Question

Explain two ways by which food industries prevent rancidity. Discuss the importance of decomposition reaction in metal industry with three points.

Answer 1

Hint: Rancidity is the spoilage of food and food turns rancid when the fats and oils within them get oxidized. To prevent rancidity we have to tell ways to prevent oxidation of food. And to answer the second part of the question we should know that in decomposition reaction, a single substance decomposes into two or more substances.

Step by step answer:
Sometimes, we observe that a foul smell is coming from nuts that have been stored for months, and also foul smell coming from potato chips that have been sitting in the kitchen cupboard for too long. When such foul odour comes from food, it is said to be rancid. In simple terms, rancidity is the spoilage of food such that it becomes unsuitable and undesirable for consumption.
We should know that food turns rancid when the fats and oils within them get oxidized and the taste and smell of the food changes. Oxidation of fats generates highly reactive molecules in the rancid food which is responsible for the unpleasant odour and flavour. These chemical reactions also reduce the nutrition of the food. Some studies show that rancid food can have harmful health effects if consumed.

Now, we know about rancidity but we should know ways to prevent it. Rancidity can be prevented using the following methods:
1. Adding antioxidants (substances which prevent oxidation) to food: Antioxidants are molecules that play an important role in preventing our food from spoiling too quickly by stopping oxidation reactions from taking place. Some antioxidants examples that we should know remember are ascorbic acid (vitamin C) and tocopherols (vitamin E). These are natural antioxidants. Synthetic antioxidants include butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), TBHQ, propyl gallate and ethoxyquin.
2. Rancidity can be prevented by packaging fat and oil containing foods in Nitrogen gas because the packed food is surrounded by a nitrogen gas which is an unreactive gas and there is no oxygen or air to cause its oxidation and make it rancid.

Now, to solve the second part of our question we should know about decomposition reactions.
We should know that a decomposition reaction can be defined as a type of chemical reaction in which under suitable conditions, one single compound splits into multiple simpler substances. A metal carbonate decomposes into a metal oxide and carbon dioxide gas. For example, calcium carbonate decomposes into calcium oxide and carbon dioxide.
\[CaC{{O}_{3}}\left( s \right)\to CaO\left( s \right)+C{{O}_{2}}\left( g \right)\]
Most decomposition reactions require an input of energy in the form of heat, light, or electricity.
Now, we should know the uses of decomposition reaction in metal industry and they are as follows:
For metallurgical processes and for extraction of metals from its oxides, chloride: We should know that in the metal industry there are three processes in which decomposition reaction is required.

Roasting: Heating of sulphide ores in the presence of excess air to convert them into oxides is known as ROASTING.

Calcination: Heating of carbonate ores in the limited supply of air to convert them into oxides is known as CALCINATION.

Reduction: Heating of oxides of metals to turn them into metal is known as REDUCTION.

Thermite welding: We should know that thermite welding is a welding process utilizing heat generated by exothermic chemical reaction between the components of the thermit (a mixture of a metal oxide and aluminium powder). Molten metal produced from the reaction, acts as filler for joining the work pieces after Solidification. Thermit Welding is mainly used for joining steel parts, therefore common thermit is composed from iron oxide (78%) and aluminium powder (22%).
\[~8Al\text{ }+\text{ }F{{e}_{3}}{{O}_{4}}\text{ }\to \text{ }9Fe\text{ }+\text{ }4A{{l}_{2}}{{O}_{3}}\]
We heat up the combustion reaction products (iron and aluminium oxide) up to $2500^oC$ . Liquid iron fills the sand (or ceramic) mould built around the welded parts, the slag (aluminium oxide), floating up, is then removed from the weld surface.
Manufacture of cement or calcium oxide: Calcium oxide can be produced by thermal decomposition of materials like limestone or seashells that contain calcium carbonate ($CaCO_3$; mineral calcite) in a lime kiln. Calcium carbonate undergoes calcination at temperatures ranging between $107^oC$ - $1270^oC$. These reactions are usually held in a rotary kiln. The products formed as a result of the reaction are burnt lime and carbon dioxide.
\[CaC{{O}_{3}}\left( s \right)\to CaO\left( s \right)+C{{O}_{2}}\left( g \right)\]

Note: We should know about three main types of decomposition reaction and they are:
Thermal decomposition reaction: This reaction is activated by thermal energy. For example decomposition of calcium carbonate into lime and carbon dioxide.
Electrolytic decomposition reaction: In this activation energy for decomposition is electricity. For example decomposition of water molecules into hydrogen and electricity due to passing of electricity.
Photo decomposition: In this reactant is broken by photons. For example: Photolysis occurs in the atmosphere wherein ozone molecules are broken down into oxygen molecules and atomic oxygen.