Objectives

Understand the manufacture of sulphuric acid .

Synthesise the manufacture of ammonia and its salts.

Understand alloys .

Evaluate the uses of glass and ceramics .

Appreciate various synthetic industrial material

S ulphuric acid

(H2SO4)

Introduction

Sulphuric acid is a highly corrosive strong mineral acid with the

molecular formula H2SO4. It is a pungent, colorless to slightly yellow

viscous liquid which is soluble in water at all concentrations. Sometimes, it

is dyed dark brown during production to alert people to its hazards. The

historical name of this acid is oil of vitriol.

Sulphuric acid is a diprotic acid and shows different properties

depending upon its concentration. Its corrosiveness on other materials, like

metals, living tissues (e.g. skin and flesh) or even stones, can be mainly

ascribed to its strong acidic nature and, if concentrated, strong dehydrating

and oxidizing property. Sulfuric acid at a high concentration can cause very

serious damage upon contact, as it not only causes chemical burns via

hydrolysis, but also secondary thermal burns via dehydration. It burns the

cornea and can lead to permanent blindness if splashed onto eyes.

Accordingly, safety precautions should be strictly observed when handling

it. Moreover, it is hygroscopic, readily absorbing water vapour from the air.

Sulphuric acid has a wide range of applications including domestic

acidic drain cleaner, electrolyte in lead-acid batteries and various cleaning

agents. It is also a central substance in the chemical industry. Principal uses

include mineral processing, fertilizer manufacturing, oil refining, wastewater

processing, and chemical synthesis. It is widely produced with different

methods, such as contact process, wet sulfuric acid process and some other

methods.

Uses of sulphuric acid

1. Sulphuric acid is used to manufacture almost all products . Some of

the example are as follows :

Almost one third of sulphuric acid is used to manufacture

chemical fertilisers .

Ammonium sulphate fertiliser is prepared from the reaction

between sulphuric acid with aqueous ammonia .

H2SO4 (aq) + 2 NH4OH (aq) ( NH4 )2SO4 (aq) + 2H2O (l)

Potassium sulphate fertiliser is prepared from the reaction

between sulphuric acid with potassium hydroxide solution .

H2SO4 (aq)+2KOH (aq) K2SO4 (aq) + 2 H2O (l )

Calcium hydrogen phosphate , Ca (H2PO4)2

(superphosphate ) is formed when sulphuric acid react with

calcium phosphate.

2H2SO4 (aq)+Ca3 (PO4)2 (s) Ca (H2PO4)2 (aq)+2CaSO4 (s)

Neutralisation of sulphuric acid with barium hydroxide solution

produces barium sulphate which is used as white pigment in paint

.Sulphuric acid used to make titanium (IV)oxide . This white

powder is used in the manufacture of pigment.

Concentrated sulphuric acid react with by products of petroleum

to form sulphonic acid by process called suphonation .

Neutralisation of sulphonic acid with an alkali produces

detergents .

Synthetic fibres like rayon is produced by the reaction of

sulphuric acid with cellulose threads soaked in alkaline solution.

Dilute sulphuric acid is used as electrolyte in lead – acid

accumulator in car batteries .

Before electroplating , sulphuric acid is used for cleaning metals

to remove the surface oxide .

Sulphuric acid is used to manufacture many type of plastics.

Sulphuric acid is also used to manufacture other chemicals like

insecticides , pharmaceuticals , tartaric acid and explosives .

2. Sulphuric acid is also used in laboratory in school as follows:

As drying agent

As dehydrating agent

As catalyst

As strong acid

Manufacture of sulphuric acid in industry

Contact process

Stage 1 : Production of sulphur dioxide in the furnace

a) Sulphur is burnt in air to produce sulphur dioxide S (s) + O2 (g) SO2 (g)

b) Sulphur dioxide can also be produced by burning metal sulphides such as zinc sulphide and lead sulphide .

2ZnS (s) + 3O2 (g) 2SO2 (g) + 2ZnO (s) 2PbS (s) + 3O2 (g) 2SO2 (g) + 2PbO (s)

c) The sulphur dioxide is the mixed with excess air and dried . The mixture is next purified in order to remove impurities such as arsenic compounds .

