Extraction of gold and silver involves leaching the metal with \(CN^-\) ion. This is also _______________ for gold or silver

Oxidation reaction

The correct answer is option 1. Oxidation reaction.

Let us delve into why the extraction of gold and silver using cyanide is primarily classified as an oxidation reaction.

Extraction of Gold and Silver Using Cyanide

The Cyanidation Process: To extract gold and silver from their ores by converting them into soluble cyanide complexes.

Gold Extraction Reaction:

Chemical Reaction:

\(4 \text{Au} + 8 \text{NaCN} + 2 \text{H}_2\text{O} \longrightarrow 4 \text{Na[Au(CN)}_2] + 4 \text{NaOH}\)

Gold (Au): In its metallic form, gold is not soluble in cyanide.

Oxidation: Gold (Au) is oxidized to form the \(\text{Au}^{3+}\) ion.

Complex Formation: The \(\text{Au}^{3+}\) ion then reacts with cyanide ions (\(CN^-\)) to form a soluble complex ion, \(\text{Na[Au(CN)}_2]\).

Silver Extraction Reaction:

Chemical Reaction:

\(4 \text{Ag} + 8 \text{NaCN} + 2 \text{H}_2\text{O} \longrightarrow 4 \text{Na[Ag(CN)}_2] + 4 \text{NaOH}\)

Silver (Ag): Silver, like gold, is initially insoluble in cyanide.

Oxidation: Silver (Ag) is oxidized to form \(\text{Ag}^+\) ions.

Complex Formation: The \(\text{Ag}^+\) ions react with cyanide ions (\(CN^-\)) to form the soluble complex ion, \(\text{Na[Ag(CN)}_2]\).

Why It’s Classified as an Oxidation Reaction:

Oxidation is the process where an atom or ion loses electrons. In this context, the metals (gold and silver) lose electrons to form positive ions (\(\text{Au}^{3+}\) and \(\text{Ag}^+\)). Cyanide (\(CN^-\)) acts as the oxidizing agent. It facilitates the loss of electrons from the metal, which is a hallmark of oxidation.

Oxidizing Agents: These are substances that gain electrons themselves (or facilitate the loss of electrons by another substance), causing oxidation.

The formation of complex ions (\(\text{Na[Au(CN)}_2]\) and \(\text{Na[Ag(CN)}_2]\)) is a result of the metal ions being stabilized in solution by bonding with cyanide ions. The metal oxidation step is crucial because it transforms the metal into a soluble form that can be recovered from the ore.

Summary:

Oxidation Reaction: The core reaction for both gold and silver involves the oxidation of the metal ions. The metals lose electrons, which is the defining feature of oxidation. The cyanide ion acts as the oxidizing agent, enabling the metals to be converted into their soluble complex forms.

Overall Process: While the overall extraction process involves both oxidation (of the metal) and reduction (of cyanide or other components), the key reaction describing the metal’s behavior is oxidation.

Thus, in the context of describing the metal’s behavior in the extraction process, **option 1: Oxidation reaction** is the most accurate description of the reaction involving gold and silver leaching with cyanide.