Sortinge Materials into Groups

 

The objects which we see around us are made of different materials like wood, glass, rubber, plastic, cotton, etc. They are of different shapes, sizes, colours and uses. For example, table, chair, bag, books, clothes, birds, cars, trees are all made of different materials. How do we group such a variety of objects?

We group objects on the basis of certain similarities and differences in their properties. This type of grouping in which similar objects are placed together is known as classification. Therefore, the above mentioned objects may be classified as living or non-living. We can also classify them as naturally occurring or man-made objects.

 

But why is it necessary to classify objects into groups?

1. Classification makes the study of things around us convenient and systematic.
2. It also helps us to have a general idea about the members of a group.
3. We come to know how each member differs from the other in the same group or in different groups.

 

OBJECTS AROUND US

1. An object may be made up of different materials. For example, a chair may be made of wood, steel or plastic.
2. Different objects may be made up of the same material. For example, utensils, parts of vehicles, bridges are all made of steel. 
3. An object may be made of many materials. For example, aerated drinks contain water, sugar and a gas dissolved in it.

All the objects that we see and feel around us have definite mass and occupy space. We can say that these objects are made up of matter. Therefore, matter is defined as anything that has mass and occupies space. The various objects and materials we discussed before, are all matter. Air is also matter since it has mass and occupies space, though we cannot see it. The amount of matter contained in an object is measured by its mass. The space occupied by an object is known as its volume.

Matter is made up of tiny particles called molecules. The arrangement of molecules decides whether an object is a solid, liquid or a gas.

 

Solid: The molecules are tightly packed and a strong attractive force acts between them. So, they have a definite shape and volume.

Liquid:

The molecules in a liquid are loosely packed and the intermolecular attractive forces between them are weak. So, liquids do not have a definite shape but they have a definite volume and take the shape of the container in which they are kept.

Gas: The molecules in a gas are far apart from each other and there is hardly any attractive force acting between them. So, a gas does not have a fixed shape or volume. The molecules move around freely and occupy the entire space available to them.

Materials-All objects are made up of substances called materials.

 

PROPERTIES OF MATERIALS

The characteristics of materials, that enable us to separate one object from the other, are called its properties. The properties of materials decide how and for what purpose they can be used. For example, wood or steel would be the most suitable material for making a cupboard but not clothes. Some of the properties of materials are discussed below.

 

Appearance

It is the external property of matter that distinguishes one material from the other. How things appear to the eyes is called appearance.

Metals like iron, copper, aluminium, gold, etc., have a shining surface. This characteristic of metals is known as lustre. Materials like wood, plastic, paper or rubber do not possess lustre and appear dull. This characteristic of non-metals is termed as non-lustre.When metals are exposed to air, most of them lose their lustre and get tarnished due to the action of air and moisture. 

On polishing or rubbing the surface with sandpaper, they regain their lustre once again. Therefore, we notice the lustre, only on their freshly cut surface. Gold and silver metals are made into ornaments due to their colour and lustre. Gold does not lose its shine on exposure to air, so ornaments made of this metal remain sparkling throughout. 

 

Hardness

Materials are grouped according to their ability to be compressed or squeezed. We can easily squeeze a piece of sponge between our fingertips but we cannot squeeze an iron ball, even if we press it with all our might. Therefore, we say that sponge is soft while iron is hard. Materials which can be compressed or scratched easily are called soft, while those materials which are difficult to compress are called hard. Diamond is one of the hardest substance

 

Metals like lead, aluminium, copper and materials like wood, stone, etc., are hard. Chalk, cotton, wax, etc., are soft materials. The shape of hard objects cannot be changed by applying any amount of force but the shape of soft objects can be altered easily. The property of hardness of a material decides the purpose for which it can be used. For example, the materials used for making vehicles, houses, roads, etc., should be hard while clothes should be made of soft materials. The soft materials can also be scratched with our nails, but not the hard materials. We can easily scratch a candle, made of wax, but it is not possible to scratch a stone.

Materials can also be smooth or rough to touch. The surface of steel utensils, polished wood, etc., are smooth. Bricks, rocks and soil have rough surfaces. Therefore, the materials can also be classified according to their smoothness or roughness.

 

Lustre, hardness, roughness or smoothness are some of the properties which describe the appearance of a material. In addition to this, we can also describe the appearance of a material by its size and weight i.e., whether it is large or small or whether it is heavy or light.

 

Solubility

Materials or substances like sugar or salt, when mixed with water, disappear completely in it. We say that, sugar or salt has dissolved in water. Substances which dissolve in water are known as soluble substances. Sand and chalk powder do not dissolve in water. They are said to be insoluble substances.

 

The substance which dissolves in a liquid is known as a solute. The liquid in which a solute dissolves is known as a solvent. The solute and solvent together make up a solution.

