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1. Food production
3. Micro organism
5. Synthetic Material
6. Metal and non metals
7.Combustion and Flame
8.Force and Pressure
Class 08 Basic sciences synthetic-materials
A. Answer these Questions
1. What is polymers?
Answer : A polymer is made up of small units called monomers that combine under specific conditions. Example: Cotton, jute, silk and wool.
2. What is the process of the formation of the formation of polymers from its monomers called?
Answer : The process of formation of a polymer from its monomer is called polymerisation.
3. Name three rayon?
Answer : Viscose, cuprammonium and acetate rayon are three widelyused rayons.
4. Mention the five uses of synthetic fibre Other than making clothes?
Answer : Other than making clothes, synthetic fibres are used in making towels, mats, curtains, cushions, furniture covers and mosquito nets
5. What are plastic?
Answer : Synthetic materials that can be moulded into a permanent shape are called plastics
6. What are the polymers is used for making bubblegums , thermocol and Synthetic erasers ?
Poly (styrenebutadiene) is used for making bubblegums.
Polystyrene is used for making thermocol.
Synthetic erasers are made from vinyl rubber, neoprene and poly (styrenebutadiene).
7. Name the three polymers that can be obtain from chemical derived from natural gas?
Answer : Polythene, polyvinyl chloride (PVC) and Bakelite are three polymers that can be obtained by using chemicals derived from natural gas.
8. What do you mean by tensile strength of material?
Answer : The force or stress that is required to break a material is called its tensile strength.
9. What are those material called that (a) that attract water (b) repel water
Answer : (a) Materials that attract water are called hydrophilic. (b) Materials that repel water are called hydrophobic.
B. Answer these Questions
1. Why are acrylics not spun from the melt?
Answer : Acrylics are so named because they are made from polymer polyacrylonitrile. They are not spun from the melt because these polymers decompose without melting. Thus, they are dissolved in a specific solvent and the solution is forced through spinnerets to obtain filaments that are spun into yarns.
2. What are Thermoplastics and Thermosetting plastics ?
Answer : Thermoplastics are those plastics that can retain their plasticity even after repeated heatings and coolings. They can also be moulded again and again.
Thermosetting plastics are those plastics that cannot be moulded again after they are set into a particular shape
3. To what use can a polythene and acetylene be put?
Answer : Acetylene is obtained from methane. It is used for making polythene, polyvinyl chloride and acrylics. Propylene is obtained from petroleum and is used for making polypropylene (a plastic).
C. Answer these Questions
1. How are polymers classified? What are the raw material used to manufacture synthetic polymers?
Answer : Polymers are classified into three types depending upon their sources:
(a) Natural polymers
(b) Semisynthetic polymers
(c) Synthetic polymers
The raw materials used to manufacture the synthetic polymers are obtained from natural gas and petroleum, either directly or indirectly.
Methane is present in natural gas, which is converted into acetylene and formaldehyde.
Acetylene is used for making polythene, PVC and acrylics and formaldehyde is used for making bakelite.
Fractional distillation and cracking of petroleum gives acetylene, propylene, butylene, benzene and naphthalene.
Benzene is used for making nylon, butylene is used for making poly (butadienestyrene), naphthalene is used for making polyester and propylene is used for making polypropylene.
2. Mention three advantages and disadvantages of synthetic fibre over natural fibre?
Answer : Advantages of synthetic fibres:
(a) They do not depend on agricultural crops and animal farming unlike natural fibres that are obtained by these methods.
(b) They are cheaper than natural fibres.
(c) They are stronger and more durable than natural fibres.
Disadvantages of synthetic fibres:
(a) They are hydrophobic and do not absorb moisture whereas natural fibres are hydrophilic and are more comfortable to wear.
(b) They are very lustrous unlike natural fibres that have soothing colours.
(c) They melt before burning and may cause severe injuries in case of an accident.
3. Describe how youwould compare the tensile strength of thread of different material?
Answer : Tensile strengths of different materials can be compared by the following activity:
Take a cotton thread. Tie its one end to a hook that is fixed with a rigid body and the other end to the pan of a balance. Now, add some weights to the pan. Keep on increasing the weight in small amounts till the thread breaks. Note the total weight including the weight of the pan required to break the thread.
Repeat the same activity with other materials and note the different weights required to break the threads. By comparing the values of the weights, one can compare the tensile strengths of different materials.
D. Complete sentence.
1. Acrylic fibres compete with wool.
2. Polythene carrybags block drains and sewers.
3. Plastics are generally nondegradable, i.e., they are not environmentally broken down to simpler, harmless substances.
4. On being burnt, plastics give harmful gases.
5. Nylon has a higher tensile strength than copper.
6. On being heated, polyester and nylon melt before they burn.
E. Chose the correct options with explanation
1. (c) Cellulose
Cellulose is a natural polymer.
2. (a) polyester
Polyester is a synthetic polymer that can be stretched several times of its original length.
3. (d) polyester
Polyester is a synthetic fibre and it is hydrophobic.
4. (c) polythene
Polythene is a bad conductor of heat because it is a synthetic polymer.
5. (a) plastic
Plastic is a bad conductor of electricity because it is a synthetic polymer
F. Match the columns
(a) Cellulose (v) Glucose
(b) Nylon (iv) Parachutes
(c) Acrylics (i) Artificial wool
(d) Acetate rayon (ii) Semisynthetic fibre
(e) Polythene (iii) Carrybags
Class 08 Basic sciences Metal and non Metal
A. Answer these Questions
1. Name ten metals?
Answer: Ten examples of metals are potassium (K), iron (Fe), platinum (Pt), tin (Sn), copper (Cu), calcium (Ca), sodium (Na), magnesium (Mg), mercury (Hg) and silver (Ag).
