Chemistry · Ch 11 — Adsorption and Colloids
Emulsions
Emulsions
An emulsion is a colloidal system in which one liquid is dispersed as fine droplets throughout another, immiscible (or only partially miscible) liquid. Fig 11.11 (attached to this section) shows the two types of emulsion. (i) Oil-in-water (o/w) emulsions: the dispersed phase is oil and the dispersion medium is water -- examples given are milk, vanishing cream and paint; milk specifically consists of fat droplets dispersed through a watery medium. (ii) Water-in-oil (w/o) emulsions: the dispersed phase is water and the dispersion medium is oil -- examples given are cod liver oil (water droplets dispersed in oil), and also butter and cream. Table 11.7 (attached to this section) gives a full point-by-point distinction between the two types, covering which liquid is continuous, what happens on adding more oil or water, the effect of a small amount of electrolyte on the emulsion's conductivity, and which kind of emulsifier (basic metal sulfates and water-soluble alkali-metal soaps for o/w; water-insoluble soaps of Zn, Al, Fe or alkaline-earth metals for w/o) is used to stabilise each type. Emulsions in general show four properties: (1) an emulsion can be diluted with any amount of its own dispersion medium, whereas mixing in the dispersed liquid instead just forms a separate layer; (2) emulsion droplets are often negatively charged and can be precipita …
What this figure shows. A pair of side-by-side schematic diagrams contrasting the two emulsion types. The oil-in-water diagram shows small oil droplets (dispersed phase) scattered through a continuous water medium; the water-in-oil diagram shows small water droplets (dispersed phase) scattered through a continuous oil medium. Comparing the two side by side visually reinforces which liquid is the droplets and which is the continuous surrounding medium in each type, matching the o/w and w/o de …
Oil in water | Water in oil
- Oil is the dispersed phase and water is the dispersion medium. | Water is the dispersed phase and oil is the dispersion medium.
- Adding water makes it miscible with the emulsion. | Adding oil makes it miscible with the emulsion.
- A small amount of added electrolyte makes the emulsion conducting. | A small amount of added electrolyte has no effect on the emulsion's conducting power.
- Water is the continuous phase. | Oil is the continuous phase. …