Matter In Our Surroundings - NCERT Solutions
In-Text Questions (Page No- 03)
1. Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume.
Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume.
Answer - Chair, air, almonds and lemon water
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.
The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.
Answer - This observation can be explained on the basis of the process
of diffusion. When hot sizzling food is being cooked,
the high temperature increases the kinetic energy of
the particles in the food, including the aromatic
molecules. This leads to an increased rate of
evaporation and releases more aromatic particles into
the air. The increased concentration of aromatic particles
in the air enables them to diffuse more readily and travel
a greater distance, allowing the smell to reach us several
meters away. On the other hand, cold food has lower evaporation
and releases fewer aromatic particles, resulting in a weaker
smell that requires us to go close to the food to perceive
the smell.
3. A diver is able to cut through water in a swimming
pool. Which property of matter does this observation show?
Answer - The diver's ability to cut through water in a swimming
pool demonstrates the property of liquids having spaces between
particles. These spaces allow the liquid particles to be
displaced and compressed, enabling the diver to create a
temporary path.
4. What are the characteristics of the particles of matter?
Answer - The characteristics of the particles of matter are as follows:
- Particles of matter possess mass.
- Particles of matter occupy space.
- Particles of matter are constantly in motion.
- Particles of matter attract each other.
- Particles of matter have empty spaces between them.
- Particles of matter can change their arrangement and spacing.
In-Text Questions (Page No- 06)
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.
Arrange the following in order of increasing density- air, exhaust from chimneys, honey, water, chalk, cotton and iron.
Answer - Increasing density order:
air, exhaust from chimneys, water, honey,
cotton, chalk, iron.
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.
(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.
Answer - (a)
(b) Rigidity - Rigidity of a substance is its ability to retain its shape under the action of an external force.
Solids are characterized by a high degree of rigidity, meaning they resist deformation and maintain their shape. Unlike solids, liquids and gases do not have a fixed shape and are hence not rigid.
Compressibility - Compressibility of a substance is its ability to be compressed under the application of pressure.
Solids have low compressibility, meaning they are difficult to compress or change in volume. Liquids have moderate compressibility, while gases have high compressibility.
Fluidity - Fluidity of a substance is its ability to flow.
Liquids and gases exhibit fluidity.
Filling a gas container - Gases have the property of completely filling the container in which they are placed, as their particles are highly mobile and can spread out to occupy all available space.
Shape - Solids have a definite shape, meaning they maintain a fixed and characteristic shape. Liquids and gases, on the other hand, take the shape of their container.
Kinetic energy - Kinetic energy is the energy possessed by an object due to virtue of its motion.
Gases possess the highest kinetic energy, followed by liquids, and then solids.
Density - Density of a substance is the amount of mass of that substance present in a unit volume of the substance.
Generally, Solids have a higher density in comparison to liquids, which have a higher density in comparison to gases.
| Solid | Gas | Liquid | |
|---|---|---|---|
| Shape | Definite | Indefinite, takes the shape of the container | Indefinite, takes the shape of the container |
| Volume | Definite | Definite | Indefinite, fills the entire container |
| Interparticle spaces | Minimum | Intermediate | Maximum |
| Interparticle forces of attraction | Maximum | Intermediate | Minimum |
| Kinetic energy of particles | Minimum | Intermediate | Maximum |
| Compressibility | Negligible | Low | High |
(b) Rigidity - Rigidity of a substance is its ability to retain its shape under the action of an external force.
Solids are characterized by a high degree of rigidity, meaning they resist deformation and maintain their shape. Unlike solids, liquids and gases do not have a fixed shape and are hence not rigid.
Compressibility - Compressibility of a substance is its ability to be compressed under the application of pressure.
Solids have low compressibility, meaning they are difficult to compress or change in volume. Liquids have moderate compressibility, while gases have high compressibility.
Fluidity - Fluidity of a substance is its ability to flow.
Liquids and gases exhibit fluidity.
Filling a gas container - Gases have the property of completely filling the container in which they are placed, as their particles are highly mobile and can spread out to occupy all available space.
Shape - Solids have a definite shape, meaning they maintain a fixed and characteristic shape. Liquids and gases, on the other hand, take the shape of their container.
Kinetic energy - Kinetic energy is the energy possessed by an object due to virtue of its motion.
Gases possess the highest kinetic energy, followed by liquids, and then solids.
Density - Density of a substance is the amount of mass of that substance present in a unit volume of the substance.
Generally, Solids have a higher density in comparison to liquids, which have a higher density in comparison to gases.
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.
(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) Gas particles have high kinetic energy and negligible intermolecular forces, allowing them to spread and occupy the entire volume of the container.
(b) Gas particles collide with the walls of the container and exert pressure due to their high kinetic energy.
(c) A wooden table is called a solid because its particles are tightly packed, have a definite shape, and resist deformation.
(d) Air particles can be easily moved as they have low intermolecular forces, while solid particles like those in wood have strong intermolecular forces, requiring significant force to move them.
