TNPSC 6th Standard - General Science Notes
TNPSC Notes for Group 4 Exam
Cement
• Cement is a mixture of limestone, clay and gypsum in definite proportion.
• This mixture is heated, cooled and powdered to get the chemical substance called cement.
• This greyish powdery cement is packed in airtight bags and sold.
• Cement is an important chemical substance used in the construction of buildings.
Joseph Aspidin (1824)
• In 1824 Joseph Aspidin, a mason in England synthesised cement. As this cement resembled the limestone found in Portland, he named the cement as Portland cement.
Setting of Cement
• When water is added to cement, it sets to a hard substance within a few hours. This is known as setting of cement.
Uses of cement
• Cement is used in different forms like mortar, concrete and reinforced cement concrete.
Mortar
• Mortar is obtained in the form of thick paste by mixing cement, sand and water. This paste is used in flooring, constructing and plastering the walls of the houses.
Concrete
• Concrete is a mixture of cement, sand, gravel and water.
• It is used in the construction of buildings, bridges,dams or reservoirs.
Reinforced Cement Concrete(RCC)
• When concrete is filled in and around a steel wire netting or skeleton of iron rods and allowed to set we get reinforced cement concrete.
• This RCC is very strong and durable. This type of concrete is used in the construction of dams, bridges, pillars and roofs of the buildings.
• It is also used in making pipes, constructing water tanks, and laying sewage and drainage canals.
Plastics
• Plastic is also a type of chemical substance.
Types of plastics are known as
Thermo Plastics
1. PET (Polyethylene terephthalate): Polythene bags, PET bottles,
2. PVC (Polyvinyl chloride): Pipes, buckets, mugs, combs, toys etc. are made of thermo plastics.
Thermo Setting Plastics
• An object made of thermo setting plastics cannot be softened or melted by heating.
• Example: Bakelite and melamine.
Bakelite
• Bakelite is a non conductor of heat and electricity. It is used to make electrical insulators,
Melamine
• Melamine is a non-inflammable substance. Moreover, it can withstand very high temperature. Therefore, it is used to make floor tiles, cookwares, fireproof clothes etc.
Plastics and environment
• When Plastics/Polythene bags are burnt, they emit toxic gases. These gases mix in air and cause respiratory problems.
• As plastics pollute land, air and water, we must avoid the usage of plastics. Instead of plastics we can use things made of cloth, jute, coir and areca-plate which are bio-degradable.
Glass
• Glass is made of chemical substances like silica (sand), calcium carbonate(limestone) and sodium carbonate.
Annealing
• The above mixture is melted into a viscous liquid by heating it to a very high temperature.
• This liquid is poured into a suitable mould and cooled to get glass objects of desired shape.
• When molten glass is cooled rapidly it becomes brittle. When the molten glass is cooled very slowly, it will not allow light to pass through.
• Therefore glass should not be cooled either very slowly or rapidly. It should be cooled gradually. This method of cooling is called annealing.
Uses of Glass
• Glass finds a wide range of application in the manufacture of window panes, automobile windows, electric bulbs, medical instruments, laboratory apparatus like standard flasks, test tubes, beakers, measuring jars etc.
Fibres
• Fibres are drawn together and twisted to get thread. Clothes are woven using the thread.
• Fibres are classified into two types based on their source.
o Natural fibres
o Synthetic fibres
Natural fibres
• Fibres which are obtained from plants and animals are known as natural fibres.
Jute
• Jute is obtained from the stem of the jute plant. It is used to make bags, curtains, carpets, etc.
Cotton
• Cotton is obtained from cotton plant. Cotton fibres are twisted to get threads which are used to make cotton cloth.
• Cotton fibre consists a chemical substance called “cellulose”.
Coir
• The fibres on the coconut shell are removed and processed to get coir. Coir is used to make ropes, carpets and other household articles.
• We get silk from the silkworms and wool from the fur of sheep.
Synthetic fibers
• The fibres which are synthesized from chemical substances using scientific technology are called synthetic fibres. Polyester, nylon, rayon are some of the examples of synthetic fibres.
• These fibres are not only used in making clothes but also used in making fishing nets, ropes and parachutes. They are also used widely in various industries.
Chemical substances are not only used to prepare the things that we have seen in this lesson but also used in the preparation, preservation, enriching taste and colouring of every substance that we use.
Thus in our daily life chemical substances are used in food, clothing, shelter, transportation, medicine, entertainment and in industries. Since they have become part of our life.
Model Questions & Answers
Choose the correct answer
1. Identify the one which is not a natural fibre.
(a) silk (b) wool (c) polyester (d) jute.
Answer: (c) polyester
2. Which kind of clothes do you prefer in summer?
(a) nylon (b) wool (c) silk (d) cotton
Answer: (d) cotton
3. The clothes, which are made from the fur of the animals
(a) woollen (b) cotton (c) silk (d) nylon
Answer: (a) woollen
4. Which of the following is widely used in the manufacture of medical instruments?
(a) polyester (b) plastics (c) glass (d) cotton
Answer: (c) glass
5. The important chemical substance used in the preparation of soap is _____________________?
(a) sodiumhydroxide (b) sodium amalgam (c) sodiumsilicate (d) sodiumbicarbonate
Answer: (a) sodiumhydroxide
Fill in the blanks
1. The basic raw materials used in the manufacture of cement are _________________, _________________ and _________________?
