Q.Explain the following terms:

Step 1 – (i) Electrophoresis. Colloidal particles are electrically charged. When an electric field is applied to a sol, the particles migrate towards the electrode of opposite charge — positively charged sols to the cathode, negatively charged sols to the anode. This migration is electrophoresis; it also proves colloidal particles are charged.

Step 2 – (ii) Coagulation. The process of settling/aggregation of colloidal particles into a precipitate is coagulation (or flocculation/precipitation). It is caused by adding an electrolyte (the oppositely charged ion neutralises the particle charge — Hardy–Schulze law), by heating, by prolonged electrophoresis, or by mixing two oppositely charged sols.

Step 3 – (iii) Dialysis. A sol usually contains dissolved electrolyte impurities. Dialysis is the process of removing these dissolved ions/small molecules from the sol by diffusion through a semipermeable (parchment/cellophane) membrane into flowing water, while the larger colloidal particles are retained. (Speeded up by an electric field = electrodialysis.) …

Give a crisp, correct one-line definition of each of the four colloidal phenomena, distinguishing electrophoresis (particle movement) f …

• Confusing electrophoresis with electro-osmosis or with dialysis.
• Defining coagulation as merely settling due to gravity rather than charge-neutralised aggregation. …