CBSE 9th Chemistry | Matter- Nature and Behaviour (Short Answer Type Question)

Matter- Nature and Behaviour (Short Answer Type Question)

Question 1. Name the two ways in which the modern day scientists have classified the matter.

Answer.

Modern day scientists have classified the matter in the following two ways –

(i) On the basis of physical properties of matter i.e., physical classification,

(ii) On the basis of chemical composition of matter i.e., chemical classification.

Question 2. Name any two factors due to which the gases show the property of diffusing very fast into other gases.

Answer.

These are:

(i) high speed of particles, of gases,

(ii) enormous intermolecular spaces in the gases.

Question 3. Why have the solids have higher density as compared to liquids or gases?

Answer.

The particles in a solid state are tightly packed into a small volume (space). Due to this they generally have a higher density as compared to liquids or gases.

Question 4. Are gas and vapour mean the same thing or different? Explain.

Answer.

They mean the same thing.

The word vapour is used for describing those gases that usually exist as liquid at room temperature e.g. water which exists as liquid at room temperature is called water vapour in gaseous state.

Oxygen is called a gas (not vapour) because it exists as a gas at room temperature.

Question 6. Write two points of difference between evaporation and boiling.

Answer.

Evaporation Boiling
1. This involves change of liquid into a gas at any temperature below its boiling point. 1. It occurs only at the boiling point of the liquid. In it the change of liquid to gaseous state occurs at constant temperature.
2. It causes cooling. 2. In it temperature remains constant.
3. It is surface phenomenon. 3. It is a bulk phenomenon.

Question 7. Which of the two scales of temperature Celsius or kelvin considered better and why?

Answer.

Kelvin scale is considered better because on this scale the sign of temperature is always positive where as in case of Celsius scale we come across a negative sign quite often.

Question 8. How does pressure help in converting a gas to a liquid state?

Answer.

A gas can be converted into liquid state by increasing the pressure. On increasing pressure the gaseous particles came closer and ultimately get condensed and in this way pressure helps to convert a gas into liquid state.

Question 9. Out of nitrogen, oxygen and carbon dioxide, the gases present in air, carbon dioxide is heaviest. However, it does not form lower layer in atmosphere. Why?

Answer.

This behaviour can be explained on the basis of the fact that gravity has no effect on the diffusion of a gas. Thus carbon dioxide (CO2) remains uniformly mixed in air and does not form the lower layer in the atmosphere.

Question 10. A bulb ‘A’ contains hydrogen and another bulb ‘B’ contains oxygen. These are connected to each other through an arrangement provided with stop cock. If now we open the stop cock what will be the constituents in bulb ‘A’ and bulb ‘B’?

 

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Answer.

In both the bulbs (‘A’ and ‘B’) we will have a mixture of hydrogen and oxygen.

Question 11. Why should we wear cotton clothes in summer?

Ans.

During summers we perspire more which helps to keep our body cool. Our body is kept cool because during evaporation of sweat the energy is absorbed from body that leaves the body cool. Cotton being a good absorber of water helps in absorbing sweat and exposing it to the atmosphere for easy evaporation.

Question 12. Why do we see water droplets on the outer surface of a glass containing ice-cold water?

Answer.

It is due to the fact that water vapours present in air on coming in contact with cold glass of water loses energy and gets converted into liquid state, which are then seen by us as water droplets.

Question 13. Predict the physical state of matter in each case from the following characteristics:

(i) It expands very little on heating.

(ii) It is rigid and highly incompressible.

(iii) It has a definite volume but no definite shape.

(iv) It represents the most compressible form of matter.

Answer.

 (i) It is solid,

(ii) It is solid.

(iii) It is liquid.

(iv) It is gas.

Question 14.

(a) Out of alcohol and carbon tetrachloride, which is more volatile?

(b) Write the full form of LPG.

Answer.

(a) Alcohol is volatile. It has a low boiling point,

(b) Liquefied Petroleum Gas.

Question 15. Define melting point of a solid? Discuss its significance.

Answer.

Melting point of a solid is the temperature at which the solid starts melting (i.e. changing into liquid state)

Significance: From the melting point of a solid we get an idea of interparticle forces that bind the constituents in a solid. Higher the value of melting point larger is the magnitude of intermolecular forces that bind the constituents.

Question 16. Name the various particles that may be involved in the assembly of solid structures.

Answer.

The particles that may be involved in the assembly of solid structures are :

(i) atoms

(ii) molecules

(iii) ions.

Question 17. Can we convert solid CO2 directly to gaseous state? If yes how?

Answer.

Solid carbon dioxide (CO2) known as dry ice gets converted directly to gaseous state, on decrease of pressure to 1 atmosphere without, coming into liquid state.Q

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