Chapter 04: Sorting Materials and Groups

    I. Multiple Choice Questions (MCQs).
    Q.1. A thing that has mass and occupies space is called
    a) matter
    b) materials
    c) substance
    d) all of these
    Answer a) matter
    Q.2. Matter is made up of tiny particles called
    a) atoms
    b) molecules
    c) both (a) and (b)
    d) materials
    Answer (b) molecules
    Q.3. 3. All objects are made up of substances called
    (a) matter (b) materials (c) atoms (d) none of these
    Ans: (b) materials
    Q.4. The characteristic of metals due to which they have a shining surface is called (a) appearance (b) transparency (c) lustre (d) none of these
    Ans(c) lustre
    Q.5. The liquids which do not mix with each other are known as
    (a) immiscible liquids (b) miscible liquids (c) solution (d) none of these
    Answer: (a) immiscible liquids

    II. Fill in the blanks by selecting appropriate words from the given list :

    List : Translucent, Magnetic, classification, solute, Bad
    Q.1. The type of grouping in which similar objects are placed together is known as _________________.
    Q.2. The substance which dissolves in a liquid is known as a _______________.
    Q.3. _________________ materials allow light to pass through them partially.
    Q.4. _________________ conductors do not conduct electricity.
    Q.5. _________________ materials are attracted by a magnet.

    Answer: 1- classification, 2- solute, 3- Translucent 4- Bad 5- Magnetic

    III. Match the items of Column A with those of Column B.

    Answer 1- (d) , 2- (c) , 3-(a) 4-( e) , 5- (b)

    IV. Write ‘T’ for the true and ‘F’ for the false statements.

    Q.1. Density is the property of a material that determines whether it is heavy or light
    for a given size.
    Q.2. The arrangement of molecules does not decide whether an object is a solid, liquid
    or a gas.
    Q.3. The molecules in a gas move around freely and occupy the entire space available
    to them.
    Q.4. Some liquids like glycerine, vinegar and lemon juice dissolve in water to form
    solutions.
    Q.5. Gases like oxygen and carbon dioxide do not dissolve in water.
    Answer: 1-T, 2-F, 3-T, 4-T, 5-F

    V. Very Short Answer Questions.
    Q.1. Define matter.
    Answer: Matter is defined as anything that has mass and occupies space.
    Q.2. What do you mean by solubility?
    Answer: The property of a substance by which it dissolves in water is solubility.

    Q.3. Define floatation.
    Answer: Certain materials float on water whereas, others sink. This property is called floatation.
    Thus, the ability to float is flotation.
    Q.4. What do you mean by electrical conductivity?
    Answer: Electrical conductivity is the ability of electric current to flow through a material.

    VI. Short Answer Questions.

    Q.1. Name four substances which have (i) lustre, (ii) no lustre.
    Ans: Substance having lustre : Gold, Silver, Copper and Aluminium
    Substance having lustre : Wood, Plastic, Paper and Rubber
    Q.2. Why is it necessary to classify objects into groups?
    Answer: Classification of objects into groups
    ▪ Makes the study of things around us convenient and systematic.
    ▪ It also helps us to have a general idea about the members of a group.
    Q.3. Why do most of the metals lose their lustre when they are exposed to air?

    Answer: When metals are exposed to air, most of them lose their lustre and get tarnished due to the action of air and moisture.

    Q.4. Discuss how property of hardness of a material decides the purpose for which it can be used. Explain with proper examples.

    Answer: 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.

    Q.5. Why are gold and silver metals made into ornaments?

    Answer: 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.
    Q.6. Describe solubility of gases in water and their importances briefly.
    Answer: 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.

    VII. Long Answer Questions.

    Q.1. What is matter? Explain its kinds on the basis of arrangement of its molecules.
    Answer: Matter is defined as anything that has mass and occupies space.

    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.

    Q.2. Explain three main properties of metals and their uses due to such properties.
    Answer: The uses of metals are related to their properties:

    • Hard and shiny appearance. 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.
    • Good conductors and heat and electricity: They are used to make pans, since they are good conductors of heat. They are used in electrical cables, because they are malleable, ductile and good conductors of electricity.
    • They are strong so used to build scaffolding and bridges.

    Q.3. What are miscible and immiscible liquids? How can you separate two immiscible liquids using a separating funnel?

    Answer: Miscible liquids: Liquids which mix together in all proportions and form a single layer are called miscible liquids.
    Immiscible liquids : Liquids which do not mix with each other and form separate layers are called immiscible liquids.

    Immiscible means that the liquids don’t dissolve in each other – oil and water are an example. It is possible to shake up the liquids and get them to mix but they soon separate. Separating immiscible liquids is done simply using a separating funnel. The two liquids are put into the funnel and are left for a short time to settle out and form two layers. The tap of the funnel is opened and the bottom liquid is allowed to run. The two liquids are now separate.

    Q.4. (a) How will you determine hardness of a given substance?
    (b) What are the important properties of materials?

    Answer: Testing for hardness
    Materials Required : Samples of several rocks, a bowl of water, a clean cloth, a coin, a glass jar, a steel file and sandpaper.
    Procedure : Clean the rock samples in water and dry them using the clean cloth. Now try to scratch each rock with your finger nail. If it scratches the rock then the rock has a hardness of 2 or less on Moh’s scale. (A finger nail has a hardness of 2 on this scale).

    Put aside the rocks scratched by the finger nail. Scratch the remaining ones with a coin (hardness 3 on Mohs’ scale). The rocks which can be scratched with the coin have hardness less than 3.
    Now scratch the remaining rocks on the glass jar. If any of the rocks make a scratch on the jar, then the minerals present in the rock are harder than glass. Keep aside the rocks that do not scratch glass as they are less hard than glass (hardness 5 – 6).

    Scratch the remaining rocks with a steel file (hardness 7) and finally with sand paper (hardness 8).

    Answer b) The characteristics of materials, that enable us to separate one object from the other, are called its properties. Following are the important properties of materials

    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. They are known as non-metals.

    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.

    Solubility: Substances which dissolve in water are known as soluble substances. For example Materials or substances like sugar or salt, when mixed with water, disappear completely in it. Substances which doesn’t dissolve in water are known as insoluble substances. Sand and chalk powder do not dissolve in water. They are said to be insoluble substances.

    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.

    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.

    Thermal and Electrical Conductivity: Materials which allow either heat or electric current to pass through them easily is known as good conductors. Materials that do not allow either heat or electric current to pass through them easily is known as bad conductors. The property by which heat is conducted through a substance is known as thermal conductivity.

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