Stage 2 : Conversion of sulphur dioxide to sulphur trioxide in the converter

a) Pure and dried mixture of sulphur dioxide and oxygen is passed through a converter .

b) The optimum condition used in the converter are as follows :

(i) Average temperature : 450o C(ii) Pressure : 1 atm

(iii) Catalyst : Vanadium (V)oxide ,V2O5

c) A high yeild of 95% of sulphur trioxide is produced . 2SO2 (g) + O2 (g) 2SO3 (g)

Stage 3 : Production of sulphuric acid in absorber and diluter

a) The sulphur trioxide is dissolved in concentrated sulphuric acid to produce oleum , H2S2O7 in the absorber .

SO3 (g) + H2SO4 (aq) H2S2O7 (l)b) The oleum is the diluted with water to produce

concentrated sulphuric acid of about 98 % in diluter . H2S2O7 (l) + H2O (l) 2H2So4 (aq)

Sulphur dioxide and environmental pollution

1. Sulphur dioxide is an acidic and poisonous gas that pollutes the environment .

2. Sulphur dioxide is produced as an intermediate product during Contact process .

3. Other sources that released sulphur dioxide in the atmosphere are as follows :

a) Extraction of metals from their sulphide ores.b) Burning of fossil fuels such as coal and petroleum with

high sulphur content .c) Burning of waste products manufactured from sulphuric

acid such as royan .d) Volcanic eruption .

4. Almost all the sulphur dioxide in the air comes from industrial source and vehicles .

5. Inhaling sulphur dioxide affects the respiratory system . It can cause coughing , chest pain , shortness of breath , bronchitis and other lung disease .

6. Sulphur oxide cause air pollution ,water pollution and soil pollution by making the air ,water and soil acidic.

7. Sulphur dioxide accounts for most of the acid rain problem .a) When sulphur dioxide dissolves in water , sulphurous acid

is formed . SO2 (g) + H2O (l) H2SO3 (aq)

b) Sulphur dioxide can react with oxygen and water to form sulphuric acid . 2SO2 (g) + 2 H2O (l) 2H2SO4 (aq)

8. Acid rain occur when the pH of rain water falls between 2.0 to 5.5 . This is due to the presence of sulphurous acid , sulphuric acid and nitric acid in rain water .

9. The effects of acid rain on the environment are as follows :

a) Pollute the air and corrodes buildings , monuments and statues made from metals and marble .

Metals like iron and calcium carbonate react with the acid in the rain slowly as follows :Fe (s) + H2SO4 (aq) FeSO4 (aq) + H2 (g)CaCO3 (s) + H2SO4 (aq ) CaSO4 (s) + H2O (g)

b) Increases the acidity of water in rivers and lakes. The acidic water kills aquatic organisms like

planktons and fishes , disturbing the ecosystem.

c) Increases the acidity of soil . The reaction of sulphuric acid with aluminium

compounds forms aluminium sulphate which can damage the roots of trees . The damage roots are easily attacked by viruses and bacteria .

d) Leaches minerals and nutrient in the soil . The acid react with minerals in the soil forming

soluble salts and they are carried away by rain water .

e) Destroys plants and trees in the forest . Apart from the acidic soil , the trees die of

combination of malnutrition and diseases.10.The following ways can be used to control the effects of acid rain

problems .

a) Use low sulphur fuels to reduce the amount of sulphur dioxide released into the air .

b) Remove sulphur dioxide from the wast gas before it is emitted in to atmosphere .

c) Neutralise the acidic soil and water by treating them with calcium oxide (lime), calcium hydroxide and calium carbonate .

Ammonia and Its Salts

(NH3)

Introduction

Ammonia or azane is a compound of nitrogen and hydrogen with the

formula NH3. It is a colourless gas with a characteristic pungent smell.

Ammonia contributes significantly to the nutritional needs of terrestrial

organisms by serving as a precursor to food and fertilizers. Ammonia, either

directly or indirectly, is also a building-block for the synthesis of many

pharmaceuticals and is used in many commercial cleaning products. Although

in wide use, ammonia is both caustic and hazardous. The global industrial

production of ammonia for 2012 is anticipated to be 198 million tonnes, a 35%

increase over the estimated 2006 global output of 146.5 million tonnes.

Ammonia, as used commercially, is often called anhydrous ammonia.

