NCERT SOLUTIONS FOR CLASS 8 SCIENCE CHAPTER – 4

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NCERT SOLUTIONS FOR  Class 8 Science Chapter – 4 Materials: Metal and Non  – metals

Q1. Which of the following can be beaten into thin sheets ?

  • Zinc
  • Phosphorus
  • Sulphur
  • Oxygen

Answer:-

 

  1. Zinc

 

Explanation: Here, Zinc is a  metal with malleability and ductility whereas Phosphorus , Sulphur and Oxygen are non – metals which lack of malleability and ductility.

 

Q2. Which of the following statement is correct ?

  • All metals are ductile.
  • All non – metals are ductile.
  • Generally , metals are ductile.
  • Some non – metals are ductile.

Answer:-

 

( c ) Generally , metals are ductile.

 

Explanation:-

 

Ductility is a property where a substances can be drawn into thin wires, Generally metals are ductile with mercury as the exception.

 

Q3. Fill in the blanks.

  • Phosphorus is a very _____ non – metals.
  • Metals are _____ conductors of heat and ______.
  • Iron is ______ reactive than copper.
  • Metals react with acids to produce  _______ gas.

Answer:-

 

  • Phosphorus is a very reactive non – metal.
  • Metals are good conductors of heat and electricity.
  • Iron is more reactive than copper.
  • Metals react with acids to produce hydrogen gas.

 

 

Q5. Mark ‘T’ if the statement is true and ‘F’ if it is false.

  • Generally, non – metals react with acids. ()
  • Sodium is a very reactive metal. ()
  • Copper displaces zinc from zinc sulphate solution. ()
  • Coal can be drawn into wires. ()

Answer:-

 

  • False
  • True
  • False
  • False

 

Q5. 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 Lustrous Dull
2. Hardness Hard Soft
3. Malleability Have property of Malleability Do not have a property of Malleability
4. Ductility Have  property of Ductile Do not have the property of Ductility
5. Heat conduction Good conductor of Heat Bad conductor of Heat
6. Conduction of electricity Good conductor of Electricity The bad conductor of electricity

 

Q6. Give reason for the following.

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

Answer:-

 

  1. Aluminium is malleable and can be drawn into thin sheets hence Aluminium foils are used to wrap food items.

 

  1. Immersion rods for heating liquids are made up of metallic substances because metals are good conductors of heat and electricity.

 

  1. Copper cannot displace zinc from its salt solution because Zinc is more reactive than copper.

 

  1. Sodium and Potassium are highly reactive metals which readily reacts wit atmospheric oxygen to catch fire hence Sodium and Potassium are stored in kerosene.

 

Q7. Can you store the lemon pickle in an aluminium utensils ? Explain.

Answer:-

 

Pickle consists of acids which react with Aluminium metal to produce salt and Hydrogen.  Hence pickle is not stored in aluminium utensils.

 

Q8. Match the  substances given in Column A with their uses given in Column B.

A 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:-

A 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

 

Q9. What happens when

  • Dilute sulphuric acid is poured  on a copper plate?
  • Iron nails are placed in a copper sulphate solution?

Write work equations of the reactions involved.

Answer:-

 

  • No reaction occurs when  dilute sulphuric acid is poured on a copper plate. However, when concentrated sulphuric acid is poured on a copper plate , hdrogen gas evolves along with the formation of blue coloured copper sulphate crystals. The chemical reaction for the reaction between concentrated sulfuric acid and copper is: Cu + H2So4= CuSo4 + H2
  • Iron being  more reactive displaces copper from copper sulphate. In this reaction , the blue colour of copper sulphate fades and there us a deposition of copper on the iron nail.

 

Fe + CuSo4 = FeSo4 + Cu

 

Q10. Saloni took a piece of burning charcoal and collected the gas evolved in a test tube

  • How will she find the nature  of the gas ?
  • Write down word equations of all the reactions taking place in this process.

Answer:-

 

  1. In a test tube containing gas,  add a few drops of water Now cover the test tube and shake well. After shaking, test the solution with blue litmus . It will change fro blue to red. Thus, gas is acidic in nature.

 

  1. Charcoal reacts with oxygen to  from carbon dioxide gas.

 

C + O2 = CO2

 

 

Q11. One day Reeta went to a jeweller 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 slight loss in weight Can you suggest a  reasons for the loss in weight?

 

Answer:-

 

In order to polish the gold ornament it is to be dipped into a liquid called Aqua regia ( a mixture of hydrochloric acid and nitric acid). On getting dissolved in the environment of aqua regia, the outer layer of gold dissolves and an inner shiny layer appears. The dissolving of the layer cause a reduction in the weight of the jewellery.