Methods of Separation - Centrifugation Method

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. The centrifugation is based on the size, shape, and density of the particles, 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.

Principle of Centrifugation:

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 dairies and home to separate butter from cream.
• Used in washing machines to squeeze out water from wet clothes.

To separate cream from milk with the help of centrifugation.

Milk is a suspension of tiny droplets of oil (cream) in a watery liquid. The process of centrifugation is used to separate cream from milk. The milk is put in a close container in a big centrifuge machine. When the centrifuge machine is switched on, the milk is rotated (or spun) at a very high speed in its container. The centrifugal force acts on the milk and due to this, the milk separates into the cream and skimmed milk. The cream, being lighter, floats over the skimmed milk and can then be removed.

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

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

Principle: Components of a mixture may have different densities. When such a mixture is shaken vigorously, lighter particle separates from the rest and float on the surface.

Procedure:

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

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

Inference/ Result: 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.