Class 8 Science Textbook Solution

Materials: Metals and Non-Metals – Class 8 Science Texrbook Solution

 Class 8 Science Chapter 4 Materials: Metals and Non-Metals
 
1. Which of the following can be beaten into thin sheets:
(a) Zinc
(b) Phosphorus
(c) Sulphur
(d) Oxygen
Answer:
(a) Zinc
 
2. Which of the following statement is correct?
(a) All metals are ductile.
(b) All non-metals are ductile.
(c) Generally, metals are ductile.
(d) Some non-metals are ductile.
Answer:
(d) Generally, metals are ductile.
 
3. Fill in the blanks:
1.    Phosphorus is a very _______ non-metal.
2.    Metals are _______ conductors of heat and __________
3.    Iron is _______ reactive than copper.
4.    Metals react with acid to produce __________ gas.
Answer:

1.    reactive
2.    good, electricity
3.    more
4.    hydrogen
 
4. Mark ‘T’ if the statement is true and ‘F’ if it is false.
1.    Generally, non-metals react with acids.
2.    Sodium is a very reactive metal.
3.    Copper displaces zinc from zinc sulphate solution.
4.    Carbon can be drawn into wires.
Answer:

1.    False
2.    True
3.    False
4.    False
 
5. Some properties are listed in the following table. Distinguish between metals and non-metals on the basis of these properties:
Properties    Metals    Non-metals

 
6. Give reasons for the following:
1.    Aluminium foils are used to wrap food items.
2.    Immersion rods for heating liquids are made up of metallic substances.
3.    Copper cannot displace zinc from its salt solution.
4.    Sodium and potassium are stored in kerosene.
Answer:

1. Aluminium is non-toxic and malleable and hence thin sheets of aluminium can be formed.
2. Metallic substances are good conductors of electricity therefore immersion rods are made up of metallic substances.
3. Copper is less reactive than zinc and hence it cannot displace zinc from its salt solution.
4. Sodium and potassium are stored in kerosene because it vigorously reacts with oxygen and water.
5. Can you store the lemon pickle in an aluminium utensil? Explain.
Answer: No, we can not store the lemon pickle in an aluminium utensil because aluminium is metal and thus will react with lemon and produce toxic substances.
7. Match the substance given in Column A with uses given in Column B.
Answer:

 
8. What happens when:
(i) Dilute sulphuric acid is poured on a copper plate.
(ii) Iron nails are placed in a copper sulphate solution. Write word equations of the reactions involved.
Answer:

(i) Copper reacts with sulphuric acid and forms copper sulphate and hydrogen (gas).
Copper + Sulphuric acid → Copper sulphate + Hydrogen gas.
Cu + H2SO4 → CuSO4 + H2 ↑
 (ii) Iron displaces copper from copper sulphate solution hence a reddish-brown copper is formed on the iron nails and the blue colour of copper sulphate solution slowly becomes light green.
Iron + Copper sulphate → Copper + Iron sulphate.
Fe + CuSO4 → Cu + FeSO4
 
9. Saloni took a piece of burning charcoal and collected the gas evolved in a test tube:
(i) How will she find the nature of the gas?
(ii) Write down word equations of all the reactions taking place in this process.
Answer:

(i) To find the nature of the gas, she will dissolve it in the water and test it with litmus paper.
(ii) (a) Charcoal (c) + Oxygen (O2) → Carbon dioxide (CO2)
(b) Carbon dioxide (CO2) + Water (H2O) → Carbonic acid (H2CO3)
The nature of this gas is acidic because it turns red litmus blue.
 
10. One day Reeta went to a jeweler’s shop with her mother. Her mother gave old gold jewellery to the goldsmith to polish. The next day when they brought the jewellery back they found that there was a loss in its weight. Can you suggest a reason for the loss of weight?
Answer:
The jeweller must have cleared the jewellery in aqua regia solution. This solution is a mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3 : 1. This acid solution dissolves some gold in it, due to which there is a loss in the weight of jewellery.

Metals and Non-Metals question and Answers
 
1. Give examples of metals.
Answer:
Examples of metals are gold, silver, sodium tungsten, cadmium, nickel, uranium, and mercury.
 
