NCERT 6th Class (CBSE) Science: Separation of Substances

Question: What is decantation?

Answer: Decantation is a process, of separation of insoluble solids from liquid. The suspension of solid particles in liquid is allowed to stand for some time. The solid particles then settle down at the bottom of the container and clean water goes up. Without disturbing the settled particles the clean water is transferred into other container.

Question: Where is decantation used? Give two examples.

Answer:

1.  Decantation is used to separate insoluble solids or liquid from liquid. Rain water is a mixture of mud and water. It is purified by decantation.
2.  Oil and water also get separated by this method because oil floats up.

Question: How will you prepare cheese (paneer)?

Answer: For making paneer, a few drops of lemon juice sire added to milk as it boils. This gives a mixture of particles of solid paneer and liquid. The paneer is then separated by filtering the mixture through a fine cloth or strainer.

Question: Explain the method that can be used for separating the following mixture:

1. Sand and husk
2. Wheat, sugar and stalk
3. Water and petrol
4. Rice and salt
5. Sand and salt

Answer:

1. Mixture of sand and husk: Sand and husk can be separated by the method of winnowing.
2. Mixture of wheat, sugar and stalk: For separating stalk from the mixture we should follow the winnowing method because milk is lighter than other two components and get separated. Wheat and sugar can be separated by sieving because they are in different sizes.
3. Mixture of water and petrol: Water does not dissolve in petrol. So, it can be separated by the use of separating funnel.
4. Mixture of rice and salt: Rice and salt can be separated by sieving.
5. Mixture of sand and salt: Sand and salt is mixed with water, salt dissolves in water and sand can be separated solution by sedimentation and decantation followed by filtration. After that using evaporation common salt is separated.