Water is the most commonly used solvent since it readily dissolves a number of substances in it. Therefore, it is called a universal solvent. Being a universal solvent, water plays an important role in the functioning of our body.

 

Some liquids like glycerine, vinegar and lemon juice dissolve in water to form solutions. They are known as miscible liquids. Vinegar and lemon juice or vinegar and glycerine are miscible with each other. In both the cases, the solvent used is not water. 

Cooking oil, kerosene oil, petrol, etc., do not dissolve in water. They separate into two distinct layers when kept undisturbed for some time. The liquids which do not mix with each other are known as immiscible liquids. Sand is insoluble in water other are known as immiscible liquids.

 

Gases like oxygen and carbon dioxide dissolve in water. These gases help the aquatic plants and animals to carry out the process of photosynthesis and respiration. Aerated or fizzy drinks also contain carbon dioxide dissolved in water under pressure.

 

Floatation

Certain materials float on water whereas, others sink. This property is called floatation. Generally, wood, leaves, plastic, paper and feathers float on water whereas rocks glass, honey, sand and metals sink. We can test these materials to see whether they float o sink in oil.

 

The materials which sink in water, will sink in oil, since oil is lighter than water. The materials which float in water, may float or sink in the oil, depending on the density of oil and the density of the materials. Hence, floating and sinking of objects will depend upon density of the liquid and the density of the objects.

Density is a property of matter that describes how heavy an object is for its size. Density compares the weight of a material to its volume. In some matter, the molecules are more closely packed together. These materials have a higher density. Scientists compare everything to water; which has density equal to 1 g/cm³. When the density of a material is less than one, it will float in water. Materials with a density greater than one will sink in water.

 

The shape of an object also affects the amount of liquid it displaces. Certain heavy objects are able to float because of their shape. For example, the shape of a ship allows it to float on water, despite the fact that it is very heavy.

 

Transparency:

The amount of light that passes through an object depends on the material with which it is made. Based on this property, materials are classified as transparent, translucent and opaque.

Transparent Materials: These materials allow light to pass through them easily. Air, glass, clear water and some plastics are transparent materials. We can see the objects clearly through these materials.

 

Translucent Materials:These materials allow light to pass through them partially. Ground glass, oiled or waxed paper are translucent materials. We cannot see the objects clearly through these materials. When you cover the palm of your hands with a torch, you can see a dull red glow. Here, the palm acts as a translucent object.

 

Opaque Materials: These materials do not allow light to pass through them at all. Metals, rocks, wood and cardboard are opaque materials. The objects are not visible through opaque materials.

So, all the materials can be grouped in these three categories without any confusion.

 

Thermal and Electrical Conductivity

Metals like silver, copper, iron and aluminium become hot when they are heated over a flame. Thus, they conduct heat. These materials are said to be good conductors of heat.

 

Materials like plastic, rubber, wood, etc., do not allow heat to pass through them. These materials are called poor conductors or bad conductors of heat. The conduction of heat through a substance is called its thermal conductivity.

 

Both pure water and air are bad conductors of heat. Pure water is bad conductor of electricity. Impurities like acids and bases present in it make it a conductor of electricity.

 

You must have noticed that some cooking vessels like pressure cookers and frying pans are made of metals but their handles are made of a plastic like material, bakelite. This is because, metals being good conductors of heat warm up the food quickly. Bakelite, being a bad conductor Lear of heat, does not get heated. Therefore, the handles can be held easily while cooking food in them.

Metals allow electric current to pass through them. So, they are known as good conductors of electricity. Plastic, rubber, wood and paper are poor conductors or bad conductors of electricity.

Materials which do not conduct electricity are known as bad conductors or insulators.

 

Magnetic property

Certain substances have the property of being attracted by a magnet. Such materials are called magnetic materials. Metals like iron, cobalt and nickel are magnetic materials. Objects made of these metals will get attracted to the magnet. The ends of a magnet are called the north pole and south pole.

The materials that are not attracted by a magnet are called non- magnetic materials. Aluminium, copper, brass, wood, plastic, paper and rubber are some of the non-magnetic materials.

 

Thus, materials can be arranged into groups according to any of  the above discussed properties. This type of grouping makes it easier to find things when they are required. It also facilitates the study of their properties and also observe any patterns in these properties.

 

IMPORTANT TERMS

 

Materials: The substances with which objects are made.

 

Classification: The process of grouping things based on similarities and differences.

 

Matter: Matter is anything that has mass and occupies space.

 

Appearance: How things appear to the eyes.

 

Lustre: The shiny appearance of materials.

Transparent materials: The materials which allow light to pass through them

Translucent materials : The materials which allow light to pass through them partially

Opaque materials : These materials do not allow light to pass through them at all)

 

Placing similar things together is called grouping.

