Problem 51 - A Complete Resource Book in Chemistry for JEE Main

Question

Gold is extracted by hydrometallurgical process, based on its property (a) of being electropositive (b) of being less reactive (c) to form complexes which are soluble (d) to form salts which are water soluble

Step-by-Step Solution

Answer

Gold is extracted based on its ability to form complexes which are soluble.

Step 1: Understanding Gold's Properties

Gold is a metal known for its low reactivity and inert nature. It doesn't react easily with other substances, making it difficult to use typical extraction methods consistently used for other metals.

Step 2: Investigating Extraction Methods

Hydrometallurgical processes involve the use of water and chemical reactions to extract metals from ores. To suit gold's unique reactivity, this process exploits its ability to interact with specific chemicals that can dissolve it, forming complexes.

Step 3: Analyzing Complex Formation

Gold tends to form chemical complexes that are soluble in water when exposed to specific ligands found in solutions like cyanide or thiourea. These complexes allow gold to be extracted from ores in a dissolved form.

Step 4: Identifying Extraction Method Property

Given that the hydrometallurgical process for gold relies on its tendency to form soluble complexes, the property allowing for its extraction is gold's ability to form water-soluble complexes.

Key Concepts

Gold Extraction

Gold extraction involves retrieving gold from its natural ore form using specialized processes. Traditional methods like smelting are often not suitable for gold due to its unique characteristics, such as low reactivity and resistance to corrosion. Instead, the hydrometallurgical process is commonly used. This process leverages chemical reactions in aqueous solutions to separate gold from its ore. It is an efficient method because it focuses on exploiting gold's ability to form specific chemical complexes, which are necessary for effectively extracting gold from less reactive ore.

Chemical Complexes

Chemical complexes play a critical role in the hydrometallurgical extraction of gold. When gold reacts with certain chemicals, such as cyanide or thiourea, it forms stable complexes. These are groups of atoms bonded together that include the gold atom centrally placed within the structure.
For example, the use of cyanide results in the formation of a gold-cyanide complex, which is highly soluble in water. Such complexes facilitate the dissolution and separation of gold from other elements found in the ore. This ability to form soluble complexes is what makes gold extraction feasible through hydrometallurgical means.

Metal Reactivity

Gold's metal reactivity is distinctly low compared to many other metals. It is known for its inertness, meaning it doesn't undergo reactions easily with other elements. This property is why gold doesn’t tarnish and remains shiny over time. However, this inertness also makes its extraction challenging, as it does not readily form bonds with the usual reagents employed in typical metallurgical processes.
In hydrometallurgy, this low reactivity works to the method's advantage because, while gold resists reaction with many substances, it does interact with specific ones, leading to the formation of soluble complexes. This selective reactivity is key to effectively extracting gold from its ores.

Solubility of Complexes

The solubility of gold complexes is a fundamental aspect of extracting this precious metal via hydrometallurgy. Gold, on its own, is not soluble in water. However, when it forms complexes with chemicals like cyanide, the resulting molecules are water-soluble, allowing them to be separated from the ore.

• Solubility enables the transport and concentration of gold during processing.
• This property allows gold to be poured, refined, and recovered from the solution it resides in after complex formation.

By understanding and utilizing the solubility of complexes, the hydrometallurgical process efficiently isolates gold, making it possible to achieve high purification levels.