INDEX – CLASS VIII
Chapters
Pages
1. Metals and Non-Metals 1 – 11
2. Materials 12 – 20
3. Combustion and Flame 21 – 31
4. Coal and Petroleum 32 – 40
EMS Academy 82/121 Pratap Nagar Jaipur (9530004698)
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INDEX – CLASS VIII
Chapters Pages
1. Metals and Non-Metals 1 – 11
2. Materials 12 – 20
3. Combustion and Flame 21 – 31
4. Coal and Petroleum 32 – 40
EMS Academy 82/121 Pratap Nagar Jaipur (9530004698)
EMS Academy 82/121 Pratap Nagar Jaipur (8107777788, 9530004698) METALS & NONMETALS 1 METALS AND NONMETALS
CHAPTER CONTENTS
Metals and Nonmetals
Characteristics of Metals
Chemical Properties of Metals
Characteristic of Non Metals
Chemical properties of Nonmetals
Uses of Some Common Nonmetals
Oxides of Metals and Nonmetals
METALS AND NONMETALS
Lavoiser classified all elements into metals, nonmetals and metalloids on the basis of their properties. Some commonly used metals, nonmetals and metalloids are given below. Metals : Iron, Copper, Gold, Silver, Aluminium, Zinc Lead are some commonly used meats. Nonmetals : Hydrogen, Oxygen, Nitrogen, Carbon, Sulphur, Phosphorus, Chlorine, Bromine, Iodine are commonly used nonmetals. Metalloids : Boron, Silicon, Arsenic and Germanium are some metalloids.
CHARACTERISTIC OF METALS
Some important characteristics of metals are : Metals are good conductors of heat and electricity. All metals except mercury are solid at room temperature. Mercury is the only metal which is liquid at room temperature. Metals are malleable and ductile – that is metals can be beaten into thin leaves and drawn into thin wires. Metals have lustre and can be polished. Metals have tensile strength. Metals are electropositive elements. That is, metals have a tendency to lose electrons and form positively charged ions, (called cations).
Occurrence of Metals
Metals occur in nature in the free as well as in the combined states. Metal in nature In free (or native) form Silver, Gold, Platinum, Mercury In the combined state (Sodium, Potassium, Calcium, Magnesium, Iron, Aluminium, Copper etc.) All metals which are not affected by water and by the gases present in the air occur in free state in nature. The naturally-occurring compounds of metals mixed with earthly materials are called minerals. A mineral from which a metal can be extracted on the commercial scale, economically and easily, is called an ore.
Physical Properties of Metals
All metals show similar physical properties. There are however a few exceptions. Physical State : Under normal pressure, all metals except mercury are solids at room temperature. Mercury is liquid at room temperature. Colour : Most metals except gold and copper are silver-grey in colour. Copper is reddish-brown and gold is golden yellow. Appearance : All metals are shiny. The characteristic shine of metals is called metallic lustre. Thus all metals have metallic lustre. Metals can be easily polished.
EMS Academy 82/121 Pratap Nagar Jaipur (8107777788, 9530004698) METALS & NONMETALS 3 Reactions with Acids : Most metals react with dilute acids produce salt and hydrogen gas. Reaction of some common metals with dilute hydrochloric acid are given below : Sodium (Na) : Sodium + Hydrochloracid(dil)^ ic^ chloride Sodium (^) + Hydrogen Vigorous Magnesium (Mg) : Magnesium + Hydrochloracid(dil)^ ic^ chloride Magnesium (^) + Hydrogen Rapid Zinc (Zn) : Zinc + (^) acid(dil) Hydrochlor ic room temp. chloride Zinc (^) + Hydrogen Moderate Iron (Fe) : Iron + Hydrochloracid(dil)^ ic^ heating chloride Iron (^) + Hydrogen Moderate Copper (Cu) : Copper + Hydrochloracid(dil)^ ic^ No reaction even on heating From the reaction conditions of the reaction given above, the order of reactivity of these metals with dilute acid is Sodium (Na) > Magnesium (Mg) > Zinc (Zn) > Iron (Fe) > Copper (Cu) USES OF SOME COMMON METALS Main uses of some common metals are listed below : Metal Main Uses Iron For making bridges, engine parts, iron sheets and bars used in construction, steels etc. Copper For making electrical wires and cables, utensils, kettles, coins etc; for making alloys Silver For making jewellery, in electroplating, in photography, silvering of mirrors Gold For making jewellery, for decorative purposes, in photography for toning Mercury Used in thermometers and barometers Alumini um For making electrical wires and cables, domestic utensils, alloys, metallic paints, aluminium foil for packaging Lead For making automobile batteries, lead pipes, alloys such as solder, protective screen for X-ray machines, for manufacturing many chemical compounds and paints. CHARACTERISTICS OF NON-METAL
Some important characteristics of metals are :
Nonmetals are soft solids, liquids or gases. Nonmetals (except graphite) are nonconductors of heat and electricity. Solid nonmetals are brittle. Nonmetals (except graphite and diamond) are low melting and low boiling. Nonmetals are electronegative elements. That is, nonmetals have a tendency to gain electrons and form negatively charged ions (called anions).
