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 d 10 electronic configuration

Electropositivity is a measure of an atom's ability to donate electrons and form positive ions. In chemical reactions, particularly those involving metals, this property determines how readily a metal will participate in redox processes.

Metals that are highly electropositive easily give up their valence electrons to become cations. These metals, often found in groups 1 and 2 of the periodic table, include alkali and alkaline earth metals like sodium and calcium. As a result of their high electropositivity, they react vigorously with nonmetals and are used as reducing agents in chemical reactions.

Zinc, for instance, has a higher electropositivity than silver, as explained in our example problem. This means zinc has a greater tendency to lose electrons and form \( \mathrm{Zn}^{2+}\) ions. Consequently, when zinc comes into contact with sodium argentocyanide, it willingly donates electrons to the \( \mathrm{Ag}^{+}\) ions, reducing them to solid silver and forming a precipitate.

Chemical precipitation occurs in redox reactions when a solid (the precipitate) forms as a result of the reaction between chemicals in solution. The precipitate settles out of the solution, which can be observed as a cloudiness or a solid appearing at the bottom of the container. Precipitation is a critical concept in fields like chemistry and environmental science, as it is used to remove contaminants from water or to isolate desired products in a reaction.

The reaction between sodium argentocyanide and zinc dust leading to the formation of silver precipitate is a classic example of chemical precipitation. Here, the oxidation of zinc to \( \mathrm{Zn}^{2+}\) and the reduction of silver ions \( \mathrm{Ag}^{+}\) to solid silver result in the separation of silver from the solution. The zinc donates electrons to the silver ions, thus causing the silver to change from its ionic to solid form and precipitate out.

Oxidation and reduction are twin halves of redox reactions in electrochemistry. Oxidation involves the loss of electrons, while reduction involves the gain of electrons. In any redox reaction, oxidation and reduction occur simultaneously; a substance cannot be oxidized unless another is reduced – hence the term 'redox' (reduction-oxidation) reaction.

In the context of the textbook exercise, zinc is oxidized as it loses two electrons to form \( \mathrm{Zn}^{2+}\) ions. This makes zinc the reducing agent because it provides electrons to be gained by another species. Oppositely, the silver ions gain electrons through reduction, becoming solid silver. This transformation from ionic to metallic silver is visually marked by the formation of the silver precipitate.

Understanding these fundamental steps of oxidation and reduction allows students to identify the changes in oxidation state that are pivotal in predicting the directionality and outcome of redox reactions, an essential skill in the study of electrochemistry.