Chapter 01 Matter in Our Surroundings Questions-02
Questions
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.
Show Answer
Answer
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 and exhaust from chimneys are in the gaseous state and have a density that is a lot less than that of water. Hence they will float above the water.
Cotton, despite being a solid, will float on water due to large air pockets between the fibres. Thus, it will come before water in the order.
Honey, chalk, and iron all have densities greater than water and therefore will sink in water.
Cotton is denser than both the gaseous materials in this list on account of it being a solid.
The exhaust from chimneys is denser than air. It has a lot of particulate matter packed in a small volume that increases its density.
Honey is less dense than both chalk and iron since it is a liquid.
The given substances in the increasing order of their densities can be represented as:
Increasing order of Density
Air $<$ Exhaust from chimney $<$ Cotton $<$ Water $<$ Honey $<$ Chalk $<$ Iron
2. (a) Tabulate the differences in the characterisitcs of states of matter.
(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.
Show Answer
Answer
(a)
| Solid: | Liquid: | Gases : |
|---|---|---|
| Solids have a definite volume. | Liquids also have a definite volume. | Gases do not have a definite volume. Their volume varies with the container in which they are stored or kept. |
| Solids do not tend to flow. | Liquids tend to flow. | Gases also tend to flow |
| Solids are rigid. | Liquids are not rigid. | Gases are not rigid. |
| Generally solids have a definite shape with very few exceptions like sponge, rubber band etc. | Liquids do not have a definite shape. They take the shape of the container. | Gases do not have a definite shape |
| Solids are generally incompressible with very few exceptions like sponge, rubber band etc. | Liquids are almost incompressible. | Gases 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 by compressing it under very high pressure. The property of compressibility (of gases) ivey sue full in this case
Shape: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.
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.
Show Answer
Answer
(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 closely packed molecules so there is no question of the movement of hand through it, in absence of suitable force in proper direction.
4. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
Show Answer
Answer
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 $(H_2 O)$ 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.
