Question

How can we prevent the following metals from corrosion.( write 2 points for each )
<1> Silver
<2>Iron
<3>Copper​

Answer 1

CORROSION

Corrosion is slowly coating the metallic surface with oxide or other salts of metal the corrosion of iron is called rusting

In corrosion, a metal is oxidised by the loss of electrons to oxygen(O2) and oxides are formed. It is electrochemical phenomenon. for example at a particular spot of iron oxidation occurs and that spot behave as anode.!

Factor which promote Corrosion

1. Reactivity of metal : more reactive metal are readily corroded.

2. In  presence of electrolytes : electrolytes if present also increase rate of corrosion.

3. Presence of impurities :  presence of impurities in metals also enhance the  chances of corrosion.

Atomospheric Oxidation

(2Fe²+) + 2H20 + 1/2O2 --------> Fe2O3 + 4H+

Fe2O3 + xH20 ---------> Fe2O3.xH20 [RUST]

Prevention of Corrosion

• By covering the surface of metal with paint or by Bisphenol.
• By covering the surface by other metals that are inert or react to save the object.
• Sacrifical protection by more reactive metals which Corrode themselves but save the other metals!

Answer 2

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When metals are exposed to moist air, they react with oxygen and water present in moist air and get oxidized to form a new substance, that destroys or corrodes the metal. This chemical reaction is called corrosion.

1. What is Rusting?

• When iron comes in contact with moist air, it undergoes a chemical change and form a reddish brown layer, called rust. This process of formation of rust is called rusting.
• Rusting is a slow process in which iron gets converted to iron oxide (ferric oxide) that forms are reddish brown layer over the iron.
• Rusting causes corrosion of iron. It makes the iron soft and porous and destroys it gradually over a period of time.
• Both oxygen and water are essential for rusting to occur.

2. Prevention of Rusting

Rusting can be prevented by a number of methods which do not allow the metal to come in direct contact with air and water. Some of these are:-

$(i)\ Painting\ or\ Greasing$

When a layer of paint or grease is applied to the iron surface, it prevents the iron surface from coming in contact with air and water vapour and thus prevents rusting.

Iron grills, nails, nuts, and bolts, iron furniture and iron bridges are painted while iron tools and machine parts are greased with oil.

$(ii)\ Chrome-Plating$

The process of coating iron with a layer of chromium is called chrome-plating. Chromium metal prevents rusting and gives a shiny appearance to the object.

Chrome-plating is done on objects like taps, car parts, kitchen gas burners, bicycle handles, wheel rims and car bumpers etc.

$(iii)\ Galvanization$

The process of depositing a layer of zinc on iron is called galvanization. Iron pipes used to carry water and galvanized to prevent rusting.

Chrome-plating and galvanization prevent the action of air and water on iron.

$(iv)\ Tinning$

The process of coating iron with a layer of tin is known as tinning.

Tin metal is shiny, non-poisonous and does not rust.

It is mainly used to make cans used for storing food. Food does not come in contact with iron and is protected from getting spoilt.

$(v)\ Alloying$

The process of mixing one or more metals to form a new substance is called alloying.

Stainless steel is an alloy, made by mixing iron with carbon and metals like chromium, nickel and manganese. Alloys do not rust at all.

Alloys are often used to make railings, bridges, railway lines and infrastructure of buildings. Alloys prevent rusting and provide strength.