In many teaching exams including REET 2021 STET 2021 etc. Science may be an interesting subject having 15 questions of Science content and 15 questions of Science Pedagogy in REET and other State TET Exams. Science comprising of various branches of studies like chemistry, physical science, and life science.
Separation of Substance
You must have seen that we clean/separate different substances – we filter tea powder while making tea, we clean rice with water before using it for cooking and so on. These are the processes we use commonly to separate substances. In this chapter, we will study some methods used to separate substances.
Handpicking : –
- Manually separating stones, dust, husk from grain, rice and wheat is referred to as handpicking.
- It is used to remove bigger particles of dust from smaller grains.
- It is a very time-consuming process .
- It cannot be used when the dust and stone particles are small in size.
Threshing : –
- Stalks of grains are dried in the sun.
- Then once they are dry, they are manually beaten hard to free the grains from the stalks. This is referred to
- Sometimes, bullocks or machines are used.
Winnowing : –
- This is a very common method to separate heavier grain particles from lighter dust particles.
- The mixture containing the grain and dust is held high (approximately at shoulder or chest height).
- It is slightly tilted and given a gentle movement such that the lighter particles like husk fall out. This is called Threshing.
Sieving : –
- A sieve is used to filter out the dust particles.
- It is very commonly used for cleaning flour.
- In Sieving, fine flour particles are allowed to pass through the holes of the sieve while the bigger impurities remain on the sieve.
Sedimentation and Decantation : –
- After all the processes used above, there could be still some small particles left in the rice we buy.
- In such cases, we wash the rice with water just before cooking. The rice is heavy and it settles down. This process of separation of heavier components by adding water to it, such that the heavier particles settles down is called
- The lighter dust particles float. The water along with dust particles is discarded. This process of removal of water (or any other solute) along with lighter dust particles is called Decantation.
- Oil and water are separated similarly. Water is lighter than oil and it settles down. The oil is then separated.
Filtration : –
- Separating using a filter like in case of tea filter is referred as
- Filtration is the process of separating solid particles from a liquid by passing through a filter or pores of filter paper
- Fruit and vegetable juices are also filtered like this.
- Sometimes, filter paper can also be used for filtration of certain substances.
Evaporation : –
- When salt is mixed with water (seawater), the water is heated until all the water becomes vapor and only the salt is left behind.
- This process of conversion of a liquid into its vapor is called Evaporation
- This is how salt is separated from seawater.
Salt-Sand mixture : –
- Sometimes, it might be necessary to use more than 1 method to separate substances. Let us consider a mixture of sand, salt.
- Mix the salt and sand mixture with water.
- The salt will dissolve in water whereas the sand won’t dissolve.
- After sometime, the sand would settle down. This is
- The water mixture which contains salt can be now poured out. This is
- Then heat the water such that it vaporizes. (Evaporation). Salt is left behind in the bowl.
- Then cool down the water vapor using a plate of ice (as shown in the figure). The vapour condenses to form water (Condensation) and can be collected in another beaker.
Saturated Solution : –
- When you keep adding a solute (the substances that dissolves in a liquid) in a solvent (liquid that is used to dissolve the solute), it initially begins to dissolve.
- When more and more solute is added, the solute does not dissolve. The solute remains undissolved and this means that the solvent has reached. its ‘Saturating point’ and no more solute can be dissolved.
- The Saturation point of a solvent depends on
- Temperature of the solvent
- Pressure of the solvent
- Nature of the solvent and solute.
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