Matter in Our Surroundings – Important Questions

Class 9 Chemistry Chapter 1

Find out the most important questions of the chapter matter in our surroundings of class 9 Chemistry. These important questions are designed by NTSE Guru Experts and are most likely to appear in exams. Matter in our surroundings is a scoring chapter of chemistry for class 9 and with the help of these questions answers a student can achieve an overall good score. Start your preparation of chemistry today with the help of matter in our surroundings class 9 questions answers.

Matter in Our Surroundings – Class 9 Questions Answers :

1. When we dissolve some salt/sugar in water, it disappears and water level doesn’t change. What could be the reason?

Ans:  When we dissolve some salt/sugar in water then it disappears and water level doesn’t changes because particles of salt/sugar occupy the intermolecular space.

2. We add a blue ink-drop in one beaker and a honey drop in second beaker, both filled with water.

a. What would you observe immediately after adding the drops in both the cases?

b. Is there any difference in observations? If yes give reason.

Ans:

(a)  Blue-ink drop dissolves immediately while the honey drop first settles down & then dissolves slowly.

(b)  Yes. There is difference between the observations because of the difference in density. Ink drop has lower density than honey drop so it dissolves immediately, whereas honey drop first settles down at the bottom of the beaker and then dissolves slowly.

3. What do you mean by diffusion? How does the rate of diffusion get affected by the temperature?

Ans:  Intermixing of different types of matter on their own is known as diffusion.  The rate of diffusion increases on increasing the temperature of the diffusing substance as particles gain kinetic energy and move faster.

4. What is dry ice? How is it obtained?

Ans:  Solid $CO_{2}$ is known as dry ice. It is obtained by cooling & compressing gas.

5. Convert the following :

(a) ${}^\circ&space;C\,to{{\,}^{{}}}K:27{}^\circ&space;C,\,-300{}^\circ&space;C,\,-273{}^\circ&space;C$

(b) $^{{}}K\,to\,{}^\circ&space;C:{{273}^{{}}}K,\,\,{{27}^{{}}}K,\,\,{{0}^{{}}}K$

Ans. (a) ${{T}_{k}}={{T}_{^{o}C}}+273$

(i) $27{}^\circ&space;C\to&space;\,K$

$T_{k}&space;=&space;27&space;+&space;273$

$T_{k}&space;=&space;300K$

(ii) $-300{}^\circ&space;C\to&space;K$

$T_{k}=-300&space;+&space;273$

$T_{k}=-27K$

(iii) $-273{}^\circ&space;C\to&space;K$

${{T}_{k}}=-273+273$${{T}_{k}}=0K$

(b)  ${{T}_{k}}={{T}_{{}^\circ&space;C}}+273\,\,\,or\,{{T}_{{}^\circ&space;C}}={{T}_{k}}-273$

(i) $273\,K\to&space;C$

$273={{T}_{^{o}C}}\,+273$

${{T}_{^{o}C}}\,={{0}^{o}}C$

(ii) $27K\to&space;C$

$27={{T}_{^{o}C}}\,+273$

${{T}_{^{o}C}}=-{{246}^{o}}C$

(iii) $0\,K\to&space;\,{}^\circ&space;C$

${{T}_{{}^\circ&space;C}}=0-273=-273{}^\circ&space;C$

6. As we go on higher altitudes, the boiling point of liquid goes on decreasing. Why?

Ans: A liquid boils when its vapour pressure becomes equal to atmospheric pressure. As we go on higher altitudes (in hilly regions), atmospheric pressure decreases and so the vapour pressure of liquid becomes equal to atmospheric pressure at a lower temperature & the liquid boils at lower temperature, i.e. its boiling point decreases.

7.  Why does state of matter changes when heat is supplied to any substance and when heat is absorbed by any substance?

Ans:  Every substance has some force of attraction between its particles, which holds them together. If a substance has to change its state then it is necessary to overcome these forces of attraction between its particles. The heat which we supply first increases the kinetic energy of particles & then it is used up to overcome the forces of attraction between the particles of a substance and thus results in change of state.

(a) Steam at $100{}^\circ&space;C$ causes more severe burns than water at $100{}^\circ&space;C$ .

(b) Ice at ${{0}^{\circ&space;}}C$ is preferable in cold drink than water at ${{0}^{\circ&space;}}C$ .

Ans: (a) Steam at $100{}^\circ&space;C$ causes more severe burns, as it contains more heat in the form of latent heat of vaporization as compared to water at $100{}^\circ&space;C$.

