Class 9 Science Chapter 1 Matter in Our Surroundings NCERT SOLUTIONS

 

Chapter 1 Matter in Our Surroundings

Question 1:

Which of the following are matter?

Chair, air, love, smell, hate, almonds, thought, cold, cold drink, smell of perfume.

Answer: Chair, air, almonds, and cold-drink.

Question 2:

Give reasons for the following observation:

The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close.

Answer: The smell of hot sizzling food reaches severed meters away, as the particles of hot food have more kinetic energy than the cold food and hence the rate of diffusion is more than the particles of cold food.

Question 3:

A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

Answer: A diver is able to cut through water in a swimming pool. This shows that the particles of water have intermolecular space and has less force of attraction.

Question 4:

What are the characteristics of particles of matter?

Answer: The characteristics of the particles of matter are:

(1) The particles of matter are very tiny.

(2) Particles have intermolecular space.
(3) Particles have intermolecular force.
(4) Particles of matter are moving continuously.

Question 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 chimney, honey, water, chalk, cotton, and iron.

Answer: The given substances in the increasing order of their densities can be represented as:

Air < Exhaust from chimney < Cotton < Water < Honey < Chalk < Iron.

Question 6:

(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.

Answer:

(a) The differences in the characteristics of states of matter are given in the following table.

Sl. No.	Solid state	Liquid state	Gaseous state
1.	Definite shape and volume.	No definite shape. Liquids attain the shape of the vessel in which they are kept.	Gases have neither a definite shape nor a definite volume.
2.	Incompressible	Compressible to a small extent.	Highly compressible
3.	There is little space between the particles of a solid.	These particles have a greater space between them.	The space between gas particles is the greatest.
4.	These particles attract each other very strongly.	The force of attraction between liquid particles is less than solid particles.	The force of attraction is least between gaseous particles.
5.	Particles of solid cannot move freely.	These particles move freely.	Gaseous particles are in a continuous, random motion.

 

 

(b) Comment on:

(i)Rigidity :The tendency of a substance to retain  their shape when subjected to external force.

(ii) Compressibility: Compressibility is the ability to be reduced to a lower volume when force is applied. This property is called compressibility. Gases and liquids are  compressible.                        

(iii) Fluidity: The tendency of particles to flow is called fluidity. Liquids and gases flow.                                                         (iv) Filling of a gas container: Gases have particles which vibrate randomly in all the directions. The gas can fill the container.

(v) Shape: Solids have maximum intermolecular force and definite shape.

Whereas liquids and gases takes the shape of container.

(vi) Kinetic energy: The energy possessed by particles due to their motion is called kinetic energy. Molecules of gases vibrate randomly as they have maximum kinetic energy.

(vii) Density: It is defined as mass per unit volume, the solids have highest density.

Question 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.

Answer:

(a) The molecules of gas have high kinetic energy due to which they keep moving in all directions and hence fill the vessel completely in which they are kept.
(b) Molecules of gas move randomly in all directions at high speed due to high kinetic energy. As a result, the molecules of gas  hit each other and also hit the walls of the container with a force. Therefore, gas exerts pressure on the walls of the container.
(c) A wooden table has a definite shape and volume. It is very rigid and cannot be compressed , it also cannot flow, these are the characteristics of a solid. Hence, a wooden table should be called a solid.
(d) Molecules of air have large spaces between them due to less intermolecular force. On the other hand, wood has little space between its molecules due to high intermolecular force. Hence, it is rigid. For this reason, we can easily move our hands in air, but to do the same through a solid block of wood, we need a karate expert.

Question 8:

Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.

Answer: Though ice is a solid, it has large number of empty spaces between its molecules. These spaces are larger as compared to the spaces present between the molecules of water.  Thus, the volume of ice is greater than that of water. As we know density = mass/volume , hence the volume of a substance increases, when its density decreases and vice versa. Hence, the density of ice is less than that of water. A substance with lower density than water can float on water. Therefore, ice floats on water.

Question 9:

Convert the following temperature to Celsius scale:
(a) 300 K (b) 573 K

Answer : (a) 300 – 273 = 27°C (b) 573 – 273 = 300°C .

Question 10: 

What is the physical state of water at:

(a) 250°C     (b) 100°C

Answer:

(a) At 250°C, Water exists in gaseous state.

(b) At 100°C, water can exist in both liquid and gaseous form.

Question 11:

For any substance, why does the temperature remain constant during the change of state?

