Worksheet 5: Class 6 Science - Separation of Substances

Welcome! In this worksheet, we will learn about the different methods used to separate substances. From your kitchen to a science lab, separation is a very important process. Let's explore how we can separate mixtures into their individual components!

Methods of Separation

When we have a mixture, we often need to separate its components for various reasons, such as to remove harmful substances or to obtain a useful substance. The method we choose depends on the properties of the components in the mixture.

Common Methods:

• **Handpicking:** Used to separate slightly larger, visible impurities like stones from rice or pulses.
• **Threshing:** A method to separate the grain from the stalks of a plant.
• **Winnowing:** The process of separating heavier and lighter components of a mixture by using wind or a blowing air current. This is often used to separate husk from grain.
• **Sieving:** Used when the components of a mixture have different sizes. A sieve allows smaller particles to pass through while retaining larger ones.
• **Sedimentation, Decantation, and Filtration:** These methods are used to separate an insoluble solid from a liquid. **Sedimentation** is when a heavier, insoluble solid settles at the bottom of a liquid. **Decantation** is the process of pouring out the liquid without disturbing the settled solid. **Filtration** is a more effective method where the liquid is passed through a filter paper.
• **Evaporation:** This method is used to separate a soluble solid from a liquid. When a liquid (like water) is heated, it turns into vapor, leaving the solid component behind. This is how salt is obtained from seawater.

Practice Questions

1. Fill in the blank: The process of separating a liquid from a solid that has settled at the bottom is called _____.

Decantation

2. True or False: Winnowing is used to separate sand from water.

False. Winnowing is used to separate a heavier and a lighter solid, while sand from water is separated by sedimentation and decantation.

3. Match the mixture with the best method of separation:

(a) Rice and stones (i) Sieving

(b) Tea leaves from tea (ii) Evaporation

(c) Sand and small pebbles (iii) Handpicking

(d) Salt from water (iv) Filtration

a - iii, b - iv, c - i, d - ii

4. What is the difference between a soluble and an insoluble substance?

A **soluble** substance (like sugar) dissolves in a liquid, while an **insoluble** substance (like sand) does not.

5. Fill in the blank: The process of converting water into its vapor is called _____.

Evaporation

6. Why is it not possible to separate salt from water by filtration?

Salt is a soluble substance, which means it dissolves completely in water. It passes through the filter paper along with the water, so it cannot be separated by filtration.

7. Name the three steps used to separate sand from water.

Sedimentation, Decantation, and Filtration.

8. What is threshing? What kind of substances does it separate?

Threshing is the process of separating grains from the stalks of a plant. It separates the grain (the desired product) from the stalks (the unwanted part).