Elements, Compounds and Mixtures — Question 16

(i) Naphthalene & sodium chloride:

(a) Principle involved: Based on the difference in sublimable and non-sublimable nature of solids.

(b) Technique of separation: The mixture of the sublimable solid and non-sublimable solid is heated in an evaporating dish covered with funnel plugged at one end with cotton.

Sublimable solids on heating sublimes and the vapours condense and collect in the pure form on the inner side of the funnel, from where the sublimable solid is scrapped off.

(ii) Common salt from a solution of common salt in water :

(a) Principle involved: Based on evaporation of the liquid component in a soluble solid-liquid mixture.

(b) Technique of separation: The soluble solid can be separated from its liquid component by allowing the liquid component to evaporate either on its own or by heating. On heating, water is lost to the atmosphere and common salt remains behind in the evaporating dish.

(iii) Pure water from impure water:

(a) Principle involved: Based on the distillation of the liquid component in a soluble solid-liquid mixture.

(b) Technique of separation: The soluble impurity can be separated from its liquid component or pure water from impure water by placing the mixture, i.e., impure water in the distillation flask. On heating the distillation flask, the solid or solid impurities in water remains behind in the distillation flask. The liquid or water vaporizes, condenses in the Leibig’s condenser and is collected in the receiver.

(iv) Kerosene & water:

(a) Principle involved: Based on the separation of two immiscible liquids (one heavy, one light) through separating funnel.

(b) Technique of separation: The kerosene & water mixture is added to the separating funnel and the funnel is kept aside for some time.

The heavier immiscible liquid i.e., water settles down in the separating funnel and is then removed from below on opening the tap and collected out separately.

The lighter immiscible liquid i.e., kerosene remains above the heavier liquid.

(v) Methyl alcohol & water:

(a) Principle involved: Based on the separation of mixture of two miscible liquids with different boiling points.

(b) Technique of separation: The mixture of two miscible liquids e.g., methyl alcohol and water having different boiling points is taken in the distillation flask and heated slowly till it boils. The component with the higher boiling point i.e., water remains behind in the distillation flask after condensation. The component with the lower boiling point i.e., methyl alcohol collects in the receiver after condensation in the Leibig's condenser.

(vi) Dyes of an ink:

(a) Principle involved: Chromatography is a method by which the various components of a mixture e.g., dyes in an ink, are separated due to their difference in the rate of flow over an adsorbent medium.

(b) Technique of separation:

• Stationary phase in chromatography, the adsorbent medium is known as the stationary phase e.g., filter paper made of cellulose.

• Mobile phase the solvent or the solution that moves due to capillary action is known as the mobile phase.

Separation of dyes in ink by paper chromatography. Ink prepared by dissolving different dyes e.g. A, B, C, D in a suitable solvent, is taken.

• A line is drawn with a pencil over a long strip of a filter paper.
• Place the ink spot containing the different dyes on the filter paper.
• The filter paper is then hung with its lower end dipped in a suitable solvent.
• The paper strip with the spot of ink at its end is dipped into the solvent in a way that the spot itself remains above the liquid surface.
• The solvent flows over the ink spot & the various components of the mixture, of dyes in the ink are separated.