The Detroit Post
Thursday, 21 October, 2021

How Does Rust Form On Untreated Iron Nails

author
Daniel Brown
• Friday, 23 October, 2020
• 15 min read

Rust is a naturally occurring phenomenon when certain metals are exposed to oxygen and water for a length of time. It is an actual chemical change which takes place when metal starts to rust.

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Contents

Left in a totally dry environment, iron or steel will not rust. It is when moisture is added that the oxidation process starts to occur.

Because the air we breathe has moisture in it, oxidation will occur even if there is no water added to the metal. There is enough hydrogen and oxygen in the air to allow the atoms to bond with the iron.

There are things you can do to prevent rust from forming on your metal surfaces. This machine also decreases the moisture in the air, reducing your chances of rust forming.

Things which are normally stored outside, like bicycles and lawn mowers, can be covered or moved indoors. Silica gel packs help to dry out the air in small places like drawers or tool boxes.

Purpose of the Experiment to know how to measure a reaction rate. The chemical composition of rust is typically hydrated iron (III) oxide (Fe2O3.nH2O), and under wet conditions may include iron (III) oxide-hydroxide (Few(OH)).

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(Source: www.shutterstock.com)

Given sufficient hydration, the iron mass can eventually convert entirely to rust and disintegrate. Nails have been galvanized by dipping them in molten zinc.

Paint, wax, vinyl and cement are commonly used substances for coating. Vinyl coating also provides greater holding power.

In this picture, the yellow color is caused by the vinyl coating. However, the state of coating was not even resulting in uneven rusting.

= / Making steel nails rust requires using substances that affect the oxygen and moisture level to create the reaction needed to promote rust.

When you expose steel nails to a mixture of sea salt and water it will increase the speed of rusting. Orange juice, vinegar and certain carbonated beverages, such as soda, can speed up the rusting process making nails more vulnerable to the effects of oxygen exposure.

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Hydrogen peroxide is another substance commonly found in your home that can rust steel nails with a combination of salt. When exposed to household bleach, nails will noticeably begin to rust due the chemical reaction in its decomposition.

Because of this reaction, the iron is being dissolved by an electrolyte called carbonic acid. The oxygen that is released by the water combines with the dissolved iron.

Corrosion: The degradation of a metal so that it loses strength and becomes unable to fulfill its intended purpose. Iron will rust when it is in contact with both oxygen and water.

Rusting is faster if the water involved contains an electrolyte, either an acid or a dissolved salt. Electrons move from the anode to the cathode through the iron.

Corrosion by rusting can be prevented by applying a coating that acts as a barrier to air and water, such as greasing, painting or electroplating. You can do simple experiments to show that BOTH oxygen and water are needed.

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(1) Put an iron nail in pure water, but exposed to air. (2) Put an iron nail into boiled water in a sealed tube, and a layer of oil too.

The boiling drives off dissolved air and the oil provides an extra barrier. (3) Put an iron nail in a sealed test tube of air and a drying agent (e.g. anhydrous calcium chloride, absorbs any moisture), very little, if any rusting even after quite a few days.

Next time you are at the seaside take a few seconds to examine any railings where the paint has flaked off and the corroding effects of sea–spray will be very evident. Rusting of iron is sped up in the presence of salt or acid solutions because of an increased concentration of ions.

The rusting metal behaves like a simple cell and more ions enable the current, and hence the electron transfer, to occur more readily. i.e. rust is an orange–brown solid hydrated iron (III) oxide formed from the reaction with oxygen and water (the equation is not meant to be balanced and the amount of water x is variable, from dry to soggy!).

The reaction proceeds via (i) iron (II) hydroxide Fe(OH) 2 which is (ii) oxidized further to the hydrated Fe 2 O 3, or if very soggy, it amounts to the formation of iron (III) hydroxide, but is usually described as hydrated iron (III) oxide, which can be quite dry or quite soggy! To fit in both definitions of oxidation (oxygen gain or electron loss), so the iron is oxidized.

So this fits in with two important definitions of oxidation explained in detail below in the next section. The rusting of iron is a major problem in its use as a structural material.

Rust is soft and crumbly and readily flakes off exposing more metal to water and oxygen (in air) i.e. the rusting chemistry just keeps on eating the metal away, eventually, completely! Corroded components or structures weakened, adding further costs in rust treatment or replacement.

Conversely, in some extremely dry desert regions, iron and steel objects barely rust at all. Remember, both oxygen (from air) and water are needed for iron and steel to rust.

Most anti–corrosion methods to stop iron or steel rusting involve the exclusion of oxygen (in air) and water i.e. some sort of barrier is applied or formed on the surface of the metal to be protected. Other methods do involve sacrificial corrosion, where some metal, more reactive than iron, is bolted onto the steel and corrodes first i.e. preferentially sacrificed to the attack of oxygen and water (more details on this method later).

Iron and steel (alloy of iron) are most easily protected by paint (of any color you want) which provides a physical barrier between the metal and air and water in the atmosphere or in contact with water containing dissolved oxygen. You can also use a thin layer of plastic which acts as a water repellent barrier.