(a) Gas particles have high kinetic energy and negligible intermolecular forces, allowing them to spread and occupy the entire volume of the container.
(b) Gas particles collide with the walls of the container and exert pressure due to their high kinetic energy.
(c) A wooden table is called a solid because its particles are tightly packed, have a definite shape, and resist deformation.
(d) Air particles can be easily moved as they have low intermolecular forces, while solid particles like those in wood have strong intermolecular forces, requiring significant force to move them.
4. Liquids generally have lower density as
compared to solids. But you must have
observed that ice floats on water.
Find out why.
Answer -
Liquids usually have lower density than solids, but ice floats on water due to its lower density when compared to liquid water. This is because when water freezes into ice, the water molecules arrange themselves in a crystal lattice structure, creating more space between the molecules. This increase in volume results in a decrease in density, causing ice to be less dense than liquid water and float on its surface.
Liquids usually have lower density than solids, but ice floats on water due to its lower density when compared to liquid water. This is because when water freezes into ice, the water molecules arrange themselves in a crystal lattice structure, creating more space between the molecules. This increase in volume results in a decrease in density, causing ice to be less dense than liquid water and float on its surface.
In-Text Questions (Page No- 09)
1. Convert the following temperature to celsius scale:
a. 300 K
b. 573 K.
a. 300 K
b. 573 K.
Answer -
a. 300 K = 27°C
b. 573 K = 300°C
a. 300 K = 27°C
b. 573 K = 300°C
2. What is the physical state of water at:
a. 250ºC
b. 100ºC ?
a. 250ºC
b. 100ºC ?
Answer -
a. At 250ºC, water is in the gaseous state (steam).
b. At 100ºC, water exists in both liquid and gaseous states.
a. At 250ºC, water is in the gaseous state (steam).
b. At 100ºC, water exists in both liquid and gaseous states.
3. For any substance, why does the temperature
remain constant during the change of state?
Answer -
The temperature remains constant during the change of state because the energy supplied is utilized in overcoming the intermolecular forces rather than increasing the temperature. This energy is used to break the existing bonds or form new ones, resulting in a change of state without a change in temperature.
The temperature remains constant during the change of state because the energy supplied is utilized in overcoming the intermolecular forces rather than increasing the temperature. This energy is used to break the existing bonds or form new ones, resulting in a change of state without a change in temperature.
4. Suggest a method to liquefy atmospheric gases.
Answer -
To liquefy atmospheric gases, the method of cooling and compression can be employed. The gases are first compressed to reduce their volume, which increases the pressure. Then, they are cooled using refrigeration or other cooling methods to reduce their temperature below their boiling point, causing them to condense into a liquid state.
To liquefy atmospheric gases, the method of cooling and compression can be employed. The gases are first compressed to reduce their volume, which increases the pressure. Then, they are cooled using refrigeration or other cooling methods to reduce their temperature below their boiling point, causing them to condense into a liquid state.
In-Text Questions (Page No- 10)
1. Why does a desert cooler cool better on a hot dry day?
Answer -
A desert cooler cools better on a hot dry day because the primary cooling mechanism of a desert cooler is evaporation. On a hot dry day, the air has low humidity, which means it can hold more water vapour. When the hot air passes through the wet cooling pads of the cooler, the water evaporates quickly, absorbing heat from the air and resulting in a greater cooling effect.
A desert cooler cools better on a hot dry day because the primary cooling mechanism of a desert cooler is evaporation. On a hot dry day, the air has low humidity, which means it can hold more water vapour. When the hot air passes through the wet cooling pads of the cooler, the water evaporates quickly, absorbing heat from the air and resulting in a greater cooling effect.
2. How does the water kept in an earthen pot (matka) become cool during summer?
Answer -
Water kept in an earthen pot (matka) becomes cool during summer due to the process of evaporation. The porous nature of the earthen pot allows water to seep through its walls and evaporate from the surface. As the water evaporates, it takes away heat energy from the remaining water inside the pot, resulting in a cooling effect.
Water kept in an earthen pot (matka) becomes cool during summer due to the process of evaporation. The porous nature of the earthen pot allows water to seep through its walls and evaporate from the surface. As the water evaporates, it takes away heat energy from the remaining water inside the pot, resulting in a cooling effect.
3. Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Answer -
When we put acetone, petrol, or perfume on our palms, we feel cold because these substances have low boiling points and evaporate quickly. As they evaporate from our skin, they absorb heat energy from the surroundings, including our palms, resulting in a cooling sensation.
When we put acetone, petrol, or perfume on our palms, we feel cold because these substances have low boiling points and evaporate quickly. As they evaporate from our skin, they absorb heat energy from the surroundings, including our palms, resulting in a cooling sensation.
4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Answer -
We are able to sip hot tea or milk faster from a saucer rather than a cup because the saucer has a larger surface area compared to the cup. This increased surface area allows for faster evaporation of the hot liquid, cooling it down more quickly and making it easier to sip without burning our mouths.
