Question

In the extraction of silver, \(\mathrm{Ag}_{2} \mathrm{~S}\) is dissolved in (a) \(\mathrm{HNO}_{3}\) (b) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (c) \(\mathrm{HCl}\) (d) \(\mathrm{KCN}\)

Short answer

(d) KCN

Step-by-step solution

Understanding Silver Extraction

In the extraction of silver, we typically aim to convert silver sulfide (ig_{2}S) into a form that can be further processed. This usually involves the use of a chemical that can effectively dissolve the silver sulfide.

Analyzing the Options

The options provided are different chemicals that could potentially react with ig_{2}S: (a) HNO_{3} (Nitric acid), (b) H_2SO_{4} (Sulfuric acid), (c) HCl (Hydrochloric acid), and (d) KCN (Potassium cyanide). We need to decide which one is used in the silver extraction process.

Identifying the Correct Chemical

In industrial extraction processes, KCN is known to be used to dissolve silver sulfide by forming a soluble complex with silver. This process is part of the cyanidation method of silver extraction, where potassium cyanide reacts with silver sulfide to create silver cyanide, which is soluble and can be further processed.

Choosing the Correct Answer

Based on the analysis, the correct answer is (d) KCN. This choice is because KCN forms a complex with silver in ig_{2}S, effectively dissolving it.

Key concepts

Silver Sulfide

Silver sulfide, chemically known as \(\mathrm{Ag}_{2}\mathrm{S}\), is a compound made from silver and sulfur. This compound is naturally occurring and is a significant ore for extracting silver. Silver sulfide is not soluble in water or most acids, making it stable under ordinary conditions.
However, its insolubility can be a challenge during the extraction of silver. In mining, silver sulfide is commonly extracted from ores using specialized methods to isolate pure silver metal for industrial use.
Understanding the chemical properties of silver sulfide is crucial for choosing the appropriate method for silver extraction. It requires a specific reagent that can effectively convert it into a more soluble and manageable form for industrial processing.

Cyanidation Method

The cyanidation method is a widely used technique in the extraction of precious metals such as silver and gold. It involves the use of a cyanide solution to dissolve and separate the desired metal from its ore. This method is favored because it effectively extracts metals, even from low-grade ores.
During cyanidation, silver sulfide is exposed to a solution containing cyanide ions, which react with the silver ions in the compound. This reaction forms a soluble complex, silver cyanide \(\mathrm{Ag(CN)}_2^-\).
The overall chemical equation can be represented as follows:

• \(\mathrm{Ag}_{2}\mathrm{S} + 4\mathrm{KCN} \rightarrow 2\mathrm{Ag(CN)}_2^- + \mathrm{K}_2\mathrm{S}\)

The result is a solution rich in silver cyanide that can be further processed to recover pure silver. Despite its effectiveness, this method requires careful handling of cyanides due to their toxic nature.

Potassium Cyanide

Potassium cyanide \(\mathrm{KCN}\) plays a crucial role in the cyanidation process of silver extraction. This chemical is known for its strong ability to dissolve precious metal compounds, thus making it an ideal choice in the mining industry.
In the presence of potassium cyanide, silver sulfide dissolves and forms a stable, soluble complex. This complexation facilitates the recovery of silver from ores and helps in processing and refining it into pure metal.
It's important to handle potassium cyanide with caution. While it's extremely useful in metallurgy and precious metal extraction, it is highly toxic and requires stringent safety protocols. This includes proper storage, handling, and disposal to mitigate environmental and health risks.