This term emphasizes the absence of water in the material. NH3 is formed by

protonation of amide ion NH2. NH2- + H+ naturally forms pure ammonia gas

NH3. It is a swifter method used by laborotist and industries to prepare ammonia

from amide ion, and the latter can easily be obtained through naturally

occurring Carbonyl organic compounds. NH3 boils at −33.34 °C (−28.012 °F) at

a pressure of 1 atmosphere, so the liquid must be stored under high pressure or

at low temperature. Household ammonia or ammonium hydroxide is a solution

of NH3 in water. The concentration of such solutions is measured in units of the

Baumé scale (density), with 26 degrees baumé (about 30% (by weight)

ammonia at 15.5 °C) being the typical high-concentration commercial product.

Uses of ammonia

1. The main use of ammonia are as follows:

The nitrogenous fertilisers are actually ammonium salts obtained

from neutralisation of ammonia with different acids. These

fertilisers include :

Ammonium Phosphate

The reaction of ammonia with phosphoric acid produces

ammonia phosphate.

2NH3 (aq) + H3PO4 (aq) (NH4)2HPO4 (aq)

Ammonium phosphate is a good fertiliser as it provides

two important nutrients, nitrogen and phosphours.

Urea

Ammonia reacts with carbon dioxide at 200oC and

atmospheric pressure of 200 to produce urea .

2NH3 (g) + CO2 (g) CO(NH2)2 (s) + H2O (l)

Urea has the highest percentage of nitrogen and is very

suitable for plant growth .

Ammonia is used to make nitric acid through Ostwald process.

Liquid ammonia is used as cooling agent in refrigerators because

ammonia is highly compressible and has a high heat capacity.

Ammonia can neutralise the acid produced by bacteria in the

latex , thus preventing latex from coagulating and can be

exported in the liquid form .

Ammonia reacts with nitric acid to form ammonium nitrate

which is used as explosive . Nitric acid can be used to make

explosives such as TNT .

As smelling salts to revive people who have fainted .

To make synthetic fibers such as nylon .

Ammonia reacts with hydrochloric acid to form ammonium

chloride . Ammonium chloride is used as electrolyte in dry cells .

NH3 (aq) + HCI (aq) NH4CI (aq)

Properties of Ammonia

1. Ammonia is a covalent compound with the following physical

properties :

a) Colourless gas

b) Pungent smell

c) Less dense than air

d) Very soluble in water

e) Alkaline gas

2. Ammonia is very soluble in water , but it ionises partially in

water to form a weak alkali . A 0.1mol dm-3 ammonia solution

has a pH of about 10 .

NH3 (g) + H2O (l) NH4+ (aq) + OH- (aq)

3. Ammonia being alkaline can undergo neutralisation with acids to

form ammonium salts .

Ammonia + Acid Ammonium salt

4. Ammonia solution can react with solutions of some metal ions

(except Na+ ion , K+ ion and Ca2+ ion ) to produce precipitate of

metal hydroxide .

Mn+ (aq) + nOH- (aq) M(OH)n (s)

5. Ammonia does not burn in air , but in the presence of platinum

catalyst in oxygen , ammonia can burn to produce nitrogen

dioxide .

4NH3 (g) + 5O2 (g) 4NO (g) + 6H2O (l)

Manufacture of Ammonia in industry

1. Most of the world supply of ammonia is manufactured through

Haber process.

2. The raw materials for the manufacture of ammonia are hydrogen

gas and nitrogen gas . The ratio for the raw materials is one

portion of three portion of hydrogen .

a) Nitrogen is obtained form the fractional distillation of

liquid air .

b) Hydrogen can be obtained by two methods :

The reaction between methane (from natural gas) or heated

coke with steam .

(i) The reaction betweeb methane (from natural gas)

and steam.

CH4 (g) + 2H2O (g) 4H2 (g) + CO2 (g)

(ii) The reaction between heated coke with steam ,

C (s) + H2O (g) H2 (g) + CO (g)

3. The optimum conditions for Haber process is

a) Average temperature : 450 oC

b) Pressure : 200 atm

c) Cataylst : red hot iron

4. During Haber process

a) A mixture of one volume of dry nitrogen gas and three

volume of pure hydrogen gas is mixed and passed to the

compressor and compressed to a pressure of about 200 atm

.

b) The mixture is then passed through layers of heated and

finely divided iron catalyst in the reactor at a temperature

of about 450 oC .

c) Ammonia is produced in the reactor but the reaction is

reversible .

