Colloids can be purified to remove impurities like ions or small molecules. Here’s a explanation of the main methods:
1. Dialysis
- How it works: Colloid is placed in a semi-permeable membrane bag.
- Small ions and molecules pass through the membrane, but colloidal particles stay inside.
- Example: Purification of proteins and gelatin sols.
2. Ultrafiltration
- How it works: Colloid is passed through a filter with very tiny pores.
- Water and small impurities pass through, but colloidal particles are retained.
- Faster than dialysis and useful for large-scale purification.
3. Electrophoresis
- How it works: Colloidal particles are made to move under an electric field.
- Impurities remain behind, while colloid particles migrate to the electrodes.
- Example: Purification of gold sol, silver sol.
4. Coagulation and Redispersion (Less common)
- Impurities are removed by coagulating the colloid and then redispersing it in pure solvent.
Simple tip:
- Small impurities removed → colloid remains
- Main methods: Dialysis, Ultrafiltration, Electrophoresis