Class 8 Science

Metals and Non-metals

NCERT Solution

Question 1: Which of the following can be beaten into thin sheets?

  1. Zinc
  2. Phosphorus
  3. Sulphur
  4. Oxygen

    Answer: (a) Zinc

Question 2: Which of the following statements is correct?

  1. All metals are ductile.
  2. All non-metals are ductile.
  3. Generally, metals are ductile.
  4. Some non-metals are ductile.

    Answer: (c) Generally, metals are ductile

Question 3: Fill in the blanks:

  1. Phosphorus is very …………….non-metal.
  2. Metals are conductors of heat and …………
  3. Iron is ……………reactive than copper.
  4. Metals react with acids to produce ………..gas.

Answer: (a) reactive, (b) electricity, (c) more, (d) hydrogen

Question 4: Mark T if the statement is true and F if it is false.

  1. Generally, non-metals react with acids.
  2. Sodium is a very reactive metal.
  3. Copper displaces zinc from zinc sulphate solution.
  4. Coal can be drawn into wires.

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

Question 5: Some properties are listed in the following Table. Distinguish between metals and non-metals on the basis of these properties.

Answer:

PropertiesMetalsNon-metals
AppearanceShinyDull
HardnessHardBrittle
MalleabilityMalleableNon-malleable
DuctilityDuctileNon-ductile
Heat conductionConductor of heatNon-conductor of heat
Conduction of electricityConductor of electricityNon-conductor of electricity

Question 6: Give reasons for the following:

(a) Aluminium foils are used to wrap food items.

Answer: Aluminium reacts with air to make a coating of aluminium oxide on it. This layer prevents aluminium from further reactions with any substance. Due to this, aluminium foils are used to wrap food items because 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 have a high melting point. Immersion rods need to heat up quickly and should not melt at high temperature. Hence, immersion rods for heating liquids are made up of metallic substances.

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

Answer: Copper is less reactive than zinc. Hence, copper cannot displace zinc from a compound of zinc.

(d) Sodium and potassium are stored in kerosene.

Answer: Sodium and potassium are highly reactive and react vigorously with water even at room temperature. The reaction is highly exothermic and the reaction mixture instantly catches fire. Sodium and potassium are stored in kerosene to prevent this reaction and to prevent accidental fire.

Question 7: Can you store lemon pickle in an aluminium utensil? Explain.

Answer: We know that metals react with acids to produce hydrogen gas. Lemon pickle contains a high amount of acid and the acid can easily react with aluminium. Hence, lemon pickles should not be stored in aluminium utensils.

Question 8: In the following Table some substances are given in Column I. In Column II some uses are given. Match the items in column I with those in Column II.

Column IColumn II
(a) Gold(1) Thermometers
(b) Iron(2) Electric wire
(c) Aluminium(3) Wrapping food
(d) Carbon(4) Jewelry
(e) Copper(5) Machinery
(f) Mercury(6) Fuel

Answer: (a) 4, (b) 5, (c) 3, (d) 6, (e) 2, (f) 1

Question 9: What happens when

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

Answer: Copper does not react with dilute sulphuric acid. So, no reaction takes place when dilute sulphuric acid is poured on a copper plate. But when concentrated sulphuric acid is poured over copper plate, effervescence is observed. This happens because of formation of hydrogen gas.

Cu + H2SO4 → CuSO4 + H2

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

Answer: When iron nails are placed in copper sulphate solution, the blue colour of copper solution is replaced by a light green colour. This happens because iron; being more reactive than copper; displaces copper from copper sulphate and makes iron sulphate.

CuSO4 + Fe → FeSO4 + Cu

Question 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?

Answer: Saloni should bring a wet litmus paper (blue) near the evolved gas. When litmus paper turns to red it indicates that the evolved gas is acidic in nature.

(b) Write down word equations of all the reactions taking place in this process.

Answer: Carbon (in charcoal) reacts with oxygen to produce carbon dioxide gas.

C + O2 → CO2

Carbon dioxide reacts with water to form carbonic acid.

CO2 + H2O → H2CO3

Question 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: Jewelers use Aqua Regia to clean jewelry. Gold is an inert metal which does not react with acids. But Aqua Regia is a mixture of hydrochloric acid and nitric acid in 3 : 1 ratio. It is so potent that it even dissolves gold and silver. Some of the gold is thus lost during cleaning of jewelry. This explains the weight loss of jewelry.


Crop Production

The science of farming is called agriculture. Farming includes cultivation of plants and rearing of animals for food and other beneficial items.

Microorganisms: Friend or Foe

An organism which cannot be seen by naked eyes is called microorganism or microbe. We need a microscope to see a microbe.

Synthetic Fibres

ibres which are man-made are called synthetic fibres, e.g. nylon, acrylic, etc. A synthetic fibre is made of multiple units of a chemical substance.

Metals Non-metals

Metals are lustrous, sonorous, ductile, and are good conductor of heat and electricity.

Coal & Petroleum

Resources which from nature are called natural resources. Examples: coal, petroleum, air, water, soil, etc.

Combustion & Flame

Combustion is a chemical process in which a substance reacts with oxygen to give off heat. Some substances may also give light along with heat during combustion.

Conservation of Plants and Animals

The part of the earth where all living organisms are present is called biosphere. Biosphere is the narrow zone between hydrosphere, troposphere and atmosphere.

Cell: The Fundamental Unit of Life

The basic structural unit of a living organism is called cell. All living beings are made up of cells.

Reproduction in Animals

The process by which an organism produces its offspring is called reproduction. Reproduction is necessary to continue the lineage of an organism.

Reaching the Age of Adolescence

Adolescence is the period of life when many changes take place in the body, leading to reproductive maturity. Adolescence begins at around 10 years of age and lasts till 18 or 19 years of age.

Force & Pressure

A push or pull on an object is called force. Pressure is the force acting on a unit area on an object.

Friction

When one surface is moving over another surface, a force comes into play and opposes their relative motion. This force is called friction or force of friction.

Sound

Sound is a kind of wave which gives us the sense of hearing. Sound is produced by a vibrating body.

Chemical Effects of Electric Current

When electric current is passed through a conducing solution, some chemical reaction takes place in the solution. This is called chemical effect of electric current.

Natural Phenomena

Transfer of charge from one object to another is called charging. The process of transfer of charge to the earth is called earthing.

Light

When light falls on a shiny surface, most of it bounces back. This phenomenon is called reflection of light.

Solar System

The solar system is made up of the sun, its planets, satellites, asteroids, comets, dwarf planets, etc. All other members of the solar system keep on revolving around the sun.

Pollution

When air is contaminated with unwanted substances and becomes harmful for the living and non-living, this is called air pollution.