Question

When sodium argentocyanide is treated with zinc dust, silver precipitates because (a) zinc forms a complex readily with cyanide (b) zinc is more electropositive than silver (c) silver is more electropositive than zinc (d) both \(\mathrm{Zn}^{2+}\) and \(\mathrm{Ag}^{+}\)ions have \(\mathrm{d}^{10}\) electronic configuration

Short answer

(b) zinc is more electropositive than silver.

Step-by-step solution

Understand the Problem

The problem asks why silver precipitates when sodium argentocyanide is treated with zinc dust. We need to identify the reason for this reaction specifically among the given options.

Analyze the Reaction

The chemical reaction involves sodium argentocyanide \((\text{Na}[\text{Ag}(\text{CN})_2])\) being in contact with zinc dust. Zinc is more reactive and has a higher tendency to lose electrons than silver. When this reaction occurs, zinc replaces silver in the complex.

Consider Electropositivity

Electropositivity is the ability of an element to lose electrons and form positive ions. Since zinc can replace silver in the complex, it must be more electropositive than silver, making it a viable option for why silver precipitates out.

Examine Complex Formation

Zinc can form stable complexes with cyanide ions as well. However, in the context of the given options, it is not explicitly stated as the primary reason for the precipitation of silver compared to zinc's electropositivity.

Confirm Electropositive Option

Between the options provided, the explanation that 'zinc is more electropositive than silver' directly leads to zinc displacing silver from the solution, causing silver to precipitate.

Key concepts

Electropositivity

Electropositivity is a crucial concept in redox reactions, particularly when discussing why certain elements can replace others in compounds. Electropositivity refers to the tendency of an element to lose electrons and form positively charged ions, known as cations. In the context of redox reactions, an element that is more electropositive has a greater ability to donate electrons compared to another element, which may lead to a chemical displacement.

In the reaction involving sodium argentocyanide and zinc dust, zinc is more electropositive than silver. Being more electropositive means zinc is more willing to lose electrons and form positive ions ( ext{Zn}^{2+}) compared to silver. This characteristic of zinc results in it displacing silver in the reaction. As zinc enters the complex ion, silver ions are freed, resulting in silver precipitating out of the solution.

This displacement is driven by zinc's inherent tendency to form cations more readily due to its higher electropositive nature. Understanding the electropositivity of elements helps predict which elements may replace others in various chemical reactions, particularly in redox switches where electron transfer is key.

Complex Formation

Complex formation plays an important role in many chemical reactions, where compounds with complex ions are formed by the coordination of ligands to a central metal ion. The ability to form complex ions depends on the metal ion's preference for certain ligands, such as cyanide in this case.

In the reaction involving sodium argentocyanide ( ext{Na}[ ext{Ag}( ext{CN})_2]), the silver ion is coordinated within a complex with cyanide ions. Complexes like these can be disrupted when a different metal shows a stronger affinity or forms a more stable complex with the same ligands, as seen with the introduction of zinc.

Zinc forms complexes with cyanide ions, and though the formation of a zinc complex with cyanide is not the primary reason silver precipitates, it's significant. This ability of zinc to also form complexes can support the displacement of silver because zinc's interaction with the cyanide ions is part of the overall reaction dynamics, ensuring that the new zinc-cyanide complex remains soluble in the reaction medium.

Precipitation Reaction

A precipitation reaction occurs when ions in a solution combine to form an insoluble compound, called the precipitate. This type of reaction is a common result when soluble salts react with each other in an aqueous solution.

In the exercise, silver precipitates out of the solution following its displacement by zinc from the argentocyanide complex. Silver ions ( ext{Ag}^+) react with other available anions in the solution to form an insoluble silver compound. This shift from a soluble to an insoluble form leads to the observable precipitation of silver metal.

The formation of the precipitate is often visible as a solid appearing in what was once a clear solution. Precipitation plays a key role in many chemical processes, allowing for the removal of specific ions from a solution. Understanding these reactions is essential for predicting and controlling the outcomes in various chemical synthesis and separation processes.