Separation of Substances

Q12. How can we separate oil and water from their mixture?

Ans. Oil floats on water and form separate layer. Separating funnel can be used to separate the two.

Q13. Why are we able to dissolve more solute in a solvent at high temperature?

Ans. We are able to dissolve more solute in a solvent at high temperature because high temperature facilitates dissolving reaction by providing energy to break bonds in the solid.

Q14. Why sieving is not used to separate very small stones from rice grains?

Ans. Sieving is not used to separate very small stones from rice grains because both are of almost same size and both will pass through the holes of the sieve.

Q15. There are 3 beakers half filled with water. Now add 3 spoon of sugar in first beaker, 5 spoon of sugar in second beaker and 7 spoon of sugar in third beaker. Stir the solution of all three beakers. Which solution is more saturated?

Ans. Third beaker

     Q16. Define the following terms:
 a.   Hand picking

Handpicking is a method used to separate larger impurities like pieces of dirt, stones etc. just by picking them out with the help of hand from the mixture.

     b.   Threshing

Threshing is a method of separating grains or seeds from the stalks by some mechanical means such as by beating with a flail or by the action of a threshing machine.

     c.   Evaporation

The process of conversion of water into water vapor is called evaporation.

     d.   Condensation

The process of conversion of water vapor into its liquid form is called condensation.

     e.   Saturated Solution

A solution in which no more solute (such as sugar or salt) can be dissolved in the given amount of solvent (such as water) at a particular temperature is known as saturated solution.

     f.    Unsaturated Solution

A solution in which more solute (such as sugar or salt) can be dissolved in the given amount of solvent (such as water) at a particular temperature is known as unsaturated solution.

     g.   Decantation

Decantation is the process of removing liquid from mixture when heavier component settles down at the bottom of container.

     h.   Solution

A mixture of soluble solid in liquid is called solution.

      i.     Solute

Substance that is dissolved is called solute.

      j.    Solvent

The liquid in which the solute dissolves is called solvent.

      k.   Strainer

Strainer is a device with holes punched in it or made of crossed wires for separating solid matter from a liquid.

Q17. What is winnowing? Where is it used?

Ans.  Winnowing is the method in which heavier components of the mixture are separated from the lighter components such as chaff, dirt, etc. by dropping mixture from height into the air. This method is used by farmers to separate husk and other lighter impurities from grains.

Q18. Why do we separate substances?

Ans. We need to separate the components of a mixture for the following reasons:

                        i.        To separate two different but useful components from the mixture.

                       ii.        To remove non – useful components from the mixture.

                      iii.        To remove impurities or harmful substance from the mixture.

                      iv.        To remove the unwanted impurities from the mixture.

                       v.        To obtain pure substances by removing the other substances.