Occurrence of Nonmetals
Many nonmetals occur free in nature, whereas metal many more occur only in the form on their compounds as minerals. The modes of occurrence of some typical nonmetal are described below : Nonmetal Free native form^ Combined form Nitrogen Air contains about 78% (by volume) of nitrogen In all living organisms as proteins, in the soil as nitrogen compounds Oxygen Air contains about 21% (by volume) of oxygen As water, oxides in the soil/rocks Nobal gases Air contains these gases in smaller amounts — Hydrogen Free hydrogen is present in stars As water Sulphur Native sulphur occurs inside the earth. As sulphide, sulphate ores, as H 2 S in certain spring water Phosphorus — As phosphate rocks, in bones of our body as calcium phosphate
EMS Academy 82/121 Pratap Nagar Jaipur (8107777788, 9530004698) METALS & NONMETALS 4 Silicon — As oxide (SiO 2 , Silica, Sand), As silicate rocks Carbon As diamonds, graphite As carbonate rocks, minerals As hydrocarbons
- petroleum, natural gas etc. As carbon dioxide in the air. Most nonmetals are either mined directly from their mines or obtained as by-products in some industrial processes. Nitrogen and Oxygen are obtained from the air by fractional distillation of liquid air. Chlorine is obtained from common salt by electrolytic method. Sulphur is mined in its elemental form Nonmetals such as phosphorus and silica are obtained from their ores by chemical methods.
Physical Properties of Nonmetals
Some common general physical properties of nonmetals are given below : Physical state : Nonmetals may occur as solids, liquids or gases at room temperature. For example, under normal conditions, sulphur, phosphorus are solids, bromine is a liquid, whereas hydrogen, oxygen and nitrogen are gases. Colour : Nonmetals come in many colours. For example, sulphur is yellow, phosphorus is white, or red, chlorine is greenish-yellow, bromine is redish-brown. Hydrogen, oxygen and nitrogen are colourless. Appearance : Nonmetals have dull appearance i.e., they do not shine. However, graphite and iodine are the only nonmetals which have metallic lustre. Malleability and ductility : Nonmetals are neither ductile nor malleable. Nonmetals cannot be drawn into wires, and beaten into leaves/sheets. Conductivity : Nonmetals do not conduct heat and electricity, i.e., nonmetals are insulators. Graphite however, is a good conductor of heat and electricity. Density : Nonmetals usually have low densities and are soft. Diamond however is an exception. Diamond is the hardest natural substance known. Tensile strength : Nonmetals have low tensile strength, i.e., Nonmetals can be easily broken. Melting and boiling points : Nonmetals except graphite have low melting and boiling points. Sound : Nonmetals do not produce sound when hit with an object, i.e., nonmetals are non-sonorous. CHEMICAL PROPERTIES OF NONMETALS Some general chemical properties of nonmetals are described below :
Electronegative Character
Nonmetals are electronegative elements. Nonmetals have a tendency to accept electrons and form negatively charged ions (anions). For examples. Chlorine + e–^ Chloride ion (an anion) Oxygen + 2e–^ Oxide ion (an anion) Thus, nonmetals are able to gain electrons from electropositive elements and act as oxidising agents. Hydrogen is the only nonmetal which can lose as well as gain an electron. Hydrogen + electropositive element froma highly e – (ananion) Hydride ion Hydrogen – electronegative element froma highly e – (acation) Hydrogen ion Thus, hydrogen can act both as an oxidising as well as reducing agent.
