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Question
Which of the following are methods employed to purify colloids?
Which of the following are methods employed to purify colloids?
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Solution
The correct option is D Dialysis
Electric charge is an important factor for the stability of a colloidal dispersion. Since the dispersed particles carry an equal and opposite charge, they neither aggregate together nor settle down.
In practice, whenever colloidal solutions are prepared, the system also contains some excess electrolytes and other soluble impurities. Hence it is necessary to purify a colloidal solution. The following methods are popular
1. Dialysis: Dialysis may be defined as the process of separating a dissolved solute from a colloid by diffusion or filtration through a fine membrane. The membrane used for the purpose is known as dialyzer. The mixture, taken in a bag made from parchment paper or an animal membrane, is dipped in warm water. Through the parchment paper only true solution solute molecules are able to pass through whereas the colloidal particles remain within the bag. The process of dialysis can be quickened by using hot water, which is called hot dialysis. Alternatively, if we employ an electric field to hasten the dialysis process, then it is termed electrodialysis.
2. Ultrafiltration: Unlike suspensions, the dispersed phase in colloids pass through ordinary filter paper because their pores are larger than the size of sol particles. But if the pores of the ordinary filter paper are clogged partially by soaking the filter paper in a solution of gelatin or collodion and subsequently hardened by soaking in a suitable solvent like formaldehyde, the treated filter paper may retain colloidal particles and allows the true solution particles to escape. Such a filter is known as ultrafilter and the process of separating colloids by using ultrafilters is known as ultrafiltration.
Electric charge is an important factor for the stability of a colloidal dispersion. Since the dispersed particles carry an equal and opposite charge, they neither aggregate together nor settle down.
In practice, whenever colloidal solutions are prepared, the system also contains some excess electrolytes and other soluble impurities. Hence it is necessary to purify a colloidal solution. The following methods are popular
1. Dialysis: Dialysis may be defined as the process of separating a dissolved solute from a colloid by diffusion or filtration through a fine membrane. The membrane used for the purpose is known as dialyzer. The mixture, taken in a bag made from parchment paper or an animal membrane, is dipped in warm water. Through the parchment paper only true solution solute molecules are able to pass through whereas the colloidal particles remain within the bag. The process of dialysis can be quickened by using hot water, which is called hot dialysis. Alternatively, if we employ an electric field to hasten the dialysis process, then it is termed electrodialysis.
2. Ultrafiltration: Unlike suspensions, the dispersed phase in colloids pass through ordinary filter paper because their pores are larger than the size of sol particles. But if the pores of the ordinary filter paper are clogged partially by soaking the filter paper in a solution of gelatin or collodion and subsequently hardened by soaking in a suitable solvent like formaldehyde, the treated filter paper may retain colloidal particles and allows the true solution particles to escape. Such a filter is known as ultrafilter and the process of separating colloids by using ultrafilters is known as ultrafiltration.
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