Metals and Non-metals – Maharashtra Board Class 8 Solutions for General Science (English Medium)
MathematicsGeneral ScienceMaharashtra Board Solutions
Solution 1.a:
Silver can be drawn into a wire because it is a metal having the property of ductility, whereas a pencil point is made of graphite, a non-metal, which is brittle and non-ductile. Therefore, a long pencil point breaks easily.
Solution 1.b:
Copper is a good conductor of electricity. It possesses the property of ductility. Hence, copper is used for electrical wiring in our houses.
Solution 1.c:
When a copper vessel is not used for a longer period of time, a coating of greenish black copper oxide is formed on its surface. When the vessel is rubbed with tamarind, tartaric acid in tamarind helps to remove the greenish black copper oxide. Hence, a copper vessel shines again after scrubbing.
Solution 1.d:
Characteristics of alloys:
- Alloys contain metals in specific proportions.
- In an alloy, the physical properties of the element change but the chemical properties of the element remain the same.
Solution 1.e:
When a metal is kept exposed to moist air, the gases present in the air react with the metal surface to form a layer of metal oxides, sulphates or nitrates on its surface. This action which wears the metal is known as corrosion.
Solution 2.a:
Gold and silver are used in coins because they are malleable, i.e. they can be beaten into thin sheets and can be given a desired shape.
Solution 2.b:
24-carat gold is considered gold of 100% purity. Pure gold is very soft, and ornaments made of pure gold break or bend easily. Therefore, ornaments are generally not made of 24-carat gold.
Solution 2.c:
Ships are made of iron. Because of the salty seawater, the metal sheets of ships rust and corrode. Paints contain metals such as zinc and magnesium. This prevents the metal surface of the ship in coming in direct contact with the salty seawater. Therefore, ships are painted at frequent intervals.
Solution 2.d:
Gold and platinum are called noble elements because they are not affected by air, water, acids, heat and do not take part in chemical reactions.
Solution 2.e:
Stainless steel has more lustre than iron because it is an alloy which does not rust and remains cleaner.
Solution 3:
| ‘A’ | ‘B’ |
| a. Mercury | 5. Thermometer |
| b. Graphite | 3. The ‘lead’ in a pencil |
| c. Sulphur | 4. Medicines |
| d. Steel | 2. Alloy of iron and carbon |
| e. Stainless steel | 1. Alloy of iron, carbon, nickel, chromium |
Solution 4:
- Gold of 100% purity is 24-carat gold.
- Bronze contains the metals copper and tin.
- The hydrogen gas is released when metals react chemically with acids.
- Oxides of metals have basic (or alkaline) properties.
- The non-metal sulphur is used in gun powder.