Corrosion and rancidity - class-IX

Electroplating is the process of plating one metal onto another by hydrolysis, most commonly for decorative purposes or to prevent corrosion of a metal. Metal cladding is the bonding together of dissimilar metals. It is different from fusion welding or glueing as a method to fasten the metals together. In metal spraying a wide range of metals is sprayed onto the surface of another metal. All of these methods are used to prevent corrosion.

Rusting of iron is a redox reaction because iron is oxidised from $0$ to $+3$ oxidation state and oxygen is reduced from $0$ to $-2.$

Rust general formula is $Fe _2O _3.nH _2O$. It is basic in nature.

Coating of iron with zinc to prevent corrosion is called galvanization.
Steel is dipped in a bath of molten zinc. The zinc coated iron is called galvanized iron. Zinc $(E^o=-0.763 : V)$ is stringer reducing agent than iron $(E^o=-0.44 : V)$ and is more easily oxidized than iron . Thus during corrosion, Zn is oxidized instead of Fe.

The following are true regarding rancidity. On keeping for long time,
the oxidation of oils and fats, changes the taste and odor of food and
makes them unfit for consumption. To prevent rancidity, food is stored in air tight containers. Rancidity can also be prevented by addition of antioxidants. To prevent rancidity, packed food items are flushed with an inert gas like nitrogen.

The condition produced by aerial oxidation of fats and oils in food, due to which unpleasant taste and smell occurs is called as rancidity.

The term used to indicate the development of unpleasant smell and taste in fat and oil containing foods due to aerial oxidation is rancidity.
The process of oxidizing fatty and oily substances is called as rancidity.

Rancidity is a very general term and in its most general meaning, it refers to the spoilage of a food in such a way that it becomes undesirable (and usually unsafe) for consumption.During the process of oxidative rancidity, oxygen molecules interact with the structure of the oil and damage its natural structure in a way that can change its odor, its taste, and its safety for consumption.

Rancidity is the oxidation of oils and fats changing their taste and smell. Specifically, it is the hydrolysis and/or auto-oxidation of fats into short-chain aldehydes and ketones which are objectionable in taste and odour.

Rancidity is decomposition of oils, fats and lipids. It normally happens when food items are stored for a long time and gets exposed to oxygen.. Rancidity can be prevented by adding anti-oxidants, vacuum packing, replacing air by nitrogen, refrigeration of the food-stuff or packaging of food items in airtight containers.

During electrochemical passivisation, the metal surface is made inactive by formation of thin invisible oxide layer on the surface. 

Iron reacts with air to form iron oxide(III) which is known by the name rust or rusting of iron. Rust is an iron oxide or red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture. Rust consist of hydrated iron oxide.

Rusting of iron takes place only when both air and moisture are present.

Damp areas alone supplies both the things air and water required for the rusting of iron.

An action of air and water gradually eats up the metal. This eating up of metals by the action of air and moisture on their surface is called corrosion.

We can prevent iron getting rusted by applying a coat of zinc or a thin coat of plastic helps to prevent rust. The process for coating metal like iron or steel with a thin zinc layer is known as galvanization.

The process where metals are degraded by reaction with moisture and air is called corrosion. When specifically referring to iron, it is called rusting.

Metal having much more positive potential will Oxidise less easily and coorrode slowly and vice-versa. So, Zinc will corrode fastly.

In corrosion $Fe^{2+}$ get oxidised to $Fe^{3+}$ which takes place on anode surface.

A thin layer of zinc coats other metals such as iron. It protects the iron from corrosion. Also since zinc is a more reactive metal it acts as a sacrificial metal. The oxygen in the air reacts with zinc to form zinc oxide, thus protecting the iron.

Iron and rust are different thing.

Architectural structures built with copper corrode to give green verdigris (copper carbonate). It can be a mixture of carbonate and sulfate compounds in various amounts, depending upon environmental conditions such as sulfur-containing acid rain.

The hydrogen ions and the dissolved gases such as carbon dioxide and water catalyze the rusting of iron.
Certain impurities also catalyze the rusting of iron.

If two metals are made to touch under the surface of an electrolyte they constitute a short circuited cell. Corrosion is a greater problem in winter when the salts are laided as chromium and iron are the two metals and NaCl act as an electrolyte.

Rusting of iron is corrosion of iron. Rusting of iron takes place when iron corrodes in the presence of water and oxygen. It is a redox reaction whereby oxygen acts as an oxidising agent while iron acts as a reducing agent. When iron is contact with water, a simple chemical cell is formed.

