Question

Colloidal gold can be prepared by:
(This question has multiple correct options.)
(A) Bredig’s arc method
(B) Reduction of $AuC{l_3}$
(C) Hydrolysis
(D) Peptization

Answer 1

To solve this question, we must first understand the basic concepts about Colloids and Colloidal Gold. Then we need to assess the preparation methods of colloidal gold and select those correct methods which are provided in the question and then only we can conclude the correct answer.

Complete step-by-step answer: Before we move forward with the solution of this given question, let us first understand some basic concepts: Colloids: the colloidal state is the state of subdivision in which molecules or polymolecular particles having at least one dimension in the range of 1 nanometre and 1 micrometre, are dispersed in some medium“. Colloids usually feature substances that are evenly dispersed in another. In such mixtures, the substance that is dispersed is referred to as the dispersed phase whereas the substance through which it is dispersed is called the continuous phase.Colloidal gold: is a sol or colloidal suspension of nanoparticles of gold in a fluid, usually water. The colloid is usually either an intense red colour.
Step 1: Among the given methods only two of them can be used to prepare colloidal gold:
Bredig's arc method: Bredig's arc method is a method of preparation of colloidal solution of metals such as gold, silver or platinum. This method consists of both dispersion and condensation.This method is suitable for preparation of colloidal solutions of metals like gold, silver, platinum etc.
Reduction of $AuC{l_3}$​ :We can obtain colloidal solutions of metals like gold, silver and platinum that can be obtained by reduction of their salts.
$2AuC{l_3}\,\, + \,\,3SnC{l_2}\,\, \to \,\,\,3SnC{l_4} + \,\,2Au$
Step 2: And the rest of the methods can’t be used for the desired purpose because Hydrolysis is used for iron, and Peptization is for Fe, Ag, Sn and Cd.

So, clearly we can conclude that the correct answer is Option (A) and (B).

Note: The properties of colloidal gold nanoparticles, and thus their potential applications, depend strongly upon their size and shape.