Corrosion and Rancidity Questions in English

(A) Nitrogen is an inert gas and does not easily react with these substances.
On the other hand,oxygen reacts with food substances and makes them rancid.
Thus,bags used in packing food items are flushed with nitrogen gas to remove oxygen inside the pack.
When oxygen is not present inside the pack,rancidity of oil and fat containing food items is avoided.

(N/A) Corrosion:
Corrosion is defined as a process where materials,usually metals,deteriorate as a result of a chemical reaction with their environment,such as air,moisture,or chemicals.
For example,iron,in the presence of moisture,reacts with oxygen to form hydrated iron oxide.
$4Fe + 3O_2 + nH_2O \to 2Fe_2O_3 \cdot nH_2O$ (Hydrated iron oxide)
This hydrated iron oxide is commonly known as rust.

(N/A) Rancidity:
The process of oxidation of fats and oils that can be easily noticed by the change in taste and smell is known as rancidity.
For example,the taste and smell of butter changes when kept for a long time.
Rancidity can be prevented by:
$1.$ Storing food in airtight containers.
$2.$ Storing food in refrigerators.
$3.$ Adding antioxidants.
$4.$ Storing food in an environment of nitrogen gas.

(B) Oils and fats are prone to rancidity,which is the oxidation of fats and oils when exposed to air.
To prevent this,food items containing oils and fats are often flushed with inert gases.
Nitrogen is an inert gas commonly used to replace oxygen in food packaging to prevent oxidation.
Helium is also an inert gas that does not react with oils.
Therefore,helium or nitrogen can be used to store fresh samples of oil for a long time to prevent rancidity.

(N/A) Metals such as silver,when exposed to substances in their surroundings like moisture,acids,or gases,undergo a process called corrosion. In the case of silver,it reacts with sulfur compounds in the air,leading to the formation of a black layer. This phenomenon is known as the corrosion of metals.
$(b)$ The black substance formed is silver sulphide. Its chemical formula is $Ag_2S$.

(A) Silver articles react with sulfur compounds present in the air, such as hydrogen sulfide $(H_2S)$, to form a coating of silver sulfide $(Ag_2S)$.
This process is a form of corrosion known as tarnishing.
The chemical reaction is: $2Ag + H_2S \rightarrow Ag_2S + H_2$.
Therefore, the black layer formed on silver is $Ag_2S$.

(D) When copper is exposed to moist air for a long time,it reacts with atmospheric carbon dioxide,oxygen,and water vapor.
This reaction leads to the formation of a green-colored layer on the surface of the copper metal.
This green substance is a mixture of copper carbonate and copper hydroxide,chemically represented as $CuCO_3.Cu(OH)_2$,which is commonly known as basic copper carbonate.

(A) Rusting of iron is a chemical change because it involves a chemical reaction between iron,oxygen,and moisture to form a new substance called iron oxide $(Fe_2O_3 \cdot xH_2O)$.
Melting of iron is a physical change because it only involves a change in the state of matter from solid to liquid,and no new substance is formed.

(B) When silver articles are exposed to air,they react with sulfur compounds present in the atmosphere,such as hydrogen sulfide $(H_2S)$.
This chemical reaction leads to the formation of a black layer of silver sulfide $(Ag_2S)$ on the surface of the silver.
This process is a form of corrosion known as tarnishing.

(N/A) The smell and taste of food containing fats and oils change because they get oxidized when exposed to air,leading to a condition known as $Rancidity$.
Process: $Rancidity$.
Two ways to slow down this process are:
$1$. Storing food in airtight containers to prevent contact with oxygen.
$2$. Flushing nitrogen gas into food packets (like chips) to replace oxygen and prevent oxidation.

(N/A) Potato chips manufacturers flush bags with nitrogen gas to create an unreactive environment,which prevents the oxidation of fats and oils,thereby stopping the chips from becoming rancid.
$(b)$ Iron articles lose their shine because they react with moisture and oxygen present in the atmosphere to form a layer of hydrated iron oxide,a process known as corrosion or rusting.
$(c)$ Foods should be kept in airtight containers to minimize their exposure to oxygen and moisture,which helps in preventing oxidation and slowing down the growth of microorganisms,thus keeping the food fresh for a longer period.

(N/A) Rancidity is the process of oxidation of fats and oils in food materials,which leads to an unpleasant smell and taste.
It can be prevented by the following methods:
$(i)$ Adding antioxidants to foods containing fats and oils.
$(ii)$ Flushing food containers with nitrogen gas to remove oxygen.

(N/A) Corrosion: The process in which metals are eaten away gradually by the action of air,moisture,or a chemical on their surface.
$(b)$ The corrosion of iron is called rusting.
$(c)$ Corrosion of silver is recognised by the development of a black coating on the surface of the metal.

