Animated Solution for Chemistry - Surface Chemistry: Which of the following is used for the preparation of colloids?

When we look at the question, we are asked to identify a specific method used for the preparation of colloids. In chemistry, different industrial and laboratory processes have very specific applications. Some are used for extracting metals, some for synthesizing heavy chemicals, and others for creating delicate colloidal systems.

To find the correct answer, we need to act like a detective and evaluate each option based on its primary chemical application. Let's break them down one by one.

The Colloidal Forge

Imagine you want to create a colloidal solution of a precious metal like gold, silver, or platinum. You can't just dissolve them in water like salt! This is where Bredig's Arc method comes into play.

In this fascinating setup, two electrodes made of the target metal are submerged in a dispersion medium (usually water with a little alkali to stabilize the colloid). The entire container is kept freezing cold using an ice bath. When a massive electrical voltage is applied, an intense electric arc strikes between the electrodes.

This arc generates so much heat that it instantly vaporizes the metal. But because the surrounding medium is ice-cold, this metal vapor immediately condenses into tiny, nanometer-sized particles. These particles are exactly the right size to form a stable colloidal sol. Thus, Bredig's Arc method involves both dispersion (vaporizing the bulk metal) and condensation (forming the particles).

Acids and Metals

Now, what about the other options? Let's see why they don't fit.

Ostwald Process: This is a heavyweight industrial process, but it has nothing to do with colloids. It is the primary method for manufacturing Nitric Acid ($HN{O}_3$). It involves the catalytic oxidation of ammonia ($N{H}_3$) over a platinum gauge at high temperatures to form nitric oxide ($NO$), which is eventually converted into nitric acid.

Mond Process: If you have impure nickel and want to make it ultra-pure, you use the Mond process. It's a metallurgical refining technique. Impure nickel is reacted with carbon monoxide ($CO$) to form a volatile gas called nickel tetracarbonyl ($[Ni(CO{)}_4]$). When this gas is heated to a higher temperature, it decomposes, leaving behind pure nickel.

van Arkel Method: Similar to the Mond process, this is also a refining technique, but it's reserved for metals like Zirconium ($Zr$) and Titanium ($Ti$). The impure metal is heated with iodine to form a volatile metal iodide (like $Zr{I}_4$). This gas is then passed over a white-hot tungsten filament, where it decomposes to deposit ultra-pure metal.

After evaluating all the candidates, the verdict is crystal clear. The Ostwald process makes acid, while the Mond and van Arkel methods refine metals. Only Bredig's Arc method is designed specifically for the preparation of colloids. Therefore, the correct choice is option (a).