N2 (g) + 3H2 (g) 2NH3 (g)

d) The production of ammonia is exothermic and gives out

heat . It is passed into the cooling chamber , then liquefied

and separated to get a better yield .

e) The unreacted nitrogen and hydrogen are recycled and

passed back into the reactor together with the new source

of nitrogen and hydrogen .

5. About 98% of nitrogen and hydrogen are converted into

ammonia .

Ammonium fertilisers

1. Nitrogen is used by plant to make protein . Protein is important

for the growth of plant . Other nutrients needed by plants include

phosphorus , potassium , calcium and magnesium .

2. Nitrogenous compounds are removed from the soil by plants ;

some are replaced naturally by bacteria . To restore the balance ,

nitrogenous fertiliser are added to the soil .

3. Nitrogenous fertilisers include ammonium fertilisers which

contain ammonium ions .

4. In the soil , the ammonium ions are converted to nitrate ions by

bacteria . This is because nitrogen can only be absorbed by plants

in the form of soluble nitrate ions .

5. Examples of ammonium fertilisers are :

a) Ammonium nitrate , NH4NO

b) Ammonium sulphate , (NH4)2SO4

c) Ammonium phosphate , (NH4)2HPO4

d) Urea , CO(NH2)2

6. The effectiveness of ammonium fertilisers is determined by the

percentage of nitrogen by mass in them.

7. The fertiliser with a higher percentage of nitrogen is more

effective for growth than those fertilisers with a low percentage

of nitrogen.

8. The percentage of nitrogen by mass can be calculated from the

formulae of the fertilisers using the following formulae :

Alloys

Introduction

An alloy is a mixture or solid solution composed of metals. An alloy

will contain one or more of the three: a solid solution of the elements (a

single phase); a mixture of metallic phases (two or more solutions); an

intermetallic compound with no distinct boundary between the phases.

Solid solution alloys give a single solid phase microstructure, while partial

solutions give two or more phases that may or may not be homogeneous

in distribution, depending on the thermal (heat treatment) history of the

material. An intermetallic compound will have another alloy or pure metal

embedded within another pure metal.

Alloys are used in some applications as their properties are superior

to those of the pure component elements for those applications. Examples

of alloys are solder, brass, pewter, phosphor bronze and amalgam.

The alloy constituents are usually measured by mass. Alloys are

usually classified as substitutional or interstitial alloys, depending on the

atomic arrangement that forms the alloy. They can be further classified as

homogeneous (consisting of a single phase), or heterogeneous (consisting

of two or more phases) or intermetallic (where there is no distinct

boundary between phases).

Arrangement of atoms in metals

1. Pure metal is made up of only type of atom , thus the atoms are of the same size .

2. Since all the atomsare same size , in solid state , these atoms are orderly arranged and closely packed together . Thus pure metals have high density .

3. The atoms in metal are oderly arranged in layer to from three-dimensional crystal lattice.

( three-dimensional crystal structure of metals )

4. Metals have high melting and boiling points due to the existence of very strong forces of attraction between the closely-packed atoms . Thus more heat energy is required to overcome the forces of attraction .

5. Although the forces of attraction between the atoms are strong , pure matals are weak and soft due to their ductility and malleability and have limited use .

6. Pure metals are ductile and soft because all the atoms are of the same size and orderly arranged , thus the layers of atoms can slide over one another when a force is applied .

7. Pure metals are malleable , weak and can be shaped . This is because there are some empty spaces in between the atoms of pure metals . When a metal is knocked or pressed , groups of atoms may slide and settle into new positions due to the imperfection .

8. Because pure metals are ductile and malleable , they are relatively soft and easily oxidised to form metal oxide .

9. To improve the properties of pure metal , it is made into alloys .

What are alloys ?

1. An alloys is a mixture of two or more elements with a certain fixed composition in which the major component is metal .

2. In the process of making alloys , one or more foreign elements are added to a molten metal . Thus , the position of some metal atoms are replaced by the atoms of foreign metal which may be bigger or smaller.

3. These foreign atoms of different sizes disrupt the orderly arrangement of the metals . Thus , the properties of the pure metal are improved .

