CBSE 9th Chemistry | Matter- Its Nature and Behaviour (Conceptual Questions with Answers)

Matter- Its Nature and Behaviour (Conceptual Questions with Answers)

Question 1. Sugar when kept in different jars gain their shape. Is sugar a solid ?

Answer.

Yes, sugar is solid because shape of each individual crystal of sugar remains fixed whether we take it in our hand or put in a plate or put it in a jar.

Question 2. Do solids show the property of fluidity?

Answer.

No, solids are rigid because in solids constituent particles are closely packed and the interparticle forces of attraction are very strong. So they have little tendency to flow and they do not show the property of fluidity.

Question 3. Why is the property of diffusion almost nil in case of solids.

Answer. It is because of the absence of translatory motion in solid state as in solids the constituent particles are very closely packed.

Question 4. A rubber band can change its shape. Is it a solid?

Answer.

Yes, rubber band is a solid because it changes its shape under the influence of applied force and regains its original shape when the applied force is removed.

Question 5. A sponge is a solid yet we are able to compress it. Explain.

Answer.

Solids are incompressible but we are able to compress sponge (a solid) because a sponge has a minute holes in which air (a gas) in trapped. When we press the sponge, the air is expelled out and we are able to compress a sponge.

Question 6. As particles of solids do not move much. So, solids do not have the property of diffusion into other solids. What will happen if two metal blocks are tightly bound together and left undisturbed for few years?

Answer.

The particles of one metal diffuse into other. [Such incidences are rare and they show diffusion of a solid into a solid]?

Question 7. On dissolving sugar in water, no increases in volume is observed. Explain.

Answer.

Due to the presence of empty space in sugar as also in water (or interparticle space) that is available, particles of sugar or molecules of water can fill these spaces and due to this there is no observable change in volume occurs on dissolving sugar in water.

Question 8. In the olden times when refrigerators were not available, butter was wrapped in wet cloth during summer. Explain.

Answer.

During summer when weather is quite hot the butter is likely to get a foul odour due to rancidity of butter. To check this, it was kept wrapped in wet cloth. This was done to keep the temperature of butter lower. The water present is wet cloth on evaporation causes cooling and due to the temperature of butter gets lowered.

Question 9. The graph shows the heating curve for a pure substance.

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(i) What is the physical state of substance at A?

(ii) What is the physical state of substance at B?

(iii) What is the physical state of substance at C?

(iv) What is the physical state of substance at D?

 

Answer.

(i) At A, it is in solid state.

(ii) At B, it exists in both solid and liquid state (melting has started)

(iii) At C, it is in liquid state.

(iv) At D, it exists in both liquid and gaseous state, (boiling has started).

Question 10. What happens when diamond is heated in vacuum (to prevent burning)?

Answer.

It does not melt because the forces of covalency between the atoms are too great to be overcome by vibration with any ordinary source of heat. At very high temperature some carbon atoms will break away, but by sublimation into the gaseous state, not by melting.

Question 11. Ethyl chloride boils at 12°C. When it is sprayed on the skin, it freezes a small part of the skin and thus serves as a local anesthetic. Explain how it cools the skin.

Answer.

The comparatively low boiling point of ethyl chloride indicates that it has a high vapor pressure at room temperature. In fact, it boils at 25°C, rapidly cooling the skin to below the freezing point of water.

Question 12. A beaker of a liquid with a vapor pressure of 350 torr at 25°C is set alongside a beaker of water and both are allowed to evaporate. In which liquid does the temperature change at a faster rate ? Why?

Answer.

The liquid other than water. The higher the vapor pressure, the faster the liquid evaporates and the liquid cools.

Question 13. At a given temperature, one liquid has a vapor pressure of 240 torr and another measures 420 torr. Which liquid probably has the lower boiling point ? Which probably has the lower heat of vapourization ?

Answer.

The liquid with the higher vapor pressure (420 torr) has the lower boiling point. It also probably has the lower heat of vaporization.

Question 14. A drop of dettol got evenly distributed in water How?

Answer.

This is because there is enough space between the particles of water and dettol gets into the spaces between the particle of other matter.

Question 15. Why do the gases exert more pressure on the walls of the container than the solids ?

Answer.

In gases, the particles move randomly at high speed and they collide with each other and with walls of the container. Due to this collision with walls of the container, the gases exert more pressure than solids.

Question 16. Why is ice at 273 K more effective in cooling than water at the same temperature ?

Answer.

Cooling takes place when we removes heat from the system. At 273 K, the ice will take away the latent heat from the medium and convert itself into water. Thus, in case of ice at 273 K there will be a change in physical state whereas in case of water at 273 K, there will be no change in state. Hence, in case of water, lesser energy will be taken away from the medium.

Question 17. Liquid nitrogen is used as a commercial refrigerant to flash freeze foods. Nitrogen boils at -196°C. What is this temperature on the Kelvin temperature scale ?

Answer.

K = °C+ 273 =-196 + 273 = 77 K

Question 18. Why do a surgeon spray ether on a portion skin, when a minor surgery has to be done.

Answer.

Surgeons perform minor surgeries on a portion of skin by spraying ether which is a volatile liquid (b.p. = 308 K). Being volatile ether evaporates at a faster rate from skin and it brings down the temperature of skin to quite a low temperature and skin becomes almost numb. Under these conditions minor cut can be easily made on skin. So, as to perform the surgery and patient will not feel any pain because of numbness that has been created.

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