Gold exists in two common positive oxidation states, +1 and +3. The standard reduction potentials for these oxidation states are Au+1aq2 + e- ¡ Au1s2 Ered ° = +1.69 V Au3+1aq2 + 3 e- ¡ Au1s2 Ered ° = +1.50 V (c) Miners obtain gold by soaking gold-containing ores in an aqueous solution of sodium cyanide. A very soluble complex ion of gold forms in the aqueous solution because of the redox reaction 4 Au1s2 + 8 NaCN1aq2 + 2 H2O1l2 + O21g2 ¡ 4 Na3Au1CN2241aq2 + 4 NaOH1aq2 What is being oxidized, and what is being reduced in this reaction?

Key Concepts

Oxidation and Reduction

Oxidation and reduction are chemical processes that involve the transfer of electrons between species. Oxidation refers to the loss of electrons, resulting in an increase in oxidation state, while reduction involves the gain of electrons, leading to a decrease in oxidation state. In redox reactions, one species is oxidized and another is reduced, which is essential for understanding the overall reaction.

Standard Reduction Potentials

Standard reduction potentials (E°) are measures of the tendency of a chemical species to be reduced, expressed in volts. A higher E° value indicates a greater likelihood of reduction occurring. In the context of the given question, comparing the E° values of Au+1 and Au3+ helps determine which species is more likely to be reduced during the reaction, guiding the identification of oxidized and reduced components.

Complex Ion Formation

Complex ions are formed when metal ions coordinate with ligands, which are molecules or ions that can donate electron pairs. In the reaction involving gold and sodium cyanide, the formation of the complex ion Na3Au(CN)2 illustrates how gold ions interact with cyanide ligands. Understanding this concept is crucial for analyzing the overall redox process and the stability of the resulting complex in solution.