s2 which means that it has 8 valency electrons. This means that Iron has multiple ion forms (2+ or 3+)3.Why Iron in transition metals produce magnetic fields? Iron produces magnetic fields because Iron is obtained from the earths core and earths magnetic field is generated deep down in the Earths core, Iron magnetic field is induced by the Earths magnetic field.

4.In the Periodic table, which element group has high electron affinity and which one has high ionization energy? Group VII (Halogen) has the highest electron affinity. Group 0 (Noble Gases) has the highest ionization energy because all the elements in Group 0 are stable in configuration

5.What iron forms is found in earths crust? How to obtain iron from minerals? Iron ore. Iron can be extracted by reduction with carbon or carbon monoxide through a process called blast furnace.

6.What reactions happen in the blast furnace when coke and limestone are present? Oxygen in the air reacts with coke to give carbon dioxideThe Limestone breaks down to form carbon dioxideCarbon dioxide produced in the first two reactions react with more coke to produce carbon monoxideThe carbon monoxide reduces the iron in the ore to give molten ironThe limestone from reaction 2 reacts with sand to form slag (Calcium Silicate)

Assignments II1.How do you write a balanced reaction of iron rusting? 4Fe3+ + 3O2 -> 2Fe2O3

2.Why iron tends to form oxides (2+ or 3+)? Because of irons valence configuration that has 2 free electrons.

3.If you have 2 gram of iron nails and you left this nails rusting by leaving it outside for one month, can you calculate the total iron rust, assume the iron becomes rust after total one month?

We assume the iron that has been left outside of room will decrease the mass of iron because it is rusting. The mass is no longer 2 gram but it becomes less than 2 gram. Rusting itself it causes by oxygen, and it can be easier to rust if there are many impacts from the outside like acid, base, water or another chemicals. There has been a reaction that causes the rust weighs more than the amount of reacted iron which increases the overall weight of the iron.

4.Are there ways to prevent rusting? Physical protection: galvanizing, painting, greasing, and electroplatingChemical protection: sacrificial protection, cathodic protection, iron/carbon cell.

Assignments III1. How iron content in water affects the drinking water?EPA Secondary Drinking Water Regulations recommend a maximum iron amount of 0.3 milligrams per liter of water. Iron water could stain plumbing fixtures, porcelain and cooking utensil. It also leaves reddish stains on clothes if used for laundry. It can also ruin the flavor of beverages (Tea, Coffee, etc.) Lethal dose of iron in human body is around 200-250 milligrams per kilogram of a persons body weight (e.g. for a 70Kg person, the lethal dose is around 14-17.5 Grams)

2. Are there other compounds that reduce the quality of water?

Water Quality ParameterImportance to Water Quality

Aquatic Weeds or AlgaeAquatic weeds or algae growth can decrease oxygen levels and increase pH, both of which can be harmful to fish. Excessive growth of these organisms can clog navigable waters and interfere with swimming and boating. Aquatic weeds and algae out-compete native submerged aquatic vegetation. Decomposition of weeds and algae can also lead to oxygen depletion.

Bacteria -E. coli(Escherichia coli) (Freshwaters and Estuarine Waters Other than Shell-fish Growing Waters)Certain bacteria and other organisms cause human illnesses that range from typhoid and dysentery to minor respiratory and skin diseases.

Bacteria - Fecal Coliform (Marine Waters and Estuarine Shellfish Growing Waters)Certain bacteria and other organisms cause human illnesses that range from typhoid and dysentery to minor respiratory and skin diseases.

Chlorophyll aElevated chlorophyll a levels indicate excessive inputs of nutrients.

Dissolved OxygenDissolved oxygen is a basic requirement for a healthy aquatic ecosystem. Most fish and beneficial aquatic insects "breathe" oxygen dissolved in water. Although oxygen concentrations fluctuate under natural conditions, human activities can result in severe oxygen depletion.

pHMany biological processes, such as everyday metabolism and reproduction, are hampered in acidic (pH too low) or alkaline waters (pH too high).

SedimentationSediment may clog and damage fish gills, suffocate eggs and aquatic insect larvae on the bottom, and fill in spaces in the gravel where fish lay eggs. Sediment may also carry other pollutants into waterbodies.

TemperatureAquatic life is temperature-sensitive and requires water that is within certain temperature ranges. When temperature exceeds tolerance levels, cold-water organisms such as salmonids become physically stressed and have difficulty obtaining enough oxygen. Prolonged exposure to temperatures outside tolerance ranges will cause death.

Total Dissolved GasElevated levels of some dissolved gases can cause impacts similar to elevated pH.

Toxic SubstancesSome toxic substances may be harmful, some may undergo chemical changes to become harmful, and some may accumulate in sediments or throughout the food chain to levels that adversely affect public health, aquatic life, or wildlife .

TurbidityTurbidity is closely related to sediment because it is a measurement of water clarity. In many cases, high turbidity indicates a large amount of suspended sediment in a stream.

3. In the lab, Ali and Budi have to solve the problem on determining the content of iron in an iron ore sample. They follow the procedure by dissolving 0.206 g of KMnO4 in 100.0 mLof water, and will be used later as titrating agent. Then 0.238 g of iron ore is dissolved in 50.0 mL and to this 1.7 mL of H2SO4 is added. This ore solution is titrated with KMnO4 solution until a red endpoint is reached at addition of 10.3 mL of KMnO4 solution. How do you know the iron content from this titration data? (calculate the concentration of solution in molarity and content of iron in ore in weight %)

Mole of KMnO4 --> mole: mass/mr = 0.206 x 1000 = 0.013 M 158 100

Equation MnO4- + 8H+ + 5e 2+ --> Mn 2+ + 4H2O + 5e- + 5Fe3+

Concentration mole of iron ore = 0.238/56= 0.004 mole

Concentration: 0.004/0.05= 0.08 M

%Weight

Limiting reactant Fe2+ --> 0.004 moleMass= 0,004 x 56 = 0.224

So ,0.224 x 100 % = 94.1 %0.238

IV. Referenceshttp://chemistry.about.com/od/elementfacts/a/iron.htmhttp://www.webelements.com/iron/atoms.htmlhttp://www.chemguide.co.uk/inorganic/extraction/iron.htmlhttp://tdwhs.nwasco.k12.or.us/staff/bfroemming/CorrosionIron.html http://www.ironmap.com/prevention-of-iron-from-rusting/ https://www.boundless.com/chemistry/textbooks/boundless-chemistry-textbook/electrochemistry-18/corrosion-133/preventing-corrosion-533-7523/ http://www.ecochemie.nl/download/Applicationnotes/Autolab_Application_Note_COR05.pdf http://www.iun.edu/~cpanhd/C101webnotes/quantchem/calculations.htmlhttp://oregonexplorer.info/umpqua/WaterQuality/WaterQualityFactors