Answer: Limestone, Clay and Gypsum
2. The expansion of P.V.C.is __________________?
Answer: PVC (Polyvinyl chloride)
3. __________________ is used to make fireproof clothes.
Answer: Synthetic Fibers
4. The process of slow and steady cooling of glass is called __________________?
• An object made of thermo setting plastics cannot be softened or melted by heating.
• Example: Bakelite and melamine.
Bakelite
• Bakelite is a non conductor of heat and electricity. It is used to make electrical insulators,
Melamine
• Melamine is a non-inflammable substance. Moreover, it can withstand very high temperature. Therefore, it is used to make floor tiles, cookwares, fireproof clothes etc.
Plastics and environment
• When Plastics/Polythene bags are burnt, they emit toxic gases. These gases mix in air and cause respiratory problems.
• As plastics pollute land, air and water, we must avoid the usage of plastics. Instead of plastics we can use things made of cloth, jute, coir and areca-plate which are bio-degradable.
Glass
• Glass is made of chemical substances like silica (sand), calcium carbonate(limestone) and sodium carbonate.
Annealing
• The above mixture is melted into a viscous liquid by heating it to a very high temperature.
• This liquid is poured into a suitable mould and cooled to get glass objects of desired shape.
• When molten glass is cooled rapidly it becomes brittle. When the molten glass is cooled very slowly, it will not allow light to pass through.
• Therefore glass should not be cooled either very slowly or rapidly. It should be cooled gradually. This method of cooling is called annealing.
Uses of Glass
• Glass finds a wide range of application in the manufacture of window panes, automobile windows, electric bulbs, medical instruments, laboratory apparatus like standard flasks, test tubes, beakers, measuring jars etc.
Fibres
• Fibres are drawn together and twisted to get thread. Clothes are woven using the thread.
• Fibres are classified into two types based on their source.
o Natural fibres
o Synthetic fibres
Natural fibres
• Fibres which are obtained from plants and animals are known as natural fibres.
Jute
• Jute is obtained from the stem of the jute plant. It is used to make bags, curtains, carpets, etc.
Cotton
• Cotton is obtained from cotton plant. Cotton fibres are twisted to get threads which are used to make cotton cloth.
• Cotton fibre consists a chemical substance called “cellulose”.
Coir
• The fibres on the coconut shell are removed and processed to get coir. Coir is used to make ropes, carpets and other household articles.
• We get silk from the silkworms and wool from the fur of sheep.
Synthetic fibers
• The fibres which are synthesized from chemical substances using scientific technology are called synthetic fibres. Polyester, nylon, rayon are some of the examples of synthetic fibres.
• These fibres are not only used in making clothes but also used in making fishing nets, ropes and parachutes. They are also used widely in various industries.
Chemical substances are not only used to prepare the things that we have seen in this lesson but also used in the preparation, preservation, enriching taste and colouring of every substance that we use.
Thus in our daily life chemical substances are used in food, clothing, shelter, transportation, medicine, entertainment and in industries. Since they have become part of our life.
Model Questions & Answers
Choose the correct answer
1. Identify the one which is not a natural fibre.
(a) silk (b) wool (c) polyester (d) jute.
Answer: (c) polyester
2. Which kind of clothes do you prefer in summer?
(a) nylon (b) wool (c) silk (d) cotton
Answer: (d) cotton
3. The clothes, which are made from the fur of the animals
(a) woollen (b) cotton (c) silk (d) nylon
Answer: (a) woollen
4. Which of the following is widely used in the manufacture of medical instruments?
(a) polyester (b) plastics (c) glass (d) cotton
Answer: (c) glass
5. The important chemical substance used in the preparation of soap is _____________________?
(a) sodiumhydroxide (b) sodium amalgam (c) sodiumsilicate (d) sodiumbicarbonate
Answer: (a) sodiumhydroxide
Fill in the blanks
1. The basic raw materials used in the manufacture of cement are _________________, _________________ and _________________?
Answer: Limestone, Clay and Gypsum
2. The expansion of P.V.C.is __________________?
Answer: PVC (Polyvinyl chloride)
3. __________________ is used to make fireproof clothes.
Answer: Synthetic Fibers
4. The process of slow and steady cooling of glass is called __________________?
Answer: Annealing
5. The fibre obtained from the stem of the plant is ______________?
Answer: Natural Fibers
5. The fibre obtained from the stem of the plant is ______________?
Answer: Natural Fibers
6. The chemical substance present in the cotton fibre is _______________:
Answer: Cellulose
7. The expansion of P.E.T. is __________________?
PET (Polyethylene terephthalate)
Answer: Match the following (Matched)
1. Glass - Silica
2. Switch - Bakelite
3. Tiles - Melamine
4. Cement - Gypsum
5. Nylon - Synthetic fiber
Answer: Cellulose
7. The expansion of P.E.T. is __________________?
PET (Polyethylene terephthalate)
Answer: Match the following (Matched)
1. Glass - Silica
2. Switch - Bakelite
3. Tiles - Melamine
4. Cement - Gypsum
5. Nylon - Synthetic fiber