SCIENCE CLASS- 7
CHAPTER-4 (The World of Metals and Non-metals)
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1. Which metal is commonly used to make food packaging materials as it is cheaper, and its thin sheets can be folded easily into any shape?
Answer: (i) Aluminium
Aluminium is malleable, lightweight, inexpensive, and can be beaten into very thin sheets. Therefore, it is commonly used for food packaging.
2. Which of the following metal catches fire when it comes in contact with water?
Answer: (iv) Sodium
Sodium is a highly reactive metal. It reacts vigorously with water, producing heat and sometimes catching fire.
3. State with reason(s) whether the following statements are True (T) or False (F).
(i) Aluminium and copper are examples of non-metals used for making utensils and statues.
Answer: False (F)
Aluminium and copper are metals, not non-metals. They are used for making utensils and statues because they are strong, malleable, and durable.
(ii) Metals form oxides when combined with oxygen, the solution of which turns blue litmus paper to red.
Answer: False (F)
Metal oxides are generally basic in nature. They turn red litmus paper blue, not blue litmus paper red.
(iii) Oxygen is a non-metal essential for respiration.
Answer: True (T)
Oxygen is a non-metal and is necessary for breathing and survival of living organisms.
(iv) Copper vessels are used for boiling water because they are good conductors of electricity.
Answer: False (F)
Copper vessels are used because copper is a good conductor of heat, not because it conducts electricity.
4. Why are only a few metals suitable for making jewellery?
Answer:
Only a few metals such as gold, silver, and platinum are suitable for making jewellery because they are lustrous, malleable, ductile, and resistant to corrosion. These properties allow them to be shaped into beautiful ornaments while retaining their shine for a long time.
5. Match the uses of metals and non-metals given in Column I with Column II.
Answer:
(i) Used in electrical wiring → (c) COPPER
(ii) Most malleable and ductile → (e) GOLD
(iii) Living organisms cannot survive without it → (a) OXYGEN
(iv) Plants grow healthy when fertilisers containing it are added to the soil → (d) NITROGEN
(v) Used in water purification → (b) CHLORINE
6. What happens when oxygen reacts with magnesium and sulfur? What are the main differences in the nature of products formed?
Answer:
When magnesium reacts with oxygen, it burns with a dazzling white flame and forms magnesium oxide. Magnesium oxide is basic in nature.
When sulfur reacts with oxygen, it forms sulfur dioxide. When sulfur dioxide dissolves in water, it forms sulfurous acid, which is acidic in nature.
Thus, the main difference is that metal oxides are basic whereas non-metal oxides are acidic.
7. Complete the following flow chart.
Answer:
Magnesium + Air + Heat → Ash
Ash + Water → Magnesium oxide solution
Add blue and red litmus solutions separately
Change in blue litmus solution → No change
Change in red litmus solution → Turns blue
This shows that magnesium oxide solution is basic in nature.
8. You are provided with the following materials. Discuss which material would be your choice to make a pan that is most suitable for boiling water and why.
Materials: Iron, copper, sulfur, coal, plastic, wood, cardboard
Answer:
Copper would be the best choice for making a pan because it is a very good conductor of heat. It transfers heat quickly and uniformly, making boiling more efficient.
Iron can also be used, but copper conducts heat better. Sulfur, coal, plastic, wood, and cardboard are unsuitable because they are poor conductors of heat and may burn or get damaged.
9. You are provided with three iron nails, each dipped in oil, water, and vinegar. Which iron nail will not rust, and why?
Answer:
The iron nail dipped in oil will not rust.
Rusting requires both air and water. The oil forms a protective layer around the iron nail and prevents contact with air and moisture. Therefore, rusting does not occur.
10. How do the different properties of metals and non-metals determine their uses in everyday life?
Answer:
Metals are used in making utensils, machinery, electrical wires, vehicles, tools, and jewellery because they are strong, lustrous, malleable, ductile, and good conductors of heat and electricity. Copper and aluminium are used in electrical wiring, while iron is used in construction and tools.
Non-metals are equally important. Oxygen is essential for respiration, nitrogen is used in fertilisers, chlorine is used in water purification, and iodine is used as an antiseptic. Thus, the properties of metals and non-metals determine their specific applications in daily life.
11. One of the methods of protecting iron from getting rusted is to put a thin coating of zinc metal over it. Since sulfur does not react with water, can it be used for this purpose? Justify your answer.
Answer:
No, sulfur cannot be used for this purpose.
Zinc forms a strong protective metallic coating on iron and prevents contact with air and water. Sulfur is a non-metal, brittle in nature, and cannot form a durable protective layer over iron. Therefore, sulfur is not suitable for preventing rusting.
12. An ironsmith heats iron before making tools. Why is heating necessary in this process?
Answer:
Heating makes iron softer and easier to shape. When iron is heated, it becomes more malleable and can be hammered into the desired shape without breaking. This allows the ironsmith to make tools such as axes, spades, and tongs efficiently.