Chhattisgarh State Class 8 Science Chapter 5 Solution

CG SCERT Chhattisgarh State Board Class 8 Science & Technology Chapter 5 Metal and Non Metals Exercises Questions and Answers.

Choose correct alternatives

1.) This is not a property of metals

a) Fragility

b) Conduction of electricity

c) High density

d) Malleability and ductility

Ans-  a) fragility

2.) Out of the three pins of gold, silver and iron which pin can get coat of copper when dipped in copper sulphate solutions-

a) Iron

b) Gold

c) Silver

d) none of these

ans-

3.) which halogen is used as an antiseptic?

a) Fluorine

b) Chlorine

c) Bromine

d) Iodine

Ans-b) chlorine

  1. Iron rusts-

a) Only in air

b) Only in presence of carbon dioxide

c) Only in water

d) In presence of both air and water

Ans- d) in presence of both air and waer

5.) An example of noble metal is

a) Iron

b) Copper

c) Gold

d) Aluminium

Ans-c) gold

6.) Which of these is classified as metal or non- metal-

a) Element

b) Compound

c) Mixture

d) All of these

Ans-a) element

2.) Fill in the blanks

1.) Nobel metals are usually ——

Ans-less reactive

2.) Breaking up of the non metals into pieces is known as—-

Ans-fragility or britlenesss

4.) The main constituent of german silver is–

Ans-copper, zinc, nickel.

5.) — alloy is used in manufacture of rail.

Ans-steel

3.) Match the following

1.) Duralumin – parts of aeroplane

2.) Stainless steel- medical instruments used in surgery

3.) Phosphours – match box

4.) Chlorine  – disinfectants

5.) Gold  – ornaments

4.) Mark the sentence true or false

  1. All metals are solid at room temperature- true except mercury
  2. Sodium is more reactive than magnesium- true
  3. Stainless steel is an alloy of iron, nickel, carbon and chromium- true
  4. Non metals react with oxygen to form alkaline oxides ( basic oxide)- false
  5. Rusting is an example of corrosion of metals- true

5.) Answer the following questions

1.) Differenciate metals and non metals on the basis of physical and chemical properties. Write three differences of each

Ans-physical properties differences-

Metals

Non- metals

Metals are the good conductor of electricity.

Non –metals are the bad conductors of electricity.
Metals are hard.

Non –metals are not hard except Diamond.

Metals shown ductility ,sonorous.

Non-metals do not show any ductility and sonorous.


Chemical properties differences-

Metals

Non metals
Metals are reacts with oxygen to forms oxides and which reacts with water to from alkaline forms.

Non-metals are reacts with the oxygen to form oxides which reacts with water to form acids.

Metals are reacts with water are differently.

Non-metals are not react with water.

2.) Why is gold and silver used for making ornaments?

Ans-the gold and silver is used for making ornaments because they are ess reactive with metals .they do not react with air, water acids or alkaline compounds. Therefore they are used for making jewellary or ornaments.

3.) What do you understand by reactivity series?

Ans-the reactivity series is the series of the metals, in which metals are placed according to order of their reactivity from l highest to lowest. From this series we can understand the reactivity order of the metals.

4.) How much carat is pure gold? Why is pure gold not used for making ornaments?

Ans-pure gold (100%) is 24 carats. Pure gold is not used for making ornaments because they are very soft and not use for making ornaments therefore 2% of silver or copper is mixed in this and 22 carat gold is used for making ornaments.

5.) What are alloys? Give names of any four alloys and write their constituents and uses.

Ans-the mixture of one metals to another metals is known as Alloy. Alloy are more tough and resistant to corrosion.

alloys constituents Uses
steel Iron, carbon Ships, brideges, eails
Stainless steel Iron ,nickel,chromium, nickel Tensils, surgical instruments.
bronze Copper. tin Staues,coins,medals
German silver Copper, zinc, nickel utensils

6.) What is metal corrosion ? what are the ways to protect corrosion?

Ans-the formation of compound on the metals surface is known as corrosion.

Following are the ways to protect from corrosion-

  1. By painting- most common method to stop corrosion is covering the metal with a layer of paint. Paint the objects made of iron and prevent them from rusting.
  2. By applying grease- by applying grease or oil the contact of the metal with air and water is broken. For protection form rust grease is apply.
  3. By metallic coating- in this method the object which is made of iron are dipped in molten zinc and coated with a layer of zinc. It is also used for preventing the metals.
  4. Manufacture of alloys- make alloys of different metals which helps to prevent from corrosion.

7.) Why is graphite used as a electrode?

Ans-graphite is non-metals but it has the property of conduction of electric current therefore it is used as electrode..

8.) Iron is not in making of railway tracks? Why?

Ans-for making railway tracts iron is not used because it will rust rapidally and expand more during summer therefore iron is not used for making railway tracts.

Updated: February 6, 2021 — 3:30 pm

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