4. Alloys are stronger , harder , more resistant to corrosion , have a better finish and more lustrous than their pure metal .

5. Most alloys are mixture of metals. Some alloys may contain mixture of a metal and a non-metal .Example :

a) Brass is a mixture of copper and zinc .b) Steel is a mixture of iron and carbon .c) Stainless steel is a mixture of iron , carbon and chromium

6. By changing the percentage composition of the metals , the properties of the resulting alloy can be altered .

Aim of making Alloy

1. The aim of making alloy is :

a) To increase the strength and hardness of a pure metal . During alloying , a small amount of atoms of other element

is added to a molten pure metal . When the alloy because solid , the positions of some atoms of other element of different sizes .

The presence of these foreign atoms of difference sizes disrupts the orderly arrangement of the atoms in the pure metal .

This reduces the layers of atoms from sliding over one another and making alloys harder and stronger than pure metals .

For example , when carbon atoms sre added to iron to form steel , the carbon atoms which are smaller size than size than iron atoms disrupt the orderly arrangement of iron atoms making it more difficult for the layers of atoms making it more difficult for the layers of atoms to slide over one other . This makes steel harder than pure iron .

b) To increases the resistance to corrosion of a pure metal . Most metal corrode readily when exposed to air . This is

because they react with oxygen and water vapour in the air .

Alloying can prevent metals from corrosion . This is because alloying helps to prevent the formation of oxide layer on the surface of the metal .

For example , carbon , chromium and nickel are added to iron to make stainless steel . Cutlery made from stainless steel does not corrode .

c) To improve the appearance of a pure metal Metals have lustrous surface . However , the formation of

dull metal oxide on the surface of metal makes it quickly lose its shine.

For example , atoms of antimony and copper are added to tin ,making pewter to have more lustrous surface than tin .

Composition , properties and uses of alloys

1. Today many alloys have been discovered and are being improved by altering their percentage composition .

2. The use of each different type of alloys depends on the properties of the alloy.

3. The table below shows the composition , properties and uses of some alloy .

Synthetic Polymers

What is Polymers ?

1. Polymers are long chained molecules formed by joining up many identical repeating sub-units called monomers .

2. Polymerisation is a process by which the monomers are joining together into chain-like big molecule known as polymers .

3. Polymerisation can be represented graphically as shown below .

PolymersationM+M+M+M+M+M+M+M+…. –M-M-M-M-M-M-M-M-M-…. Many monomers Polymer

4. A polymer is a macromolecule and may consist of thousands of monomers . Hence it normally has a larger relative molecular mass.

5. The properties of a polymer are very different from the properties of its monomer .

6. Polymers can be divided into two type :a) Natural polymers

Exist in living things in nature. Examples : Protein , cellulose ,wool , silk , starch ,

natural rubber and DNA

b) Synthetic polymers

Man-made in laboratory through chemical processes .

Examples : Plastic , synthetic fiber , synthetic rubber .

Naturally occurring polymers

1. Naturally occurring polymers are polymers obtained from living things such as plants and animals .

2. Natural rubber is obtained from rubber trees , Hevea brasiliensis as latex . The monomer for natural rubber is isoprene or 2-methyl-but-1 , 3-diene . Each isoprene unit has two double bonds and undergoes addition polymerisation to form polyisoprene or natural rubber .

3. Carbohydrates such as starch and cellulose are formed by plants through polymerisation from a simple sugar called glucose .

4. Wool , meat and silk are made up of a variety of proteins . They are all naturally occurring polymers that consist of amino acid as the monomer .

Synthetic polymers

1. Through continuous research and development , scientists are able

to copy the structure of naturally occurring polymers to produce

synthetic polymers .

2. Synthetic polymers are polymers made by man through chemical

reactions in industry from polymerisation of monomers .

3. The monomers are usually obtained from the fractillation of

petroleum after going through refining and cracking process .

4. Synthetic polymers are commonly known as plastic .

5. Example of synthetic polymers are : polythene , polypropene ,

polyvinyl chloride or PVC , polystyrene , perspex , nylon and

terylene .

How are synthetic polymers made ?

1. Synthetic polymers are made through two types of polymerisation :

a) Addition polymerisation

Addition polymerisation involves monomers with carbon-

carbon double bonds between the carbon atoms .