Phosphoric acid will not form a protective coating of iron oxide on the surface of iron. A strong oxidizing agent such as nitric acid is required for this process.

• One of the properties of iron is that it reacts with oxygen in the presence of moisture and gets corroded by forming rust.
• Air contains oxygen and moisture. Hence, iron readily rust when exposed to air.
• Steel (stainless steel, not mild steel) is an alloy of iron having the property to resist corrosion including rusting. Hence, stainless steel, though it contains iron, does not undergo corrosion. 

In cathodic protection, the more easily oxidized metal is attached to the metal which is to be protected. This results in corrosion of more easily oxidized metal. The other metal is thus protected from corrosion.

In the activity series, metals are on the top of the series react and corrode easily as these metals are highly reactive like iron corrodes easily in the presence of water and air forming its oxide layer while metals present at the bottom are least reactive and do not corrode easily like gold, silver and platinum are some of them.

If edible oil is allowed to stand for a long time in an iron or tin container the fatty acids in the oil react with rust flakes or powder to form salts. These salts contaminate the oil and hence the oil becomes rancid. Thus the above statement is true.

'X' is copper (Cu) and the black-coloured compound formed is copper oxide(CuO). The equation of the reaction involved on heating copper is given below:

The $Na^{\oplus}$ and $Cl^{\ominus}$ present in saline water increase the conductance of the solution in contact with the metal surface. This accelerates the formation of $Fe^{2+}$ ions and hence that of rust, $Fe _2O _3 \cdot xH _2O$

Rust is an iron oxide, usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture. Given sufficient time, oxygen and water, any iron mass will eventually convert entirely to rust and disintegrate. No rusting takes place in absence of moisture. 

Oxide of iron is rust. Iron in presence of oxygen forms iron oxide. The chemical name of rust is ferrous oxide. It further oxidises to ferric oxide.

Cathodic protection: A technique to control corrosion of a metal surface by making it work as a cathode of an electrochemical cell by placing in contact with the metal to be protected another more easily corroded metal to act as the anode of the electrochemical cell. Most commonly used to protect steel, water pipelines, and storage tanks.

Anodic protection: A technique to control corrosion of a metal by making it work as anode developing a passive film on the metal. It used in extremely corrosive conditions and most extensively used to store and handle sulphuric acid container.

Hence, option A and C are correct

Correct statements are given below:

The presence of electrolyte increase the concentration of electron and thus increasing the mobility of electron due to which rate of corrosion increases.

Corrosion resistance of aluminium is due to formation of thin layer of aluminium oxide that forms when metal is exposed to air and prevents further oxidation. It is called as protective passivation.

Corrosion is basically oxidation of metal in presence of oxygen. So it can be prevented by cutting off ${ O } _{ 2 }$

Rusting of iron involves oxidation.

Copper gets oxidized to form green oxide layer in the presence of air but this is not rusting, this layer is known as patina means tarnishing of copper into bluish green layer.

Corrosion of lead is strongly accelerated by traces of acetic acid. Acetic acid in the presence of oxygen rapidly attacks lead and produces very soluble lead(II) acetate which precludes the use of lead to process or store wine or fruit juice.

The metals lose their shine and become dull when exposed to air for a long time. Due to the formation of oxides, when the surface is rubbed by a sand paper, then the outer corroded layer is removed.

Copper reacts with $CO _2$ present in the air and forms a green coating on its surface due to the formation of basic copper carbonate.

Corrosion can be defined as the deterioration of materials by chemical processes. 

Damp air supplies both the things needed for rusting of Iron. Ordinary water has some air dissolved in it. So, it can do the same.

Corrosion occurs when a redox reaction takes place.

The green coat is due to the basic copper carbonate formation and is a mixture of copper carbonate and copper hydroxide $(CuCO _3$ and $Cu(OH) _2)$.

Titanium is used for building boats.

This is due to higher rusting power of iron.

The presence of $CO _2$ in the atmosphere will do iron oxide rusting. When a drop of water hits an iron object, two things begin to happen almost immediately. 

The tarnishing of silver ornaments in atmosphere is due to formation of silver oxide $Ag _{2}O$ and silver sulphide $Ag _{2}S$.

Aluminium in air is ordinarily protected by a molecule-thin layer of its own oxide. This aluminium oxide layer serves as a protective barrier to the underlying aluminium itself and preventing chemical reactions with the metal.

Corrosion requires acidic medium. Hence zinc corrodes in 2 $M$ acid solution.

The rusting or iron occurs in acidic medium. Hence it is catalyzed by $ { H }^{ + } $ ions.