The Class 8 is an important year in a student’s life and Maharashtra State Board Science is one of the subjects that require dedication, hard work, and practice. It’s a subject where you can score well if you are well-versed with the concepts, remember the important formulas and solving methods, and have done an ample amount of practice. Worry not! Home Revise is here to make your Class 8 journey even easier. It’s essential for students to have the right study material and notes to prepare for their board examinations, and through Home Revise, you can cover all the fundamental topics in the subject and the complete Maharashtra State Board Class 8 Science Book syllabus.
Q1. Try to find it.
a. Plastic shows ……property, hence it can be moulded to any shape.
b. Motor cars are coated with …….
c. Thermocol melts at ……ºC.
d. ……glass dissolves in water.
Answer a: Plastic shows malleable property, hence it can be moulded to any shape.
Answer b: Motor cars are coated with Teflon.
Answer c: Thermocol melts at 240 ºC.
Answer d: Water glass dissolves in water.
Q2. Who is my partner?
| ‘A’ column | ‘B’ column |
| Lead glass | Plates |
| Bakelite | Mattresses |
| Thermocol | Electric bulb |
| Optic glass | Electric switch |
| Polypropylene | Lens |
Answer:
| ‘A’ column | ‘B’ column |
| Lead glass | Electric bulb |
| Bakelite | Plates |
| Thermocol | Electric switch |
| Optic glass | Lens |
| Polypropylene | Mattresses |
Q3. Answer the following.
a. Thermocol is produced from which material?
b. Write uses of PVC.
c. Write the natural or manmade raw material of the following items.
Mattress, glass vessel, bangle, chair, gunny bag, broom, knife, pen.
d. Which are the main ingredients of glass?
e. How is plastic produced?
Answer a: Thermocol is a form of a complex material called polystyrene. It transforms into a liquid state on heating at more than 100 ºC temperature and returns to solid state on cooling. Due to this, we can give any desired shape to it. Being a good shock-absorber, it is used in packing of delicate items.
Answer b : Polyvinyl chloride (PVC) is a plastic polymer made of monomer vinyl chloride. PVC are used for manufacturing toys, combs, plates, bowls etc.
Answer c:
| Items | Natural raw material | Man made raw material |
| Mattress | Plastic | |
| Beaker | Silica Glass | |
| Bangles | Glass | |
| Chair | PVC | |
| Gunny Bags | Jute | |
| Broom | Broomcorn | |
| Knife | Steel, Metal | Plastic |
| Pen | Metal | Plastic |
Answer d : Glass is the non-crystalline, hard but brittle solid material formed from mixture of silica and silicate. Silica i.e. SiO2 to which we refer to as sand. Depending upon the proportion of silica and other components in the glass; there are different types of glass as soda-lime glass,
boro-silicate glass, silica glass, alkali silicate glass, etc.
Answer e: A man made material showing the property of plasticity and made up of organic polymers is plastic. Structure of all the plastics is not the same. Some are linear while some are circular.
Q4. Distinguish between.
a. Manmade material and natural material
b.Thermoplastic and thermosetting plastic.
Answer a:
| Differences between Natural and Manmade material | |
| Natural Material | Manmade Material |
| Comes from nature | Man made material |
| Natural colour | Color as per requirement is added in colour bath |
| During spinning process spinneret is not necessary | During spinning process spinneret is necessary for the production of filament |
| Chances of containing dust or impurities | No chance of any dust or impurities |
| Less durable than synthetic | More durable than natural |
Answer b:
| Differences Between Thermoplastic and Thermosetting Plastic | |
| Thermoplastic | Thermosetting Plastic |
| Thermoplastic can be synthesized by the process called addition polymerization. | Thermosetting plastics are synthesized by condensation polymerization. |
| Thermoplastic is processed by injection moulding, extrusion process, blow moulding, thermoforming process and rotational moulding. | Thermosetting Plastic is processed by compression moulding, reaction injection moulding. |
| Thermoplastics have secondary bonds between molecular chains. | Thermosetting plastics have primary bonds between molecular chains and held together by strong cross-links. |
| Thermoplastics have low melting points and low tensile strength. | Thermosetting plastics have high melting points and tensile strength. |
| Thermoplastic is lower in molecular weight, compared to thermosetting plastic. | Thermosetting Plastic is high in molecular weight. |
5. Answer the following in your own words.
a. Explain the effect and remedial plans of following materials on environment and human health.