During addition polimerisation , the double binds between

pairs of carbon atoms break and the carbon atoms of abjecent

molecules join together .

Example of monomer that can undergo addition

polymerisation are : ethene , chloroethene and styrene . They

undergo addition polymerisation to form polyethene ,

polychloroethene and polystyrene respectively .

Polymerisation of ethene is shown below .

b) Condensation polymerisation

Condensation polymerisation involves the joining up of

monomers with the formation of other smaller and simple

molecules such as water .

Example of polymers produced by condensation are nylon

and terylene .

Plastic

(i) Plastics are made from the products of cracking of

petroleum fractions such as alkenes molecules

through addition polymerisation .

(ii) Plastics are the largest group of synthectic polymers

with the following properties :

Can be easily moulded and coloured

Low density

Strong

Inert to chemicals

Insulator of heat and electricity

Impermeable

Non-biodegradable

(iii) Table below shows some examples of commonly

used plastic , how they are formed , their properties

and use .

Synthetic fibers

(i) Polyamides and polyesters are two group of

synthetic fiber with high strength , not easily

stretched and used as textile .

(ii) Nylon is an example of polyamide polymers .

Terylene is an example of polyester polymers .

(iii) Nylon and terylene are produced through

condensation polymerisation.

Synthetic rubber

(i) Synthetic rubbers are elastic and regain their original

length and shape after being stretched and pressed.

(ii) The structure of synthetic rubbers is similar to that

of natural rubber .

(iii) Synthetic rubbers are produced by addition

polymerisation .

(iv) Neoprene and styrene-butadiene rubber (SBR) are

example of synthetic rubber .

(v) Neoprene is elastic and resistant to oil and is suitable

to make rubber host and toys .

(vi) Styrene-butadiene rubber , SBR rubber is very

suitable for making car tires and shoes because it is

elastic and hard .

Synthetic polymers in daily life

1. Synthetic polymers have been widely used to replace many other building material such as stones, metals , wood , clay , cotton , wool and natural rubber .

2. Synthetic polymers are very stable . Unlike metals , wood or paper ,they do no rust , rot or decay easily in the presence of water , oxygen or other chemicals or in sunlight .

3. Below is some example of use of synthetic polymers :a) Adhesives , fibers , household items and othersb) Toys and leisure itemsc) Furnitured) Transportation industrye) Electrical and electronic industryf) Building industryg) Packaging industry

4. One of the advantages of synthetic polymers is that they can be made with special properties to suit the job required . They are chosen for the job because they have a suitable combination of properties .

5. The following are the typical properties of synthetic polymers :a) Chemically stableb) Mostly are soft and flexible but some are hardc) Non-flammabled) Low densitye) Relatively cheapf) Easy to mould or shapeg) Can be coloured easily

6. The stable property of synthetic polymers makes them very useful , but this also means that they are difficult to dispose of as they are not easily biodegradable .

7. The wide usage of non-biodegradable synthetic polymers with their properties has created a serious effect on our environment . They pollute our land ,water dan soil .

8. Land Non-biodegradable synthetic polymer wastes will block or clog

up the drainage system , thereby causing flash flood . Plastic containers which are not properly disposed of will become breeding ground for mosquitoes which will cause the spread of diseases such as dengue .

9. Water The waste pollutes lakes and rivers with chemicals , causing the

water not suitable for aquatic organisms to live in it.

10. Air The open burning of synthetic polymers gives out harmful ,

pungent ,acidic and poisonous gases that pollute the air . It cause green house effect and acid rain problem .

11.There are number of ways to solve the problems caused by use of synthetic polymers :

1. Find alternative to non-biodegradable synthetic ploymers Non-biodegradable plastic shopping begs and bottles

are now replaced by biodegradable and photodegradable plastic .

2. Recycle Collection of polymer waste Storing of polymer waste Granulation Fabrication

3. Reuse Many plastic container can be collected , cleaned

and reused for a certain number of times . Used plastic materials can be converted into decorative item .

4. Proper way of disposal of unwanted synthetic polymers Waste plastice can be disposed by pyrolysis , a

process of heating the plastic wastes in the absence of air to break them down .This will prevent toxic gases from escaping to the atmosphere.

