NCERT Solutions Class 8 Science Materials Metals and Non-Metals

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NCERT Solutions for Class 8 Science fopr chapter 4 Materials Metals and Non-Metals

Question.1 - Which of the following can be beaten into sheets? 

(a) Zinc

(b) Phosphorous

(c) Sulphur

(d) Oxygen

Answer.

Correct option is (a) Zinc.

Explanation: Generally metals can be beaten into sheets. Zinc is metal while phosphorus, sulphur and oxygen are non-metals.


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.

Correct statement is option (c), Generally, metals are ductile.

Explanation: Mercury is a metal but it cannot be drawn into wires because it is liquid at room temperature. Therefore, it is non-ductile.


Question.3 Fill in the blanks.

(a) Phosphorous 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.

Answer.

(a) Phosphorous is a very reactive non-metal.

(b) Metals are good conductors of heat and electricity.

(c) Iron is more reactive than copper.

(d) Metals react with acids to produce hydrogen gas.


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)

Generally, non-metals react with acids.

(F)

(b)

Sodium is a very reactive metal.

(T)

(c)

Copper displaces zinc from zinc sulphate solution.

(F)

(d)

Coal can be drawn into wires.

(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

Lustrous

Non-lustrous

2. Hardness

Hard

Soft

3. Malleability

Can be beaten into thin sheets

Cannot be beaten into thin sheets

4. Ductility

Can be drawn into wires

Cannot be drawn into wires

 

5. Heat Conduction

Good conductors of heat

Poor conductors of heat

6. Conduction of Electricity

Good conductors of electricity

Poor conductors of electricity


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.

Answer.

(a) Aluminium is a highly malleable cheap metal which does not react with food items. Therefore, aluminium foils are used to wrap food items.

(b) Metals are good conductors of heat and electricity. Therefore, immersion rods for heating liquids are made up of metallic substances.

(c) A less reactive metal cannot replace more reactive metal from its salt solution. Since, copper is less reactive than zinc, therefore, it cannot replace zinc from its salt solution.

(d) Sodium and potassium are very reactive metals. They react vigorously with oxygen and water. A lot of heat is generated in the reaction. If kept in open, they react with oxygen and moisture present in air and catch fire immediately. Therefore, sodium and potassium are stored in kerosene.


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

Answer.

No, lemon pickle cannot be stored in an aluminium utensil. This is because lemon pickle contains acid which reacts with aluminium (metal) to liberate hydrogen gas. The liberated hydrogen gas can spoil lemon pickle.


Question.8

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


Question.9 What happens when

(a) Dilute sulphuric acid is poured on a copper plate?

(b) Iron nails are placed in copper sulphate solution?


Answer.

(a) When sulphuric acid is poured on a copper plate, the copper metal reacts with sulphuric acid to form copper sulphate and hydrogen gas.

image

(b) Iron is more reactive than copper therefore, it displaces copper from copper sulphate solution to form iron sulphate.

image

Initially, copper sulpahte solution is blue in colour. when iron nail is placed in it, the blue colour of copper sulphate solution fades. The solution turns green due to formation of iron sulphate. Copper gets deposited on iron nail.

Question.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?

(b) Write down word equations of all the reactions taking place in this process.

Answer.

(a) To find the nature of the gas, add a small amount of water into the test tube in which gas is collected. Quickly cover the test tube and shake it well. Now test the solution with red and blue litmus paper one by one. You will observe that solution turns blue litmus red while red litmus remains unaffected. This confirms that gas evolved during burning of charcoal is acidic in nature.

(b) Name of the product formed in the reaction of charcoal with oxygen is carbon dioxide. When carbon dioxide is dissolved in water, carbonic acid is formed. The carbonic acid turns blue litmus paper red. Generally, oxides of non-metals are acidic in nature.


Question.11 - 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?

Answer.

To polish gold jewellery, it is dipped in a mixture of acids called aqua regia (a mixture of hydrochloric acid and nitric acid). The outer layer of gold jewellery dissolves in the acid mixture and the inner shiny layer appears. Due to dissolution of upper layer of gold, its weight gets reduced.

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