The separation of substances is crucial because most things around us are not pure but are mixtures of various components. We separate them for three main reasons:

• To Remove Undesirable or Harmful Constituents: To ensure safety and cleanliness. For example, separating **stones from rice** or **germs from water** to make it safe for consumption.
• To Obtain Useful Constituents: To get valuable components from a mixture. Examples include obtaining **salt from seawater** through evaporation or separating **butter and ghee from milk**.
• To Obtain Pure Substances: For specific, high-precision applications. Pure substances are vital in **laboratory experiments** and the **medicine industry** to ensure product effectiveness and safety.

Hand-picking is a simple, manual method used when the unwanted particles are:

• Visibly Different: The particles differ in **shape, size, color, or appearance** from the main substance.
• Present in Small Quantities: The amount of the mixture to be cleaned is small, and the impurities are few.
• Example: This method is perfect for removing tiny **stones and husks from cereals and pulses** before cooking.

A **sieve** is a device, typically a mesh with pores, used to separate substances based on the size of their particles. The process is called **sieving**.

When a mixture is placed in a sieve and shaken, the **smaller particles** pass through the pores, while the **larger particles** are retained on the mesh. This is an effective way to separate components of different sizes.

Common Uses: Separating fine flour from husk, or stones from sand at a construction site.

Different mixtures require specific separation methods based on the properties of their components:

• Chalk powder and water: Use **sedimentation** to let the chalk settle, then **decantation** to pour off the water. For a cleaner result, follow with **filtration**.
• Sand and rice grains: Use **hand-picking** if the particles are visibly different, or **sieving** if their sizes are distinct.
• Sugar and wheat flour: You could try **sieving** if particle sizes differ. A more complete way is to dissolve the mixture in water; **wheat flour is insoluble** and can be separated by filtration, while **sugar is soluble** and can be recovered by evaporating the water.
• Paper bits, salt, and water: First, use **filtration** to remove the insoluble paper bits. Then, use **evaporation** on the remaining saltwater solution to obtain the salt.
• Dry grass bits and wheat grains: Use **winnowing**, leveraging the difference in weight. The wind will blow away the lighter grass bits, and the heavier wheat grains will fall.
• Sugar, sand, and pebbles: Use **sieving** with different meshes to separate pebbles (largest) and sand. Then, dissolve the sugar in water to separate it from the sand, which can be filtered out. Recover the sugar by evaporation.

Purifying drinking water is a multi-step process to ensure it's safe for consumption:

1. Screening: Large impurities like leaves and sticks are removed using large screens.
2. Sedimentation: The water flows into a tank where heavy impurities settle at the bottom. **Alum** is often added to help finer, lighter particles settle more quickly.
3. Filtration: The water then passes through a layer of sand and gravel, which acts as a filter to remove very fine dirt particles.
4. Chlorination: **Chlorine** is added to the water to kill any harmful germs or bacteria.
5. Storage: The now-purified water is stored in tanks before being distributed to homes.