Final answer:
The reduction of aqueous gold(III) cations to solid gold is a chemical reaction where gold ions are reduced by gaining electrons, using a reducing agent in a redox reaction, resulting in the formation of solid gold.
Step-by-step explanation:
The reduction of aqueous gold(III) cations to solid gold involves a chemical reaction where gold ions (Au3+) gain electrons to form solid gold (Au). This type of reaction is known as a reduction reaction, which is part of a larger group of reactions referred to as redox reactions.
In redox reactions, one species is reduced by gaining electrons, while another is oxidized by losing electrons. An example from a similar process is when silver ions are reduced to solid silver with the help of a reducing agent like zinc.
For instance, in the precipitation of silver from a cyanide solution, zinc acts as the reducing agent:
2[Ag(CN)2] (aq) + Zn(s) → 2Ag(s) + [Zn(CN)4] 2−(aq).
In a similar way, for gold, a reducing agent such as sodium borohydride (NaBH4), citrate, or another less noble metal can donate electrons to gold(III) ions resulting in the deposition of solid gold. During this process, the reducing agent is oxidized, thus completing the redox cycle.