Sedimentation, Decantation, and Filtration

Separating Solids from Liquids

When you have a mixture of an insoluble solid (like mud, sand, or tea leaves) and a liquid, we use a three-step approach: Sedimentation, Decantation, and Filtration.

1. Sedimentation

If you mix sand in water and let it stand undisturbed, the sand particles are heavier than water. Gravity pulls them down.

• Definition: The process of settling down of the heavier insoluble component at the bottom of a liquid is called sedimentation.
• The solid layer at the bottom is called sediment.

2. Decantation

Once the sediment has settled, the clear liquid remains on top. We can carefully pour this liquid out without disturbing the sediment.

• Definition: The process of removing the liquid (water) by tilting the vessel after sedimentation is called decantation.
• Example: Separating oil from water (since oil floats) is also a form of decantation. Washing rice involves decanting the cloudy water.

3. Filtration

Decantation is not perfect. Sometimes fine particles (like tea leaves or fine mud) flow out with the liquid. To remove these, we use a filter.

• Definition: The process of separating insoluble solid components from a liquid by passing it through a filter is called filtration.

Types of Filters:

1. Strainer: Metal or plastic mesh (used for tea).
2. Cloth: Woven threads create pores. Multiple layers make the pores smaller.
3. Filter Paper: Has extremely fine pores, suitable for laboratory experiments.

Experimental Setup: Filtration

• Residue: The solid left on the filter paper.
• Filtrate: The clear liquid collected in the flask.