Answer: During a change of state, the temperature remains constant because all the heat supplied  is utilised in changing the state by overcoming the forces of attraction between the molecules. Therefore, this heat does not contribute in increasing the temperature of the substance.

Question 12:

Suggest a method to liquefy atmospheric gases.

Answer:

By applying pressure and reducing the temperature, atmospheric gases can be liquefied.

Question 13:

Why does a desert cooler cool better on a hot dry day?

Answer: The outer walls of the cooler get sprinkled by water constantly. This water evaporates due to hot dry weather. Evaporation causes cooling of air present inside the cooler. This cool air is then sent in the room by the cooler fan.

Question 14:

How does water kept in an earthen pot (matka) become cool during summers?

Answer: The earthen pot has lot of pores on it, the water comes out through these pores hence, the water gets evaporated at the surface of the pot . As we know evaporation causes cooling , thereby  the pot  becomes cold and the water inside the pot cools by this process.  In this way, water kept in an earthen pot becomes cool during summers.

Question 15:

Why does our palm feel cold when we put some acetone or petrol or perfume on it?

Answer: Acetone , perfume and petrol are volatile substances hence when we put either of the substances on our Palm it immediately takes heat from our Palm and evaporates. As we know evaporation causes cooling , thereby our palm feel cold when we put some acetone or petrol or perfume on it . 

Question 16:

Why are we able to sip hot tea or milk faster from a saucer than a cup?

Answer: we know that the rate of evaporation is faster with increased in surface area. A tea or milk has a larger surface area in a saucer than in a cup. Thus, it evaporates faster and cools faster in a saucer than in a cup. Hence ,we are able to sip hot tea or milk faster from a saucer than a cup. 

Question 17:

What type of clothes should we wear in summers?

Answer: We should wear light coloured cotton clothes in summer. Light coloured cloth  because they are the poor absorber of heat, so they reflect heat. cotton cloths because it is a good absorber of water and hence it absorbs all the Sweat coming out from our body and exposes it into the air. When the sweet is exposed to air it evaporates does leaving a body cooler and more comfortable.

Question 18:

Convert the following temperatures to Celsius scale.

(a) 293 K             (b) 470 K

Answer:

(a) 293 K = (293 − 273) °C  = 20 °C

(b) 470 K = (470 − 273) °C = 197 °C

Question 19:

Convert the following temperatures to Kelvin scale.

(a) 25°C         (b) 373°C

Answer:

(a) 25 °C = (25 + 273) K   = 298 K

(b) 373 °C = (373 + 273) K  = 646 K

Question 20:

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.

Answer:

 (a) Naphthalene balls disappear with time without leaving any solid, because naphthalene balls are volatile in nature hence, sublime and directly changes into vapour state without leaving any solid.

(b) We can get the smell of perfume sitting several metres away because perfume contain volatile solvent and thus diffuse faster and can reach people sitting several metres away.

Question 21:

Arrange the following substances in increasing order of forces of attraction between the particles—water, sugar, oxygen.

Answer: 

Oxygen —> water —> sugar.

Question 22:

What is the physical state of water at−−

(a) 25°C               (b) 0°C                (c) 100°C

Answer: 

(a) Water at 25°C is present in the liquid state.

(b) At 0 °C, water can exist as both solid and liquid. 

(c) At 100 °C, water can exist as both liquid and gas.

Question 23:

Give two reasons to justify−

(a) water at room temperature is a liquid.

(b) an iron almirah is a solid at room temperature.

Answer:

(a) At room temperature (25 °C), water is a liquid because it has the following characteristic of liquid:

(i) At room temperature, water has no shape but has a fixed volume that is, it occupies the shape of the container in which it is kept.

(ii) At room temperature, water flows.

(b) An iron almirah is a solid at room temperature (25 °C) because:

(i) it has a definite shape and volume like a solid at room temperature.

(ii) it is rigid as solid at room temperature.

Question 24:

Why is ice at 273 K more effective in cooling than water at the same temperature?

Answer:

Ice at 273 K will absorb heat energy  from the medium to overcome the fusion to become water. Hence the cooling effect of ice is more than the water at same temperature because water does not absorb this extra heat from the medium.

Question 25:

What produces more severe burns, boiling water or steam?

Answer:

Steam has more energy than boiling water. It possesses the additional latent heat of vaporization. Therefore, burns produced by steam are more severe than those produced by boiling water.

Question 26:

Name A, B, C, D, E and F in the following diagram showing change in its state.

Answer: