Chemistry · Ch 12 — Surface Chemistry
Preparation of Colloids
Preparation of Colloids
Several important methods produce colloids.
(a) Chemical methods
A chemical reaction — double decomposition, oxidation, reduction or hydrolysis — makes molecules that then aggregate into a sol:
(b) Electrical disintegration — Bredig's Arc method
This combines dispersion and condensation and is used for sols of gold, silver, platinum, etc. As Fig. 5.8 shows, an electric arc is struck between metal electrodes immersed in the dispersion medium (kept cool in an ice-bath). The intense heat vaporises the metal, which then condenses into colloidal-sized particles.
(c) Peptization …
What this figure shows. Apparatus diagram of Bredig's Arc method. A container (beaker) sits within a surrounding ice-bath (the outer region shown as a grey mottled block, labelled 'Ice-bath' by a leader line on the right). Inside the beaker is the dispersion medium (a light blue liquid region, labelled 'Dispersion medium' by a leader line on the right). Two red rod electrodes are dipped from above into the medium, angled toward each other so their lower tips nearly meet just below the liquid surface, with an electric arc struck between them. The upper ends of the electrodes curl outward and connect to external wires/terminals. Above the electrodes is the label 'Electrodes' with a '+' marked over the left electro …