Q.Explain the terms, Zeta potential, electro-phoresis and electro-osmosis.

All three terms describe the electrical double layer around a colloidal particle and its behaviour under an applied electric field.

Colloidal particles carry a surface charge (due to preferential adsorption of ions or ionisation of surface groups), which attracts a layer of oppositely charged ions from the medium close to the surface (the fixed/compact layer) and a further, more loosely held diffused layer.

1. Zeta potential (electrokinetic potential): the difference in potential between the fixed (compact) layer of ions tightly bound to the particle surface and the diffused layer of oppositely-charged ions in the surrounding medium. It arises because the two layers have a net separation of charge, and it determines the stability and electrokinetic behaviour of the colloid.

2. Electrophoresis: when an electric field is applied across a colloidal sol, the charged colloidal particles themselves move towards the oppositely charged electrode (e.g., negatively charged particles move towards the anode) while the dispersion medium stays stationary. This directed movement of the dispersed particles under an electric field is called electrophoresis.

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