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.

Solution:

Matter: Chair, air, almonds, cold-drink, smell of perfume and smell.

Explanation: Anything that occupy space and has volume and mass are matter.

Here, chair, air, almond and cold-drink are matter as they occupy space and have volume and mass. Smell and smell of perfume are also classified as matter because we sense smell of anything because of gas coming out from an object, since we smell anything because of gas coming out from that object, thus smell is classified as matter also.

Question: 2. Give reasons for the following observation:

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

Solution: Sizzling food are hot foods. Because of heat particles of gas coming out from sizzling food move more rapidly and travel more distance in less time because of more kinetic energy. That?s why the smell of sizzling food reaches you several meters away. While smell of gas coming out from cold food has very less or almost negligible kinetic energy, so smell of cold food do not diffuse with air quickly and to get smell we have to go close.

Question: 3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

Solution: A diver is able to cut through water in a swimming pool, shows that water, which is a matter is made of small particles and there are space between those particles.

Explanation:

Water is a liquid and has more space between its particles compare to a solid. Apart from this particles of liquid are bonded together with less forces of attraction compare to a solid. Thus a diver is able to cut through water in a swimming pool.

Question: 4. What are the characteristics of the particles of matter?

Solution:

Characteristics of particles of matter:

Particles of matter are very small in size i.e. have microscopic size.

Particles of matter are moving continuously.

Particles of matters are bonded with force of attraction in the case of solid and liquid.

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 chimneys, honey, water, chalk, cotton and iron.

Solution :

Air < Exhaust from chimneys < Water < honey < cotton < chalk < Iron

Explanation:

Air has very less density among given matters. Exhaust from chimneys consists of many gases, such as carbon dioxide, carbon monoxide along with small particles expelled out because of burning of substances in the factory, thus exhaust from chimneys has more density than air.

Water is liquid and has more density than air and exhaust from chimneys because particles of water have more force of attraction.

Cotton is a type of solid because they have definite mass, size and volume. Thus, cotton is denser than air, exhaust from chimneys and honey.

Chalk and iron both are solid and have definite shape, size, mass and volume. But the force of attraction among particles of iron is stronger than that of chalk, that?s why chalk is soft and iron is hard. Thus, chalk has less density than iron.

Question: 6. (a) Tabulate the differences in the characteristics of states of matter.

Solution:

(b) Comment upon the following:

Rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.

Solution:

Rigidity: A property of matter, especially solid, which resist from getting distorted. Because of property of rigidity solid cannot be distorted.

Compressibility: The ability of a matter in gaseous state to be reduced to a lower volume because of great space between particles of gases is called compressibility.

Because of this property of compressibility, a gas can be compressed to lower volume. For example CNG is compressed natural gas and used in households to cook food and in vehicles to rum them.

Fluidity: Fluidity is the ability to flow. This is one of the characteristics of matters in liquid and gaseous state. Liquid and gas can be flow because of less force of attraction between their particles.

Filling a gas container: A gas gets the shape and volume of gas container in which it is filled. This happens because particles of gas move in all direction and force of attraction between the particles of gas is negligible.

Shape: Shape defines the definite boundary. A solid has definite shape while a liquid and gas do not. A liquid and gas get the shape of container in which they kept.

Kinetic Energy: The particles of matter possessed energy because of which they have kinetic energy. Thus kinetic energy is the energy possessed by particles due to their motion. Because of kinetic energy particles of matter are moving continuously.

Density : Mass per unit volume of a matter is called density.

Question: 7. Give reasons

(a) A gas fills completely the vessel in which it is kept.

Solution: The particles of gas moves in all directions freely as force of attraction between them is negligible and particles of gas exert pressure on the wall of container in every direction. This is the cause that a gas fills completely the vessel in which it is kept.

(b) A gas exerts pressure on the walls of the container.

Solution: The particles of gas moves in all direction as the force of attraction between them is negligible. This is the cause that a gas exerts pressure on the wall of the container.

(c) A wooden table should be called a solid.

Solution : A wooden table has definite shape, size, mass and volume which is the property of a solid.

Thus a wooden table is 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 : Air is a gas. The force of attraction between particles of gas is negligible because of which particles of gas are neither attracted to each other nor they are closely packed. On the other hand force of attraction between particles of a solid block of wood is highest this makes the particles of a solid block closely packed.