2. Give examples of non-metals?
Answer:
Examples of non-metals are chlorine, helium, oxygen, carbon, fluorine, sulphur, iodine, and bromine.
 
3. Name the metal which is liquid at room temperature.
Answer:
Mercury
 
4. Write the physical properties of metals.
Answer:
The physical properties of metals are:
•    Metals are solid at room temperature except for mercury.
•    Metals generally have high melting points.
•    The surface of most metals has a shiny appearance.
•    Metals are malleable, i.e., they can be beaten into sheets.
•    Metals are ductile, i.e., they can be stretched into wires.
•    Metals are good conductors of electricity.
•    Metals are good conductors of heat.
•    Metals are sonorous, i.e., they produce sound when they are struck by themselves or by any other object.
 
5.
(i) What do you observe when magnesium ribbon is heated over a flame?
(ii) What change do you observe in the colour of red and blue litmus papers when they are dipped into solution obtained by mixing solid residue from (i) in water? What do you conclude?
(iii) Write chemical equations for the above two reactions.
Answer:

(i) When magnesium ribbon is heated over the flame then it burns with brilliant light and gets converted into a white solid residue.
(ii) The solution obtained by mixing white solid residue produced above with water turns red litmus into blue colour and blue litmus remains unaffected. This shows that the solution is alkaline hence oxide formed is basic in nature.
(iii) 2Mg + O2 → 2MgO
MgO + H2O → Mg(OH)2
 
6. What happens when a small piece of sodium metal is dried and kept in water?
Answer:
When a small piece of sodium metal is dried and kept in the water we observe that the sodium piece starts moving in water with a hissing sound and sodium catches fire.
2Na + 2H2O → 2NaOH + H2 ↑
 
7. Does magnesium react with cold water? What happens when the water is heated?
Answer:
Magnesium does not react or mildly react with cold water. When water is heated then magnesium reacts with hot water or steam vigorously and produces magnesium hydroxide and hydrogen.
Mg + 2H2O → Mg(OH)2 + H2
(Magnesium) + Water → Magnesium Hydroxide + Hydrogen
 
8. How do metals react with dilute acids?
Answer:
Metals usually displace hydrogen from dilute acids and salt is formed. Only the less reactive metals like copper, silver, and gold do not displace hydrogen from dilute acids.
Metal + Hydrochloric acid → Metal chloride + Hydrogen (gas)
Metal + Sulphuric acid → Metal sulphate + Hydrogen (gas)
 
9. Write the word equation for the reaction of magnesium with dil. hydrochloric acid.
Answer:
Magnesium reacts with dil. hydrochloric acid to form magnesium chloride and hydrogen gas is evolved.
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
 
10. What happens when iron nails are added to copper sulphate solution?
Answer:
When iron nails are added to copper sulphate solution the blue colour of copper sulphate starts fading and iron sulphate is formed. Iron displaces copper from copper sulphate and copper gets deposited on the iron nails.
Fe + CuSO4 → FeSO4 + Cu
 
11. What happens when strips of magnesium are added to iron sulphate solution?
Answer:
When strips of magnesium are added to iron sulphate solution then magnesium displaces iron from iron sulphate solution and forms magnesium sulphate. Iron gets deposited on the magnesium strips.
Mg + FeSO4 → MgSO4 + Fe
 
12. What would you observe when a strip of zinc is dipped in the solution of copper sulphate?
Answer:
When a strip of zinc is dipped in the solution of copper sulphate solution then zinc displaces copper from copper sulphate solution. A red-brown coating of copper forms on the strips of zinc.
 
13. Write the uses of metals.
Answer:
The metals are used for:
•    making machines
•    making buildings
•    making automobiles, aeroplanes, trains, satellites, industrial gadgets
•    making cooking utensils and water boilers
•    making electric gadgets
•    making electric cables
•    fine electric contacts in computers and solar cells
•    for making jewellery, mirrors
•    making foils for wrapping of food items, medicines, chocolates, cigarettes, etc.
 
14. Why is iron used for making machines, automobiles, and buildings?
Answer:
Iron is very strong, hard, and rigid therefore, it is used for making machines, automobiles, and buildings.

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