1. Plastic
2. Glass.
3. Thermocol.
b. Which measures will you arrange to minimize the environmental problems arising due to non-degradable plastic?
Answer a: The effects of the following materials on environment and human health are:
1) Plastic –It is non-biodegradable and a man made material which causes a lot of land pollution. Due to its non-biodegradable characteristics it remains in the soil and water for a very long time, thus causing pollution. The smoke released after burning of plastic is also harmful for human health.
2) Glass –While glass production, mixture needs to be heated up to 1500 ºC. During this, greenhouse gases like sulphur dioxide, nitrogen dioxide, carbon dioxide are released through burning of fuel. As the glass is non-degradable, if pieces of the waste glass material flow into water body, it may affect that ecosystem. Similarly, drainage may be blocked due to these pieces.
3) Thermocol –Being carcinogenic ingredients in styrene, the person in contact with thermocol for long duration may have the possibility of blood cancer like leukemia and lymphoma. It takes a long duration for natural degradation of thermocol; hence many people opt for destroying it by burning. However, it is still more hazardous method as it releases poisonous gases in atmosphere. In mass gatherings, plates and cups used to offer the food, water, tea are made up of thermocol. It affects their health. If the food kept in thermocol is reheated, styrene may dissolve in that food. Due to this, there is possibility of health problems.
Answer b:
Q6. Write short notes.
a. Glass production.
b. Optic glass
c. Uses of plastic.
Answer a: For glass production, mixture of sand, soda, lime, and small quantity of magnesium oxide is heated in furnace. Sand i.e. silicon dioxide melts at 1700 0C. So as to melt the mixture at low temperature, pieces of discarded glass are added to it. Due to this, mixture melts at 850 ºC. Once all the ingredients of mixture are liquified, it is heated up to 1500 ºC and immediately cooled. Due to sudden cooling, mixture becomes homogeneous, amorphous and transparent instead of crystalline. This is called Soda-lime glass.
Answer b: Optical glass is produced from the mixture of sand, soda, limestone, barium oxide and boron. This type of pure glass is useful in production of spectacles, lenses, microscopic lenses, etc.
Answer c: Following are the uses of plastics
Q7. Write the properties of glass?
Answer: The properties of glass are as follows
Q8. Explain properties of plastics.
Answer: The properties of glass are:
Q9. Define degradable and non-degradable material?
Answer: Some materials are naturally degraded, they are called degradable materials while some materials are not naturally degraded they are called non-degradable material.
Q10. How many types can plastics be classified into?
Answer: Depending upon the effect of heat, plastic can be classified into two types. The plastic that can be molded as per our wish is called thermoplastic. Eg. Polythene, PVC are used for manufacturing the toys, combs, plates, bowls etc. Another plastic is such that once a specific shape is given with the help of mold, its shape cannot be changed on heating. It is called thermosetting plastic. eg. Electric switches, coverings over the handles of cookers, etc.
Q11. Explain the uses of thermoplastic and thermosetting plastic?
Answer: The uses of thermoplastic and thermosetting plastic:
| Thermoplastic | |
| Polyvinyl chloride (PVC) | Bottles, raincoat, pipes, handbags, shoes, electric cable insulation, furniture, ropes, toys, etc. |
| Polystyrene (PS) | Thermo-insulating parts of electric appliances like refrigerators, gears of machines, toys, protective coverings like covers of CD and DVD, etc. |
| Polyethylene (PE) | Milk bags, packing bags, flexible garden pipes, etc. |
| Polypropylene (PP) | Parts of loudspeakers &vehicles, ropes, mattresses, laboratory appliances, etc. |
| Thermosetting plastic | |
| Bakelite | Cabinets of radio, T.V., telephones, electric switches, toys, coverings over handles of cookers, etc. |
| Melamine | Domestically useful items like cup – saucers, plates, trey, some spare parts of airplane engines, electric and sound insulating coverings, etc. |
| Polyurethane | Surfing boards, small boats, furniture, seats in vehicles, etc. |
| Polyester | Fiberglass, toners of laser printers, textile industry, etc. |
Q12. Explain the types of glass and uses.
