NCERT Book Class 6 Science Separation of Substances

Separation of Substances

There are many instances when we notice a substance being separated from a mixture of materials. Tea leaves are separated from the liquid with a strainer, while preparing Grain is separated from stalks, while harvesting. Milk or curd is churned to separate the butter (Fig. 5.2). As we learned in Chapter 3, we gin cotton to separate its seeds from the fibre. Perhaps you might have eaten salted daliya or poha. If you found that it had chillies in it, you may have carefully taken them out before eating. Suppose you are given a basket containing mangoes and guavas and asked to separate them. What would you do? Pick out one kind and place them in a separate container, right? Seems easy, but what if the materials we want to separate are much smallerthan mango or guava? Imagine you are given a glass of sand with salt mixed in it. Impossible, even to think of separating salt from this mixture by picking out grains of sand by hand!Activity 1 In Column 1 of Table 5.1, are given a few processes of separation. The purpose of separation and the way separated components are used is mentioned in Column 2 and 3 respectively. However,the information given in Columns 2 and 3 is jumbled up. Can you match each process with its purpose and the way separated components are used? We see that, before we use a substance, we need to separate harmful or non-useful substances that may be  mixed with it. Sometimes, we separateeven useful components if we need to use them separately. The substances to be separated may be particles of different sizes or materials. These may be solids, liquids or even gases. So, how do we separate substances mixed together if they have so many different properties?

5.1 METHODS OF SEPARATION

We will discuss some simple methods of separating substances that are mixed together. You may come across some of these methods being used in day to day activities. Hand Picking Activity 2 Bring a packet of grain purchased from a shop to the classroom. Now, spread the grain on a sheet of paper. Do yo find only one kind of grain on the sheetof paper? Are there pieces of stone, husks, broken grain and particles of an other grain in it? Now, remove with your hand the pieces of stone, husks and other grains from it. This method of handpicking can be used for separating slightly larger sized impurities like the pieces of dirt, stone, and husk from wheat, rice or pulses (Fig. 5.3). The quantity of suc impurities is usually not very large. In such situations, we find that handpicking is a convenient method of separating substances.harvesting the crop. Stalks are dried in the sun before the grain is separated from them. Each stalk has many grain seeds attached to it. Imagine the number of grain seeds in hundreds of bundles of stalk lying in the field! How does the farmer separate grain seeds from those bundles of stalks? One may pluck mangoes or guavas from the trees. But, grain seeds are much smaller than mangoes or guavas. So, plucking them from their stalks would be impossible. How does one separate grain seeds from their stalks? The process that is used to separate grain from stalks is threshing. In this process, the stalks are beaten to free the grain seeds (Fig. 5.4). Sometimes, this mixture on a plate or a newspaper. Look at this mixture carefully. Can the two different components be made out easily? Are the sizes of particles of the two components similar? Would it be possible to separate the components by handpicking?

Now, take your mixture to an open ground and stand on a raised platform. Put the mixture in a plate or sheet of paper. Hold the plate or the sheet of paper containing the mixture, at your shoulder height. Tilt it slightly, so that the mixture slides out slowly. What happens? Do both the components — sand and sawdust (orpowdered leaves) fall at the same place? Is there a component that blows away? Did the wind manage to separate the two components?

This method of separating components of a mixture is called winnowing. Winnowing is used to separate heavier and lighter components of a mixture by wind or by blowing air.

Exercises 

1. Why do we need to separate different components of a mixture? Give two examples.

2. What is winnowing? Where is it used?

3. How will you separate husk or dirt particles from a given sample of pulses before cooking.

4. What is sieving? Where is it used?

5. How will you separate sand and water from their mixture?

6. Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?

7. How would you obtain clear water from a sample of muddy water?

8. Fill up the blanks

(a) The method of separating seeds of paddy from its stalks is called ___________.

(b) 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 ___________.

(c) Salt is obtained from seawater by the process of ___________.

(d) 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 ___________.

9. True or false?

(a) A mixture of milk and water can be separated by filtration.

(b) A mixture of powdered salt and sugar can be separated by the process of winnowing.

(c) Separation of sugar from tea can be done with filtration.

(d) Grain and husk can be separated with the process of decantation.

10. Lemonade is prepared by mixing lemon juice and sugar in water. You wish to add ice to cool it. Should you add ice to the lemonade before or after dissolving sugar? In which case would it be possible to dissolve more sugar?

Please refer to attached file for NCERT Class 6 Science Separation of Substances