JEE Main 2020 · 2 September · morning · Single correct · +4 / −1
Which of the following is used for the preparation of colloids?
- (a) Van Arkel Method
- (b) Bredig’s Arc Method
- (c) Mond Process
- (d) Ostwald Process
Answer and solution
Answer (b) Bredig’s Arc Method
Solution
Chemistry ma’am · 2 steps
Only one of these four names makes a colloid; the other three refine metals or make an acid.
- Bredig's arc. An electric arc is struck between two metal electrodes held under cold water containing a trace of alkali. The heat vaporises the metal, and the vapour condenses into particles of colloidal size. This gives sols of gold, silver and platinum.
Method What it does Makes a colloid? Van Arkel method Refines Zr or Ti through a volatile iodide that decomposes on a hot filament No Bredig's arc method Vaporises a metal in an arc under water; the vapour condenses as a sol Yes Mond process Refines Ni through volatile Ni(CO)₄ No Ostwald process Makes HNO₃ by catalytic oxidation of NH₃ No - So. Bredig's arc method, option (b), is the one used to prepare colloids.
The idea to keep. Bredig's arc is both dispersion and condensation: the arc breaks the metal into vapour, and the vapour condenses into colloidal particles. Remember it for metal sols like Au, Ag and Pt.
Answer from the NTA final answer key. Solution by PrepWiser.