NCERT Solutions for Class 7 Curiosity Chapter 4 The World of Metals and Non-metals
Page 43
Question 1.
Can you give some examples of metal sheets?
Answer:
Some examples of metal sheets are silver foil and aluminium foil.
Page 46
Question 2.
Can you name some metals that are used for making cooking vessels?
Answer:
Metals like aluminium, copper, and stainless steel are commonly used for making cooking vessels.
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Question 3.
Have you ever seen an electrician using a screwdriver? What type of material is used for making its handle?
Answer:
Yes. The handle of a screwdriver is usually made of plastic or rubber.
Exercise
Question 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?
(i) Aluminium
(ii) Copper
(iii) Iron
(iv) Gold
Answer
(i) Aluminium
Question 2.
Which of the following metal catches fire when it comes in contact with water?
(i) Copper
(ii) Aluminium
(iii) Zinc
(iv) Sodium
(v) Sodium
Question 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.
(ii) Metals form oxides when combined with oxygen, the solution of which turns blue litmus paper to red.
(iii) Oxygen is a non-metal essential for respiration.
(iv) Copper vessels are used for boiling water because they are good conductors of electricity.
Answer:
- [F], Aluminium and copper are examples of metals, not non-metals.
- [F], Metal oxides are basic, they turn red litmus paper to blue.
- [T], Oxygen is a non-metal and is essential for respiration.
- [F], Copper vessels are used for boiling water because copper is a good conductor of heat.
Question 4.
Why are only a few metals suitable for making jewellery?
Answer:
Only a few metals are suitable for making jewellery because they are lustrous. These metals are also soft, which allows them to be easily shaped into various designs. Also, they do not react easily with air or water, so they do not rust or lose their shine over time.
Question 5.
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.
| Column I | Column II |
| (i) Used in electrical wiring | (a) ENXYGO |
| (ii) Most malleable and ductile | (b) NECOHIRL |
| (iii) Living Organisms cannot survive without it. | (c) PEPORC |
| (iv) Plants grow healthy when fertilisers containing it are added to the soil. | (d) TENGOINR |
| (v) Used in water purification | (e) OGDL |
Answer:
| Column I | Column II |
| (i) Used in electrical wiring | (c) PEPORC |
| (ii) Most malleable and ductile | (e) OGDL |
| (iii) Living Organisms cannot survive without it. | (a) ENXYGO |
| (iv) Plants grow healthy when fertilisers containing it are added to the soil. | (d) TENGOINR |
| (v) Used in water purification | (b) NECOHIRL |
Question 6.
What happens when oxygen reacts with magnesium and sulphur. What are the main differences in the nature of products formed?
Answer:
When oxygen reacts with magnesium, it forms magnesium oxide, which is a basic oxide and turns red litmus paper to blue. However, when oxygen reacts with sulphur, it forms sulphur dioxide, which is an acidic oxide and turns blue litmus paper to red.
Question 7.
Complete the following flowchart:
Answer:
Question 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?
Answer:
For boiling water, the pan must be made of a material that is a good conductor of heat. Among the given materials, only iron and copper are metals and both are good conductors of heat. However, copper is the best choice because it is highly resistant to rust compared to iron. Therefore, a pan made of copper is the most suitable choice for boiling water.
Question 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 because the oil prevents the iron nail from coming into contact with air or moisture. It forms a protective layer on the metal, which prevents rusting.
Question 10.
How do the different properties of metals and non-metals determine their uses in everyday life?
Answer:
Metals and non-metals have various properties that make them useful in our everyday life.
- Metals:
- Metals are malleable, for example, aluminium foil is used for wrapping food.
- Metals are ductile, wires made of copper or aluminium are used in electrical fittings.
- Metals are sonorous, they produce a ringing sound.
- Metals are good conductors of heat, so they are used in making cooking vessels.
- Metals are good conductors of electricity, making them ideal for electrical wires.
- Non-metals:
- Generally non-metals are poor conductor of heat and electricity; for example, sulphur and carbon are used in insulating materials to prevent the transfer of heat or electricity.
- Non-metals are brittle: for example, sulphur and phosphoros are often used in matchsticks as they break easily or react quickly.
- Non-metals are gaseous at room temperature: for example, oxygen is essential for breathing.
- Non-metals are non-lustrous: carbon (as graphite) are used in pencils and dry cell batteries.
Question 11.
One of the methods of protecting iron from getting rusted 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.
Answer:
No, sulphur cannot be used to protect iron from rusting. While sulphur does not react with water, it does not have the property of forming a protective layer over iron like zinc. It cannot prevent air and moisture from coming into contact with the iron.
Question 12.
An ironsmith heats iron before making tools Why is heating necessary in this process?
Answer:
For making tools, a ironsmith first heats a piece of iron until it becomes red-hot. This is because heating makes the iron soft, more malleable and easier to bend, hammer and mould into the desired shape for tools.
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