Science and Technology Class 9 Important Questions Chapter 14 Maharashtra Board

Substances in Common Use

Short Questions

1. What is table salt’s chemical name?

• Table salt’s chemical name is sodium chloride (NaCl).

2. What is the pH value of a neutral salt like NaCl?

• The pH value of a neutral salt like NaCl is 7.

3. What gas is released when sodium chloride is electrolysed in brine?

• Chlorine gas is released at the anode during electrolysis.

4. What is baking soda’s chemical name?

• Baking soda’s chemical name is sodium bicarbonate (NaHCO3).

5. What is one use of baking soda in cooking?

• Baking soda is used to make cakes and bread porous.

6. What is the chemical name of bleaching powder?

• Bleaching powder’s chemical name is calcium oxychloride (CaOCl2).

7. What does bleaching powder release when it reacts with carbon dioxide?

• It releases chlorine gas.

8. What is washing soda’s chemical formula?

• Washing soda’s chemical formula is Na2CO3·H2O.

9. How does washing soda help with hard water?

• Washing soda softens hard water by forming insoluble salts with calcium and magnesium.

10. What is one use of washing soda?

• Washing soda is used for washing clothes.

11. What is water of crystallization?

• It is the water molecules present in the crystalline structure of salts.

12. Name one salt with water of crystallization.

• Potash alum (K2SO4·Al2(SO4)3·24H2O) has water of crystallization.

13. What is radioactivity?

• Radioactivity is the property of some elements to emit high-energy radiation spontaneously.

14. Name one type of radiation emitted by radioactive substances.

• Alpha radiation is one type emitted by radioactive substances.

15. What are alpha rays attracted to in an electric field?

• Alpha rays are attracted to the negatively charged plate.

16. What is one use of radioactive isotopes in medicine?

• Radioactive isotopes like iodine-123 are used to treat hyperthyroidism.

17. What is a harmful effect of artificial food colours?

• Artificial food colours can cause ADHD in children.

18. What is a dye?

• A dye is a coloured substance used to impart colour to articles like cloth.

19. What is Teflon’s chemical name?

• Teflon’s chemical name is polytetrafluoroethene (C2F4)n.

20. What is one property of Teflon?

• Teflon is resistant to water and oil, making it non-stick.

Long Questions

1. How is sodium chloride (table salt) useful in daily life?

• Sodium chloride, or table salt, is used to add a salty taste to food and preserve it by preventing bacterial growth. It is also used in industries to produce other salts like baking soda and washing soda.

2. Why is baking soda used in cooking and for health purposes?

• Baking soda (NaHCO3) is added to cake batter to make it porous by releasing carbon dioxide gas when heated. It is also used to reduce stomach acidity because of its basic nature.

3. How does bleaching powder help in disinfecting water?

• Bleaching powder (CaOCl2) releases chlorine gas when it reacts with water, which kills harmful microbes. This makes it useful for disinfecting drinking water and swimming pools.

4. What happens when washing soda is added to hard water?

• Washing soda (Na2CO3) reacts with calcium and magnesium salts in hard water to form insoluble compounds that settle down. This softens the water, making it suitable for washing clothes.

5. What are some salts that contain water of crystallization, and what are their uses?

• Salts like potash alum (used in water purification) and borax (used in cleaning) contain water of crystallization. These water molecules are part of their crystal structure and help in their specific functions.

6. What are the three types of radiation emitted by radioactive substances?

• Radioactive substances emit alpha, beta, and gamma rays, which were discovered by scientists like Rutherford. Alpha rays deviate slightly, beta rays deviate more, and gamma rays do not deviate in an electric field.

7. How are radioactive isotopes used in agriculture?

• Radioactive isotopes like cobalt-60 are used to preserve food by killing bacteria and preventing sprouting in onions and potatoes. They also help modify genes in seeds to improve crop growth.

8. What are the harmful effects of artificial food colours on health?

• Artificial food colours in jams and sauces can contain lead and mercury, which harm the body if consumed regularly. They may also cause disorders like ADHD in children due to overconsumption.

9. Why is Teflon coating used in kitchenware and other items?

• Teflon coating is used in kitchenware because it prevents food from sticking and is resistant to high temperatures. It is also used in electronics and vehicle parts due to its poor conductivity and durability.

10. What is the process of powder coating, and why is it used?

• Powder coating involves spraying a charged powder on a metal surface, which is then heated to form a hard layer. It is used to prevent rusting on iron objects and make them durable and attractive.