Man-made Materials

Apart from the various naturally occurring compounds, we make use of many man - made compounds synthesized in the laboratories and huge factories. Let us look at some useful man-made materials.

1.0Cement and Concrete

1. Cement : Cement is an important building material. In the preparation of cement, limestone and clay are mixed and grind into a fine powder. The addition of water to this powder produces a slurry (a semi - liquid mixture). The slurry is injected into a flame of burning gas, oil or coal dust with temperatures reaching 1500°C. The product is ground to a fine powder which is called cement.

It is a grey powder made from quicklime, clay, gypsum and coal dust. It quickly forms a hard mass with water. It is used:

For leveling a concrete surface smoothly.

For joining bricks and for plastering in the form of mortar, which is a mixture of cement and sand in the ratio of 1 : 4

For roofing and for making bridge pillars, railway sleepers and electric poles in the form of concrete, which is a mixture of cement, gravel and sand in the ratio of 1 : 2 : 3. Gypsum is added to cement so as to enhance its settling time period.

2. Concrete : Concrete, another important building material, is a mixture of cement, sand, water and gravel. When added to water, the cement crystal grows. These crystals interlock with the sand and gravel, causing them to bind together. We can make different types of concrete which can be made even stronger by pouring it over a framework of steel rods. The product obtained is called reinforced concrete. Reinforced concrete is used in the construction industry.

2.0Glass

Glass is an amorphous and transparent or translucent substance obtained by solidification of a mixture of silicates of different metals, one of which is always an alkali metal. It is thus rightly called a supercooled liquid.

Glass is formed by a combination of sand (silica) sodium carbonate, lime or limestone, lead monoxide, borax, aluminium oxide and some colouring matter.

It is thought that the Egyptians were the first people to use glass objects. They are thought to have coiled molten glass into jars and used them for storing perfumes.

The composition generally varies with the nature of the glass. For example, ordinary glass is a mixture of sodium and calcium and silica.

Some Important Types of Glass Are Mentioned Below

Note : A high technology class of glass fibre is optical fibre. It can carry audio, video and data signals using conventional cables.

Coloured Glasses            

The addition of transition metal compounds to the glass mixture imparts colour to glass. Small amounts of Cr(III), Mn(IV), Co(II) and Fe(III) compounds impart green, violet, blue or brown colour respectively.

Important Properties of Glass

(i)  It is transparent.

(ii)  It does not react with strong acids and bases.

(iii) It is a bad conductor of heat and electricity.

(iv) It can be easily moulded into desired shapes and sizes.

(v)  It is easy to clean, dry and can be reused.

3.0Silicones

Silicones are a special kind of substance prepared from silicon with extensive uses. They are chemically inert, good electrical insulators, waterproof and highly resistant to the effects of heating. Silicones are used :

(i) to make insulation materials for wiring in electric motors.

(ii) to make waterproof motors.

(iii) for making non-stick pans because it prevents things from sticking together.

(iv) as a lubricant for automobiles and in waxes and polished for furniture and floors.

4.0Plastics

A substance which can be formed by synthetic method from a simple substance and which can be moulded or given any shape is called plastic.

Plastics are mouldable and are available in many shapes.

The word 'plastic' stems from the Greek word 'plastikos' meaning 'fit to shape'.

Materials with naturally plastic quantities, including horn, tortoise shell and shellac have been used for thousands of years to make ornaments. The first synthetic plastic was Bakelite, invented in 1908 by Leo Baekeland. It was a hard plastic and a good electrical insulator used to make cameras, telephones and plugs.

Classification of Plastics                       

Plastics can be classified into thermoplastic and thermosetting plastics.

(i) Thermoplastics : On heating these become soft and can be shaped and moulded. For example, Perspex, polythene, polyvinyl chloride (PVC)

(ii) Thermosetting plastics : The plastics which can be softened and modulated only once are called thermosetting plastics. For example, urethane, foam, Bakelite, silicones.

These plastics are used especially for making items and appliances that get heated up during use, for example, electric switches, ashtrays, handles of electric iron, etc., so that they do not become soft on becoming hot. They may also be used to make cabinets for radio and television.

General Characteristics of Plastics

(i) Resistant to corrosion and abrasion: Plastics prepared by synthetic methods are superior to natural material.

(ii) Strength and touchiness : Plastics possess enough strength and toughness to meet the stress and pressure on them.

(iii) Transparent : Some varieties of plastics are transparent to light.

(iv) Insulators : They are non - conductor of electricity and find applications in insulation of wires.

