Agricultural Chemicals and Explosives

Chemicals used in Agriculture

Fertilisers :

These are the chemical substances which are rich in a particular nutrient.

They supply nitrogen phosphorus and potassium.

Excess used of fertilisers can reduce the fertility of soil.

Good fertilizers are easily dissolved in water and stable so that elements are retained for longer duration.

It should not disturb the pH level of the soil.

Urea is the best fertilisers.

Calcium super phosphate, nitro phosphate, triple phosphate and phosphatic slag (Thomas slag) are some important phosphatic fertilisers.

Mixture of nitrogenous, phosphatic and potash fertilisers in proper ration is called NPK fertilisers.

NP fertilisers are prepared by mixing nitrogenous and phosphatic fertilisers in a definite ratio.

Pesticides :

Pesticides are the chemicals which are used to kill pests which adversely affect the crops e.g. DDT and malathion. They can be categorised into the following category:

Insecticides

Fungicides

Nematicides

Molluscicides

Herbicides

Rodenticides: Zinc phosphide is used to kill rodents.

Explosives :

These are the substance which contains a great amount of stored energy that can produce an explosion.

Chemical explosives may consist of either a chemically pure compound such as nitroglycerine or a mixture of a fuel and an oxidiser.

The largest commercial application of explosives is mining.

Explosive materials may be categorized by the speed at which they expand.

Materials that detonate (the front of the chemical reaction moves faster through the material than the speed of sound) are said to be “high explosives” .

materials that deflate are said to be “low explosives”.

Types of Explosives:

Primary Explosives:

A relatively small amount of energy is required for initiation.

Use in detonators e.g. acetone peroxide, silver azide and ammonium permanganate.

Secondary Explosives:

Are less sensitive and require more energy for initiation.

RDX and TNT are some secondary explosives.

Tertiary Explosives:

Used in large scale mining and construction operation and in terrorism.

Nitroglycerineis a highly unstable and sensitive liquid also called Noble’s Oil.

Dynamite is a mixture of highly sensitive nitroglycerine with saw dust, powered silica.

RDX (Research and development explosive) is a very powerful explosive.

Dyes :

Coloured substances used for colouring wool, textiles materials and foodstuffs.

A material which is used as dyes must be able to fix itself to the material it is applied and must be resist the action of water, acids and alkalies.

The dye is generally applied in an aqueous solution, and may require a mordant to improve the fastness of the dye on the fiber.

Both dyes and pigments are colored, because they absorb only some wavelengths of visible light.

Dyes are usually soluble in water whereas pigments are insoluble

Some dyes can be rendered insoluble with the addition of salt to produce a lake pigment lake pigment.

The first synthetic dye, mauveine, was discovered serendipitously by William Henry Perkin in 1856.

Dyes can be classified into the following category:

Azo Dyes:

These dyes contain the azo group (-N=N-).

Formed during the coupling reactions, e.g. red, orange.

Indigoid Dyes:

These dyes contains indigoid group in their molecules e.g. indigo.

Anthraquinone dyes :

any of a group of organic dyes having molecular structures based upon that of anthraquinone.

Theanthraquinonevat dyes, valued for their brilliant colours and fastness to light and washing, are insoluble in water but become soluble upon treatment with a reducing agent, usually sodium hydrosulfite.

Phthalein Dyes

Acid dyes:used as their sodium salts which are soluble in water.

Basic dyes:In acidic medium these dyes are used to dye modified nylons and polyesters e.g. aniline yellow and malachite green.