Basic Science Solutions for Class 8 Science Chapter 5 Synthetic Materials are provided here with simple step-by-step explanations. These solutions for Synthetic Materials are extremely popular among Class 8 students for Science Synthetic Materials Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Basic Science Book of Class 8 Science Chapter 5 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Basic Science Solutions. All Basic Science Solutions for class Class 8 Science are prepared by experts and are 100% accurate.

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Question A.1:

Answer:

A polymer is made up of small units called monomers that combine under specific conditions. Example: Cotton, jute, silk and wool.

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Question A.2:

A polymer is made up of small units called monomers that combine under specific conditions. Example: Cotton, jute, silk and wool.

Answer:

The process of formation of a polymer from its monomer is called polymerisation.

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Question A.3:

The process of formation of a polymer from its monomer is called polymerisation.

Answer:

Viscose, cuprammonium and acetate rayon are three widely-used rayons.

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Question A.4:

Viscose, cuprammonium and acetate rayon are three widely-used rayons.

Answer:

Other than making clothes, synthetic fibres are used in making towels, mats, curtains, cushions, furniture covers and mosquito nets.

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Question A.5:

Other than making clothes, synthetic fibres are used in making towels, mats, curtains, cushions, furniture covers and mosquito nets.

Answer:

Those synthetic materials that can be moulded into a permanent shape are called plastics.

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Question A.6:

Those synthetic materials that can be moulded into a permanent shape are called plastics.

Answer:

Poly (styrene-butadiene) is used for making bubblegums.
Polystyrene is used for making thermocol.
Synthetic erasers are made from vinyl rubber, neoprene and poly (styrene-butadiene).

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Question A.7:

Poly (styrene-butadiene) is used for making bubblegums.
Polystyrene is used for making thermocol.
Synthetic erasers are made from vinyl rubber, neoprene and poly (styrene-butadiene).

Answer:

Polythene, polyvinyl chloride (PVC) and bakelite are three polymers that can be obtained by using chemicals derived from natural gas.

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Question A.8:

Polythene, polyvinyl chloride (PVC) and bakelite are three polymers that can be obtained by using chemicals derived from natural gas.

Answer:

The force or stress that is required to break a material is called its tensile strength.

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Question A.9:

The force or stress that is required to break a material is called its tensile strength.

Answer:

(a) Materials that attract water are called hydrophilic.
(b) Materials that repel water are called hydrophobic.

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Question B.1:

(a) Materials that attract water are called hydrophilic.
(b) Materials that repel water are called hydrophobic.

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.

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Question B.2:

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.

Answer:

Thermoplastics are those plastics that can retain their plasticity even after repeated heatings and coolings. They can be moulded again and again.
Thermosetting plastics are those plastics that cannot be moulded again after they are set into a particular shape.

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Question B.3:

Thermoplastics are those plastics that can retain their plasticity even after repeated heatings and coolings. They can be moulded again and again.
Thermosetting plastics are those plastics that cannot be moulded again after they are set into a particular shape.

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).

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Question C.1:

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).

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 (butadiene-styrene), naphthalene is used for making polyester and propylene is used for making polypropylene.



Page No 56:

Question C.2:

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 (butadiene-styrene), naphthalene is used for making polyester and propylene is used for making polypropylene.

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.

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Question C.3:

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.

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.

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Question D:

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.

Answer:

1. Acrylic fibres compete with wool.
2. Polythene carrybags block drains and sewers.
3. Plastics are generally non-degradable, 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.

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Question E.1:

1. Acrylic fibres compete with wool.
2. Polythene carrybags block drains and sewers.
3. Plastics are generally non-degradable, 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.

Answer:

(c) Cellulose

Cellulose is a natural polymer.

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Question E.2:

(c) Cellulose

Cellulose is a natural polymer.

Answer:

(a) polyester

Polyester is a synthetic polymer that can be stretched several times of its original length.

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Question E.3:

(a) polyester

Polyester is a synthetic polymer that can be stretched several times of its original length.

Answer:

(d) polyester

Polyester is a synthetic fibre and it is hydrophobic.

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Question E.4:

(d) polyester

Polyester is a synthetic fibre and it is hydrophobic.

Answer:

(c) polythene

Polythene is a bad conductor of heat because it is a synthetic polymer.

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Question E.5:

(c) polythene

Polythene is a bad conductor of heat because it is a synthetic polymer.

Answer:

(a) plastic

Plastic is a bad conductor of electricity because it is a synthetic polymer.

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Question F:

(a) plastic

Plastic is a bad conductor of electricity because it is a synthetic polymer.

Answer:

A B
(a) Cellulose (v) Glucose
(b) Nylon (iv) Parachutes
(c) Acrylics (i) Artificial wool
(d) Acetate rayon (ii) Semi-synthetic fibre
(e) Polythene (iii) Carrybags



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