Separation of Substances

1 a. A pure substance contains one kind of particles.

Eg: distilled water.

b. An impure substance contains more than one kind of particle.

Eg: tap water.

Most of the substances found in nature are impure.

2. Separation of impure substances is often done because of the following reasons:

a. To separate harmful substances from useful substances

Eg: Dirt or germs are separated from drinking water before consuming it.

b. To separate non-useful substances from useful substances

Eg: Separating husk from grain

c. To separate different but useful things

Eg: Separating notebooks from pencils.

3. The method of separation used depends on various factors:

a. Size of components

b. Use of components

c. Quantity of component

4 a. Handpicking Method:

As the name suggests we separate various components by using our hands.

b. The method of handpicking can be used for separating slightly larger sized impurities found in less quantity like the pieces of dirt, stone, and husk from wheat, rice or pulses.

5 a. Threshing:

Beating something to that the loose part gets separated

b. Grain is separated from stalks etc. using threshing. In this process, the stalks are beaten to free the grain seeds. Sometimes, threshing is done with the help of bullocks. Machines are also used to thresh large quantities of grain.

6 a. Winnowing:

To separate lighter component from heavier component by blowing or using air/ wind

b. Husk is separated from seeds using winnowing. The husk particles are carried away by the wind. The seeds of grain get separated and form a heap near the platform for winnowing. The separated husk is used for many purposes such as fodder for cattle.

7 a. Sieving:

In this method a wired gauge (called sieve) is used which permits the finer component to pass through and collects the bigger impurities.

b. Common uses of sieving include separating impurities from flour; and separating pebbles and stones from sand

8 a. Sedimentation:

Settling of heavier component when water is added.

b. Rice or pulses are usually washed before cooking. When you add water to these, the impurities like dust particles get separated. These impurities go into water.

8 c. When the water (along with the dust) is removed, the process is called decantation. The component that forms the top layer can then be separated by decantation.

d. Oil and water from their mixture can be separated by sedimentation and decantation.

e.

9 a. Filtration:

This method is similar to sieving, however, a more porous substance (eg: filter paper, linen cloth) is used).

b. Common uses include the process of preparing cottage cheese (paneer).

10 a. Evaporation:

The process of conversion of water into its vapours is called evaporation.

b. Common salt is separated from sea water using this method.

Process:

When sea water is allowed to stand in shallow pits, water gets heated by sunlight and slowly turns into water vapour, through evaporation. In a few days, the water evaporates completely leaving behind the solid salts.

11 a. Condensation:

The process of conversion of water vapour into its liquid form by cooling the vapours is called condensation.

b. The dew formed in winters is due to condensation.

12 a. often more than 1 method is used to separate a mixture.

b. Separating salt and sand.

First add water to the mixture, this will allow salt to dissolve in water while the sand will remain undissolved.

Next sand could be separated by using a filter paper.

To separate salt from water, we can use evaporation.

13 a. Many liquids (especially water) dissolves a number of substances in it. However, a given quantity of the liquid has an upper limit to the amount of substance which is dissoluble.

b. A saturated solution is one in which no more of that substance can be dissolved.

c. Saturation limit of a substance can be increased by heating the mixture, i.e., if a solution of water and sugar is saturated, we will be able to add more sugar to the solution if we start heating it.