We are able to sip hot tea or milk faster from a saucer rather than a cup because the saucer has a larger surface area compared to the cup. This increased surface area allows for faster evaporation of the hot liquid, cooling it down more quickly and making it easier to sip without burning our mouths.
5. What type of clothes should we wear in summer?
Answer -
In summer, it is recommended to wear light-coloured and loose-fitting clothes made of breathable fabrics such as cotton or linen. These fabrics allow air to circulate around the body, promoting better ventilation and sweat evaporation, which helps in keeping the body cool. Additionally, wearing clothes that cover the skin and provide protection from direct sunlight can help prevent sunburn and overheating.
In summer, it is recommended to wear light-coloured and loose-fitting clothes made of breathable fabrics such as cotton or linen. These fabrics allow air to circulate around the body, promoting better ventilation and sweat evaporation, which helps in keeping the body cool. Additionally, wearing clothes that cover the skin and provide protection from direct sunlight can help prevent sunburn and overheating.
Exercises
1. Convert the following temperatures to the celsius scale.
(a) 293 K
(b) 470 K
(a) 293 K
(b) 470 K
Answer -
a. 20 C
b. 197 C
a. 20 C
b. 197 C
2. Convert the following temperatures to the kelvin scale.
(a) 25°C
(b) 373°C
(a) 25°C
(b) 373°C
Answer -
a. 298 K
b. 646 K
a. 298 K
b. 646 K
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.
(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 undergo a process called sublimation, where they transform directly from a solid to a gaseous state without passing through the liquid phase. Hence, they disappear without leaving any solid residue.
b. Due to the high speed of gas particles and the relatively large spaces between them, gases exhibit the property of rapid diffusion. The particles of the perfume get mixed with the particles of air and spread quickly. Thus, we can get the smell of perfume sitting several metres away.
a. Naphthalene balls undergo a process called sublimation, where they transform directly from a solid to a gaseous state without passing through the liquid phase. Hence, they disappear without leaving any solid residue.
b. Due to the high speed of gas particles and the relatively large spaces between them, gases exhibit the property of rapid diffusion. The particles of the perfume get mixed with the particles of air and spread quickly. Thus, we can get the smell of perfume sitting several metres away.
4. Arrange the following substances in increasing order of forces of attraction between the particles—
water, sugar, oxygen.
water, sugar, oxygen.
Answer -
Oxygen , Sugar , Water.
The forces of attraction between the particles are highest in solids, intermediate in liquids and least in gases.
Oxygen , Sugar , Water.
The forces of attraction between the particles are highest in solids, intermediate in liquids and least in gases.
5. What is the physical state of water at—
(a) 25°C
(b) 0°C
(c) 100°C?
(a) 25°C
(b) 0°C
(c) 100°C?
Answer -
a. At 25 C, water exists in a liquid state.
b. At 0 C, water exists in both liquid and solid states.
c. At 100 C, water exists in both liquid and gaseous states.
a. At 25 C, water exists in a liquid state.
b. At 0 C, water exists in both liquid and solid states.
c. At 100 C, water exists in both liquid and gaseous states.
6. Give two reasons to justify—
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
Answer -
a. Firstly, at room temperature, the average kinetic energy of water molecules is sufficient to overcome the intermolecular forces of attraction, allowing water to remain in a liquid state.
Secondly, water has relatively weak intermolecular forces compared to other substances, contributing to its liquid state at room temperature.
b. The particles in an iron almirah, which are closely packed, have strong intermolecular forces of attraction. These forces are significant enough to keep the particles in a fixed position, resulting in the solid state of the iron almirah at room temperature.
a. Firstly, at room temperature, the average kinetic energy of water molecules is sufficient to overcome the intermolecular forces of attraction, allowing water to remain in a liquid state.
Secondly, water has relatively weak intermolecular forces compared to other substances, contributing to its liquid state at room temperature.
b. The particles in an iron almirah, which are closely packed, have strong intermolecular forces of attraction. These forces are significant enough to keep the particles in a fixed position, resulting in the solid state of the iron almirah at room temperature.
7. Why is ice at 273 K more effective in cooling than water at the same temperature?
Answer -
At 273 K, both water and ice co-exist with water having more heat energy in the form of latent heat of fusion. As ice has less heat energy than water, it is more effective in cooling than water at the same temperature.
At 273 K, both water and ice co-exist with water having more heat energy in the form of latent heat of fusion. As ice has less heat energy than water, it is more effective in cooling than water at the same temperature.
8. What produces more severe burns, boiling water or steam?
Answer -
Steam produces more severe burns than boiling water. This is because steam has more heat energy than boiling water in the form of latent heat of vapourisation.
Steam produces more severe burns than boiling water. This is because steam has more heat energy than boiling water in the form of latent heat of vapourisation.
9. Name A, B, C, D, E and F in the following diagram showing change in its state.
Answer -
a. melting
b. vaporization/boiling
c. condensation
d. freezing
e. sublimation
f. deposition
a. melting
b. vaporization/boiling
c. condensation
d. freezing
e. sublimation
f. deposition