Methods of Separation - Centrifugation Method

Centrifugation is the process of separation of insoluble materials from a liquid where normal filtration does not work well. The method of separating denser particles and lighter particles from a mixture by using a centrifuging machine is called centrifugation.

Centrifuge

The centrifugation is based on the size, shape, and density of the particles, the viscosity of the medium, and the speed of rotation. The principle is that the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly. The apparatus used for centrifugation is called a centrifuge. This method is useful in case the suspended particles in a liquid are too small to be retained by filter paper.

Working:

• In a centrifuge machine, test tubes containing the mixture are placed at the rim of a rotating disc. When the disc spins at high speed, a force pushes the solid particles towards the bottom of the test tubes.
• This separates the solids from the liquid efficiently. For example, blood plasma can be separated from blood cells, and cream can be separated from milk using centrifugation.
• This method is useful for separating solid-liquid mixtures where regular filtration isn’t effective.

When a mixture is rotated very fast, the denser particles are forced to go to the bottom of the centrifuge and the lighter particles stay at the top.

Applications:

• Used in diagnostic laboratories for blood and urine tests.
• Used in dairy and home to separate butter from cream.
• Used in washing machines to squeeze out water from wet clothes.

1. Aim: To separate cream from milk with the help of centrifugation

2. Requirements: Full-cream milk, test tube, centrifuging machine/milk churner

3. Principle: The components of a mixture may have different densities. When such a mixture is shaken vigorously, lighter particles separate from the rest and float on the surface.

4. Procedure

• Take some full-cream milk in a test tube.
• Centrifuge it by using a centrifuging machine for two minutes.

5. Observation: Skimmed milk is separated from cream, which floats at the top.

6. Inference/Result: The cream is lighter than the rest of the mixture. As a result, when we shake milk vigorously, it separates and starts floating on the surface.