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NCERT Class 8 Science Chapter 4 Materials: Metals and Non-Metals
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Materials: Metals and Non-Metals
Chapter: 4
NCERT TEXT BOOK EXERCISES
Q. 1. Which of the following can be beaten into thin sheets?
(a) Zinc.
(b) Phosphorus.
(d) Oxygen.
(c) Sulphur.
Ans. (a) Zinc.
Q. 2. Which of the following statements is correct?
(a) All metals are ductile.
Ans. ×.
(b) All non-metals are ductile.
Ans. ×.
(c) Generally, metals are ductile.
Ans. ✓.
(d) Some non-metals are ductile.
Ans. ×.
Q. 3. Fill in the blanks:
(a) Phosphorus is very __________ non-metal.
Ans. Reactive.
(b) Metals are __________ conductor of heat and __________.
Ans. good, electricity .
(c) Iron _________ reactive than copper.
Ans. less.
(d) Metals react with acids to produce _________ gas.
Ans. hydrogen.
Q. 4. Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) Generally, non-metals react with acids.
Ans. F.
(b) Sodium is a very reactive metal.
Ans. T.
(c) Copper displaces zinc from zinc suphate solution.
Ans. F.
(d) Carbon can be drawn into wires.
Ans. F.
Q. 5. Some properties are listed in the following table. Distinguish between metals and nonmetals on the basis of their properties.
| Properties | Metals | Non-metals |
| 1. Appearance | ||
| 2. Hardness | ||
| 3. Malleability | ||
| 4. Ductility | ||
| 5. Heat Conduction | ||
| 6. Conduction of Electricity |
Ans.
| Properties | Metals | Non-metals |
| 1. Appearance | lustrous | non – lustrous |
| 2. Hardness | hard except sodium and potassium | generally soft except diamond |
| 3. Malleability | generally malleable | non-malleable |
| 4. Ductility | generally ductile | non-ductile |
| 5. Heat Conduction | good conductors | poor conductors |
| 6. Conduction of Electicity | good conductors | poor conductors |
Q. 6. Give reasons for the following:
(a) Aluminium foils are used to wrap food items.
Ans. Aluminium foils are used to wrap food items because aluminium can be beaten in sheets to form these thin wrapping sheets and it is soft and it does not react with food items.
(b) Immersion rods for heating liquids are made up of metallic substances.
Ans. Immersoin rods are made up of metallic substances because metals are good conductors of heat and electricity. They get hot very soon on passage of current and warm the water.
(c) Copper cannot displace zinc from its salt solution.
Ans. Copper cannot displace zinc from its salt solution because copper is less reactive than zinc. A less reactive metal cannot displace a more reactive metal from its solution.
(d) Sodium and potassium are stored in kerosene.
Ans. Sodium and Postassium are stored in kerosene because they are very reactive and quickly react in air.
Q. 7. Can you store acidic lemon pickles in an aluminium utensils? Explain.
Ans. No, we cannot store acidic lemon pickles in aluminium utensils because aluminium is metal. Metals readily react with acids to produce hydrogen gas. So, when the aluminium metal comes in contact with acidic lemon pickles, it would react to release hydrogen, which would spoil the food and render it unfit to consume.
Q. 8. In the following table some subs-tances are given in Column I. In Column II some uses are given. Match the items in Column I with those in Column II.
| Column I | Column II |
| (i) Gold | (a) Thermometers |
| (ii) Iron | (b) Electric wire |
| (iii) Aluminium | (c) Wrapping food |
| (iv) Carbon | (d) Jewellery |
| (v) Copper | (e) Machinery |
| (vi) Mercury | (f) Fuel |
Ans.
| Column I | Column II |
| (i) Gold | (d) Jewellery |
| (ii) Iron | (e) Machinery |
| (iii) Aluminium | (c) Wrapping food |
| (iv) Carbon | (f) Fuel |
| (v) Copper | (b) Electric wire |
| (vi) Mercury | (a) Thermometers |
Q. 9. What happens when:
(i) Dilute sulphuric acid is poured on a copper plate?
Ans. When sulphuric aicd is poured on copper plate the acid present in sulphuric acid reacts with copper to form copper sulphate and hydrogen. The copper plate gets eroded from place.
Sulphuric acid + Copper → Copper sulphate + Hydrogen
(ii) Iron nails are placed in copper sulphate solution? Write word equations of the reactions involved.
Ans. When iron nails are placed in copper sulphate solution, the iron being more reactive will replace copper in its salt solution.
(Ferrous sulphate) → Iron + Copper
sulphate → Iron Sulphate + Copper
The blue colour turns into green.
Q. 10. Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.
(a) How will she find the nature of the gas?
Ans. She will test it with litmus paper to check the acidic or basic nature of gas. If red litmus turns blue, it is basic in nature. If blue litmus turns red, it is acidic in nature.
(b) Write down equations of all the reactions taking place in this process.
Ans. Sulphur dioxide (SO₂) + Water (H₂O) → Sulphurous acid (H₂SO₂).
Q. 11. One day Reeta went to a Jeweller’s shop with her mother. Her mother gave old gold jewellery to the goldsmith to polish. 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 in weight?
Ans. When gold is washed in acidic solution, it being a metal reacts with acid and forms the hydrogen gas with some metallic oxide. This causes the loss of gold in form of gold oxides. This losses the weight of gold.
