Brownian Motion Zig Zag Motion

Introduction

Brownian motion in simple words can be defined as the random movement of dust particles or microscopic particles in liquids or gases( fluids). When observed under a microscope, it was seen that these particles are never still. But it is seen that this movement results due to the particles colliding with each other. This movement was first observed by Robert Brown in 1827. He observed the movement of pollen grains suspended in water under a microscope. He was puzzled to see the movement even though the grains were dead, so he started some other phenomena occurring. But this was later clarified by Albert Einstein and Perrin, stating that this movement is due to the movement of molecules of the fluid.

When a foreign particle is suspended in a fluid, it moves in a random zigzag motion. This is due to the collision of the particle with the molecules of the fluid.

Brownian Movement

This irregular movement is seen in all types of fluids and is free from all types of external forces. But it is attributed due to the thermal movement of the molecules of the fluids. The velocity with which the molecules move is directly proportional to the square of the temperature. The general characteristics of Brownian motion are

• The motion of the particles is not seen in any particular direction, it is random.

• This motion depends upon the viscosity of the fluid; less viscosity results in more speed of the particles.

• All the particles show different motions.

• This motion increases with an increase in temperature.

What is the Brownian motion in Chemistry?

Brownian motion in Chemistry can be defined as the irregular, perpetual and random motion of the particles suspended in a viscous solution. This motion arises due to the collision of the suspended particles with the surrounding particles of the fluid. It depends on various factors like temperature, viscosity, and size of the particles but is unaffected by external factors.

Brownian motion has many applications in Chemistry.

• Determining Avogadro number − To determine the Avogadro number, we have to measure the root mean square displacement of the Brownian particle. Thus, we can say that the value of the Avogadro number is based on the Brownian motion of the particles.

• Diffusion − The movement of particles from lower concentration to higher concentration is due to the Brownian motion of the particles. So, Brownian motion is responsible for the process of diffusion.

Brownian Movement in Colloids

A colloid is a heterogeneous mixture of larger particles suspended in another particle. The size of colloidal particles varies from 1-1000 nanometres. There are mainly four types of colloidal particles,

• Sol − Suspension of solid particles in a liquid.

• Emulsion − Suspension of liquid in liquid.

• Aerosol − Suspension of liquid or solid in the air.

• Foam − Suspension of gas particles in solid or liquid.

When a colloidal solution is observed under the microscope, the colloidal particles are seen in an irregular motion. The larger particles stay suspended in the mixture due to the Brownian motion. The smaller particles in the mixture collide with the larger particles, and thus the particles do not settle down because of gravity.

The Brownian motion does not depend upon the nature of the colloidal mixture but depends upon the viscosity of the mixture and the size of the particles suspended in the colloid. A less viscous solution is directly proportional to Brownian motion. and it is inversely proportional to the size of the particles.

Cause of Brownian Motion

The primary cause of the Brownian Movement is the collision of particles in the fluid. It is affected by all the factors that affect the movement of the particles.

• Temperature − Temperature plays a vital role in determining the speed of the particles. The higher the temperature, the higher the speed of the particles suspended in the fluid.

• Size − Particles with small sizes show very high Brownian movement. This is because momentum is inversely proportional to the mass, thus collision increases in speed.

• Viscosity − Viscous medium exerts higher friction on the particles, thus decreasing the movement of particles. Therefore, viscosity is inversely proportional to the Brownian motion.

• Increased particle number − An increase in the number of particles increases the frequency of the collision, this increases the Brownian motion.

Effects of Brownian motion

• The main effect of Brownian motion is that it does not allow the suspended particles to settle down due to the action of gravity; this gives stability to colloidal solutions.

• With the help of this motion, we can separate homogeneous solutions from colloidal solutions. Homogeneous solutions show uniform bombardment, but colloidal particles show non-uniform bombardment, thus exhibiting random movements.

Conclusion

The random and zigzag movement of the particles is known as the Brownian movement. The collisions of the fluid molecules cause this movement with the suspended particles. It is mostly not affected by external factors but the factors like temperature, viscosity and size play a vital role in the determination of this movement. This movement is seen in colloidal solutions where the size of the particles varies from 1-1000 nanometres. In a colloidal solution, the bombardments between the particles are random and non-uniform so it prevents the particles from settling down.

Brownian motion is said to be the basis of the kinetic theory of gases and atomic theory as both these theories are dependent on the motion of the particles. The common examples of this movement that are visible to our naked eyes are the diffusion of pollutants in the air, the motion of pollen grains in still water, the movement of dust particles in a dark room, etc.

FAQs

1. Give an example of the Brownian movement in the human body.

The absorption of calcium by the bones is the best example of the Brownian movement in the human body. Calcium is absorbed by the bones through the process of diffusion.

2. Is Brownian motion observed in solids?

This motion is not observed in solids. This is because Brownian movement requires random movement of the particles but in the case of solids, the particles are closely packed so the movement of particles is exhibited.

3. How does the number of particles present in the fluid affect the Brownian motion?

If the number of particles is increased, the frequency of bombardment increases, and this increases the Brownian motion.

4. Why does Brownian movement not occur in larger particles?

Brownian movement is not observed in larger particles as the particles have high mass and the collision may not have enough energy to move the particles. Also due to the force of gravity, these particles may easily settle down.

5. How does Brownian motion depend upon the temperature?

With the increase in temperature, Brownian motion increases. This is due to the fact as the temperature increases the particles will attain high kinetic energy, which will result in increased Brownian motion.