Class 6 Science Chapter 3 Important Questions

We need to separate harmful or non-useful substances that may be mixed with the substance used. Sometimes, we separate even useful components if we need to use them separately.
For example: Tea leaves are separated from the liquid with a strainer, while preparing tea. Grain is separated from stalks, while harvesting. Milk or curd is churned to separate the butter.

A mixture in which all of its components are evenly distributed throughout the mixture is known as homogeneous mixture e.g. mixture of salt and water.
A mixture in which its components are not distributed evenly throughout the mixture is known as heterogeneous mixture. e.g. mixture of oil and water.

When sand and powdered leaves are at the same place, and sand reaches that place vertically and leave are blown away, because sand is heavier than powder leaves. This process is called winnowing.

Handpicking can be used for separating slightly larger sized impurities like the pieces of dirt, stone, and husk from wheat, rice or pulses. The quantity of such impurities is usually not very large. In such situations, we find that handpicking is a convenient method of separating substances.
As an example: Spread the grain on a sheet of paper. There are many pieces of stone, husks, broken grain and particles of any other grain in it. Now, remove with your hand the pieces of stone, husks and other grains from it. This method is called “handpicking”.

The process used for separating grain seeds from their stalks is called threshing. It can be done by –
i) Manually beating the dry stalks on the ground or a hard surface to shake off the dried grains.
ii)Trampling them under the feet of animals like bullocks.
iii)Using threshing machines.

When we get a mixture of dry sand with sawdust or powdered dry leaves. And keep this mixture on a plate or a newspaper. Look at this mixture carefully.
There are lots of question can arise. Can the two different components be made out easily? Would it be possible to separate the components by handpicking?
In that condition, when the sizes of particles of the two components are similar. Winnowing is used to separate heavier and lighter components of a mixture by wind or by blowing air.
This method is commonly used by farmers to separate lighter husk particles from heavier seeds of grain.

The method of separating heavier with lighter components of a mixture by wind or by blowing air, is called winnowing.

Filtration is better method than decantation to separate tea leaves from prepared tea.

The best way to carry out the filtration of the mixture of water and sand is to use filter paper not cloth because filter paper has fine pore while cloth has larger holes than filter paper. The particles of sand do not pass through filter paper but these may pass from cloth to filtrate.

Rice or pulses are usually washed before cooking. When we add water to these, the impurities like dust and soil particles get separated. These impurities go into water, which becomes a little muddy. And the heavier component in a mixture settles after water is added to it, the process is called sedimentation.

Decantation is a method of separation used after sedimentation in which when insoluble particles settle down, the clear liquid is poured into another container.

The process of separating insoluble components from a mixture using a filter paper or cloth is called filtration.

The clear liquids that remains above the sediments is called supernatant.

The process of adding of alum in muddy water which loads the mud particles and speeds up sedimentation, is known as loading.

The process of conversion of water vapor into its liquid form is called condensation. Take a metal plate with some ice on it. Hold the plate just above the spout of the kettle. When the steam comes in contact with the metal plate cooled with ice, it condenses and forms liquid water. The water drops that you observed falling from the plate, were due to condensation of steam.

Sea water is allowed to stand in shallow pits. Due to solar heat, water in the pits get evaporated. After some days, the water evaporates completely and the solid salts remain in the pits. These salts are further purified to get pure common salt.

We will differentiate between the distilled water and the solution of salt water without tasting by the process of evaporation. On evaporation, the salt water container will leave a caky residue which is absent from the distilled water.

To separate sand and water from their mixture we follow the following steps:
i)Leave mixture to stand undisturbed for some time in a container.
ii)Sand settles at the bottom of the container it is called sedimentation.
iii)Gently pour the water in another container (called decantation).
iv)We may also use filter paper to remove fine particles of sand (called filtration).

A solute is the substance that is dissolved in the solvent to form the “solution”.
The ability of a substance to dissolve in water to form a solution is known as “solubility”.

If a large quantity of a substance is forced to dissolve in the fixed amount of water then after a certain quantity of the substances has been dissolved, it will not dissolve due to saturation.

Steps for the separation of iron nails, salt, oil and water.
Iron nails are separated from the mixture by using magnets. Then by using decantation oil and water is separated. Oil being lighter forms the upper layer in the beaker and we can decant off the upper layer of oil.
Now, the mixture contains dissolved salt and water. Salt can be obtained from the water by the process of evaporation. The water present in salt solution will form water vapor and then the salt is left behind.