Moving parts on machines can be protected by a water repellent oil or grease layer i.e. this keeps the water from reaching the iron or steel surface. Blocks of a more reactive metal like magnesium can be bolted to the steel hulls of ships or underground iron pipes and the more reactive magnesium atoms preferentially lose electrons rather than the iron, i.e. the magnesium stops the iron rusting.

The block of metal e.g. magnesium must be replaced when the bulk of it has corroded away. The chromium, like aluminum, forms a protective oxide layer.

Coating iron or steel with a thin ZINC layer is called galvanizing '. For examples and full explanations see Electroplating surfaces with metals including silver and copper.

In the plating process, the iron /steel object is made the negative cathode in a bath of a zinc salt solution. The zinc acts as a physical barrier between the iron /steel and oxygen/water AND it has a second protective effect because it is higher in the metal reactivity series than iron ... ... and the more reactive zinc preferentially corrodes or oxidizes to form a zinc oxide layer that doesn't flake off like iron oxide rust does (a similar effect to the aluminum oxide layer that forms on aluminum).

This means aluminum structures last a lot longer than those made of iron or steel. It can be made harder, stronger and stiffer by mixing it with small amounts of other metals (e.g. magnesium) to make alloys.

COPPER and LEAD are both used in roofing situations because neither is very reactive and the compounds formed do not flake away as easily as rust does from iron. This is a combination of the hydroxide Cu(OH) 2 and carbonate Cuzco 3 e.g. seen as corroded green copper roofs on buildings).

Silver's very low reactivity makes it a valuable jewelry metal as it doesn't corrode easily and retains its attractive silvery appearance. Gold has an extremely low reactivity makes it a valuable jewelry metal as it doesn't corrode easily and retains its shiny attractive yellow appearance.

Platinum also has a very low reactivity makes it a valuable jewelry metal as it doesn't corrode easily and retains its attractive silvery appearance. The Group 1 Alkali Metals rapidly corrode in air and need to be stored under oil.

Oxidation is electron loss by something (atom, ion or molecule). These are called half equations and show the movement or transfer of electrons in a chemical reaction.

Reduction is electron gain by something (atom, ion or molecule). In the examples in the first double column section below, the equations are not meant to be complete or balanced.

(g) Redox reaction analysis based on the oxygen definitions of oxidation and reduction (2) iron (III) oxide + carbon monoxide = iron + carbon dioxide Fe 2 O 3 (s) + 3CO(g) = 2Fe(l) + 3CO 2 (g) The iron (III) oxide is reduced to iron (oxygen loss) by the CO and the carbon monoxide is oxidized to carbon dioxide, CO is the reducing agent (removes oxygen from Fe 2 O 3) and gets oxidized in the process to CO 2, the Fe 2 O 3 is the oxidizing agent (O donator to CO).

(a) magnesium + iron (II) sulfate = magnesium sulfate + iron Mg(s) + Peso 4(a) = GSO 4(a) + Fe(s) this is the 'ordinary molecular' equation for a typical metal displacement reaction, but this does not really show what happens in terms of atoms, ions and electrons, so we use ionic equations like the one shown below. (b) Exactly the same reaction occurs if you add iron filings to copper sulfate solution.

A brown precipitate of copper forms on the surface of the iron filings and the blue color fades as the less reactive copper is displaced by the more reactive iron. Iron + copper sulfate = iron sulfate + copper Fe (s) + USO 4(a) = Peso 4(a) + Cu(s) iron + copper(II) ion = iron (II) ion + copper The fully balanced symbol ionic equation is ... Fe (s) + Cu 2+ (a) = Fe 2+ (a) + Cu(s) The sulfate ion is a spectator ion and is NOT shown in the ionic equation.

Iron (Fe) is the reducing agent (electron donor) and the copper(II) ion (Cu 2+) is the oxidizing agent (electron remover or acceptor). The magnesium atoms transfer electrons to the copper(II) ion.

(5) Electrode reactions in electrolysis are electron transfer redox changes at the negative cathode positive ions are attracted: metal ions are reduced to the metal by electron gain. Iron + copper(II) sulfate = iron (II) sulfate + copper Fe(s) + USO 4 (a) = Peso 4 (a) + Cu(s) iron + copper(II) ion = iron (II) ion + copper Fe(s) + Cu 2+ (a) = Fe 2+ (a) + Cu(s) Sulfate, SO 4 2– (a), is colorless BUT a blue to pale green color change is observed in the solution as the blue copper(II) ion is replaced by the pale green iron (II) ion as well as the pink–dark precipitate of copper metal.

If it is oxidized e.g. with chlorine a yellow = orange =brown color develops as iodine is formed from the colorless iodide ion. This indicates what is called the oxidation state of an atom in a molecule or ion.

Explain why a more reactive metal prevents iron from rusting All copyrights reserved on revision notes, images, quizzes, worksheets etc.

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