2. How tensile strength of metal used?
Answer: Metals have a high tensile strength, i.e., they cannot be broken easily. Example: This property of metals is used to make steel cables for carrying heavy loads.
3. Why cant you
(a) draw wires from a piece of wood or coal
(b) use nylon or jute ropes for electrical transmission
(c) use a cooking utensil made of cardboard
Answer: (a) We cannot draw wires from a piece of wood or coal because they are brittle. They break down on stretching.
(b) We cannot use nylon or jute ropes for electrical transmission because they are bad conductors of electricity.
(c) We cannot use a cooking utensil made of cardboard because it is a bad conductor of heat and it will start burning itself if kept on fire.
4. Name the five non metal found in gaseous form?
Answer: Hydrogen (H), nitrogen (N), oxygen (O), chlorine (Cl) and argon (Ar) are five nonmetals that are gaseous at room temperature
5. Name two metals react vigorously with cold water. Name one metal which,if ignited continue to burn in steam?
Answer: Potassium and sodium are two metals that react vigorously with cold water.
Magnesium is a metal that continues to burn in steam, if it is ignited.
6. Mention three uses of oxygen.
Answer: Three uses of oxygen:
(a) It is required in all combustion processes.
(b) It is used in the productions of nitric acid and sulphuric acid.
(c) It is used in extraction of metals from their ores.
7. Mention three uses of nitrogen?
Answer: Three uses of nitrogen:
(a) It is used by plants for making proteins.
(b) It is used in manufacturing ammonia and urea.
(c) It is used for filling food packets.
8. Define an alloy?
Answer: An alloy is a homogenous mixture of metals or metals and nonmetals.
B.Answer these Questions
1. Mention five physical properties of metals.
Five physical characteristics of metals are:
(a) They have a high tensile strength; therefore, they cannot be broken down easily.
(b) They are malleable; i.e., they can be beaten into thin sheets.
(c) They are ductile; i.e., they can be stretched into thin wires.
(d) They are good conductors of heat.
(e) They are good conductors of electricity.
2. Mention five physical properties of non metals.
Answer: Five physical characteristics of nonmetals are:
(a) They are brittle; i.e., they are not flexible.
(b) They are not sonorous.
(c) They have no lustre (except graphite and iodine).
(d) They are bad conductors of heat.
(e) They are bad conductors of electricity.
3. Name a non metal which When redhot reacts with steam.What happen as a result of the reaction
Answer: Carbon is a nonmetal. When it is redhot, it reacts with steam. This reaction forms a gaseous mixture of carbon monoxide and hydrogen, called water gas. The following reaction occurs:
C (red hot) + O2 --------------> (water gas)
4. Mention three uses of metals, giving reason?
Answer : Three uses of metals are:
(a) Iron is used for making tools, machines and agricultural equipment because it is very strong, tough and cheap.
(b) Aluminium is malleable so Aluminium foil is used to pack food and medicines.
(c) Mercury is a good conductor of heat and does not stick to glass. Thus, it is used in thermometers.
5. Describe the uses of carbon?
Answer: Uses of carbon:
(a) Graphite is used in making pencils.
(b) Diamond is used as a gem and for cutting glass and rocks.
(c) Graphite is a good conductor of electricity. Thus, it is used as an electrode.
C. Answer these Questions
1. How would you use the activity series while studying the displacement of hydrogen from acids by metal?
Answer: Activity series is an ordered arrangement of metals and hydrogen (nonmetal) with respect to their activities.
The reactivity of a metal decreases top to bottom in the activity series.
For example : Metals that are placed above hydrogen in the activity series can displace hydrogen from dilute hydrochloric acid and sulphuric acid.
Metals that are placed below hydrogen in the activity series cannot displace hydrogen from acids.
2 NA + 2HCl ------------------> 2NaCl + H2
Cu + HCl ------------------> No reaction
2. Describe an activity to show that the lead of pencil is good conductors of electricity but sulpher doesnot.
Following activity shows that the lead of a pencil conducts electricity and sulphur does not.
Take a pencil and sharpen both its ends. Connect the ends of the pencil to an electric circuit, formed by connecting a bulb to the cell. The bulb glows when pencil is connected to it. This shows that the lead of a pencil conducts electricity. This occurs because lead contains graphite, which is a good conductor of electricity.
Now, replace the pencil with a piece of sulphur. The bulb will stop glowing. This shows that sulphur does not conduct electricity.
D. Complete sentence:
1. Graphite and iodine are lustrous nonmetals.
2. All metals are good conductors of heat and electricity.
3. The socalled lead (black part) of a pencil is made of clay and graphite.
4. Though a metal, mercury is a liquid at ordinary temperatures.
5. Argon is used for filling electrical bulbs.
6. Liquid nitrogen is used to preserve donated organs.
E.Choose the correct options
1. (d) bromine
Bromine is a nonmetal that is liquid at ordinary temperatures.
2. (d) All of these
All the given options are solid nonme
3. Answer :
Silver is the best conductor of electricity.
4. (d) all of these All the mentioned metals are placed above copper in the reactivity series and can replace copper from a solution of copper (II) sulphate
5. (d) neon Neon is used in advertisement signs.
F. Match the coloumn
Substance Property 1 Property 2
1. Neon A. Metal p. Ductile
B, s B. Nonmetal q. Malleable
2. Graphite C. Solid r. Kills germs
B, C, u D. Liquid s.Nonreactive
3. Iodine t. Cuts glass
B, C, r u. Conducts electricity
A, C, p, q, u
B, C, t
A, D, s
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