Class 9 science question answer of chapter number 1 part 2
Question 1:The mass per unit volume of a substance is called density. (Density = mass/volume).Arrange the following in order of increasing density–Air, exhaust from chimneys, honey, water, chalk, cotton and iron.
Solution:We can solve this question by keeping this concept in mind. The correct order of density for gas, liquid and solid are: Gas < Liquid < Solid. Thus, Air, exhaust from chimneys water, honey, cotton , chalk ,iron Gas Liquid Solid -------------------------------------------------------------------------------------------> Increasing order of Density
Question 2:(a) Tabulate the differences in the characteristics of states of matter.
(b) Comment upon the following:
Rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.
Solution:
(a)Solid :Solids have a definite volume.Solids do not tend to flow. Solids are rigid.Generally solids have a definite shape with very few exceptions like sponge, rubber band etc.Solids are generally incompressible with very few exceptions like sponge, rubber band etc.
Liquid :Liquids also have a definite volume.Liquids tend to flow.Liquids are not rigid.Liquids do not have a definite shape. They take the shape of the container.Liquids are almost incompressible.
Gases :Gases do not have a definite volume. Their volume varies with the container in which they are stored or kept.Gases also tend to flow Gases are not rigid.Gases do not have a definite shapeGases are compressible.
(b)Rigidity:Property by which an object retains its shape and size is called as rigidity. Solids are rigid whereas liquids and gases are not. Compressibility: Compressibility is the property; due to which a substance can be compressed, means its volume can be decreased. Gases are compressible whereas solids and liquids are not.Fluidity: Flowing tendency of a substance called fluidity. Gases and liquids are fluids, solids are not.Filling a gas container: a large volume of gas can be filled in a gas container bycompressing it under very high pressure. The property of compressibility (of gases) ivey sue full in this caseShape:The property of having a definite geometry is called shape of a particular substance. Solids have a definite shape whereas gases and liquids do not have.Kinetic energy: The energy possessed by a moving object or by the moving molecules of called kinetic energy. On increasing the temperature,kinetic energy of a substance (or its molecules) also increases. Molecules of gases posses highest kinetic energy.Density : The mass per unit volume of a substance is called density.
Mass
Density = ----------
Volume
Question 3:Give reasons:(a) A gas fills completely the vessel in which it is kept. (b) A gas exerts pressure on the walls of the container. (c) A wooden table should be called a solid.(d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.
Solution:(a) Force of attraction between the molecules of gases is negligible. So, molecules of gases occupy the maximum space available to them. High kinetic energy possessed by their molecules also helps for the same. (b)The motion of particles is random and having very high speed in the gaseous state.Due to this random movement, the particles hit each other and also the walls of the container. The pressure exerted by the gas is due to this force exerted by these particles per unit area on the walls of the container.(c) There is a strong force of attraction between the molecules of wood and the intermolecular space is the least. So, a wooden table has a definite shape and volume and it should be called a solid.(d) Air molecules are very-very far from each other due to negligible force of attraction working between them. So, our hand gets sufficient. space to move in air and we also displace some air molecules by applying force. But a solid block of wood has closelypacked molecules so there is no question of the movement of hand through it, in absence of suitable force in proper direction.
Question 4:Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why?
Solution:Liquids have lower density than that of solids. Water is also a liquid so it should also have less density than that of solid that is ice.But the case is not so and the reason for the same is the cage-like structure of ice. i.e., presence of vacant spaces between water (H2O) molecules when they linked in ice. The number of these spaces is comparatively less in water. Being more porous than water, ice is lighter than water and floats over the surface of water.
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