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?
- Aluminium
- Copper
- Iron
- Gold
Answer
Aluminium
Reason — Aluminium is cheaper than copper and gold, and it is highly malleable. Therefore, its thin sheets can be easily folded into different shapes and are commonly used for wrapping and packaging food items.
Which of the following metal catches fire when it comes in contact with water?
- Copper
- Aluminium
- Zinc
- Sodium
Answer
Sodium
Reason — Sodium reacts vigorously with water and generates a large amount of heat, which may cause it to catch fire. Therefore, sodium is stored in kerosene to prevent its contact with air and moisture.
State with reason(s) whether the following statements are True [T] or False [F].
- Aluminium and copper are examples of non-metals used for making utensils and statues. [ ]
- Metals form oxides when combined with oxygen, the solution of which turns blue litmus paper to red. [ ]
- Oxygen is a non-metal essential for respiration. [ ]
- Copper vessels are used for boiling water because they are good conductors of electricity. [ ]
Answer
(i) False [F]
Corrected statement — Aluminium and copper are metals, not non-metals. They are lustrous, hard, malleable, and good conductors, and are used for making utensils and statues.
(ii) False [F]
Corrected statement — Metals form oxides which are basic in nature. The solution of a metal oxide turns red litmus paper blue, not blue litmus paper red.
(iii) True [T]
(iv) False [F]
Corrected statement — Copper vessels are used for boiling water because copper is a good conductor of heat, not because it is a good conductor of electricity.
Why are only a few metals suitable for making jewellery?
Answer
Only a few metals like gold and silver are suitable for making jewellery because they are highly malleable and ductile, so they can be easily beaten into thin sheets and drawn into wires to create fine designs. They are also lustrous and do not corrode easily, so they retain their shine for a long time.
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) E N X Y G O |
| (ii) Most malleable and ductile | (b) N E C O H I R L |
| (iii) Living organisms cannot survive without it. | (c) P E P O R C |
| (iv) Plants grow healthy when fertilisers containing it are added to the soil. | (d) T E N G O I N R |
| (v) Used in water purification | (e) O G D L |
Answer
| Column I | Column II |
|---|---|
| (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 |
What happens when oxygen reacts with magnesium and sulfur. What are the main differences in the nature of products formed?
Answer
When magnesium burns in oxygen, it burns with a dazzling white flame and forms a white powder called magnesium oxide. When sulfur burns in oxygen, it forms sulfur dioxide gas.
The main difference is in the nature of the products formed:
| Reaction | Product | Nature of product |
|---|---|---|
| Magnesium + Oxygen | Magnesium oxide | Basic (turns red litmus blue) |
| Sulfur + Oxygen | Sulfur dioxide | Acidic (turns blue litmus red on dissolving in water) |
Magnesium is a metal, so its oxide is basic in nature, while sulfur is a non-metal, so its oxide is acidic in nature.
Complete the following flow chart:
Answer
The completed flow chart is as follows:
Magnesium + Air + Heat ⟶ Ash (magnesium oxide)
On adding water to magnesium oxide, a basic solution is obtained.
On adding blue and red litmus solutions separately:
- Change in blue litmus solution → No change; it remains blue.
- Change in red litmus solution → It turns blue.
This shows that the solution formed is basic in nature.
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?
Iron, copper, sulfur, coal, plastic, wood, cardboard
Answer
Copper would be the most suitable material for making a pan for boiling water.
Copper is a good conductor of heat, so it transfers heat efficiently to the water. It is also strong and can be shaped into a pan. Sulfur, coal, plastic, wood, and cardboard are unsuitable because they are poor conductors of heat or may get damaged on heating. Iron is also a metal and conducts heat, but it can rust in the presence of air and moisture. Hence, copper is the better choice.
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 forms a protective layer around the nail and prevents it from coming in contact with air and moisture. Both air and water are necessary for rusting to occur.
How do the different properties of metals and non-metals determine their uses in everyday life?
Answer
The properties of metals and non-metals determine their uses in everyday life:
- Metals are good conductors of heat, so they are used to make cooking vessels.
- Metals are good conductors of electricity, so they are used in electrical wiring.
- Metals are malleable and ductile, so they can be made into sheets, wires, and jewellery.
- Metals are sonorous, so they are used to make bells and musical instruments.
- Non-metals like oxygen are essential for respiration, nitrogen is used in fertilisers, chlorine is used in water purification, and iodine is used as an antiseptic.
Thus, a material is chosen for a particular use according to its properties.
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.
Sulfur is a brittle non-metal and cannot form a strong, continuous, and durable protective coating over iron. Therefore, it cannot protect the iron surface from contact with air and moisture as effectively as a coating of zinc.
An ironsmith heats iron before making tools. Why is heating necessary in this process?
Answer
An ironsmith heats iron because hot iron becomes easier to hammer and shape. Due to its malleability, the heated iron can be beaten into the required shape to make tools such as axes, spades, and tongs.