Grouping makes it easier to find things when they are required.

Things are grouped together for convenience and to study their properties.

 

Objects are classified based on similarities and differences. Some materials are shiny in appearance while others are not. Some are hard and some soft. Similarly, some materials are rough, others are smooth.

 

Substances which dissolve in water are called soluble substances while substances which do not dissolve are called insoluble. Some materials float on water whereas some sink in it.

 

 

 

Exercise

1. What is the process of grouping objects with similar properties called?

Identification

Classification

Separation

Observation

Answer: (b) Classification

Explanation: Classification is the process of grouping objects based on their similarities and differences in properties. It helps in organizing a wide variety of objects, making them easier to study.

 

Q2. Which of the following can be used as a criterion to classify objects?

Size and Color

Similarities and Differences

Price and Value

Age and Weight

Answer: (b) Similarities and Differences

Explanation: Objects are classified based on similarities and differences in their properties such as material, shape, size, or function. This helps us place similar objects together and understand their relationships.

 

3. Why is it necessary to classify objects into groups?

To create confusion

To make the study of objects easier and systematic

To eliminate some objects

To separate them into equal parts

Answer: (b) To make the study of objects easier and systematic

Explanation: Classification helps in the systematic study of objects by grouping similar items together, making it convenient to understand and compare their characteristics.

 

4. How can objects be classified besides being living or non-living?

According to their uses

As naturally occurring or man-made

Based on their weight

Based on their color

Answer: (b) As naturally occurring or man-made

Explanation: Another common method of classification is grouping objects into naturally occurring (e.g., trees, animals) and man-made (e.g., plastic, cars) objects, making it easier to understand their origin and purpose.

 

5. Which of the following is a correct statement about matter?

Matter has no mass or volume

Matter occupies space and has mass

Matter only exists in liquid form

Matter is always visible to the human eye

Answer: (b) Matter occupies space and has mass

Explanation: Matter is defined as anything that has mass and occupies space. This includes solids, liquids, gases, and even air, which, though invisible, is still considered matter.

 

6. Which of the following is true about solids?

They have a definite shape but no definite volume

They have neither definite shape nor volume

They have a definite shape and volume

They do not occupy space

Answer: (c) They have a definite shape and volume

Explanation: In solids, the molecules are tightly packed, resulting in a definite shape and volume. The strong intermolecular forces keep the structure intact.

 

7. What property of liquids differentiates them from solids?

Liquids have a definite shape

Liquids do not have a definite shape but have a definite volume

Liquids do not have volume

Liquids are made of tightly packed molecules

Answer: (b) Liquids do not have a definite shape but have a definite volume

Explanation: Liquids have molecules that are loosely packed, allowing them to take the shape of their container. However, they still retain a definite volume.

 

8. Why do gases occupy the entire space available to them?

Because their molecules are tightly packed

Because there is a strong force between the molecules

Because their molecules are far apart and move freely

Because gases have a definite shape and volume

Answer: (c) Because their molecules are far apart and move freely

Explanation: In gases, the molecules are far apart, and there is little to no attractive force between them. This allows them to move freely and fill any container they are placed in, occupying all available space.

 

9. Which of the following objects is made of more than one material?

A wooden chair

A steel bridge

An aerated drink

A plastic bottle

Answer: (c) An aerated drink

Explanation: An aerated drink is composed of water, sugar, and dissolved gas, making it an example of an object made from multiple materials. Other examples like a wooden chair or steel bridge are made from a single material.

 

10. What is the term used for the external property of matter that distinguishes one material from another?

Solubility

Hardness

Appearance

Miscibility

Answer: (c) Appearance

Explanation: Appearance refers to how materials look or appear to the eyes. It is an external property that helps distinguish one material from another, such as the shiny surface of metals versus the dull appearance of non-metals.

 

11. Which of the following materials is known for retaining its lustre even after exposure to air?

Iron

Gold

Copper

Aluminium

Answer: (b) Gold

Explanation: Gold does not lose its lustre when exposed to air, which is why it is used for making ornaments. Unlike most metals, gold remains shiny without tarnishing.

 

12. What is the property of materials that describes their ability to be compressed or scratched?

Solubility

Hardness

Appearance

Roughness

Answer: (b) Hardness

Explanation: Hardness is the property of materials that determines how easily they can be compressed or scratched. Hard materials like iron and diamond cannot be easily scratched, while soft materials like wax or sponge can be compressed and scratched easily.

 

13. Which of the following substances is not soluble in water?

Sugar

Salt

Sand

Vinegar

Answer: (c) Sand

Explanation: Sand is an insoluble substance and does not dissolve in water, whereas sugar, salt, and vinegar are soluble in water and form solutions.

