4. Materials : Metals And Non-Metals Science class 8 in English Medium ncert book solutions Text books exercise

Exercise

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

(a) Zinc       (b) Phosphorus

(c) Sulphur    (d) Oxygen

Answer: (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.  

Answer: (c) Generally, metals are ductile. 

Q3. Fill in the blanks :

(a) Phosphorus is 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: (I) reactive

(II) good, electricity

(III) more

(iv) hydrogen.        

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. ( )

Answer: (a) (F), (b) (T), (c) (F), (d) (F).  

Q5. Some properties are listed in the following Table. Distinguish between metals and non-metals on the basis of these properties.

Answer: 

Metals: 

1. They are lustrous.

2. They are hard.

3. They can be beaten into thin sheets. 

4. They can be drawn into wires.

5. They are good conductors of heat.

6. They are also good conductors of electricity. 

Non-Metals: 

1. They are dull.

2. They are soft.

3. They cannot be drawn into thin sheets.

4. They cannot  be drawn into wires.

5. They are poor conductors of heat.

6. They are also poor conductors of electricity.

Q6. Give reason for the following:

(i) Copper cannot displace zinc from its salt solution.

(ii) Aluminium foils are used to wrap foods items.

(iii) Sodium and potassium are stored in kerosene.

(iv) Immersion rods for heating liquids are made up of metallic substances.

Answer:

(i) In an aqueous solution, a metal can displace a less reactive metal from its salt. But zinc is more reactive than copper. And because of it, copper cannot displace zinc from its salt solution.

Cu(s) +ZnSO4 (aq)        No reaction

(ii) Aluminium foils are used to wrap foods items because aluminum metal is malleable and it can be beaten into foil.

(iii) Sodium and potassium are stored in kerosene because they are highly reactive elements and can easily catch fire with the contact of air.

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

Q7. Do you think it is possible to store lemon pickle in an aluminum utensil?

Answer:

No, it is not possible to store lemon pickle in an aluminum utensil because lemon pickle contains an acid which can react with aluminum (metal) liberating hydrogen gas. This may spoil the pickle.

Q8. Match the following with column A with column B

Column-A               Column-B

Q9. What happen when:

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

(ii) Dilute sulphuric acid is poured on a copper plate? Write word equations of the reaction involved.

Answer:

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

Fe + CuSO4        FeSO4 + Cu

ii) when dilute sulphuric acid is poured on a copper plate, there will be evolution of hydrogen gas along with the formation of blue color crystal of copper sulphate.

CuSO4 + H2SO4       CuSO4 + H2

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

a) How will she find out the nature of gas?

b) Mention the equation of the reaction taking place in this process.

Answer-

a) 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 and red litmus. It will change from blue to red. Thus, the gas is acidic in nature.

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

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

Question-11

One day Reeta along with her mother went to the jeweler’s shop. Her mother gave old gold jewelry to the goldsmith to polish. Next day when they brought the jewelry back, they found that there was a slight loss in his weight. Can you suggest a reason for the loss in weight?

Answer-

In polishing, the jewleller put the gold jewellery in a mild acidic solution, which on reaction with acid goes into the solution. So, in this process certain amount of gold is lost to the acidic solution.