FSc Notes Part 2 Chemistry Important Chemicals Paints, Varnish, Fertilizers and Plastic

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Paints

Definition

Paints are fluids that are applied on a surface to form a hard continuous film on it for protection or decoration.

Wooden and metallic articles are coated with paints to decorate them as well as to protect from corrosion or rusting.

Composition of Paints

Paints are usually composed of three components.

1. Pigments
2. Binders
3. Volatile Solvent

To make a paint, a suitable solvent is used in which both the binder and the pigment are dissolved.

1. Pigments

The pigment of paint gives it colour, it also gives hardness and bulk. Common pigments are titanium dioxide – TiO2 (white), Iron oxide – Fe2O3 (brown or red), Carbon Black – C (black), Chrome Yellow – PbCrO4 (yellow) and organic dyes of various colours.

2. Binders

The binder or vehicle is the part of the paint that carries the pigment particles and hold the entire film of the paint on the surface. Generally some plant oils such as linseed oil, natural and synthetic resin (liquid plastics) are used as binders.

3. Volatile Solvents

To make paint a suitable solvent is selected in which both the pigment and binder are dissolved. The solvent evaporates after the paint is applied. Solvent does not effect the quality of dry paint. Commonly, water or turpentine is used as solvent.

Classification of Paints

On the basis of nature of solvent, the paints are classified into the following two classes.

1. Oil Based Paints
2. Water Based Paints

1. Oil Based Paints

In these paints turpentine is used as solvent. Turpentine is a liquid mixture of hydrocarbon that is obtained from pine trees.

2. Water Based Paints

In these paints, water is used as solvent. Both binders and pigments form a suspension in water

Varnish

Varnish is a mixture of resin, volatile organic solvents and drying oils. To prepare Varnish such as resin (plastic in liquid state) is dissolved in volatile organic solvents, such as ether or alcohol and then drying oil such as linseed oil is added to it.

The drying oils such as linseed oil consist of esters of highly unsaturated acids containing two or more double bonds. When exposed to air, these oils absorb oxygen and form hard and tough film. The film is insoluble in water.

When a Varnish is applied to the surface, the volatile organic solvents evaporate quickly and the drying oil absorbs oxygen and a hard tough glossy film is obtained. The glossy appearance of the film is due to the presence of resin. Varnish differ from paints in such a manner that, it does not has any added pigment.

Fertilizers 

Definition

Fertilizers are the water soluble substances which provide one or nutrient materials to the soil essential for the nourishment of plants.

Explanation

Fertilizers are water-soluble salts that are absorbed by the plants through osmosis process. Fertilizers are mostly inorganic salts containing nitrogen phosphorus or potassium etc. these elements are essential for the growth and development of plants. Those nutrient materials which plant needs in large quantities are called Macro Nutrients. Those nutrient elements which plant need in small quantities are called Micro Nutrients.

Functions of Fertilizers

The main functions of fertilizers are

1. It helps the soil to make up the deficiency of nutrient element and becomes fertile again.
2. The main function of fertilizers is to maintain the pH of soil to neutrality (7 – 8) or slightly alkalinity (10).

Types of Fertilizers

Fertilizers have been classified into the following types.

1. Natural Fertilizers
2. Artificial Fertilizers

1. Natural Fertilizers

Natural Fertilizers are also known as organic fertilizers. The main source of natural fertilizers is the excretory product of animals and decade product of plants.

2. Artificial Fertilizers

Artificial Fertilizers are also known as synthetic fertilizers and mineral fertilizers. They are obtained from raw mineral materials.

Artificial fertilizers have been further classified into

a. Nitrogenous Fertilizer

In these fertilizers, nitrogen is present as the essential element.

Example

Ammonium Nitrate – NH4NO3

Ammonium Sulphate – (NH4)2SO4

b. Potassic Fertilizer

In these fertilizers, Potassium is present as the essential element.

Example

Chilli Salt Peter – KNO3

c. Phosphatic Fertilizer

In these fertilizers, phosphate is present as the essential element. Phosphatic fertilizers are further classified into following.

i. Super Phosphate

The raw material of super phosphate fertilizer is phosphorite. The molecular formula of Phosphorite is [Ca3(PO4)2]3 CaF2. This rock reacts with sulphuric acid and converts into water soluble super phosphate.

Ca3(PO4)2 + 2H2SO4 —-> Ca(H2PO4)2 + 2CaSO4

The mixture of calsium dihydrogen phosphate and gypsum is called super phosphate.

ii. Triple Phosphate

This phosphate fertilizer is obtained by the decomposition of phosphate rock or phosphorite with phosphoric acid.

Ca3(PO4)2 + 4H3PO4 —-> 3Ca(H2PO4)2

Plastic

Definition

Plastics are macromolecules, which are formed by the polymerization of simple molecules.

Explanation

In other words we can say that plastic are the polymers formed from monomers. The phenomenon in which simple and smaller molecules are combined together to form complex and large molecules, is called polymerization. The simple and smaller molecules are called monomers and the large and complex molecules are called polymers.

Types of Plastic

There are the following two types of plastics.

1. Thermo Plastic
2. Thermosetting Plastic

1. Thermo Plastic

Thermo plastic is also known as Thermo-softening plastic. This type of plastic is manufactured by heating, softening melding and cooling the raw materials, this process can be repeated and it does not effect the properties of plastic.

2. Thermosetting Plastic

Thermosetting plastics are those materials, which cannot be heated, only once before they set, i.e. they cannot be reworked.

Examples of Plastic

1. Polyethene (Polythene)

In presence of traces of oxygen, when ethene is heated at 200ºC, under 100 atm pressure then polymerization takes place. As a result, polyethene is formed, which is commonly known as polythene.

Uses

Polythene is the most common plastic used to form polythene bags and to package food.

2. Poly Vinyl Chloride (PVC)

PVC or Poly Vinyl Chloride is the polymer of vinyl chloride. When vinyl chloride is heated at 80ºC in the presence of catalyst hydrogen peroxide, then polymerization takes place. As a result, Poly Vinyl Chloride is formed.

Uses

PVC is used for insulating covering for electrical cables, for the manufacture of gramophone, records, suitcase covering etc.

3. Poly Vinyl Acetate (PVA)

Poly Vinyl Acetate (PVA) is the polymer of vinyl acetate.

Uses

PVA is used in the manufacture of chewing gums and in the water proofing of textiles.

4. Bakelite

Bakelite is a polymer of phenol and formaldehyde. By the condensation of two molecules of phenol with formaldehyde, a polymer Bakelite is obtained.

Uses

Bakelite is used to make buttons, switches, electrical boards, camera, radio, telephone etc.

Quality of Plastics

During the polymerization, some other components are also mixed to improve the quality of the plastic. For example, plasticizer is mixed with the polymer. It reduces the brittleness and improves the elasticity of plastic. Fillers are also mixed with the polymer, which usually increases the mechanical strength of plastics, Some pigments or dyes are added to get various coloured plastics.

Plastic Industry of Pakistan

The plastic industry in Pakistan essentially consists of moulding of plastic powders into various articles of daily use.