NCERT Solutions for Class-8 Science Chapter-4 Materials: Metals and Non-Metals

NCERT TEXTBOOK EXERCISES

Question 1. Which of the following can be beaten into thin sheets?
(a) Zinc
(b) Phosphorus
(c) Sulphur
(d) Oxygen
Answer:
(a) Zinc.

Question 2. Which of the following statements 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:
(c) Generally, metals are ductile.

Question 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 acids to produce ………………. gas.
Answer:
1. reactive
2. good, electricity
3. more
4. hydrogen.

Question 4. Mark T’ if the statement is true and ‘F’ if it is false.
(a ) Generally, non-metals react with acids. [   ]
(b) Sodium is a very reactive metal. [    ]
(c) Copper displaces zinc from zinc sulphate solution. [   ]
(d) Coal can be drawn into wires. [    ]
Answer:
(a) F
(b) T
(c) F
(d) F.

Question 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
1. Appearance 2.  Hardness 3.  Malleability 4.  Ductility 5.  Heat Conduction 6.  Conduction of Electricity

Answer:

Properties	Metals	Non-metals
1. Appearance	have metallic luster	dull
2. Hardness	hard	soft
3. Malleability	malleable	non-malleable
4. Ductility	ductile	non-ductile
5. Heat Conduction	good conductors	bad conductors
6. Conduction of Electricity	good conductors	bad conductors/insulators

Question 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. It maintains the temperature of food items intact as it is a good conductor of heat.
2. Metals are good conductors of electricity. That is why immersion rods are made up of metals.
3. It is because copper is less reactive than zinc.
4. It is because sodium and potassium react vigorously when coming in contact with air or water.

Question 7. Can you store the lemon pickle in an aluminium utensil? Explain.
Answer: Aluminium is a metal. Metals are more reactive to acids. That is why acidic foodstuffs like lemon pickles must not be stored in aluminium utensils.

Question 8. Match the substances given in Column A with their uses given in Column B.

Column A	Column B
(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

Answer:

Column A	Column B
(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

Question 9. What happens when,
(1) Dilute sulphuric acid is poured on a copper plate?
(2) Iron nails are placed in copper sulphate solution?
Write word equations of the reactions involved.
Answer:
1. Copper sulphate is formed and hydrogen gas is released.
    Copper + dil. sulphuric acid → Copper sulphate + Hydrogen (gas)
2. Brown coating is deposited on the iron nails. This is because of the displacement of copper from copper sulphate solution by iron.
    Iron + Copper sulphate (solution) → Iron sulphate (solution) + Copper

Question 10. Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.
(1) How will she find the nature of the gas?
(2) Write down word equations of all the reactions taking place in this process.
Answer:
1. She will bring a wet litmus paper in contact with the gas. If the gas turns wet blue litmus paper into red, the gas will be acidic.
2. Carbon + Oxygen → Carbon dioxide.
    Carbon dioxide + Water → Carbonic acid.

Question 11. One day Reeta went to a jeweller’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 slight loss in its weight. Can you suggest a reason for the loss in weight?
Answer: In polishing, the jeweller put the gold jewellery in a mild acidic solution, which in reaction with acid goes into the solution. So, in this process, a certain amount of gold is lost to the acidic solution.