CBSE Class 8 - Science - Ch4 - Metals and Non-Metals #eduvictors

Metals and Non-Metals

Class 8 - NCERT Chapter Solutions

Q1. Which of the following can be beaten into thin sheets?
(a) Zinc
(b) Phosphorus
(c) Sulphur
(d) Oxygen

Answer: (a) Zinc, as it is a metal. The rest of these are non-metals.

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.
Mercury (metal) is liquid at room temperature and cannot be drawn into wires. Therefore, it is non-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.

Answers:
(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. ( )

Answers:
(i) Generally, non-metals react with acids. (F) Generally, metals react with acids.
(ii) Sodium is a very reactive metal. (T)
(iii) Copper displaces zinc from zinc sulphate solution. (F) The reactivity of zinc is higher than copper. So, copper cannot displace zinc from zinc sulphate solution.
(iv) Coal can be drawn into wires. (F) Coal, being a non-metal, is non-ductile.

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	They are lustrous.	They are dull
2. Hardness	They are hard.	They are soft.
3. Malleability	They are malleable. Can be beaten into thin sheets	They are not malleable. Cannot be beaten into thin sheets
4. Ductility	They are ductile. Can be drawn into wires	They are not ductile. Cannot be drawn into wires.
5. Heat Conduction	They are good conductors of heat.	They are 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. 
Answer: Aluminium foils are used to wrap food items because aluminium is highly malleable. It can be beaten into thin sheets. Moreover, it does not react with food.

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

(c) Copper cannot displace zinc from its salt solution. 
Answer: The reactivity of zinc is higher than copper. Only metal of higher reactivity can displace a metal of lower reactivity from its salt solution. So, copper cannot displace zinc from zinc sulphate solution.

(d) Sodium and potassium are stored in kerosene. 
Answer:  Sodium and potassium are highly reactive elements. They can easily catch fire even when they come in contact with air. So, they have to be kept in kerosene.

Q7. Can you store the lemon pickle in an aluminium utensil? Explain.
Answer: No, we cannot store the lemon pickle in aluminium utensils, as metals react with acids to liberate hydrogen gas. The pickle can be spoiled.

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

Answer: (a) When the dilute sulphuric acid is poured on copper, it does not react.
When concentrated sulphuric acid is poured on a copper plate, copper reacts with sulphuric acid to liberate hydrogen gas.

Cu               +   H2SO4              →    CuSO4                        +    H2
Copper            Sulphuric acid        copper sulphate        hydrogen

(b) Iron nails are placed in copper sulphate solution? Write word equations of the reactions involved.

Answer: b) The reactivity of iron is more than copper. So, iron will displace copper from the copper sulphate solution.  In this reaction, the blue colour of copper sulphate fades.

Fe   +     CuSO4                  →   FeSO4    +  Cu
Iron      copper sulphate      →  Iron Sulphate + Copper

Q.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) Add some water to the test tube in which gas is collected. Now, cover the test tube. Shake it well. Test the solution with blue litmus and red litmus. Blue litmus turns red. Thus, the nature of gas is acidic.

(b) Charcoal when reacts with oxygen forms carbon dioxide gas.
C      +    O2  →    CO2
Carbon dioxide reacts with water to form carbonic acid, which turns blue litmus paper red.
CO2               +              H2O    →    H2CO3
Carbon dioxide   +   water   →    Carbonic acid

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. The 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 of weight?

Answer: To polish a gold ornament, it is dipped in an acid (called aqua regia). The outer layer of gold dissolves in the acid and the inner shiny layer is visible. Because of the loss of the upper layer of jewellery, its weight is reduced.

Q12: List the different uses of metals that you find in your surroundings.

Answer: Metals are used in the following:

1. machinery
2. cooking utensils
3. electrical wires and devices (e.g. heater)
4. automobiles, planes, ships, trains
5. construction material e.g. sheets, bars etc.

Q13: Define ductility.

Answer: Ductility is the property of metals due to which the metals can be drawn into wires.

Q14: What is meant by metallurgy?

Answer: Metallurgy is the science of extracting and purifying metals from their ores.

Q15: What are noble metals?

Answer: Metals which has the least tendency to react and occur in a free state are known as noble metals. Gold, Silver and Platinum as known as noble metals.  They have the property to maintain their metallic lustre for a long time.
e.g. Gold does not react with air, water or even with acids. It dissolves in aqua regia (a mixture of nitric acid + hydrochloric acid).