Reaction with Oxygen
Nonmetals react with oxygen to give covalent oxides. Such oxides are either neutral or acidic in nature. Acids oxides of nonmetals dissolve in water to form corresponding acids. Reaction of some common nonmetals with oxygen are described below: Nitrogen : Nitrogen reacts with oxygen under different conditions to form five different oxides. Some of these are neutral, while others are acidic in nature.
EMS Academy 82/121 Pratap Nagar Jaipur (8107777788, 9530004698) METALS & NONMETALS 6 For example with chlorine, Phosphorus + Chlorine Heat Phosphorus trichloride Phosphorus + Chlorine Heat Phosphorus pentoxide Hydrogen + Chlorine sunlight Hydrogen chloride Sulphur reacts with fluorine at higher temperature to give sulphur hexafluoride. Sulphur + Fluorine high temp. Sulphur hexafluoride
Reaction with Hydrogen
Nonmetals react with hydrogen to form covalent hydrides. Thus in the hydrides of nonmetals,
hydrogen is bonded to the nonmetal atom by covalent bonds. The hydrides of nonmetals atom by
covalent bonds. The hydrides of nonmetals do not conduct electricity. The hydrides of nonmetals
may be acidic, basic or neutral depending upon the nature of the nonmetal.
For example, Sulphur with hydrogen gives hydrogen sulphide (H 2 S). H 2 S is weakly acidic in nature. Hydrogen + Sulphure Hydrogen(weaklyacidic^ sulphide) Nitrogen reacts with hydrogen to give ammonia (NH 3 ). Ammonia is basic in nature. Hydrogen + Nitrogen Ammonia(basic) Oxygen reacts with hydrogen to given water (H 2 O). Water is neutral in nature. Hydrogen + Oxygen electric spark Water
Reaction with Acids
Nonmetals do not displace hydrogen from dilute acids. This is because nonmetals are not able to give electron(s) for the reduction of H+. Some nonmetals however react with concentrated oxidising acids to form the corresponding oxyacids. For example, sulphur reacts with conc. nitric acid to give sulphuric acid. Sulphur + Nitric(conc^ acid.) Sulphuric acid + Nitrogen dioxide + Water
EMS Academy 82/121 Pratap Nagar Jaipur (8107777788, 9530004698) METALS & NONMETALS 7
Displacement Reactions
Certain more reactive nonmetals displace less reactive nonmetals from their salt solutions. For example, Chlorine displaces bromine from bromides and iodine from iodies. Potassium bromide + Chlorine Potassium chloride + Bromine Potassium iodide + Chlorine Potassium chloride + Iodine USES OF SOME COMMON NONMETALS Main uses of some common nonmetals are listed below : Nonmetal Main Uses Carbon In the form of diamond, it is used for making jewellery, cutting and grinding equipments. In the form of graphite it is used for making black lead pecils, and high temperature crucibles Sulphur For the manufacture of gun powder, Sulphuric acid and in the vulcanization of rubber Phosphorus For the manufacture of matchsticks, rat poison, phosphoric acid and fertilizers. Oxygen Supporter of combustion, for respiration by living organisms. Nitrogen For manufacturing ammonia, nitric acid etc. Chlorine For bleaching, sterilizing water, manufacturing chlorine compounds Hydrogen As a fuel, in oxygen-hydrogen flame used in welding For manufacturing ammonia, hydrogen chloride, vegetable ghee by hydrogenation of oils, and as a reducing agent. Iodine For preparing iodised common salt , tincture iodine is used as an antiseptic. OXIDES OF METALS AND NONMETALS Both metals and nonmetals react with oxygen (present in the air) to form oxides. The oxides of metals and nonmetals differ in their properties.
Oxides of Metals
The oxides of metals are basic in nature. When dissolved in water, metal oxides give alkaline (or basic) solution which turn red litmus blue. For example, magnesium (Mg) burns in air to give magnesium oxide (MgO), which is basic in nature. Magnesium + (^) (from^ Oxygenair^ ) Magnesium(basicoxide^ oxide) Magnesium oxide + Water turnsredlitmusblue Magnesium hydroxide (basicinnature)
Oxides of Nonmetals
The oxides of nonmetals are acidic in nature. When dissolved in water nonmetal oxides give acidic
give solutions which turn blue litmus red.
