The World of Metals and Non-metalsClass 7 Science NCERT Solutions
10 Solutions
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Q1Let Us Enhance Our Learning
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
Solution
The correct answer is (i) Aluminium. Aluminium is used for food packaging because it is cheaper, malleable, and can be easily folded into any shape.
Q2Let Us Enhance Our Learning
Which of the following metal catches fire when it comes in contact with water?
(i)
Copper
(ii)
Aluminium
(iii)
Zinc
(iv)
Sodium
Solution
The correct answer is (iv) Sodium. Sodium reacts vigorously with water, generating heat and catching fire.
Q3Let Us Enhance Our Learning
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. [ ]
Solution
(i)
False [F]. Aluminium and copper are metals.
(ii)
False [F]. Metal oxides are generally basic in nature, so their solutions turn red litmus paper blue.
(iii)
True [T]. Oxygen is a non-metal required for respiration.
(iv)
True [T]. Copper is a good conductor of heat, making it suitable for boiling water in vessels.
Q4Let Us Enhance Our Learning
Why are only a few metals suitable for making jewellery?
Solution
Only a few metals are suitable for making jewellery because of their properties such as lustre, malleability, ductility, resistance to corrosion, and rarity. Metals like gold, silver, and platinum possess these desirable properties, making them ideal for jewellery making. Their lustrous appearance and ability to be shaped into intricate designs contribute to their use in ornaments.
Q5Let Us Enhance Our Learning
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)
NECOHIRL
(iii)
Living organisms cannot survive without it.
(c)
PEPORC
(iv)
Plants grow healthy when fertilisers
(d)
TENGOINR containing it are added to the soil.
(v)
Used in water purification (e) O G D L
Solution
(i)
Used in electrical wiring - (c) PEPORC (COPPER)
(ii)
Most malleable and ductile - (e) O G D L (GOLD)
(iii)
Living organisms cannot survive without it - (a) E N X Y G O (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)
Q6Let Us Enhance Our Learning
What happens when oxygen reacts with magnesium and sulfur. What are the main differences in the nature of products formed?
Solution
When oxygen reacts with magnesium, magnesium oxide is formed:
. Magnesium oxide is basic in nature. It turns red litmus paper blue.
When oxygen reacts with sulfur, sulfur dioxide is formed:
. When sulfur dioxide is dissolved in water, sulfurous acid is formed, which is acidic in nature. It turns blue litmus paper red.
The main difference is that magnesium oxide is a basic oxide, while sulfur dioxide forms an acidic solution when dissolved in water.
Q7Let Us Enhance Our Learning
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?
Solution
A pan made of copper would be most suitable for boiling water. Copper is a good conductor of heat, which means it transfers heat quickly and efficiently. This allows the water to heat up faster and boil more quickly. Iron is also a good conductor of heat, but copper is generally better. Sulfur, coal, plastic, wood, and cardboard are poor conductors of heat and are not suitable for making a pan for boiling water.
Q8Let Us Enhance Our Learning
You are provided with three iron nails, each dipped in oil, water and vinegar. Which iron nail will not rust, and why?
Solution
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, preventing it from coming into contact with both air and water. The nail in water will rust because it is exposed to both air and water. The nail in vinegar will rust more quickly because vinegar is acidic and accelerates the rusting process.
Q9Let Us Enhance Our Learning
How do the different properties of metals and non-metals determine their uses in everyday life?
Solution
The different properties of metals and non-metals determine their uses in everyday life. Metals are strong, malleable, ductile, and good conductors of heat and electricity. These properties make them suitable for making utensils, wires, machinery, and structural components. Non-metals, on the other hand, have properties like being poor conductors of heat and electricity. Some non-metals like oxygen are essential for respiration, while others like nitrogen are used in fertilizers. Chlorine is used for water purification. The specific properties of each element make them suitable for different applications.
Q10Let Us Enhance Our Learning
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.
Solution
No, sulfur cannot be used to protect iron from rusting, even though it does not react with water. The primary reason a coating of zinc (galvanization) protects iron is that zinc corrodes preferentially. Zinc reacts with air and moisture to form a protective layer of zinc oxide and zinc carbonate. This layer prevents the iron underneath from coming into contact with air and water, thus preventing rust. Additionally, zinc is more electrochemically active than iron. If the zinc coating is scratched, the zinc will still corrode in preference to the iron, providing continued protection. Sulfur does not form a protective layer like zinc, and it is not more electrochemically active than iron. Therefore, it cannot provide the same level of protection against rusting.