To Separate Components of a Mixture

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Experiment 3(A)

Aim

To separate a mixture of common salt and sand.

Theory

In the given mixture of common salt and sand, only common salt is soluble in water. As such when the mixtured is stirred with water, only common salt goes into solution leaving behind the sand undissolved. The suspension is filtered when sand is obtained as a residue an the filter paper. The filtrate, a solution of common salt in water, is evaporated to dryness to obtain common salt.

Materials Required

A 250 ml beaker, china dish, glass rod, funnel, funnel stand, wire gauze, tripod stand, Bunsen burner, filter paper, distilled water and given mixture of common salt and sand.

Procedure

• Take nearly 100 ml of distilled water in the beaker and heat it to 70^° C (very hot to touch).
• Add nearly 10 g of the given mixture to the hot water and stir it well with glass rod.
• Filter the hot contents of the beaker and collect the filtrate in a china dish. Wash the sand with a few drops of water on the filter paper itself and dry it. The first component i.e., sand is obtained on the filter paper as residue.
• Place the china dish, containing the solution of common salt in water, on a wire gauze which is directly heated by the flame of bunsen burner.
• Evaporate the water slowly and carefully to get the second component of the mixture i.e., common salt.

Note : If the mixture is suspected to contain some soluble impurities, other than common salt, pure common salt can be obtained by crystallisation. In such a case the solution is evaporated to crystallisation point and is allowed to cool slowly to get a crop of crystals of crystals a of common salt.

Precautions

• To dissolve the given mixture use minimum quantity of water.
• Heat the china dish slowly and carefully. Alternatively use a sand bath to heat the china dish.
• Do not heat the china dish to dryness. let the last few drops of water to evaporate without heating.

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Experiment 3(B)

Aim

To separate a mixture of common salt and ammonium chloride.

Theory

In this mixture both the components are water soluble. However, when the mixture is heated only ammonium chloride sublimes leaving behind common salt. As such the components of this mixture can be separated by sublimation.

Materials Required

A china dish, glass funnel, tripod stand, wire gauze, Bunsen burner, cotton, etc.

Procedure

• Take the given mixture in a china dish, and place it over a burner by using a wire gauze and tripod stand.
• Put an inverted glass funnel over the china dish.
• Plug the stem of the funnell with some cotton.
• Heat the china dish containing the mixture slowly.
• When the white fumes inside the inverted funnel subsides, stop heating the china dish.
• Let the apparatus cool throughly. Lift the funnel carefully and scrap out the ammonium chloride sticking into it, on to a paper.
• The residue in the china dish is common salt.

Precautions

• The diameter of the funnel should be slightly less than that of china dish.
• Use only a glass funnel. Don’t use the plastic funnel.
• Lift the funnel very carefully after the experimen. A jerk can dislodge the sublimate.
• Lift the funnel only when the apparatus is throughly cool.

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Experiment 3(C)

Aim

To separate the components of a mixture of sand, common salt and ammonium chloride (or comphor) by suitable methods.

Theory

The given mixture can be separated into its components by sublimation followed by extraction with water. Sublimation will remove the volatile component ( ammonium chloride or comphor) from the mixture. The remaining mixture now contains common salt and sand. Out of these two, only common salt is soluble in water. As such, when this mixture is extracted with water, common salt dissolves in water leaving behind the insoluble sand as residue on the filter paper. Evaporating the solution of common salt in water to dryness gives the last component i.e., common salt.

Materials Required

250 ml beakers (3 Nos), glass funnel (2 Nos), china dish (2 Nos), funnel stand, tripod stand, glass rod, filter paper, wire gauze, Bunsen burner, cotton, distilled water etc.

Procedure

• Take the mixture in a china dish and place it over a Bunsen burner by using a wire gauge and stand.
• Put and inverted funnel over the china dish. Plug the stem of the funnel with some cotton.
• Heat the china dish containing the mixture slowly.
• When the white fumes inside the inverted funnel subsides, stop heating the china dish.
• Let the apparatus cool thoroughly. Lift the funnel carefully and scrap out the ammonium chloride sticking into it, on to a paper.
• The residue in the china dish contains common salt and sand.
• Heat nearly 100 ml of water in a 250 ml beaker to nearly 70°C.
• Put the residue obtained in step 6 into the warm water and stir it well with a glass rod.
• Filter this mixture through a filter paper and collect the filtrate in a china dish. Wash the sand on the filter paper with a few drops of water. Dry the sand to obtain the second component of the mixture.
• Place the china dish, containing the solution of common salt in water over a wire gauze which is directly heated by the flame of a Bunsen burner.
• After the evaporation of water, the third component of the mixture i.e., common salt to obtained in the china dish.

Precautions

• The diameter of the glass funnel used for sublimation sholud be slightly less than that of china dish.
• Use only a glass funnel for sublimation. Don’t use a platic funnel.
• Lift the inverted funnel very carefully after sublimation. A jerk can dislodge the sublimate.
• Lift the funnel only when the apparatus is throughly cool.
• To dissolve the mixture of common salt and sand, use minimum quantity of distilled water.
• Heat the china dish containing the solution of common salt slowly and carefully. Alternatively use a sand both to heat the china dish.
• Don’t heat the china dish to dryness. It may break it. Let the last few drops of water to evaporate without further heating.
• In this experiment it is very important to follow the sequence in which different operations are carried out.