Answer: The types and uses of glass are as follows:
Silica glass : This is produced by using the silica. Items made up of silica glass show minimum expansion on heating. It is not affected by acid and alkali. Due to this, silica glass is used to produce laboratory glass-wares.
Borosilicate glass : Borosilicate glass is produced by melting the mixture of sand, soda, boric acid and aluminium oxide. This glass does not show any effect on medicines. Hence, the bottles made up of borosilicate glass are used in pharmaceutical industry to store the medicines.
Alkali silicate glass : Alkali silicate glass is produced by heating the mixture of sand and soda. As this glass is soluble in water, it is called a ‘water glass ’.
Lead glass is produced by melting the mixture of sand, soda, limestone and lead
oxide. Being very clear / transparent, it is used in manufacturing light bulbs, tubes, etc.
Optical glass : Optical glass is produced from the mixture of sand, soda, limestone, barium oxide and boron. This type of pure glass is useful in production of spectacles, lenses, microscopic lenses, etc.
Coloured glass : Soda lime glass is colorless. So as to impart a desired colour, oxide of specific metal is mixed during manufacturing process. eg. Ferrous oxide is mixed to get bluish green glass and copper oxide to get red glass.
Processed glass : So as to improve the quality and utility, some processing is performed on glass and various types like reinforced glass, plain glass, fiberglass, fen glass, translucent glass, etc. are produced.
Q13. Explain the harmful effects of plastic for the environment?
Answer: The harmful effects of plastic for the environment are as follows:
Q14. How can we manage plastic waste management?
Answer: There are primarily three ways of managing plastics:
Reduce
This refers to the reduction or decreased consumptions of plastic artifacts.
Reuse
Recycle
Q15. Explain the advantages of plastic.
Answer: The following properties of plastic make it the material of choice for making many articles:
Plastics are non-reactive: Most of the metals get corroded by air and water. But plastics do not react with air or water. So, they cannot be corroded easily. Therefore, it is used for making many utensils and storing various chemicals.
Plastics are light, strong and durable: The articles made up of plastics are very light. Plastic being light, strong and durable can be molded into many shapes and sizes as required by the user. They are cheaper than metals and hence, widely used in making various household products.
Plastic is a poor conductor: They are poor conductors of heat and electricity and therefore plastics are used for coating electric wires and switches. The handles of frying pans are also made up of plastic due to this property.
Q16. What is glass?
Answer: Glass is the non-crystalline, hard but brittle solid material formed from mixture of silica and silicate. Silica i.e. SiO2 to which we refer to as sand. Depending upon the proportion of silica and other components in the glass; there are different types of glass such as soda-lime glass, boro-silicate glass, silica glass, alkali silicate glass, etc.
Q17. Write the effect on persons working in thermocol factories?
Answer: Persons staying in contact with thermocol for long term may develop the problems of eyes, respiratory system, skin, digestive system, etc. Pregnant women may face miscarriage. Liquid styrene may cause skin-burns.
Q18. Which material is wrapped around the items of glass or similar material during transport to prevent from breaking up?
Answer: Bubble wrap is used around the items of glass or similar material during transport to prevent from breaking up. Glass or other similar material are fragile in nature. Bubble wrap has
got air bubbles, which prevent the glass ware from shock that might lead to breakage.
Q19. Which type of glass is used in vehicles to avoid injuries in accidents?
Answer: Glass used in making car is called safety glass. The glass used in the windshield is laminated glass. These are all special types of glasses which are used for making cars so that they don’t break easily, and when they break they don’t cause much injury.
Q20. What is a plastic?
Answer: A man made material showing the property of plasticity and made up of organic polymers is plastic. Structure of all the plastics is not the same. Some are linear while some are circular.