NCERT Solutions for Class 9th Science
Chapter 1 – MATTER IN OUR SURROUNDINGS
(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)
Q.1 Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume.
Ans Anything that occupies space and has mass is called matter. It is made up of particles and exists in three states— solid, liquid and gas.
So the matter from the list given in question are:
Chair, Almonds – Matter in Solid state
Cold Drink – Matter in Liquid state
Air, Smell of Perfume – Matter in Gaseous state
Q.2 Give reasons for the following observation:
The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.
Ans Particles of matter are continuously moving, i.e. they possess kinetic energy. As the temperature rises, particles move faster due to increase in kinetic energy. This increases the rate of diffusion and hence the smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.
Q.3 A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Ans It shows that matter is made up of particles which have spaces between them. The particles of water (bonded to each other through a force of attraction) got displaced as force applied by the diver overcome these forces of attraction.
Q.4 What are the characteristics of the particles of matter?
Q.5 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.
Q.6 (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.
Q.7 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.
Ans (a) The force of attraction between particles of gas is very small and thus they move freely in all directions. Therefore, a gas fills completely the vessel in which it is kept.
Q.8 Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
Q.9 Convert the following temperature to celsius scale:
a. 300 K b. 573 K.
Q.10 What is the physical state of water at:
a. 250ºC b. 100ºC ?
Q.11 For any substance, why does the temperature remain constant during the change of state?
Q.12 Suggest a method to liquefy atmospheric gases.
Q.13 Why does a desert cooler cool better on a hot dry day?
Q.14 How does the water kept in an earthen pot (matka) become cool during summer?
Q.15 Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Q.16 Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Q.17 What type of clothes should we wear in summer?
Ans We should wear cotton clothes in summer because in summer we perspire a lot and cotton, being a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation. During this evaporation, particles on the surface of the liquid gain energy from our body surface, making the body cool.
EXERCISES
Q.1 Convert the following temperatures to the celsius scale.
(a) 293 K (b) 470 K.
Ans Thought Process:
Temperature in Celsius = Temperature in Kelvin – 273
a) 293 K = 293 – 273 = 20°C
b) 470 K = 470 – 273 = 197°C
Q.2 Convert the following temperatures to the Kelvin scale.
(a) 25°C (b) 373°C.
Q.3 Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
Ans (a) Naphthalene balls disappear with time without leaving any solid because of sublimation in which it directly gets converted into gas.
(b) Particles of gas possess high kinetic energy and large spaces between them. This increases the rate of diffusion and hence we can get the smell of perfume sitting several meters away.
Q.4 Arrange the following substances in increasing order of forces of attraction between the particles— water, sugar, oxygen.
Q.5 What is the physical state of water at—
(a) 25°C (b) 0°C (c) 100°C?
Q.6 Give two reasons to justify—
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
Q.7 Why is ice at 273 K more effective in cooling than water at the same temperature?
Q.8 What produces more severe burns, boiling water or steam?
Q.9 Name A,B,C,D,E and F in the following diagram showing change in its state.