Van Arkel Method of Purification of Metals

Introduction:
The Van Arkel method, also known as the Van Arkel-de Boer process, is a technique used for the purification of metals. This method involves the conversion of the metal into a volatile unstable compound, which is subsequently decomposed to obtain a highly pure metal.

Process:
The process of purification using the Van Arkel method typically involves the following steps:

1. Formation of a volatile compound: The metal to be purified is reacted with a suitable compound to form a volatile unstable compound. This compound is typically formed by heating the metal with a reactive non-metal, such as iodine or a halogen.

2. Formation of a solid compound: The volatile compound is then condensed and converted into a solid compound. This is achieved by cooling the reaction mixture, causing the volatile compound to condense and form a solid.

3. Decomposition: The solid compound is then subjected to controlled heating in the presence of an inert gas, such as argon or helium. This decomposition process results in the formation of the pure metal and the release of the non-metallic component as a gas.

4. Collection of the pure metal: The pure metal is collected, while the non-metallic component is captured and removed from the system.

Reason for selecting volatile unstable compounds:
The Van Arkel method involves the use of volatile unstable compounds for the following reasons:

1. Selectivity: The formation of a volatile unstable compound ensures the selective removal of impurities present in the metal. The impurities are usually less reactive and do not form volatile compounds, allowing for their separation from the desired metal.

2. Decomposition: The decomposition of the volatile unstable compound at high temperatures facilitates the removal of impurities, as they are released as gases. This process ensures the production of a highly pure metal.

3. Volatility: The volatility of the compound ensures its easy separation from the metal. The volatile compound can be condensed and collected separately, while the pure metal remains behind.

4. Thermodynamic stability: The use of volatile unstable compounds allows for the purification of metals with high thermodynamic stability. The formation of a volatile compound provides a means to overcome the strong bonding and high stability of the metal.

Therefore, the Van Arkel method of purification of metals involves converting the metal into a volatile unstable compound. This volatile compound is subsequently decomposed to obtain a highly pure metal, free from impurities.