Chapter 2: Is Matter around us Pure?

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Is Matter around us pure?

Question:

Q.1: Which separation techniques will you apply for the separation of the following?

(a)     Sodium chloride from its solution in water

(b)     Ammonium chloride from a mixture containing sodium chloride and ammonium chloride

(c)     Small pieces of metal in the engine oil of a car

(d)     Different pigments from an extract of flower petals

(e)     Butter from curd

(f)     Oil from water

(g)     Tea leaves from a tea

(h)     Iron pins from sand

(i)      Wheat grains from husk

(j)      Fine mud particles suspended in water

Answer:

(a) The process in which the liquid changes its state to a gas at a temperature below its boiling point is called evaporation. It is used to separate the non-volatile solute from the volatile solvent. For example, the separation of salt from its solution. When the salt solution is heated, water is evaporated leaving the salt behind.

(b) Sublimation is the process in which the substance changes its state from solid to gas. Ammonia chloride is a sublimable salt. When the mixture containing sodium chloride and ammonium chloride are heated, ammonium chloride vapourises leaving sodium chloride behind.

(c) The process which is used to separate a solid substance from a liquid by allowing the liquid substance to pass through the filtering medium is called filtration. In the process of filtration, the liquid is allowed to pass through the filter paper attached to a funnel while the solid will remain on the filter paper. When a mixture of engine oil and metal is filtered, the engine oil passes through the filter paper while the metal remains on the filter paper.

(d) Chromatography is the technique used for the separation of those solutes that dissolve in the same solvent. It works on the principle of interaction between the solute and solvent. It is commonly used to separate pigments from flower petals.

(e) Centrifugation is the technique in which the mixture is separated through spinning and the denser particles are forced to the bottom while the lighter particles stay at the top when spun rapidly. It is commonly used to separate butter from curd.

(f) The immiscible liquids can be separated by using a separating funnel. The principle used in separating the funnel is based on the difference in densities of the two liquids. The denser liquid is settled at the bottom of the funnel, while the lighter liquid will remain at the top. When a mixture of oil and water is added to the separating funnel, the water settles at the bottom while oil appears at the top.

(g) The process which is used to separate a solid substance from a liquid by allowing the liquid substance to pass through the filtering medium is called filtration. When the tea is passed through the funnel, the tea leaves appear on the filter paper while the tea passed through the filter paper.

(h) Magnetic separation is the technique in which the magnetic materials are separated from the mixture by using magnets. Iron is a magnetic substance that is separated from sand using a magnet.

(i) Winnowing is the method of separation of heavier and lighter components of a mixture by wind or by blowing air. This method is used by the farmer to separate husk particles from heavier seeds of grain.

It can also be separated by a technique called sedimentation. Sedimentation is the process of settling down suspended particles in a liquid. When the mixture of wheat grain and husk is added to water, the lighter husk floats on the surface while the wheat grain settles at the bottom.

(j) Fine mud particles can be separated from water by sedimentation followed by decantation. Sedimentation is the process of settling down suspended particles in a liquid. Mud does not dissolve in water and settles at the bottom, which can be removed by the decantation process.


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