NCERT SOLUTIONS FOR CLASS 8 SCIENCE MATERIALS: METALS AND NON-METALS CHAPTER 4

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

(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.

(c) Generally, metals are ductile

Question 3.
Fill in the blanks.
(a) Phosphorus is a very ____ non-metal.
(b) Metals are _____ conductors of heat and _____
(c) Iron is ______ reactive than copper.
(d) Metals react with acids to produce ______ gas.

(a) reactive
(b) good, electricity
(c) more
(d) 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.

(a) False
(b) True
(c) False
(d) False

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 lustre 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.
(a) Aluminium foils are used to wrap food items.
(b) Immersion rods for heating liquids are made up of metallic substances.
(c) Copper cannot displace zinc from its salt solution.
(d) Sodium and potassium are stored in kerosene.

(a) Aluminium is highly malleable and it can be easily beaten in sheets to make its foil for wrapping purposes. It is also soft and does not react with food items. That is why aluminium foils are used . to wrap food items.
(b) Immersion rods made up of metallic substances because metals are good conductors of heat and electricity. They get hot very soon on the passage of electric current and warm the water.
(c) Copper is less reactive than zinc. So it cannot displace zinc from its solution.
(d) Sodium and potassium are highly reactive, so they are stored in kerosene.

Question 7.
Can you store the lemon pickle in an aluminium utensil? Explain.

No, we cannot store lemon pickle in an aluminium utensil because aluminium is a metal and metals readily react with acids to produce hydrogen. When aluminium comes in contact with lemon, which is acidic, would react to give hydrogen and the pickles will be spoiled.

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

A B
Gold Thermometers
Iron Electric wire
Aluminium Wrapping food
Carbon Jewellery
Copper Machinery
Mercury Fuel

(i) (d)
(ii) (e)
(iii) (c)
(iv) (f)
(v) (b)
(vi) (a)

Question 9.
Match the substances given in Column I with their uses given in Column II. 

Column I Column II
(a) Gold (i) Thermometers
(b) Iron (ii) Electric wire
(c) Aluminium (iii) Wrapping food
(d) Carbon (iv) Jewellery
(e) Copper (v) Machinery
(f) Mercury (vi) Fuel
Column I Column II
(a) Gold
(b) Iron
(c) Aluminium
(d) Carbon
(e) Copper
(f) Mercury		 (iv) Jewellery
(v) Machinery
(iii) Wrapping food
(vi) Fuel
(ii) Electric wire
(i) Thermometers

Question 10.

What happens when 

  1. Dilute sulphuric acid is poured on copper plate ?
  2. Iron nails are placed in copper sulphate solution ? Write word equations of the reactions involved.
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  1. When sulphuric acid is poured on copper plate, copper sulphate and hydrogen gas are produced.
    Copper + Sulphuric acid ——-> Copper sulphate + Hydrogen (gas).
  2. When iron nails are placed in copper sulphate solution, iron sulphate and copper are formed.
    Iron + Copper sulphate ——-> Iron sulphate + Copper

Question 11.
Non-metals cannot be drawn into wires. Why?

Non-metals are not ductile, therefore they cannot be drawn into wires.

Question 12.
Complete the following equation :
Zn + 2HCl ——-> __+ __ 

Zn + 2HCl ——-> ZnCl2 + H2o.

Question 13.
Which of the following can be beaten into thin sheets ? [NCERT]

  • Zinc
  • Phosphorus
  • Sulphur
  • Oxygen.

Zinc.

Question 14.
The number of metals is much ………….. than non-metals.

More.

Question 15.
……… are the good conductors of heat and electricity.

Metals.

Question 16.
Examples of metals are ………., ……. and ………

Iron, sodium and nickel.

Question 17.
Examples of non-metals are ………. , …….. and …….

Sulphur, chlorine and oxygen.

Question 18.
Explain the term ‘metallurgy’.

Metallurgy is the science of extracting metals from their ores and purifying them for various uses.

Question 19.
State general steps involved in metallurgy of a metal.

The general steps of metallurgy are :

  • Concentration of ore.
  • Reduction of the metal compound.
  • Refining of metal

Question 20.
Metals are (softer/harder) than non-metals.

Harder.

Question 21.
Most non-metals are (bad/good) conductors of heat.

Bad.

Question 22.
The property that allows the metals to be hammered into thin sheets is called (ductility/ malleability).

Malleability.