For example, sulphur on burning in air, gives sulphur dioxide (SO 2 ) which is acidic in nature.
Sulphur + (^ Oxygenfromair)^ Sulphur(acidicoxide^ dioxide)
Sulphur dioxide + Water
turnsbluelitumsred (acidicinnature ) Sulphurous acid
EMS Academy 82/121 Pratap Nagar Jaipur (8107777788, 9530004698) METALS & NONMETALS 9 EXERCISE # 2 SHORT ANSWER TYPE QUESTIONS Q.1 What happens when sulphur di-oxide reacts with water? Give the chemical reaction involved. Q.2 Why lemon pickle cannot be stored in an aluminium foil? Q.3 Write two important properties of metals. Q.4 Why copper cannot displace zinc from zinc sulphate solution? Q.5 Why immersion rods for heating are made up of metallic substances? Q.6 What happens when iron nails are dipped in water in a test tube for a week? Q.7 What happens when iron reacts with oxygen and water? Give the chemical reaction involved. Q.8 What happens when copper vessel is exposed to moist air for a long time? Give the chemical reaction that takes place. Q.9 Why gold is preferred in making jewellery? Q.10 What happens when dilute sulphuric acid is poured on a zinc plate? Write the chemical reaction takes Q.11 What happens when magnesium ribbon is burnt in air? Q.12 Why metals are used in making aeroplanes, bridges, satellites etc. Q.13 Complete the following chemical reactions. Zn + H 2 SO 4 2Cu + H 2 O + CO 2 2Fe + O 2 + H 2 O SO 2 + H 2 O Cu + HCl LONG ANSWER TYPE QUESTIONS Q.14 What will happen when ash of magnesium is dissolved in water? Is the solution acidic or basic? What effect does litmus show in case of oxides of metals? Q.15 Explain the following terms : (i) Malleability (ii) Ductility (iii) Sonorous (iv) Lustrous (v) Metalloids.
EMS Academy 82/121 Pratap Nagar Jaipur (8107777788, 9530004698) METALS & NONMETALS 10 ANSWER KEY EXERCISE # 1 Sol.1 Metals : Copper Non-Metals : Sulphur Sol.2 Silver Sol.3 Ductility Sol.4 Hydrogen gas Sol.5 Blue Sol.6 The oxides of non-metals are acid in nature. Sol.7 Sodium Sol.8 Malleability Sol.9 Sulphur di oxide is formed. S + O 2 = SO 2 Sol.10 Phosphorus Sol.11 Hydrogen gas Sol.12 The reactions in which more reactive metals displace less reactive metals from their compounds in aqueous solution are called displacement reaction. Sol.13 Chlorine is used in purification of water Sol.14 Metalloids are those which posses the character of both metals and non-metals. Sol.15 Aluminium
EMS Academy 82/121 Pratap Nagar Jaipur (8107777788, 9530004698) MATERIALS 12 MATERIALS
CHAPTER CONTENTS
Materials
Synthetic Materials
Some Common Synthetics
Plastics and Their Uses
Synthetic Fibres
General Characteristics of
Synthetic Plastics/Fibres
Raw Materials for Making
Synthetic Plastics
Classification of material
Synthetics Plastics
MATERIALS
Different things contain different kinds of matter. All these different kinds of matter may be called by a common name materials.
CLASSIFICATION OF MATERIALS
Natural Materials : The materials which occur in nature and used as such are called natural materials. For example, Wood, Cotton, Coal, Graphite, Diamond and many minerals of metals and non- metals are natural materials. The man-made materials are also called synthetic materials. The materials obtained from natural materials (also called raw materials) by chemical processes are called man-made materials.
SYNTHETIC MATERIALS
The synthetic or man-made materials are of following two types : (i) Synthetic Plastics (ii) Synthetic Fibres
SYNTHETIC PLASTICS
We are probably passing through the plastic age. Almost everything around is made of one or the other kind of plastic. Here we describe some commonly used plastic materials. A synthetic material which can be easily moulded into any desired shape on heating is called a plastic. Plastics are synthetic (man-made) actually polymers. Some common plastics are, (i) Bakelite (ii) Nylon (iii) Terylene (iv) Polythene (v) Polyvinyl chloride (PVC) etc. Kinds of Synthetic Plastics Plastics are of two types, viz. : (i) Thermoplastics (ii) Thermosetting plastics Thermoplastics : A plastic which can be softened on heating and moulded repeatedly in the desired shapes is called a thermoplastic. PVC, Polystyrene, Nylon, Polythene are some common thermoplastics. Thermoplastics are good for making pipes etc. Thermosetting Plastics : A plastic substance which once moulded into a shape cannot be softened or melted on reheating is called a thermosetting plastic. Thus, thermosetting plastics can be processed only once and cannot be reprocessed. This is due to the formation of cross-links between the adjacent polymer chain on heating. Bakelite, Melamine-formaldehyde are common thermosetting plastics. Thermosetting plastics are suitable for making handle of pressure cooker etc.
