CBSE Class 6 Science Chapter 5: Separation of Substances NCERT Solutions

We need to separate different components of a mixture for several reasons. Primarily, it is done to remove harmful or non-useful substances that might be mixed with a desired substance, making it safe and suitable for use. Sometimes, even useful components are separated if they need to be utilized individually. For instance:

1. Removing impurities from food grains: Before cooking, we often separate small pieces of dirt, stones, or husk from grains like wheat, rice, or pulses. This is commonly done using the handpicking method, where larger impurities are manually removed.
2. Washing grains: Grains like rice or pulses are usually washed before cooking. When water is added, lighter impurities such as dust and soil particles float or get washed away with the water, separating them from the grains.

Winnowing is a separation technique used to separate lighter components from heavier components of a mixture by using wind or blowing air. This method is particularly effective for separating grains from their husk or chaff. The lighter husk particles are carried away by the wind, leaving the heavier grains behind.

Usage: Winnowing is commonly used by farmers to clean harvested grains like paddy, wheat, or other seeds, separating the edible grain from the unwanted lighter husk.

To separate husk or larger dirt particles from a sample of pulses before cooking, the most suitable method is handpicking. This involves manually picking out the visible pieces of husk and dirt from the pulses. For smaller, lighter dust particles that might be mixed, washing the pulses with water would also help remove them.

Sieving is a process used to separate components of a mixture based on their particle size. It involves passing the mixture through a sieve, which has small holes. The finer particles pass through the holes, while the larger particles or impurities are retained on the sieve.

Usage: Sieving is widely used in various situations:

• Flour mills: To separate fine flour from any broken particles of grains or other larger impurities.
• Construction sites: To separate lumps and smaller stones from sand or cement mixtures, ensuring a uniform consistency.

To separate sand and water from their mixture, we can use a combination of sedimentation and decantation, and optionally filtration:

1. Sedimentation: First, allow the mixture to stand undisturbed in a container for some time. The heavier sand particles will settle down at the bottom of the container.
2. Decantation: After the sand has settled, gently and carefully pour the water from the top into another clean container. This process of pouring off the liquid is called decantation.
3. Filtration (Optional): If there are still very fine particles of sand suspended in the water, the water can be further purified by filtering it through a filter paper or a fine cloth. This process is called filtration.

Yes, it is possible to separate sugar mixed with wheat flour. This can be achieved using the sieving method. Since the sugar crystals and wheat flour particles are of different sizes, passing the mixture through a sieve will allow the finer flour particles to pass through the holes, while the larger sugar crystals will be retained on the sieve.

To obtain clear water from a sample of muddy water, the following steps involving sedimentation, decantation, and filtration are used:

1. Sedimentation: Allow the muddy water to stand undisturbed in a container overnight or for a sufficient period. The mud particles, being heavier, will settle down at the bottom of the container.
2. Decantation: After the mud has settled, gently pour the clear water from the top into another clean container. This process is called decantation.
3. Filtration: To remove any remaining finer impurities that might still be suspended in the water, the decanted water can be filtered using a filter paper or a fine cloth. This process, called filtration, will yield clear water.

1. The method of separating seeds of paddy from its stalks is called threshing.
2. When milk, cooled after boiling, is poured onto a piece of cloth the cream (malai) is left behind on it. This process of separating cream from milk is an example of straining (or churning, which leads to cream separation).
3. Salt is obtained from seawater by the process of evaporation.
4. Impurities settled at the bottom when muddy water was kept overnight in a bucket. The clear water was then poured off from the top. The process of separation used in this example is called sedimentation and decantation.