4. The World of Metals and Non-metals
Complete solutions to Let Us Enhance Our Learning. CBSE / NCERT Class 7 Science (Curiosity).
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Let Us Enhance Our Learning
Answer: (i) Aluminium
Answer: (iv) Sodium
Sodium reacts vigorously with water and air. That is why it is stored in kerosene.
(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. Their solution turns red litmus blue.
(iii) Oxygen is a non-metal essential for respiration. — True
Oxygen is a non-metal. We cannot survive without breathing it.
(iv) Copper vessels are used for boiling water because they are good conductors of electricity. — False
Copper vessels are used because copper is a good conductor of heat.
Metals like gold, silver and platinum are used for making jewellery because:
- they are shiny (lustrous) and keep their shine for a long time,
- they do not corrode or rust easily in air and moisture,
- they are highly malleable and ductile, so they can be shaped into fine designs,
- they are rare and costly.
Most other metals lose their shine or corrode. So they are not suitable for jewellery.
| Column I | Column II (unscrambled) |
|---|---|
| (i) Used in electrical wiring | (c) PEPORC → Copper |
| (ii) Most malleable and ductile | (e) OGDL → Gold |
| (iii) Living organisms cannot survive without it | (a) ENXYGO → Oxygen |
| (iv) Plants grow healthy when fertilisers containing it are added to the soil | (d) TENGOINR → Nitrogen |
| (v) Used in water purification | (b) NECOHIRL → Chlorine |
Magnesium: It burns with a dazzling white flame and forms a white powder called magnesium oxide. Its solution turns red litmus blue. So it is basic.
Sulfur: It burns to form sulfur dioxide gas. When dissolved in water, it forms sulfurous acid, which turns blue litmus red. So it is acidic.
Difference: Oxides of metals (like magnesium) are basic, while oxides of non-metals (like sulfur) are acidic.
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My choice is copper.
- Copper is a very good conductor of heat. So water boils quickly.
- It is malleable, so it can be shaped into a pan.
- It does not rust like iron.
Sulfur, coal, plastic, wood and cardboard are poor conductors of heat. Some of them may also burn or melt. So they are not suitable.
The nail dipped in oil will not rust.
Rusting needs both air (oxygen) and moisture. Oil forms a layer on the nail. This layer prevents air and moisture from reaching the iron.
The uses of a material depend on its properties.
- Metals are good conductors of heat. So cooking utensils and pans are made of metals.
- Copper and aluminium are good conductors of electricity and are ductile. So electric wires are made of them.
- Aluminium is malleable. So it is used to make foils for packing food.
- Gold and silver are lustrous. So they are used for jewellery.
- Metals are sonorous. So school bells are made of metals.
- Non-metals are poor conductors. So handles of pans and coverings of wires are made of non-metallic materials.
- Oxygen is needed for breathing. Nitrogen is used in fertilisers.
- Chlorine is used for water purification. Iodine solution is used as an antiseptic on wounds.
No, sulfur cannot be used.
- Sulfur is a non-metal. It is brittle and not malleable. So it cannot form a thin, smooth and strong coating on iron.
- It breaks easily and the layer would crack, letting air and moisture reach the iron.
Heating makes iron soft. Soft iron can be easily beaten and bent into different shapes. So the ironsmith heats iron to give it the shape of a tool.
Exploratory Projects
Exploratory Projects are hands-on tasks. Do them with your classmates under the guidance of your teacher, and write your own observations.