Class 8 Science

Metals Non-Metals

Short Answer Questions

Question 1: Which reaction takes place during rust formation?

Answer: Iron reacts with oxygen and moisture to form iron oxide. Iron oxide is brown in colour and is commonly known as rust.

Fe + O2 + H2O → Fe2O3

Question 2: Copper coins develop greenish patches when kept unused for a long time. Why?

Answer: When copper is exposed to moist air for a long time, it acquires a greenish coating. The green coat is a mixture of copper hydroxide and copper carbonate.

2Cu + H2O + CO2 + O2 → Cu(OH)2 + CuCO3

Due to this, copper coins develop greenish patches when kept unused for a long time.

Question 3: How does a base react with metals and non-metals?

Answer: Reaction of base with metals and non-metals is as follows:

  • Metals react with sodium hydroxide to produce hydrogen gas.
  • Non-metals' reaction with sodium hydroxide is much complex.

Question 4: What happens when zinc granules are kept in copper sulphate solution?

Answer: When zinc granules are kept in copper sulphate solution, the blue colour of copper sulphate disappears and the solution becomes colourless. Zinc is more reactive than copper and hence displaces copper from copper sulphate solution and forms zinc sulphate.

CuSO4 + Zn → ZnSO4 + Cu

Question 5: What happens when copper turnings are kept in zinc sulphate solution? Give reason for your answer.

Answer: Copper is less reactive than zinc. Hence, copper cannot displace zinc from a compound. Hence, no reaction takes place when copper turnings are kept in zinc sulphate solution.

Question 6: How do metals react with acids?

Answer: Metals generally react with acids and produce hydrogen gas. Confirmation of hydrogen gas is done by bringing a burning matchstick or a burning candle near the gas. When the burning matchstick or candle burns with a pop sound it confirms the evolution of hydrogen gas. But copper does not react with dilute sulpuric acid.

Question 7: Write a brief note about physical state of metals.

Answer: Most of the non-metals are available as solid at room temperature. But mercury is present as liquid at room temperature.

Long Answer Type Questions

Question 1: Differentiate between metals and non-metals on the basis of malleability, ductility and conductivity.

Answer:

PropertyMetalNon-metal
MalleabilityMetals are malleable, i.e. they can be beaten into thin sheets.Non-metals are not malleable.
DuctilityMetals are ductile, i.e. they can be drawn into thin wires.Non-metals are not ductile.
ConductivityMetals are good conductors of heat and electricity.Non-metals are bad conductors of heat and electricity. (exception: graphite)

Question 2: Differentiate between metals and non-metals on the basis of luster, sonority and physical state.

Answer:

PropertyMetalNon-metal
SonorousMetals are sonorous, i.e. they produce a typical metallic sound when hit with something.Non-metals are not sonorous.
LustrousMetals have metallic shine; called lustre.Non-metals are usually dull. (exceptions: diamond and graphite)
Physical StateMost of the non-metals are available as solid at room temperature; except mercury. Sodium and potassium are so soft that they can be cut with knife.Non-metals are available in all the three states of matter.

Question 3: How do metals and non-metals react with water?

Answer: Some metals react vigorously with water, while some others do not react at all with water.

Example: Sodium is a highly reactive metal and reacts vigorously with water. This is a highly exothermic reaction. During this reaction; sodium catches fire because of too much heat being evolved. Due to this, sodium is stored in kerosene to prevent accidental fire.

  • Iron reacts slowly with water.
  • Copper does not react with either cold or hot water, but reacts with steam.
  • Silver and gold do not react with water at any temperature.

Usually, non-metals do not react with water, but some non-metals react vigorously with air. Such non-metals are stored in water to prevent their reaction with air. For example; phosphorus is stored in water to prevent its reaction with air.

Question 4: List some uses of metals.

Answer: Uses of metals:

  • Metals are used for making machines and tools.
  • Iron is used for making ships, bridges, railway lines, etc.
  • Copper is used for making electric wires.
  • Aluminium is used for making utensils.
  • Gold and silver are used for making ornaments.

Question 5: List some uses of non-metals.

Answer: Uses of non-metals:

  • Oxygen is used by all living beings for respiration.
  • Carbon dioxide is used by plants for photosynthesis.
  • Chlorine is used for water purification.
  • Iodine solution is used as antiseptic and applied on wounds.
  • Coal (carbon) is an important fuel.

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.