(b) Ice at ${{0}^{\circ&space;}}C$ is preferable in cold drink because ice at ${{0}^{\circ&space;}}C$absorbs more heat in the form of latent heat of fusion from cold drink and makes it more cooler as compared to  water at ${{0}^{\circ&space;}}C$

9. Define evaporation? On what factors does it depend? How evaporation is different from boiling?

The phenomenon in which a liquid gets converted into its vapour, at any temperature below its boiling point is called evaporation.

Factors Affecting Evaporation:

(a) Temperature            (b) Surface area                    (c) Humidity, and

(d) Wind speed

 Boiling Evaporation 1. Boiling takes place at a particular temperature (at boiling point) when the liquid is heated. 1. Evaporation occurs on its own at all temperatures. 2. Boiling is a bulk phenomenon, i.e., it involves formation of bubbles of the vapours from bulk (whole) of the liquid. 2. Evaporation is a surface phenomenon, i.e., it takes place only from the surface of the liquid. 3. No cooling is caused during boiling. 3. Evaporation always causes cooling. 4. It is a fast process. 4. It is a slow process. 5. Heating is required. 5. Heating is not required.

10. Account for the following:

(a) A windy day is good day for drying

(b) When you take a block of butter out of the fridge, it is quite hard. However, after 15 minutes it is soft enough to spread.

Ans.     (a)  Yes, because on a windy day rate of evaporation will increase

(b)  Yes, because when we take a block of butter out of the fridge, its particles have stronger inter molecular force of attraction. However after 15 minutes due to absorption of heat from the surroundings the intermolecular force of attraction weakens and the butter becomes soft enough to spread.

11. Using the ideas of particles, explain why:

(a)   It is easy to pour a liquid.

(b)   A gas will completely fill any container.

Ans.  (a)  Since a liquid has weak force of attraction between the particles, the particles are able to move away from each other to some extent, that is a liquid can flow, so it is easier to pour a liquid.

(b)    Since in a gas the force of attraction between the particles is very low or negligible, the particles of gas move freely & can fill any container completely.

12. How does the water kept in an earthen pot (Matka) become cool during summer?

Ans.  The earthen pot (Matka) has a large number of extremely small pores in it. Some of the water continuously seeps out through these pores to the outside of the pot and evaporates continuously. During evaporation, it takes the latent heat required for vaporization from its surroundings & the water present inside the pot. In this way, the water inside the pot loses heat and becomes cool.

13. Give reasons for the following observations.

(a) Naphthalene balls disappear with time without leaving any solid.

(b) We can get the smell of perfume sitting several meters away.

Ans.  (a) Naphthalene undergoes sublimation slowly at room temperature. As a result, solid naphthalene gets converted into vapours which become a part of the air around us. Therefore, naphthalene balls disappear without leaving any solid.

(b)  We get the smell of perfume sitting several meters away due to diffusion. The particles of the perfume get diffused in air and the smell of perfume reaches us even if we are sitting several meters away.

14. Define:    (a) latent heat of fusion        (b) Boiling point

(c) Sublimation

Ans.     (a) Latent heat of fusion:

Latent heat of fusion of a solid is the amount of heat in joules or kilo joules, required to convert 1 kg of solid to liquid, at its melting point, at atmospheric pressure.

For example: Latent heat of fusion of ice = 334 kJ/kg.

(b) Boiling point:

The temperature at which a liquid boils and changes into gaseous state rapidly at atmospheric pressure is called boiling point of the liquid.

For example: Boiling point of water is $100{}^\circ&space;C$.

(a) Sublimation:

The changing of a solid directly into vapours on heating, without passing through the liquid state and vice-versa, is known as sublimation.

For example: Camphor and naphthalene undergo sublimation.

15. What are plasma & Bose-Einstein condensate?

Ans.  (a)   Plasma: This is the fourth state of matter which consists of super energetic and super excited particles obtained by ionization of gases. The fluorescent tube and neon sign bulbs consist of plasma.

The sun and the stars glow because of presence of plasma in them. The plasma is created in stars because of very high temperature.

(b)   Bose–Einstein condensate (BEC): The BEC is the fifth state of matter formed by cooling a gas of extremely low density (about one–hundredth to thousandth of the density of normal air), to super low temperatures.

If you want to prepare more questions of it and other subjects as well, then go through important questions of class 9