Question 23.
Melting point of most non-metals is (higher/lower) than metals.

Lower.

Question 24.
(Metals/non-metals) display lustre

Potassium, magnesium, iron, gold.

Question 26.
Can copper displace iron from iron sulphate solution ? Give reasons.

Copper cannot displace iron from iron sulphate because copper is less reactive than iron

Question 27.
(Platinum/iron) is the member of the family of noble metals.

Platinum.

Question 28.
Pure gold is (24/100) carats.

24

Question 29.
International standards of weights are made of (gold-silver/platinum-iridium) alloy.

Platinum-iridium.

Question 30.
Gold dissolves in (aqua regia/aqueous solution of silver nitrate).

Aqua regia.

Question 31.
Silver tarnishes due to (nitrogen oxides/hydrogen sulphide) in the air.

Hydrogen sulphide.

Question 32.
Why is aluminium used in making aeroplanes ?

Aluminium is used in making aeroplanes, as it is light and has high resistance to corrosion when exposed to air which aircrafts demand the most.

Question 33.
What type of oxides are formed by metals ?

Metals form basic oxides.

Question 34.
What type of oxides are formed by non-metals ?

Non-metals form acidic or neutral oxides.

Question 35.
How does phosphorus occur in nature ?

Phosphorus occurs in nature in the combined state as it has strong affinity for oxygen.

Question 36.
Give the different forms of silica in nature.

Silica occurs in nature as ordinary sand, flint, quartz and opal.

Question 37.
Which metal foil is used in packing of some medicine tablets ?

Aluminium.

Question 38.
Name the soft metal which can be cut with a knife.

Sodium or potassium.

Question 39.
Name the non-metal used in vulcanization.

Sulphur.

Question 40.
Name one metal which is not malleable.

Zinc or arsenic.

Question 41.
White phosphorous has to be kept in water. Why?

Phosphorus is to be kept in water to prevent its contact with the air because it is highly reactive.

Question 42.
Can you store lemon pickle in an aluminium utensils ? Explain. 

We cannot store acidic food stuffs in aluminium utensils because aluminium reacts with acids. The food gets spoilt.

Question 43.
One day Reeta went to a jeweller’s shop with her mother. Her mother gave an old gold jewellery to the goldsmith to polish. 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 ?

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Question 44.
Write short notes on

  1. Metallurgical processes
  2. Uses of common metals and non-metals
  3. Noble metals
  1. Metallurgical process can be divided into following steps :
    • Concentration of the ore
    • Reduction of metal compound to get free metal
    • Refining of metal.
  2. Uses of common metals and non-metals :
    Uses of metals – for making machinery, automobiles, industrial gadgets, building, bridges, cooking utensils, electrical gadgets, jewellery, sheets.
    Uses of non-metals – oxygen is used by plants and animals for their survival, nitrogen is used by plants for their growth, chlorine is used in water purification to kill germs, sulphur is used for making sulphuric acid, tincture iodine has antiseptic properties.
  3. Noble metals – Gold, silver and platinum are noble metals. They occur free in nature . and maintain their lustre for a long time. Platinum, gold and silver are used for making jewellery as they do not tarnish.

Question 45.
Purity of gold is 15 carat. What is the percentage’of gold in the ornaments ?

24 carat purity of gold =100
∴ 1 carat purity or gold = 100/24
15 carat purity of gold = (100*15)/24 = 62.5 %

Question 46.
Give two uses of sulphur in chemical industry.

  • It is used in the manufacture of sulphuric acid.
  • It is used in the manufacture of carbon disulphide, which is used as an industrial solvent.

Question 47.
How is sulphur useful in agriculture ? How is sulphur useful in medicine ?

Sulphur powder is an excellent insecticide and fungicide. It is used in spraying fruit trees.

  • Sulphur is the main constituent of skin ointments.
  • Metallic sulphides of sulphur are used in the preparation of Ayurvedic medicines.

Question 48.
Give two important uses of silver.

  • It is used for making coins.
  • Silver salts (silver bromide and silver iodide) are used for making photographic films.

Question 49.
Give two uses of gold.

  • Gold is used for making ornaments.
  • Gold foils are used in the preparation of Ayurvedic medicines.

Question 50.
Give two uses of platinum.

  • It is used as a catalyst in the manufacture of sulphuric and nitric acid.
  • Platinum catalytic converters use platinum as catalytic agent.
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