7/26/2019 7.06-States of Matter-2 PU

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States of Matter -2(KTG & Liquid State) - 7.06

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PU-11

Homework Questions

1. Arrange the following liquid in the increasing order of surface tension: water, hexane and methanol.

Give reasons

2. Why does the sharp edge of a glass rod become smooth heating upto its melting point?

3. Arrange the following liquids in the increasing order of viscosity: water, hexane, glycerol. Give reasons4. What is the effect of temperature on surface tension and viscosity?

5. What is meant by laminar flow of a liquid?

6. What is the SI unit of coefficient of viscosity? How is it related to a poise?

Solutions

1. Surface tension increases with increase in the magnitude of the intermolecular forces of attraction.

Intermolecular forces are strongest in water due to strong H bonding. Methanol has weaker

hydrogen bonding. Hexane is nonpolar and has weakest intermolecular forces. Hence, the order of

surface tension is : hexane < methanol < water

2. On heating the sharp edges, glass melts and takes up rounded shape so that it has minimum surface

area. This occurs due to the property of surface tension of the molten glass which tends to minimise its

surface area

3. The order is hexane < water < glycerol

Viscosity increases with an increase in the intermolecular forces of attraction. Glycerol with three - OH

groups has strongest intermolecular forces due to strong H bonding. Water has relatively weaker H

bonding ( two OH groups). Hexane being nonpolar has the weakest intermolecular forces of

attraction

4. Both the properties increase with increase in intermolecular forces of attraction. On increasing the

temperature, the kinetic energy of molecules increases and they are able to overcome the forces of

attraction between them. Thus, both surface tension and viscosity decrease with increase in

temperature

5. There is a gradient in the velocity on going from one layer to the next within a liquid. This is called the

laminar flow of a liquid

6. The SI unit is : 1 1 2 Kgm s or Nm s Pas

1 poise1 1 20.1 0.1 Kgm s or Nm s