EMS Academy 82/121 Pratap Nagar Jaipur (8107777788, 9530004698) MATERIALS 13 Difference between thermosetting plastics and thermoplastics Thermosetting plastics and thermo-plastics differ from each other in many ways. S.No. Thermosetting plastic Thermoplastic
- Thermosetting plastics are the polymers in which chains get highly cross-linked on heating. Themoplastics are long chain polymers with no cross-linking. Heating also does not produce any cross- linking between the chains.
- Once molulded, thermosetting plastics cannot be reprocessed. Example : Bakelite, Melamine- formaldehyde resin. Thermoplastic can be processed repeatedly. Example : Polythene, PVC, Polystyrene, Nylon, Polyesters, etc.
RAW MATERIALS FOR MAKING
SYNTHETIC PLASTICS
All synthetic polymers are obtained from small organic molecules or from their suitable compounds. These small molecules are obtained from petroleum, and natural gas. For example, the compounds which are used as raw materials for making synthetic polymers/synthetic fibres / synthetic plastics are : Methane Methanol Ethane Ethanol Ethene Propene Ethyne Butene Vinyl chloride etc.
SOME COMMON SYNTHETICS
PLASTICS AND THEIR USES
Some common synthetic plastic of general use are described below : Polythene (or polyethylene) Polythene (or polyethylene) is obtained from ethylene (CH 2 = CH 2 ) under high temperature, high pressure and in the presence of a catalyst. Properties Polythene is a thermoplastic polymer. So, it can be moulded into any shape and any number of times. Polyethene is a whitish, translucent material. It is light weight and can be transported easily. It is unbreakable, corrosion-resistant, tough and flexible. It is not affected by acids, alkalies and most organic solvents. It is an insulator that is it does not allow electricity to flow through it. It is impermeable to water. Uses : Polythene is used for making sheets, sachets for packaging. for making containers for storing water, oil and other materials. for making pipes for transporting water and other liquids. for water proofing. Polyvinyl chloride (PVC) Polyvinyl chloride (PVC) is also a thermoplastic. It is obtained by the polymerisation of vinyl chloride. PVC is tougher than polythene. Uses : Polyvinyl chloride is used for the manufacture of rain coats, hands bags, plastic dolls, bathroom curtains etc. for manufacturing flooring and floor / ceiling tiles. as an insulation cover in electrical wires / cables. for making shoe-soles, and shoes. Polystyrene Polystyrene is obtained from the monomer styrene (C 6 H 5 – CH = CH 2 ). Polystyrene is a thermoplastic. It is lighter than polythene. Polystyrene is a highly transparent polymer. Uses : Polystyrene is used for making hot drink cups, toys, household articles, etc. as safe packaging material. for making styrofoam (or thermocole). as an insulating material.
EMS Academy 82/121 Pratap Nagar Jaipur (8107777788, 9530004698) MATERIALS 15 for making machine parts.
Polyesters
Terylene, Decron, and Terene are polyesters fibres. Polyesters are made from petroleum products. Properties Polyester fibres are quite strong. So, the fabrics made from polyesters last longer. Polyester fibres absorb very little water. Therefore, clothes made of polyester dry quickly after washing. Polyesters are wrinkle resistant. Therefore, the fabrics made from polyesters retain their crease. Uses : Polyesters are used for manufacturing sarees, dress materials, curtain cloth etc. for making blends with other fibres e.g., terylene with cotton gives terycot, with wool it gives terywool. Clothes made from blends are more comfortable to wear. for making sails for sail boats. for making water hoses for fire fighting. for making conveyer belts.
Acrylic fibre
Acrylic fibre has a feel similar to that of wool. It is used for making sweaters, shawls, blankets and carpets.
