Liquid State Answer

1. Name the physical property behind rise of liquids in capillary tube.
Ans: Surface Tension

2. Define aqueous tension. Why is it subtracted from the total pressure to determine the pressure of a dry gas?
Ans: Aqueous tension is defined as the partial pressure of the water vapour present in the moist gas.
When the gas is colleced over the water, it becomes moist due to presence of small quantity of water vapour caused by evaporation.

Then, pressure exerted by moist gas = pressure exerted by dry gas + pressure of water vapour (aqueous tension).

i.e. Pmoist = Pdry + f (aqueous tension)

or, Pdry = Pmoist – f

Therefore, aqueous tension should be subtracted from the total pressure to get pressure of the dry gas.

3. What is evaporation? How does it differ from boiling?
Ans: Evaporation is defined as the process of conversion of liquid into vapour from the surface of the liquid at room temperature.

Evaporation Boiling

It takes place at any temperature. It takes place at boiling point only.

It takes place at the surface of liquid. It takes place at the entire volume of the liquid.

It is slow and silent process. It fast and noisy process.

4. Define coefficient of viscosity. How coefficient of viscosity is related with viscous force?

Ans: Coefficient of viscosity is defined as the tangential force per unit area required to maintain unit velocity gradient between the layers of liquid. (……………….)

5. Why is Glycerine more viscous than water?
Ans: Because the intermolecular force is large in glycerine than in water.

6. Why is a mercury droplet spherical?

Ans: Due to surface tension. Surface tension is the property of liquid due to which it tries to aquire minimum surface area. Since, for a given volume sphere has a minimum surface area, a mercury droplet is spherical.

7. In terms of vapour pressure, what do you mean by a boiling point of a liquid?

Ans: Boiling point is the temperature at which the vapour pressure becomes equal to atmospheric pressure.

8. The meniscus for mercury in a glass tube is concave downward. Explain.

Ans: Because cohesive force between molecules of mercury is greater than the adhesive force between mercury and glass molecules.

9. What do you understand by viscosity?

Ans: Viscosity is defined as the property of fluid by virtue of which an internal friction comes into play when the fluid is in motion and opposes the relative motion of its different layers.

10. What is the effect of temperature on: (a) Surface tension (b) Viscosity (c) Vapour pressure of liquid
Surface tension: It decreases on increase in temperature and vice versa.
Viscosity: It decreases on increase in temperature and vice versa.
Vapour pressure: It increases with increase in temperature and vice versa.

11. What do you understand by the term ‘surface tension’?
Surface tension is defined as the property of the liquid due to the intermolecular focre of attraction between the liquid molecules due to which liquid tries to gain minimum surface area.

12. How is surface tension of a liquid originated?

13. Define Vant Hoffs factor. What for it used?

14. What do you mean by boiling point and evaporation?
Boiling point is the temperature at which the vapour pressure becomes equal to atmospheric pressure.
Evaporation is defined as the process of conversion of liquid into vapour from the surface of the liquid at room temperature.

16. Give reason:

a) Falling liquid drops are spherical.
Due to surface tension. Surface tension is the property of liquid due to which it tries to aquire minimum surface area. Since, for a given volume sphere has a minimum surface area, a mercury droplet is spherical.

b) Evaporation takes place from the surface of liquid.
Since, the kinetic energy of the surface molecule is greater than the bulk molecule, evaporation takes place from the surface of liquid.

c) It is more efficient to wash clothes in hot water than cold water.
Surface tension decreases on increase in temperature. Due to this hot water can wet the clothes more effectively then cold water. So, it is more e to wash clothes in hot water than cold water

17. What happens to the vapour pressure of a solvent, when non volatile solute particles are dissolved in it?

A non volatile solute particle lowers the vapour pressure of solvent because solute particles become surrounded by solvent particles when dissolved. This causes the particles of solvent to evaporate less because it requires more energy for the particles to do this since the solvent to solute attraction are strong. So the vapour pressure of a solution is less than that of the pure solvent.

Vapour pressure depends on

• Nature of liquid
• Temperature
• Presence of impurities

18. Why does boiling point of liquid rise on increasing pressure?

As the pressure applied to the liquid surface is increased, the energy needed for the liquid molecules to expand to gas phase also increases. Hence, a higher temperature is required to change liquid to gas phase. So, boiling point of liquid rises on increasing pressure.
Read more at here.

19. Mention physical properties of liquid due surface tension.
Spherical shape of liquid drop.
Rise and fall of liquid in a capillary tube.