Glass and CeramicsGlass

1. The raw material for making glass is sand (silicon dioxide or silica ) which is abundant in the Earth’s crust .

2. Glass is formed when silicon dioxide is melted and mixture with other substances like lead (II)oxide , boron oxide , sodium carbonate or calcium carbonate .

3. Generally , glass can be made by heating a mixture of silicon dioxide and metal carbonates to a temperature above 1500 oC .

4. In glass , every silicon atom is bonded covalently by four oxygen atoms in a tetrahedral manner . Every oxygen atom is also bonded to two silicon atoms to form a three-dimensional gigantic covalent molecule .

(Macromolecular structure of silicate )

5. The physical properties of glass depend on the percentage of the various silicates present . Generally , all type of glass have the following common properties :

a) Transparentb) Hard but brittlec) Impermeable to liquid d) Heat insulatore) Bad conductor of electricityf) Chemically inert

6. There are different types of glass depending on what is added to silicon dioxide .There are fused glass , soda-lime glass , borosilicate glass and lead crystal glass .

Ceramics

1. Ceramics are made from clay and composed of aluminium silicate mixed with sand .]

2. The white clay used to make ceramics is kaolin which is rich in kaolinite or hydrated aluminosilicate , Al2.O32SiO2.2H2O.

3. Red clay consists of iron (III)oxide which gives the red colour . Bricks , tiles , mugs and clay pots are some examples of traditional ceramics.

4. During the making of ceramics , the shaped object are heated tovery high temperature ; they undergo a series of chemical reactions and are hardened to form ceramics.

5. These chemical reactions are irreversible and the ceramics cannot be melted and remoulded .

6. The process to make ceramics :a) Wet clay can be shaped easily because the tiny crystals in it can

slide over each other . Clay has a plastic property .When the clay dries up , it keeps its shape as crystals are now stuck together .

b) When heated to above 1500 o C , a series of chemical reaction produce other chemicals and glass which packs the tiny mineral crystals together .

c) The object is now glazed and heated again . The reactions in the glaze cause the surface to be waterproof .

7. The general properties of ceramic are as follows :a) Very hard and strongb) Brittlec) Chemically inert and does not corroded) Good insulator of electricity and heate) Very high melting point and heat resistance f) Porous but can be made impervious by glazing

Composite Materials

What are composite materials ?

1. A composite material is a structural material that is formed by combining two or more different substance like metals, alloys, glass, ceramics and polymers . Usually , the new composite materials formed have properties that are superior to those of the original components.

2. Composite materials combine the advantageous properties of more than one material and overcome the limitations of the component materials . Thus , they are more useful for particular purposes than the individual components .

3. During the production of a new composite material, normally a continuous serial of research and tests has to be done on its properties in different direction , its effects on human health and also on the environment .

4. Wood and bones are natural composite materials . Wood consists of strong and flexible cellulose fibre surrounded and held together by stiffer material called lignin . Bone is composite of the strong yet soft protein collagen and the hard , brittle mineral apatite .

5. Plywood is a conventional composite material . It is built in layers . Each layers is reinforced with long fibre laid in a single direction. It exhibits enhanced strength only along the direction of the fibres . Fibres woven into three-dimensional structure can produce stronger plywood . These fibres are laid along three mutually perpendicular axes .

6. Some examples of common composite materials are reinforced concrete , specific super conductor , fibre optic , fibre glass and photochromic glass .

Reinforced concretes 1. Concrete is a mixture of cement ,sand , gravels and water and

therefore is a composite material .

2. When cement is mixed with water to form a paste , it is soft and can be moulded into different shapes . This paste hardens when dry into a hard but brittle solid called concrete .

3. A concrete slab is weak in tensile strength and brittle . It will crack if a heavy load is placed on it but it is strong against compression , hard , fireproof , easy to maintain and comparatively cheap .

4. Steel is strong in tensile strength and corrode easily but expensive . Steel and concrete have about the same coefficient of expansion .

5. To improve the tensile strength , steel is used to reinforce the concrete . When concrete is reinforced with steel wires , bars or netting , the resulting combination is a very tough material with more tensile strength and does not crack easily . Reinforced concrete is relatively cheap and can be moulded easily . Thus, it needs very low building cost and very little maintenance .

6. Reinforced concrete is used to make multi-storey high-rise buildings , bridges , highways , airport runways and oil platforms.

