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SCIENCE CLASS 8

CHAPTER - 4

MATERIALS : METALS AND NON METALS

EXERCISES

Question no. 1

Which of the following can be beaten into thin sheets?
a-  Zinc                 b-  Phosphorus               c-  Sulphur          d-  Oxygen

Answer no. 1

a-  Zinc

Question no. 2

Which of the following statement 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 no. 2

c- Generally, metals are ductile

Question no. 3

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-  Metal react with acid to produce ___________________ gas

Answer no. 3

a-  reactive
b-  good, electricity
c-  more
d-  hydrogen

Question no. 4

Mark  T if the statement is true and  F  if it is false.
a-  Generally, non metals react with acid
b-  Sodium is very reactive metal
c-  Copper displaces zinc from zinc sulphate solution
d-  Coal can be drawn into wires


Answer no. 4

a-  False
b-  True
c-  False
d-  False


Question no. 5

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

 1. Appearance
2. Hardness
3. Malleability
4. Ductility
5. Heat Conduction
6. Conduction of Electricity

Answer no. 5

Properties                   Metals                   Non -metals

Appearance                 lustrous                 non -lustrous
Hardness                      hard                       soft
Malleability                 malleable              non -malleable
Ductility                       ductile                    not ductile             
 Heat conductors      good conductors     bad conductors
Conductor of            good conductors     bad conductors
   electricity                 of electricity             of electricity

Question no. 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 solutions.
d-  Sodium and potassium are stored in kerosene.

Answer no. 6

a-  Aluminium foil are used to wrap food items because it is soft malleable metal it can be beaten to thin sheets which is used in wrapping. Advantage of Aluminium foil is it does not reacts with food items.

 b-  Immersion rods are made of metallic substances, because metals are good conductors of heat and electricity. They get hot very soon when electric current is passed through them and thus warm the water.

 c-  Copper cannot displace zinc from its salt solution because copper is less reactive then zinc. A less reactive metal cannot displace to more reactive metal from its solution.

 d-  Sodium and potassium are very reactive. They reacts vigorously with oxygen and water. A lot of heat is generated in the reaction. Hence they are stored in kerosene.

Question no. 7

Can you store lemon pickle in an aluminium utensil ? Explain

Answer no. 7

Pickle contains of acid which reacts with aluminium to produce salt and hydrogen. Therefore pickle is not stored in aluminium utensil.

Question no. 8

Match the substance 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 no. 8

(i)   - (d)
(ii)  - (e)
(iii) - (c)
(iv) - (f)
(v)  -  (b)
(iv) - (a)

Question no. 9

What happen when
a-  Dilute sulphuric acid is poured on a copper plate ?
b-  Iron nails are placed in copper sulphate solution ?
      Write word equations of the reactions involved.

Answer no. 9

a-  No reaction occurs when dilute sulphuric acid is poured on a copper plate.
b-  When iron nails are placed in copper sulphate. Iron being more reactive displace copper from copper sulphate. There is a decomposition of copper on the iron nail.
    Fe    +    Cuso4              =         FeSo4             +     Cu
  Iron + Copper sulphate   =  Iron sulphate + Copper

Question no. 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 no. 10

a-  Add a few drops of water in the test tube. Now cover the test tube and shake well. After shaking test the solution with blue litmus. If it will change from blue to red colour, so it indicate that gas is acidic in nature.

 b-  Charcoal reacts with oxygen to form carbon dioxdi gas
        C    +     O2                            =             CO2
Carbon from + Oxygen   =      Carbondioxide
charcoal

Question no. 11

One day Reeta went to a jeweller’s shop with her mother. Her mother gave 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 no. 11

To polish the gold ornament, it is dipped into a liquid aqua regia which is a mixture of hydrochloric acid and nitric acid. On getting dissolved in the aqua regia, the outer layer of gold dissolve in liquid and a shiny layer appears. The dissolving of the layer causes a reduction in the weight of the jewellery.

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