GENERAL CHARACTERISTICS OF
SYNTHETIC PLASTICS/FIBRES
Synthetic polymers (or synthetic plastics) show the following general characteristics. Light weight : Synthetic plastics are much lighter in weight as compared to wood, metals etc. Synthetic fibres are much lighter than natural fibres such as cotton, jute, wool etc. Toughness or Tensile strength : Synthetic plastics vary in their tensile strength from material to material. In general, synthetic plastics have much less toughness as compared to metals and alloys like steel. Synthetic fibres have very high tensile strength as compared to the natural fibres such as cotton, silk, wool, jute etc. as compared to the natural fibres such as cotton, silk, wool, jute etc. Insulating property : Synthetic plastics/synthetic fibres are insulators. These do not allow heat and electricity to flow through them. Reactivity towards air and water : Synthetic plastics / synthetic fibres are not affected by water, air, soil etc. Thus these are biodegradable. Chemical reactivity : Synthetic plastics / synthetic polymers are not affected by acids and alkalies. The natural polymers such as cotton, wool etc. are damaged by acids and alkalies. Appearance and workability : Most plastics (except bakelite, melamine etc.) are transparent / translucent. These can be coloured in any colour and be given any shape.
EMS Academy 82/121 Pratap Nagar Jaipur (8107777788, 9530004698) MATERIALS 16 EXERCISE # 1 VERY SHORT ANSWER TYPE QUESTIONS Q.1 What are natural fibres? Q.2 What are man made fibres? Q.3 Name two natural fibres obtained from plants. Q.4 Name two natural fibres obtained from animals. Q.5 What is a polymer? Q.6 Name a natural polymer? Q.7 Name a synthetic fibre which resembles silk. Q.8 How is rayon prepared? Q.9 Name the first fully synthetic fiber. Q.10 Name the raw material used in synthesis of nylon. Q.11 Name the repeating unit of polyester. Q.12 Name two common forms of polyester. Q.13 Name the raw materials used for making synthetic fibre. Q.14 What are thermoplastics? Q.15 What are thermosetting plastics? Q.16 Give two examples of thermoplastics. Q.17 Give two examples of thermosetting plastics. Q.18 Why Bakelite is used in making electrical switches? Q.19 Name the chemicals which give fruits like characteristic smell. Q.20 Name the different types of plastics. Q.21 Name the man made fiber made of wood pulp. Q.22 Name the fabric, which is used to imitate wool. Q.23 Why nylon is used for making carpet, toothbrush bristles and tyre? Q.24 Handles of frying pans are made of plastic. Why? Q.25 Electrical wires have covering of plastic. Why? Q.26 How are clothes, fabrics are related to each other? Q.27 Define (i) Fabric (ii) Cloth. Q.28 Why scientists tried to discover a fabric like silk? Q.29 Why nylon is used in making clothes?
EMS Academy 82/121 Pratap Nagar Jaipur (8107777788, 9530004698) MATERIALS 18 ANSWER KEY EXERCISE # 1 Sol.1 Fibers which are obtained from either plants or animals are called natural fibers. Sol.2 The fibers which are made by human being are called synthetic fibres. Sol.3 Cotton and jute are natural fibers obtained from plants. Sol.4 Wool and silk are natural fibers obtained from animals. Sol.5 Many small units combine to form single large unit called as polymer. They are building blocks of many synthetic fibers. Sol.6 Cotton is a natural polymer. Sol.7 Rayon is a synthetic fibre which resembles silk. Sol.8 Rayon is prepared by chemical treatment of wood pulp. Sol.9 Nylon is first fully synthetic fiber. Sol.10 Nylon is prepared from coal, water and air. Sol.11 The repeating units of polyester are ester. Sol.12 Two common forms of polyester are terylene and PET. Sol.13 The raw materials used for making synthetic fibers are of petroleum origin and are called petrochemicals. Sol.14 A plastic which becomes soft on heating and can be repeatedly remolded into desired shape is called thermoplastic. Sol.15 A plastic which once molded cannot be softened and molded into other shape on heating is called thermosetting plastic. Sol.16 PVC(Poly Vinyl Chloride) and Polythene are examples of thermoplastics. Sol.17 Bakelite and melamine are examples of thermosetting plastics. Sol.18 Bakelite is used in making electrical switches because it is poor conductor of electricity. Sol.19 Esters are the chemicals which give characteristic smell to fruits. Sol.20 Two different types of plastic are- Thermoplastics and Thermosetting plastics. Sol.21 Rayon is man made fiber made of wood pulp. Sol.22 Acrylic is a fibre used to imitate wools. Sol.23 It is used for making carpet, toothbrush bristles and tyre because it is a strong fiber. Sol.24 Handles of frying pans are made of plastic because plastic is a bad conductor of heat. Sol.25 Electrical wires have covering of plastic because plastic is bad conductor of electricity. Sol.26 The clothes are made of fabrics. Fabrics are made from fibres which are obtained from either natural or artificial sources. Sol.27 (i) Fabric is any material made by weaving, knitting, crocheting, or bonding. It is thermal insulation and prevents excessive heat-loss from the body. (ii) Cloth is a finished piece of fabric that can be used for various a purposes like wearing over body or covering a surface. Sol.28 The scientists tried to discover a fabric like silk because the fabric obtained from silk fibre was very costly. At the same its beautiful texture fascinated everybody and all wanted to wear it. Sol.29 Nylon fibre was strong, elastic and light. It was lustrous and easy to wash. Therefore, it is used for making clothes.
