Methods of preparation and purification of colloidal solution
Answers
Answer:
Dispersion method
Aggregation method
Dispersion Method:
In this type of preparation method, the larger particles are broken down into particles of the range of colloidal particle size.
Some of the dispersion methods are:
Mechanical Dispersion:
In this method, solid and the liquid dispersion medium are poured into the colloidal mill to form a colloidal sol.
Bredig’s Arc method (Electrodispersion):
Hydrosols of metals e.g., platinum, silver, gold are prepared by this method. The metal electrodes are kept at the two sides of the arc which is enclosed by deionized water. The excessive heat provided by the spark vaporizes some traces of the metal and water gets condensed by vapor. Some amount of KOH is added to water as a stabilizing agent.
Peptization:
In peptization method, some electrolytes are added to form a colloidal sol from a freshly prepared precipitate.
Example: Ferric chloride is added to a freshly prepared precipitate of ferric hydroxide which converts it into a colloidal sol of reddish brown in color.
Aggregation methods:
In this method, small particles are aggregated to form colloidal size particles.
Double Decomposition:
Example: Arsenious oxide is mixed with hydrogen sulfide to form arsenic sulfide sol. The excess amount of hydrogen sulfide is removed by passing stream of hydrogen.
As2O3 + 3H2S → As2S3 (sol) + 3H2O
Reduction:
Example: Noble gases are reacted with organic reducing agents like ethanol, tannic acid, formaldehyde to form their respective sol.
AgNO3 + tannic acid → Ag-sol
Oxidation:
When hydrogen sulfide is passed through a solution of sulfur dioxide it forms a sulfur sol.
2 H2S + SO2 → 2H2O + S
Explanation: