Page 148 - Let us Enhance our Learning
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1. Define the following.
A) malleability: The property by which materials can be beaten into thin sheets is called malleability.
B) ductility: The property of materials by which they can be drawn into wires is called ductility.
C) sonority: The property of metals that enables them to produce a ringing sound when struck or dropped is called sonority.
D) corrosion: The gradual deterioration of metal surfaces caused by air, water, or other substances is known as corrosion.
E) rusting: The process of formation of a brown deposit (rust / hydrated iron oxide) on objects made of iron when exposed to moist air is called rusting. -
2. If a substance can be drawn into wires and conducts electricity, which of the following properties does that substance show?
Answer: D: both ductility and conductance of electricity
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3. Which of the following metal catches fire when it comes in contact with water?
Answer: D) Sodium (Sodium reacts vigorously with oxygen and water, generating a lot of heat).
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4. Why are only a few metals suitable for making jewellery?
Only a few metals—such as gold and silver—are suitable for making jewellery because they possess high metallic lustre, exceptional malleability and ductility (allowing them to be shaped into intricate designs and fine wires), and high resistance to corrosion and tarnishing compared to common metals like iron.
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5. What happens when oxygen reacts with magnesium and sulphur? What are the main differences in the nature of products formed?
When magnesium (a metal) burns in oxygen, it forms magnesium oxide, which dissolves in water to form a basic solution (turns red litmus blue). When sulphur (a non-metal) burns in oxygen, it forms sulphur dioxide, which dissolves in water to form sulphurous acid, an acidic solution (turns blue litmus red). Thus, metal oxides are basic in nature, whereas non-metal oxides are acidic in nature.
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6. An ironsmith heats iron before making tools. Why is heating necessary in this process?
Heating iron makes it soft and malleable, allowing the ironsmith to beat and shape it easily into desired tools like axes, spades, and flat pans without breaking.
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7. Students made statements about magnesium oxide solution:
Amar: It is basic. Turns red litmus blue.
Nandu: It is acidic. Turns blue litmus red.
Whose statement/s is/are correct.
Answer: A) Only Amar
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8. 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: A) Aluminium (due to its high malleability used for aluminium foils).
Page 150 - Let us Enhance our Learning (Continued)
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9. Match the uses of metals and non-metals given in Column I with the jumbled names of metals and non-metals given in Column II.
A Ans B (i) Used in electrical wiring ( c ) (a) ENXYGO (ii) Most malleable and ductile ( e ) (b) NECOHIRL (iii) Living organisms cannot survive without it. ( a ) (c) PEPORC (iv) Plants grow healthy when fertilisers containing it are added to the soil. ( d ) (d) TENGOINR (v) Used in water purification ( b ) (e) OGDL -
10. The apparatus shown contains an iron nail suspended inside a closed bottle. Silica gel is placed at the bottom of the bottle. The setup is kept undisturbed for 10 days. What will be observed after 10 days?
Answer: C) The iron nail does not rust because moisture is absent (Silica gel makes the air dry, and both water/moisture and air are required for rusting).
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11. You are provided with three iron nails, each dipped in oil, water and vinegar. Which iron nail will not rust, and why?
The iron nail dipped in oil will not rust. Oil forms a protective layer over the nail that cuts off direct contact with air and moisture (oxygen and water), both of which are essential for rusting.
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12. Complete the following flow chart:
* First box (?) [Left side before Air + Heat]: Magnesium
* Second box (?) [Below Water]: Magnesium hydroxide solution
* Third box (?) [Bottom under Change in blue litmus solution]: No change
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13. How do the different properties of metals and non-metals determine their uses in everyday life?
The unique physical and chemical properties of metals and non-metals dictate their practical applications. For example, the malleability and ductility of metals allow them to be shaped into sheets, utensils, and wires, while their thermal and electrical conductivity make them ideal for cooking vessels and electrical wiring. Conversely, non-metals like oxygen are essential for respiration, nitrogen for plant growth, and chlorine/iodine for purification and antisepsis.
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14. State with reason(s) whether the following statements are True [T] or False [F].
Statement Ans (i) Aluminium and copper are examples of non-metals used for making utensils and statues. False (Aluminium and copper are metals, not non-metals) (ii) Metals form oxides when combined with oxygen, the solution of which turns blue litmus paper to red. False (Metal oxides are basic and turn red litmus paper to blue) (iii) Oxygen is a non-metal essential for respiration. True (iv) Copper vessels are used for boiling water because they are good conductors of electricity. False (Copper vessels are used because they are good conductors of heat) -
15. 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 provided: Iron, copper, sulphur, coal, plastic, wood, cardboard.Copper (or iron) would be the most suitable choice to make a pan for boiling water because metals are good conductors of heat, allowing heat from the stove to transfer quickly and efficiently to the water. Non-metals and insulators (like sulphur, coal, plastic, wood, and cardboard) are poor conductors of heat and would either burn or fail to heat the water properly. -
16. One of the methods of protecting iron from rust is to put a thin coating of zinc metal over it. Since sulphur does not react with water, can it be used for this purpose? Justify Your answer.
No, sulphur cannot be used to coat iron for protection against rusting. Sulphur is a non-metal that is brittle, non-malleable, and non-ductile, meaning it cannot form a tough, continuous protective metallic layer like zinc (galvanisation). Furthermore, it does not possess the structural strength or adhesive properties required to shield iron from moist air.
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