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Monday, June 22, 2020

Materials – Metals and Non-Metals | Science 8th | Chapter 11 |

Book Cover Science Class 8th jandkncert


Science – Jammu and Kashmir | jandkncert | Class 8th |

Materials – Metals and Non-Metals | Science 8th | Chapter 11 |

Chapter 11: Materials – Metals and Non-Metals

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

(a) Zinc (b) Phosphorus (c) Sulphur (d) Oxygen

Ans. (a) Zinc

Q2. 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.

Ans. (c) Generally, metals are ductile. However, mercury metal− a liquid at room temperature − cannot be drawn into wires and is not ductile.

Q3. 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.

Ans.

(a) Phosphorus 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.

Q4. 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. ( )

Ans.

(i) Generally, non-metals react with acids. (F)

(ii) Sodium is a very reactive metal. (T)

(iii) Copper displaces zinc from zinc sulphate solution. (F)

(iv) Coal can be drawn into wires. (F)

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

 

 

Malleability

 

 

4. Ductility

 

 

5. Heat conduction

 

 

6. Conduction of Electricity

 

 

 

Ans. Properties of Metals Non-metals

 

Properties

Metals

Non-metals

1. Appearance

Lustrous

Dull

2. Hardness

Hard

Soft

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

 

Q6. 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.

Ans.

(a) Aluminium foils are used to wrap food items because the aluminium metal is malleable. Therefore, it can be beaten into thin foils.

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

(c) A metal can displace a less reactive metal from its salt in an aqueous solution. But zinc is more reactive than copper. Therefore, copper cannot displace zinc from its salt solution.

Cu(s) + ZnSO4 (aq) → No reaction

(d) Sodium and potassium are stored in kerosene because they are highly reactive elements. They can easily catch fire even when in contact with air.

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

Ans. Lemon pickle cannot be stored in aluminium utensils because lemon pickle contains acids, which can react with aluminium (metal) liberating hydrogen gas. This can lead to the spoiling of the pickle.

Q8. Match the substances given in Column I with their uses are given in Column II.

 

Column I

Column II

(i) Gold

(ii) Iron

(iii) Aluminium

(iv) Carbon

(v) Copper

(vi) Mercury

(a) Thermometer

(b) Electric wire

(c) Wrapping food

(d) Jewellery

(e) Machinery

(f) Fuel

  

Ans.

 

Column I

Column II

(i) Gold

(ii) Iron

(iii) Aluminium

(iv) Carbon

(v) Copper

(vi) Mercury

(d) Jewellery

(e) Machinery

(b) Electric wire

(f) Fuel

(c) Wrapping food

(a) Thermometer

 

Q9. What happens when

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

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

Write word equations of the reactions involved.

Ans.

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

Copper (Cu) + Sulphuric acid (H2SO4) → Copper sulphate (CuSO4) + Hydrogen gas (H2)

(b) Iron being more reactive displaces copper from copper sulphate solution. In this reaction, the blue colour of copper sulphate fades and there is the deposition of copper on the iron nail.

Iron (Fe) + Copper sulphate (CuSO4) → Iron sulphate (FeSO4) + Copper (Cu)

Q10.  Sarish 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.

Ans. (a) Add a few drops of water in the test tube containing gas. Now, cover the test tube and shake it well. After shaking, test the solution with blue litmus and red litmus. It will turn blue litmus red. Thus, gas is acidic in nature.

(b) Charcoal reacts with oxygen to form carbon dioxide gas.

C                          +                 O2          CO2

(Carbon from charcoal)           (Oxygen)              (Carbon dioxide)

Carbon dioxide reacts with water to form carbonic acid, which turns blue litmus paper red.

CO2 + H2O → H2CO2 (Carbonic Acid – Turns blue litmus red)

Q11. One day Reeta went to a jeweller ’s shop with her mother. Her mother gave a piece of 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 l loss in weight?

Ans. To polish a gold ornament, it is dipped in a liquid called aqua regia (a mixture of hydrochloric acid and nitric acid). On getting the environment of aqua regia, the outer layer of gold dissolves and the inner shiny layer appears. The dissolving of the layer causes a reduction in the weight of the jewellery.

Q12. Why phosphorous is stored in the water?

Ans. Phosphorous is stored in water to prevent it from contacting with atmospheric oxygen because it is highly reactive non-metal and catches fire if exposed to air. It occurs in combines state as phosphates in rocks and soil and as phosphoproteins in living beings. Phosphorous is an essential constituent of bones, teeth, blood and nerve tissues. Bone ash contains 80% of phosphorous.

Worksheet 1: Page No. 137

Q1. Why sodium metal is stored in kerosene?

Ans. Sodium metal is very reactive. It is an alkali metal. It reacts vigorously with oxygen and water. A lot of heat generated in the reaction. Therefore, it is stored in kerosene or liquid paraffin to protect it from the action of air.

Q2. Oxides of __________ are basic in nature.

Ans. Oxides of metals are basic in nature.

Q3. Oxides of __________ are acidic in nature.

Ans. Oxides of non-metals are acidic in nature.

Q4. An acid is a substance which turns blue litmus ________.

Ans. An acid is a substance which turns blue litmus red.

Q5. A base is a substance which turns red litmus _________.

Ans. A base is a substance which turns red litmus blue.

Worksheet 2: Page No. 141

Q1. Write three uses of metals and three uses of non-metals.

Ans. Three uses of Metals:

i. Metals are used in making machines.

ii. Metals are used in the construction of buildings and bridges etc.

iii. It is used in automobiles and utensils.

Three uses of non-metals:

i. Non-metals are used in fertilisers to enhance the growth of plants.

ii. These are used in water purification.

iii. Non-metals are used in medicines and firecrackers.

Q2. Name the metals present in Chlorophyll and Haemoglobin.

Ans. Magnesium (Mg) is present in chlorophyll. Ferrous (Fe) or Iron (II) is present in the haemoglobin of blood.


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