Mechanical Properties of Colloidal Solution (Brownian Movement)

Colloidal particles present in a colloidal solution exhibit a very important property called Brownian movement.

Q1. WHAT IS BROWNIAN MOVEMENT ?

Answer: “The continuous zig-zag movement of the colloidal particles in a colloidal solution is called Brownian movement. “

NOTE 1: The property was discovered by a botanist Robert Brown in 1827, when he observed that pollen grains suspended in water exhibit random zig-zag motion. After the name of the discoverer, the property was named as Brownian movement.

NOTE 2: More significantly, Albert Einstein’s later explained the Brownian motion more clearly in his paper stating that the pollen was moved by water molecules. This discovery served as great evidence of the existence of atoms and molecules.

Understanding Brownian movement is crucial as it forms a base for the modern atomic theory. The kinetic theory of gases is also based on the Brownian motion model of particles.

Q2. WHAT IS THE  CAUSE OF BROWNIAN MOVEMENT?

Ans: Brownian movement is due to the unequal bombardments                                  

of the moving molecules of dispersion medium on colloidal particles. 

The moving molecules of the dispersion medium continuously attack on colloidal particles from all sides and impart momentum to them.

Since the chances of their collisions are unequal, the net driving force on a colloidal particle forces it to move a particular direction.

As the particle moves in that direction, other molecules of the medium again collide with it and the particle changes its direction. The process continues. This results in a random zigzag movement of the colloidal particle.

Q3. WHAT ARE THE EXAMPLES OF BROWNIAN MOTION?

Ans: 1. Dust and smoke particles show continuous motion in beam of light in cinema hall.

2. Brownian motion is also observed in the plasma of cells in which the particles in the cell are also in random motion without making plasma in the cell dry.

3. Pollen grains suspended in water exhibit random zig-zag motion.

Q4. WHAT ARE THE IMPORTANCE OF BROWNIAN MOVEMENT?

                                                                 OR

HOW IS BROWNIAN MOTION IS RESPONSIBLE FOR STABILITY OF SOL?

Ans: Brownian movement plays an important role in imparting stability to a sol. This is because Brownian movement opposes the gravitational forces acting on colloidal particles and prevents them from getting settled down.

Q5. HOW DOES THE  SIZE OF COLLOIDS PARTICLES AFFECT  BROWNIAN MOTION?

Ans: The size of the particles is inversely proportional to the speed of the motion, i.e. Small particles exhibit faster movements. This is because the transfer of momentum is inversely proportional to the mass of the particles. Lighter particles obtain greater speeds from collisions.

Q6. HOW DOES THE  VISCOSITY OF DISPERSION MEDIUM AFFECT  BROWNIAN MOTION?

 Ans:The speed of the Brownian motion is inversely proportional to the viscosity of the fluid. The lower the viscosity of the fluid, the faster the Brownian movement.

Notes Credit: Pradeep Sharma