This is the cause that we can easily move our hand in air but to do the same through a solid block of wood we need a karate expert who has enough practice to break a wooden block of wood.

Although to move hand through a solid wooden block to break it by a karate expert requires high amount of energy.

Question: 8. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.

Solution : A solid has higher density compare to a liquid. But in the case of ice during freezing some air bubbles get packed within ice blocks, this makes the density of ice lowe than that of water which makes them float over water.

Question: 9. Convert the following temperature to Celsius scale:

(a) 300 K

Solution:

We know that, Temperature in Kelvin (K) = Temperature in Celsius scale + 273

Therefore, 300K = Temp in Celsius + 273

∴ Temperature in Celsius = 300 K – 273 = `27^oC`

Thus, 300K = `27^oC`

(b) 573 K

Solution :

We know that, Temperature in Kelvin (K) = Temperature in Celsius + 273

Therefore, 573K = Temp in Celsius + 273

∴ Temperature in Celsius = 573 K – 273 = `300^oC`

Thus, 573 K = `300^oC`

Question: 10. What is the physical state of water at:

(a) 250⁰C

Solution :

Since, water boils at `100^o\ C` and starts converting into vapour. Thus, physical state of water at `250^o\ C` is gaseous.

(b) `100^o\ C`

Solution :

Since, water boils at `100^o\ C` and starts converting into vapour. Thus, at `100^o\ C` water is in transition phase i.e. partially in liquid state and partially in gaseous state.

Question: 11. For any substance, why does the temperature remain constant during the change of state?

Solution :

When heat is supplied to the matter, say water, when temperature rise and remains constant at `100^o\ C` until all water turns into vapour even continuous supply of heat. This supplied heat is utilized in the phase change of water (liquid) to vapour (gas). This heat is called latent heat. This happens while change from solid to liquid and from change of phase from liquid to gas.

Thus, temperature of the system remains constant during the change of state of any substance.

Question: 12. Suggest a method to liquefy atmospheric gases.

Solution : An atmospheric gas can be liquied by decreasing of temperature and increasing of pressure.

Question: 13. Why does a desert cooler cool better on a hot dry day?

Solution :

A desert cooler works on the theory of evaporation.

In evaporation, liquid at surface area has more kinetic energy and it gets temperature from its surroundings to get evaporated.

Rate of evaporation increases with decreases in humidity. In hot dry days there is less humidity or negligible humidity present in atmosphere which increases the rate of evaporation resulting in better cooling by a desert cooler.

Thus a desert cooler cools better on a hot dry day rather than humid days, i.e. in rainy seasons.

Question: 14. How does the water kept in an earthen pot (matka) become cool during summer?

Solution : Earthen pots are pores. When water is kept in an earthen pot, pores of earthen pot absorbs water, which increases the surface area of water. Water on the surface area, i.e. pores of earthen pot gets evaporated continuously. While evaporation particles of water gets energy from other particles of water just after the particles lie on surface area, this reduces the temperature of water particles just after the surface area. This process continues, which cools the water kept in the earthen pot.

Thus, water kept in an earthen pot (matka) become cool during summer.

Question: 15. Why does our palm feel cold when we put some acetone or petrol or perfume on it?

Solution:

Acetone, petrol or perfume is volatile material. When acetone, petrol or perfume is put palm its surface areas increases. Because of increase in surface area and volatile nature acetone, petrol or perfume are evaporated quickly. While evaporation, particles of acetone, petrol or perfume absorbs heat energy from our palm which reduces the temperature of palm.

This the cause that 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 of milk faster from a saucer rather than a cup?

Solution :

When hot tea is kept in a saucer, tea is spread over a larger area than that of a cup. Increase in surface area increases the evaporation rate of tea. While evaporation particles of tea absorb energy from its surrounding which lowers the temperature of surroundings resulting in lowers the temperature of hot tea or milk.

Decrease in temperature of hot tea or milk kept in saucer enables us to sip faster than that of a cup.

Question: 17. What type of clothes should we wear in summer?

Solution :

We should wear cotton clothes in summer because:

In summer we perspire more than in cold days. Perspiration (producing of sweat) is a mechanism that keeps our body cool in hot days. Cotton clothes are good absorbent, which absorbs the sweat coming out from our body. After get absorbed by cotton clothes particles of sweat gets evaporating continuously. Evaporation of sweat lowers the temperature of surroundings and we feel cool and comfortable in summer days while wearing cotton clothes.