(N/A) The chemical phenomenon responsible for these coatings is $Corrosion$.
Silver coins develop a black coating of $Silver \text{ } Sulphide$ $(Ag_2S)$ due to the reaction with sulphur compounds present in the air.
Copper coins develop a green coating of $Basic \text{ } Copper \text{ } Carbonate$ $(CuCO_3 \cdot Cu(OH)_2)$ due to the reaction with moist carbon dioxide and oxygen in the air.

(N/A) $(i)$ Airtight containers prevent air (oxygen) from coming into contact with the food,which inhibits the oxidation of fats and oils present in the food. Since oxidation is the primary cause of rancidity,preventing it ensures that the food does not become rancid,thereby preserving its original smell and taste.

(N/A) Chemically,marble is $CaCO_3$ (calcium carbonate). When exposed to the atmosphere for a long time,it reacts with acidic pollutants like $SO_2$ and $NO_2$ present in the air,which dissolve in rainwater to form acids (acid rain).
These acids react with the calcium carbonate of the marble to form soluble salts,which are then washed away by rain,leading to the slow corrosion of the statues.
The chemical reaction is as follows:
$CaCO_3(s) + H_2O(l) + CO_2(g) \rightarrow Ca(HCO_3)_2(aq)$

(B) Rust is chemically known as hydrated iron$(III)$ oxide.
When iron reacts with oxygen and moisture in the air,it forms a reddish-brown substance called rust.
The general chemical formula for rust is $Fe_2O_3 \cdot xH_2O$,where $x$ represents a variable number of water molecules.

(C) Corrosion is the process where metals are eaten away by the action of air, moisture, or chemicals.
$1$. Iron $(Fe)$ reacts with oxygen and moisture to form hydrated iron$(III)$ oxide $(Fe_2O_3 \cdot xH_2O)$, which is brown in colour (rust).
$2$. Silver $(Ag)$ reacts with sulfur compounds in the air to form silver sulfide $(Ag_2S)$, which is black in colour (tarnish).
$3$. Copper $(Cu)$ reacts with moist carbon dioxide in the air to form a green coating of basic copper carbonate $(CuCO_3 \cdot Cu(OH)_2)$.
Therefore, the order of colours for iron, silver, and copper is brown, black, and green respectively.

(D) When fats and oils are exposed to air,they undergo oxidation.
This process is known as rancidity.
During oxidation,the chemical structure of fats and oils changes,leading to the development of an unpleasant odor and a foul taste.
Therefore,they become rancid and their smell and taste change.

(A) Substances that are easily oxidised (like fats and oils in food) undergo rancidity when exposed to oxygen.
To prevent this,food items are flushed with an inert gas like $N_2$ (nitrogen) to displace oxygen.
Additionally,keeping them in airtight containers prevents further contact with atmospheric oxygen,thereby extending their shelf life.

(A) The statement is $True$.
Food items containing fats and oils get oxidized when exposed to air, which leads to rancidity, resulting in an unpleasant smell and taste.
By keeping food in airtight containers, the exposure to oxygen is significantly reduced or prevented.
This reduction in oxygen contact slows down the oxidation process, thereby preserving the freshness and quality of the food for a longer period.

(A) The statement is True.
$1$. Iron $(Fe)$ reacts with moisture and oxygen to form hydrated iron$(III)$ oxide $(Fe_2O_3 \cdot xH_2O)$, which is a reddish-brown substance known as rust.
$2$. Copper $(Cu)$ reacts with moist carbon dioxide in the air to form a green coating of basic copper carbonate $(CuCO_3 \cdot Cu(OH)_2)$.
$3$. Silver $(Ag)$ reacts with sulfur compounds in the air (like hydrogen sulfide) to form a black coating of silver sulfide $(Ag_2S)$.

(B) When silver articles are exposed to air for a long time, they react with sulfur compounds present in the air, such as hydrogen sulfide $(H_{2}S)$.
This chemical reaction leads to the formation of a black coating of silver sulfide $(Ag_{2}S)$ on the surface of the silver.
The chemical equation for this process is: $2Ag + H_{2}S \rightarrow Ag_{2}S + H_{2}$ (or more accurately in the presence of oxygen: $4Ag + 2H_{2}S + O_{2} \rightarrow 2Ag_{2}S + 2H_{2}O$).

(A) Rust is a hydrated iron$(III)$ oxide,which forms when iron reacts with oxygen and moisture in the air.
Its chemical formula is represented as $Fe_{2}O_{3} \cdot xH_{2}O$,where $x$ represents a variable number of water molecules.