Question

Also known as the electro-dispersion method, the Bredig’s arc method applies a high voltage between two electrodes of a metal (like gold or silver) immersed in a dispersion medium to obtain a colloidal sol of the metal. Which of the following regarding the electrodes?

• A. The electrodes are made of different metals
• B. The electrodes are made of the same metals
• C. The electrodes are kept very far apart
• D. The electrodes are kept close to each other and the dispersion medium is cooled by a freezing mixture

Answer 1

Answer: (B), (D)

The correct options are
B The electrodes are made of the same metals
D The electrodes are kept close to each other and the dispersion medium is cooled by a freezing mixture

When an electric arc is struck between two electrodes of a metal, like gold, silver, platinum or copper, immersed in dispersion medium, the metal is found to be converted into a colloidal solution. If water is the dispersion medium, the process is carried out with traces of an Alkali, which acts as a stabilizer. The intense heat produced vaporizes the metal, which is then cooled rapidly by the freezing mixture surrounding the container. The vapours condense to form particles of colloidal size.


Obviously, the electrodes are made of the same metal, whose sol is what we intend to prepare.