AimStudy the Diffusion of Solids in Liquids

Introduction

When substances are brought in contact with each other, they intermingle with each other. This phenom-enon is known as Molecular diffusion. Molecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion. The result of diffusion is a gradual mixing of material. In a phase with uniform temperature, absent external net forces acting on the particles, the diffusion process will eventually result in complete mixing or a state of equilibrium.

Diffusion in the most general state refers to the ran-dom, thermal motion of particles. The first thing to remember about diffusion is that all movement is driven by heat energy

Diffusion takes place very rapidly in case of gases, to a lesser extent in case of liquids, and not at all in the case of solids. However, diffusion of solids in liquids does take place at a very slow rate.

Molecules of solute are in constant random motion ,called Brownian movement due to the collision between molecules of solute and that of the solvent. It is this physical interaction between solute-solvent particles that leads to diffusion. The force of the heat does not move the molecule in a particular direction but pushes it randomly. The atoms (and molecules and other microscopic particles) move every which way, constantly bumping into each other and changing direction

.

Brownian movement

If a solid is kept in contact with excess of solvent in which it is soluble, some portion of the solid gets dissolved. This process is known as dissolution of a solid in liquid, and it takes place due to the diffusion of solid particles into liquid medium.

Objective

To demonstrate that rate of diffusion depends upon the following factors:

Temperature: As temperature increases, the kinetic energy of the particles increases. Thus, the speed of particles also increases, the amount of energy available for diffusion is increased. This means that a given particle will move faster at a higher temperature. Thus the rate of diffusion will be faster as the temperature increases.

Size of the particle: As the size of particle increases, rate of diffusion decreases. The source of energy for the movement of particles in diffusion is the heat in the environment. At a given temperature, a smaller particle (molecule) moves faster than a larger one. Thus the rate of diffusion is inversely proportional to the size of the

particle. That is, a smaller particle will

diffuse faster than a larger one.

Mass of the particle: As the mass of the particle increases, the rate of diffusion decreases because the speed of particle decreases and hence the kinetic energy of the particle decreases so the particle becomes less mobile. So as the mass increases the rate of diffusion decreases

Diffusion of two gases

Experiment 1

AimTo study diffusion when copper sulphate is brought in contact with water (liquid).

RequirementsCopper sulphate (CuSO4) crystals, 100 mL beaker

Procedure Take about two grams of copper sulphate

crystals in 100 mL beaker.

Add about 50 mL of water and allow it to stand for few minutes.

Note the development of blue colour in water.

Allow to stand undisturbed further till it is observed that all copper sulphate disappears.

Note the blue colour change in water.

Appearance of blue colour in water when Copper sulphate crystals are Added to it

Conclusion

When solids such as copper sulphate are brought in contact with liquids such as water, the molecules of copper sulphate intermingle with the molecules of water due to their constant random motion , which is clearly observed from development of blue coloration in water i.e., diffusion takes place.

Experiment 2AimTo study the effect of temperature on the rate of diffusion of solids in liquids.

RequirementsCopper sulphate (CuSO4) crystals, three 100 mL beakers, watch glass, wire gauge, burner, tripod stand, thermometer, stop watch.

Procedure

Take five gram of copper sulphate each in three beakers.

Pour 100 mL of distilled water slowly in one of the beakers.

Cover this beaker with a watch glass. Pour 100 mL of cold water in a second beaker

slowly. Place a third beaker containing 100 mL of water

on a tripod stand for heating. Observe the diffusion process which begins in all

the beakers. Record of copper sulphate the time taken for the

dissolution of copper sulphate in all the three cases.

Observations:-

BEAKER Temperature of Water Time Taken to Diffuse

1 10 °C 18 minutes

2 25 °C 15 minutes

3 70 °C 7 minutes

Conclusion:-

The rate of diffusion of copper sulphate in water is in the order as given below: Beaker 3 > Beaker 2 > Beaker 1 Faster diffusion will take place if the surroundings are warmer. Increase in temperature means an increase in molecules' speed (kinetic energy). So the molecules move faster and there will be more spontaneous spreading of the material which means that diffusion occurs quicker.

GRAPHICAL REPRESENTATION OFVARIATION OF RATE OF DIFFUSION WITH TEMPERATURE

Experiment 3

AimTo study the effect of size of particles on the rate of diffusion of solids in liquids.

RequirementsGraduated 100 mL measuring cylinders, copper sulphate (CuSO4) crystals of different sizes, stop watch.

Procedure Add 50 mL of water to each of the three

cylinders.

Take five gram each of big size, medium size, small size crystals of copper sulphate, and add them separately in three cylinders.

Allow to them to stand for some time.

Note the time taken for blue colour to reach any fixed mark in each of the cylinders and note the observations.

Observations:-

BEAKER Crystal size Time Taken to Diffuse

1. Big 19 minutes

2. Medium 13 minutes

3. Small 5 minutes

ConclusionThe rate of diffusion of copper sulphate in water is in the order as given below:

Beaker 3 > Beaker 2 > Beaker 1

We know that smaller particles have larger surface area. So the small particles of the third beaker interact more with the water molecules than the particles in the first and the second beaker, the diffusion hence is fastest in third beaker and slowest in the first beaker. So larger the size of the particle slower is the rate of diffusion

Result When solids such as copper sulphate

are brought in contact with liquids such

as water, intermingling of substances, i.e., diffusion takes place.

The rate of diffusion varies directly with temperature.

Small particles undergo diffusion more quickly than bigger particles.

Diffusion ofSolids

in liquids

Name: PAVNEET SINGH School: G.G.N.PUBLIC.SCHOOL class: 12th

Acknowledgements

"There are times when silence speaks so much more loudly than words of praise to only as good as belittle a person, whose words do

not express, but only put a veneer over true feelings, which are of gratitude at this point of time."

I would like to express my sincere gratitude to my chemistry mentor Mrs. KIRANJEET KAUR, for her vital support, guidance and encouragement - without which this project would not have come forth. I would also like to express my gratitude to the staff of the Department of Chemistry at G.G.N.PUBLIC.SCHOOL for their support during the making of this project.