(v) Light weight : They weigh much less than metal and glass. Plastic goods are easier to transport and store.

(vi) Appearance : Plastics can be suitably coloured and shaped as per the requirement.

5.0Synthetic Fibres

Like plastics, synthetic fibres also find great use in daily life. Synthetic fibres used in modern societies are mostly nylon, terylene, dacron, orlon, etc. They are all synthesized from various chemical substances. First chemically synthesized fibre is nylon which was synthesized in 1938. From that date till now, various fibres have been synthesized of which terylene, dacron, orlon, lica, acrylon, herculin etc., are most important from an industrial point of view.

Note : Chlorine and slaked lime react in a complicated way forming bleaching powder, long used as a source of chlorine for bleaching.

6.0Soaps and Detergents

A substance, which along with water is used for cleaning an article, is called a detergent. Soap is a type of detergent, but the term 'detergent' usually refers to synthetic detergents only, which are chemically different from soaps.

(1) Soaps : Soaps are the sodium salts (or potassium salts) of the long chain carboxylic acids (fatty acids). Soaps have been used as detergent for about 2500 years. Soap is obtained by the hydrolysis of oils or fats with caustic soda.

When the oils or fats are treated with a solution of sodium hydroxide they split to form sodium salts of fatty acids and glycerol.

The process of splitting fats or oils using alkalis is called saponification.

Cleansing Action of Soap 

The soap molecule may be visualised as a tadpole having a 'head' and a 'tail'.

When soap is added to water, the 'tail' ends repel water, sink into the dirt or grease. Pull them away from the surface to which they cling and thus clean the surface.

The 'head' end being soluble in water take away the drift particles from the clothes or other articles.

Cleansing action of soap

Limitations of Soap

It is found that soap does not form lather with hard water. Hard water contains calcium and magnesium salt which react with the soap molecules to form salts like calcium stearate, magnesium palmitate etc. These salts are insoluble in water and form a scum. So the soap is not able to produce the lather.

Also, the scum sticks to the particle being cleaned. This leads to the formation of dirty marks on the article and the container, which is used for cleaning.

To overcome this difficulty, synthetic detergents are used.

Mechanism to Prepare Soap in The Laboratory  

Materials required

(i) Vegetable oil (like Castor oil, cotton seed oil, Linseed oil or Soyabean oil)

(ii) Sodium hydroxide (Caustic soda)

(iii) Sodium chloride (Common salt)

Procedure

Soap can be prepared in the laboratory (or at home) as follows :

(i) Take about 20 mL of castor oil (cottonseed oil, linseed oil or soyabean oil) in a beaker.

(ii) Add 30 mL of 20% sodium hydroxide solution to it.

(iii) Heat the mixture with constant stirring till a paste of soap is formed.

(iv) Add 5 to 10 grams of common salt (sodium chloride).

(v) Stir the mixture well and allow it to cool. On cooling the solution, soil soap separates out.

(vi) When the soap sets, it can be cut into pieces called 'soap bars'. (We can also add perfumes before the soap sets).

(2) Synthetic detergents : Synthetic detergents are not affected by the calcium and magnesium ions present in hard water. So they work equally well with soft water and hard water. They produce lather even in sea water and acidic water. Detergents are the sodium salts of long chain benzene sulphonic acids or long chain alkyl hydrogen sulphates.

Study of foam production in Hard water and soft water with soap

Method

1. Take about 10 mL of distilled water (or rainwater) and 10 mL of hard water (from a tubewell or hand-pump) in separate test tubes.

2. Add a couple of drops of soap solution to both.

3. Shake the test tubes vigorously for an equal period of time and observe the amount of foam formed.

Observation

1. The test tube containing distilled water has more foam.

2. The test tube containing hard water has curdy white precipitate.

Discussion and conclusion

(i) Soap easily forms lather with soft water.

(ii) Hard water prevents lathering of soap by forming curdy precipitate called scum.

Na – Soap + Ca²⁺/Mg²⁺ ⎯→ [Soap-Ca/Mg] + Na⁺

7.0Paints and Enamels

Paints are coloured liquids used to produce decorative works or to protect and improve the appearance of buildings and machines.

Paints consists of three parts 

Pigment : Pigments such as red lead and zinc chromate help the paint to protect metal surfaces against rusting.

Binder : It is a chemical mix with the paint to hold the pigment in place. This comprises one or more resins. Resins are stickily substances obtained from plants or manufactured by means of complicated chemical processes.

Resins help to determine the adhesive quality, drying time, gloss and hardness of paints. Many of them are colourless.

