Thursday, July 26, 2012

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

Metals and Non-Metals
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. 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:

PropertiesMetalsNon-Metals
1. AppearanceThey are lustrous.They are dull
2. HardnessThey are hard.They are soft.
3. MalleabilityThey are malleable.
Can be beaten into thin sheets
They are not malleable.
Cannot be beaten into thin sheets
4. DuctilityThey are ductile.
Can be drawn into wires
They are not ductile.
Cannot be drawn into wires.
5. Heat ConductionThey are good conductors of heat.  They are poor conductors of heat.
6. Conduction of
Electricity
Good conductors of electricityPoor 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 a 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 lemon pickle in an aluminum utensil? Explain.
Answer: No, we cannot store lemon pickle in aluminum 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.

AB
(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:

AB
(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 dilute 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 copper sulphate solution.  In this reaction, the blue colour of copper sulphate fades.

Fe   +     CuSO4                  →   FeSO4    +  Cu
Iron      copper sulphate      →  Iron Sulphase + Ccopper

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 in 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 jeweler 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 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 loss of 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 in to 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 free state are known as noble metals. Gold, Silver and Platinum as known as noble metals.  They have the property to maintain their metallic lusture for long time.
e.g. Gold does not react with air, water and even with acids. It dissolves in aqua regia (a mix ture of nitric acid + hydrochloric acid).


17 comments:

  1. These questionnaire contains very important exam oriented questions which are helpful for preparation.
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    ReplyDelete
  2. These questions help to excel in exam thanks .keep on posting
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    ReplyDelete
  3. these questions have very main points to learn for exams

    ReplyDelete
  4. i had the exam and these q/a and mcqs helped me a lot. i got 97/100 in my exam.thanks a lot. keep uploading.

    ReplyDelete
  5. these are very helpful to all 8th class students

    ReplyDelete
  6. For the question 5, non metals are brittle. they are not soft because if they were soft, they would be malleable.

    ReplyDelete
  7. these que very useful to us........
    thank u so much.....

    ReplyDelete
  8. thankss a ton for such precious info... :)

    ReplyDelete
  9. in the question 9, the answer shud be...no reaction because metals under hydrogen do not react with acids and do not displace hydrogen

    ReplyDelete
  10. IT IS VERY GOOD FOR PRAACTICE BUT SHOULD BE TAKEN AS QUIZ

    ReplyDelete