7. Concrete can also be reinforced with other materials such as glass fiber , silicon carbide , aluminium oxide particles and polymer fibres .

8. The fibre reinforced concrete is of greater strength than ordinary concrete and has increased resistance to impact . It has been used in the construction of roads and aircraft runways and rocket launching pads .

9. Concrete reinforced with polymer fibres is suitable to build buildings that are subjected to earthquakes .

Superconductor 1. Superconductors are materials capable of conducting electricity

without any electrical resistance when cooled to an extremely low temperature .

2. Most of the known superconductors are alloys or compounds of metal or ceramic with metal oxides . Some superconductors are made from composite materials .

3. A mixture of barium oxide , BaO , copper (II) oxide ,CuO, and itrium oxide Y2O3 , can be made into ceramic superconductor called perovskite ,YBa2CU3O7 .

4. These superconductors are widely used taday . Superconductor can be made into a very powerful and light magnets .

5. Superconductors are used in :a) Bullet trains in Japanb) Medical magnetic-imaging devices like magnetic resonance

imaging (MRI) in hospitalc) Magnetic energy storage systemd) Magnetically levitated traine) Motors and generatorsf) Transformersg) Computer partsh) Very sensitive devices for measuring magnetic fields ,

voltage or current .

6. The main advantages of devices made from superconductors are low power dissipation , high-speed operation and high sensitivity .

Fiber optic 1. Fiber optic is a composite material that is used to transmit

electronic data , voice and images in digital form at great speed .

2. A fibre optic cable consists of bundle od glass . A light wave travels along the glass fiber by total internal reflection .

3. Fiber optic is used in :a) Instrument to examine internal parts of the body (endoscopy)b) Inspecting the interiors of manufactured structural productsc) replacing copper wires in long distance telephone linesd) linking computers within local area networks (LAN)e) closed circuit television security systemf) as laser beam to perform surgeryg) cellular phonesh) video cameras

4. Advantages of fibre optic over the traditional metal communications lines are :

a) Cheap in material costb) Thinner , easily bent and lighterc) Less susceptible to interferenced) Greater bandwidth than metal cables , thus can carry more

datae) Chemically more stablef) Data transmitted by fiber optic cables can be transmitted

digitally rather than analogicallyg) High transmission capacity

5. The main disadvantages of fibre optic cables are that the cables are much more expensive to install , more fragile and are difficult to split .

Fiberglass 1. Fiberglass is composite material with high tensile strength made

from glass fibre and plastic .

2. Glass is hard , strong . chemically inert and has quite high density but is relatively brittle .

3. Plastic is elastic , flexible with low density but not that strong.

4. The combination of glass fibres and plastic with their own properties results in a tough , strong and yet very light composite material called fibreglass.

5. Fibreglass has high tensile strength , chemically inert ,can be colour easily , low in density , can be made into thin layers and yet still strong .

6. Fibreglass has been used to make many of our household products such as water storage tanks , badminton rackets , helmets , small boats , skis and motor vehicle bodies .

Photochromic glass 1. A photochromic material is one that changes from transparent to

coloured when it is exposed to ultraviolet light , and reverts to transparency when the light id dimmed or blocked .

2. Photochromic glass can be produced by embedding photochromic substances like fine silver chloride or silver halide crystals in glass or transparent polymers as the matrix.

3. When exposed to light , the silver ions , Ag+ are converted to silver and the glass darkens . The photochromic glass becomes transparent again when the silver atoms lose electrons to form silver ions when light is blocked . This is because the halogen formed during the decomposition of silver halide cannot escape from the glass , so it recombines with the silver atom in the dark and image fades .

4. The chemical can also undergo a chemical process that causes it to change shape . The new structure absorbs a portion of the light causing the lenses to darken . The number of atoms that change shape varies with the intensity of the light .

5. Photochromic glass is used to make :a) optical lenses in glassesb) car windshieldsc) smart energy efficient windows in buildingsd) information display panelse) photoelectrochromic panels for computersf) camera lensesg) light intensity meters for measuring the intensity of light

6. When making lens and windshield , the photochromic glass helpsa) to protect our eyes from harmful ultraviolet rays and glare

from the sun.b) to protect our eyes from harmful ultraviolet rays and glare

from the sun.c) to control the amount of light that passes through

automaticallyd) our eyes to cope when they are exposed to different light

condition.