Chapter 7 – Metals and Nonmetals
1. Complete the table
| Use in everyday life | Property of metal |
|---|---|
i. Ductility | |
ii. Malleability | |
iii. Conduction of heat | |
iv. Conduction of electricity | |
v. Sonority |
Ans:
| Use in everyday life | Property of metal |
|---|---|
i. Ductility | Electrical wires of copper and aluminium |
ii. Malleability | Gold and silver ornaments, aluminium foil |
iii. Conduction of heat | Copper coating on the bottom of stainless steel utensils |
iv. Conduction of electricity | Electrical wires of copper and aluminium |
v. Sonority | School bells |
2. Identify the odd terma. Gold,
a. Silver, iron, diamond
Ans: Diamond
Reason: Diamond (an allotrope of carbon) is nonmetal while others are metals.
b. Ductility, brittelness, sonority, malleability
Ans: Brittleness
Reason: Brittleness is the property of nonmetal while others are the properties of metals.
c. Carbon, bromine, sulphur, phosphorus
Ans: Bromine
Reason: Bromine is a liquid while others are solids at room temperature.
d. Brass, bronze, iron, steel
Ans: Iron
Reason: Iron is a metal while others are alloys.
3. Write scientific reasons.
a. The stainless steel vessels in kitchen have copper coating on the bottom.
Ans:
(i) Copper is a good conductor of heat.
(ii) It readily transfers heat to food inside the vessel.
(iii) Copper is very expensive, and therefore, copper utensils are expensive.
(iv) Hence, instead of copper vessels, stainless steel vessels with a copper coating on the bottom are used in the kitchen.
b. Copper and brass vessels are cleaned with lemon.
Ans:
(i) A green coloured deposit of copper carbonate is formed on copper and brass (an alloy of copper and zinc) vessels due to corrosion.
(ii) The green deposit of copper carbonate is basic in nature.
(iii) The acidic ingredient (citric acid) present in lemon reacts with the basic deposit of copper carbonate formed on copper and brass vessels.
(iv) This helps to remove the copper carbonate layer from the vessels.
(v) Hence, copper and brass vessels are cleaned with lemon.
c. Sodium metal is kept in kerosene.
Ans:
(i) Sodium is a very reactive metal.
(ii) It readily reacts with moisture present in the air and catches fire.
(iii) Hence, to prevent its contact with moisture, sodium is kept under kerosene.
4. Answer the following.
a. What is done to prevent corrosion of metals?
Ans:
(i) Corrosion can be prevented by applying layers of oil, grease, varnish, and paint on metal surfaces so that contact with air and moisture is prevented.
(ii) Corrosion can also be prevented by plating metals with another noncorroding metal. This isolates the metals from direct contact with air and moisture and thus prevents corrosion.
(iii) The corrosion of iron can be prevented by coating it with zinc.
b. What are the metals that make the alloys brass and bronze?
Ans:
(i) Brass: It is made from copper and zinc.
(ii) Bronze: It is made from copper and tin.
c. What are the adverse effects of corrosion?
Ans:
(i) It causes contamination of water and other products due to mechanical damage to underground water pipes.
(ii) It causes a loss of efficiency in machines due to damage to metallic equipment.
(iii) It causes accidents due to mechanical collapse of buildings, bridges, ships, cars, machinery, etc.
(iv) Cooking vessels made of copper and brass get a greenish coating due to corrosion. This greenish coating on a copper or brass vessel is poisonous. If food is kept in such a vessel, it gets spoiled.
d. What are uses of Noble metals?
Ans:
(i) Gold, silver, and platinum are used in making ornaments.
(ii) Silver is used in medicines as it has antibacterial properties.
(iii) Gold and silver are also used to make medals.
(iv) Gold and silver can be used to make some electronic devices.
(v) Platinum and palladium are used as catalysts.
5. Three experiments to study the process of rusting are given below. Observe the three test tubes and answer the following questions.
a. Why the nail in the test tube 2 is not rusted?
Ans:
(i) The rusting of iron occurs in the presence of air and moisture.
(ii) In test tube 2, the oil layer over the boiled water prevents the contact of the nail with air.
(iii) Thus, the nail is in contact with moisture (water) but not with air.
(iv) Hence, the nail in test tube 2 is not rusted.
b. Why is the nail in the test tube 1 is rusted highly?
Ans: In test tube 1, the nail is in contact with both air and water. Hence, the nail in test tube 1 is highly rusted.
c. Would the nail in the test tube 3 get rusted?
Ans:
(i) The test tube 3 contains dry air, but it does not contain moisture.
(ii) Further, calcium chloride in test tube 3 would absorb traces of moisture if present.
(iii) Thus, the nail is in contact with air but not with moisture. Hence, the nail in test tube 3 would not get rusted.