EMS Academy 82/121 Pratap Nagar Jaipur (8107777788, 9530004698) MATERIALS 19 EXERCISE # 2 Sol.1 The wood pulp contains cellulose. It is treated with chemicals and transformed in different form. Them rayon fibre is made from it. Therefore, rayon is man-made fiber. Sol.2 Nylon is used in many articles, such as socks, ropes, tents, toothbrushes, car seat belts, sleeping bags, curtains and parachute ropes. Sol.3 The fabric made from this fibre does not get wrinkled easily. It remains crisp and is easy to wash. Therefore, it is quite suitable for making dress material. Sol.4 PET is a familiar form of polyester. It is used for making bottles, utensils, films, wires and many other useful products. PET bottles and PET jars for storing rice, sugar and other eatable things. Sol.5 Acrylics are type of synthetic fibre. They resemble wool. They are available in a variety of colours. They are used for making sweaters, shawls and blankets. Many of these are actually not made from natural wool, through they appear to resemble wool. The clothes made from acrylic are relatively cheap. Sol.6 Polyester is synthetic fiber. These fabric melts and sticks to the body of the person wearing it when they catch fire. Therefore, we should, not wear synthetic clothes while working in the kitchen or in a laboratory. Sol.7 Synthetic fibres possess unique characteristics. They dry up quickly, are durable, less expensive, readily available and easy to maintain. So they are preferred as clothing material. Sol.8 Melamine is resists to fire and can tolerate heat better than other plastics. Therefore, it is used for making kitchenware and fabrics which resist fire. Sol.9 Plastic containers are convenient to store because of their light weight, lower price, good strength and easy handling. Sol.10 Acrylic is warm, soft, lightweight fiber having wool like appearance. It is easy to wash and dries up quickly. It retains the shape. It can be dyed easily to different colours. Therefore, acrylic is considered cheap substitute of wool. Sol.11 (i) Rayon is cheaper than silk and can be woven like fibres. (ii) It can be dyed in a wide variety of colours. (iii) Rayon is mixed with cotton to make bed sheets or mixed with wool to make carpets. Sol.12 (i) Synthetic fibers are usually stronger than either natural fiber. (ii) Synthetic fibers are lighter than natural fibers. (iii) Synthetic fibers are cheaper. Sol.13 (i) Plastic is non reactive. (ii) Plastic is light, strong and durable. (iii) Plastics are poor conductors of heat and electricity. Sol.14 (i) Synthetic fibers are non-biodegradable. (ii) Synthetic fibers do not absorb sweat (water). So they are not comfortable to wear on humid day. (iii) The main source of synthetic fibers is petroleum. With increase in use of synthetic fibers this natural resource is depleting quickly. Sol.15 (i) Synthetic fibers are cheap and affordable. (ii) Synthetic fibers are wrinkle free. So they do not need ironing. They do not need maintenance like natural fibers. (iii) Synthetic fibers dry quickly. (iv) Synthetic fibers are more elastic as compared to natural fibers. (v) Synthetic fibers are more durable as compared to natural fibers. (vi) Synthetic fibers do not shrink.