 

14. What is the term used for liquids that do not mix with each other?

Miscible liquids

Immiscible liquids

Soluble liquids

Insoluble liquids

Answer: (b) Immiscible liquids

Explanation: Immiscible liquids are liquids that do not mix with each other and separate into distinct layers, such as oil and water. Miscible liquids, on the other hand, mix completely to form solutions.

 

15. Which of the following gases dissolve in water and help aquatic plants and animals in photosynthesis and respiration?

Nitrogen

Hydrogen

Oxygen and Carbon dioxide

Methane

Answer: (c) Oxygen and Carbon dioxide

Explanation: Oxygen and carbon dioxide dissolve in water, enabling aquatic plants and animals to perform photosynthesis and respiration. These dissolved gases are essential for life in aquatic ecosystems.

 

16. What is a universal solvent?

Vinegar

Water

Kerosene

Alcohol

Answer: (b) Water

Explanation: Water is called the universal solvent because it dissolves a large number of substances, making it essential for various biological and chemical processes, including its role in the human body.

 

17. Which of the following is the hardest material?

Wax

Chalk

Diamond

Lead

Answer: (c) Diamond

Explanation: Diamond is one of the hardest known substances and is extremely difficult to compress or scratch. It is used in cutting tools because of its superior hardness.

 

18. What property of a material determines whether it will float or sink in water?

Shape

Volume

Density

Hardness

Answer: (c) Density

Explanation: The ability of a material to float or sink in water depends on its density. If the density of the material is less than that of water, it will float. If it is greater, it will sink.

 

19. Why does a metal ship float on water even though it is made of metal, which normally sinks?

The density of metal decreases when shaped into a ship

The shape of the ship allows it to displace enough water to stay afloat

The ship is made of a special type of metal

Ships have internal heat that keeps them afloat

Answer: (b) The shape of the ship allows it to displace enough water to stay afloat

Explanation: Even though metal has a high density, the shape of a ship allows it to displace enough water, reducing its overall density compared to water, which allows it to float.

 

20. Which of the following is an example of a translucent material?

Clear glass

Wood

Ground glass

Iron

Answer: (c) Ground glass

Explanation: Translucent materials allow some light to pass through but do not provide a clear image. Ground glass is a good example of a translucent material.

 

21. Which of the following materials would be classified as opaque?

Clear water

Plastic wrap

Cardboard

Transparent glass

Answer: (c) Cardboard

Explanation: Opaque materials do not allow any light to pass through them. Cardboard is an opaque material, meaning objects cannot be seen through it.

 

22. Why are cooking vessels made of metals but their handles made of materials like Bakelite?

Metals do not heat up quickly

Bakelite is stronger than metal

Metals are good conductors of heat, while Bakelite is a poor conductor of heat

Bakelite conducts heat better than metal

Answer: (c) Metals are good conductors of heat, while Bakelite is a poor conductor of heat

Explanation: Metals conduct heat efficiently, which helps in cooking, while Bakelite, being a poor conductor of heat, is used for handles to prevent them from getting too hot to touch.

 

23. Which of the following materials is a good conductor of electricity?

Rubber

Copper

Plastic

Wood

Answer: (b) Copper

Explanation: Copper is a metal and a good conductor of electricity. Materials like rubber, plastic, and wood are poor conductors and are often used as insulators.

 

24. What is the term used for materials that are not attracted by a magnet?

Magnetic materials

Non-magnetic materials

Conductors

Insulators

Answer: (b) Non-magnetic materials

Explanation: Non-magnetic materials, such as wood, plastic, and rubber, are not attracted to magnets. Magnetic materials, like iron, cobalt, and nickel, are attracted to magnets.

 

25. What is the name of the property that allows certain materials to float on water?

Transparency

Floatation

Conductivity

Magnetic property

Answer: (b) Floatation

Explanation: Floatation is the property of materials that determines whether they float on water. This is influenced by the density of the material compared to the density of the water.

 

26. Which of the following substances is an immiscible liquid when mixed with water?

Vinegar

Glycerine

Cooking oil

Lemon juice

Answer: (c) Cooking oil

Explanation: Cooking oil does not mix with water and forms a separate layer when kept undisturbed. It is an example of an immiscible liquid.

 

28. What is matter?

Anything that has color and shape

Anything that has mass and occupies space

Only solid substances

Substances that dissolve in water

Answer: (b) Anything that has mass and occupies space

Explanation: Matter is defined as anything that has mass and occupies space. This includes solids, liquids, and gases.

 

29. What is lustre?

The roughness of a material

The hardness of a material

The shiny appearance of materials

The softness of a material

Answer: (c) The shiny appearance of materials

Explanation: Lustre refers to the shiny or glossy appearance that some materials, especially metals like gold and silver, exhibit.