Zinc oxide is used as a white pigment in paints. It is particularly bright as it absorbs UV light and reflects it as white light. Paints containing zinc oxide are used as an anticorrosive coating for various metals.

Solvent : The solvent is the ingredient that makes paint a liquid. The solvent in a paint depends on the resins that are being used. Most household paints use water as a solvent.

Other commonly used solvents include mineral spirits, naphtha and xylene. Solvents are sometimes called paint thinners.

When a surface is painted and left to dry, the solvent in the paint evaporates into the air. This leaves the binder and the pigments close together. They react to a tough weather - resistant film.

They are either lead and aluminium compounds or organic substances. They are used :

(i) To protect metals and other objects from corrosion and decay.

(ii) To improve the appearance of some objects.

Painting is generally done on heavy iron parts of vehicles, machinery, buildings etc, for better look and to avoid corrosion. E.g. red lead, aluminium, paint, etc.

Enamelling is done on domestic articles like pots, pans, stoves, refrigerators, etc.

E.g. organic compounds, silicates.

8.0Dyes

A dye is a compound that gives a long lasting, distinctive colour to textiles (fibres, yarns and fabrics); food, paper and ink, plastic, wood and many other materials.

A substance called mordant is added to the dye bath to improve the colour - fastness. Mordant fixes the dye molecules to the fabric.

E.g. Indigo blue, alizarin (red), martius yellow etc.

9.0Fertilisers

Just like us, plants also need nutrition for proper growth. They require potassium, calcium, magnesium, nitrogen, phosphorus and sulphur along with traces (very small amounts) of iron, manganese, copper, zinc, molybdenum and boron. Natural manures like cow dung, compost, plant roots (left in the soil during harvesting) and dry leaves are helpful in increasing the fertility of the soil. The use of some man-made chemicals, like ammonium sulphate, urea, superphosphate of lime and potassium chloride, tremendously increases the fertility of the soil. Such chemicals are called artificial fertilisers.

The trace elements mentioned are usually present in the soil. But if they are not, they are added to the soil as and when required. Nitrogen, phosphorus and potassium are the elements mostly required to make soil fertile. Let us now study some artificial fertilisers containing these elements, either singly or in combination. Artificial fertilizers are either water soluble inorganic salts or organic compounds rich in one or more nutrients essential for the growth of plants.

Nitrogenous fertilisers : Plants require nitrogen for synthesising proteins. So, the following chemicals, rich in nitrogen, are used as nitrogenous fertilisers.

(i) Ammonium Sulphate.

(ii) Urea.

(iii) Calcium Ammonium Nitrate (CAN).

(iv) Diammonium Phosphate (DAP).

(v) Potassium Nitrate.

Phosphatic fertilisers : Phosphorus, in the form of phosphate, is essential for the growth of plants. In higher classes you will learn that the phosphate ion provides energy for biochemical reactions. The following phosphatic fertilisers are commonly used.

Phosphorus helps roots to grow and helps crops to ripen.

(i) Superphosphate of lime.

(ii) Diammonium Phosphate (DAP). 

Potassium (or potash) fertilisers : Plants need potassium for the following reasons.

(i) Potassium helps in the proper formation of roots.

(ii) It helps plants to fight diseases.

(iii) It helps in the synthesis of carbohydrates.

(iv) Potassium helps plants to produce proteins, and to resist diseases.

The following potassium fertilisers are commonly used.

(i) Potassium nitrate.

(ii) Potassium chloride.

(iii) Potassium sulphate.

Mixed fertilisers : Nowadays, mixed fertilisers called NPK (nitrogen, phosphorus and potassium) are commonly used. Some examples of such combinations are given in Table.

10.0Pesticides

Many living organisms destroy crops, spread diseases and may cause other harm. They are collectively known as pests. Man has manufactured chemicals, called pesticides, to kill them.

Pests include insects (like ants and cockroaches) and fungi (like the one that affects potato leaves). To kill them we use insecticides and fungicides respectively. Rodents like rats, mice and moles are also pests. They eat up grain stored in granaries and our homes. Rodenticides are used to kill rodents.

Unwanted plants in crop fields are called weeds. Weeds affect the growth of crops by consuming nutrients from the soil. They are destroyed by using herbicides. Insecticides, fungicides, herbicides and rodenticides are collectively known as pesticides. Some common examples are given below.

Insecticides : DDT, aluminium phosphide, Gammaxene

Fungicides : Thiram, Bordeaux mixture (CuSO₄·5H₂O + Ca(OH)₂)

Rodenticides : Aluminium phosphide

Herbicides : Benzipram, Benzadox