Notes on Sedimentation and Centrifugation

Sedimentation

• Definition: The process by which heavier particles in a liquid settle to the bottom when the liquid is allowed to stand still.
• Application: Used to separate suspended materials from liquids.
• Limitation: Ineffective for very light materials which take a long time to settle.

Centrifugation

• Purpose: To expedite the process of sedimentation, especially for lighter suspended materials.
• Definition: A technique used to separate substances of different densities using a centrifuge.

Experiment Demonstrating Centrifugation

• Equipment Needed:
  • Handy centrifuge machine
  • Muddy water
  • Mixture of calcium carbonate in water
  • Four centrifuge test tubes
• Procedure:
  1. Place samples of muddy water in the test tubes.
  2. Place calcium hydroxide mixture in the test tubes.
  3. Insert test tubes in the centrifuge machine.
  4. Rotate the machine rapidly for a few minutes.
  5. Stop rotation and remove test tubes.
  6. Observe the settlement of mud particles and white precipitate at the bottom of the test tubes.

Principles of Centrifugation

• Centrifugal Force: Objects in a centrifuge experience a force directed away from the center, pressing materials against the tube walls.
• Dependence Factors:
  • Mass of the particles
  • Speed of rotation
• Separation Mechanism: Denser particles are forced to the bottom, lighter particles remain on top.
• Efficiency: Increased rotation speed allows even lighter materials to settle.

Applications of Centrifugation

• Diagnostic Laboratories: Used for blood and urine tests.
• Dairies and Homes: Used to separate butter from cream.