Question

The IUPAC name of the complex ion formed when gold dissolves in aqua regia is:

• A. \( \text{Tetrachloroaurate (I)} \)
• B. \( \text{Dichloridoaurate (III)} \)
• C. \( \text{Tetrachloridoaurate (III)} \)
• D. \( \text{Tetrachloroaurate (II)} \)

Hint:

In IUPAC naming of coordination compounds, the ligands are named first using prefixes like "tetra-" for four ligands, and the central metal is named with its oxidation state in Roman numerals. For example, \( [\text{AuCl}_4]^- \) becomes Tetrachloridoaurate (III) because gold has an oxidation state of +3.

Answer 1

The Correct Option is C

When gold (Au) dissolves in aqua regia, a mixture of concentrated nitric acid and hydrochloric acid, it reacts to form a complex ion. The process is represented by the following reaction: \[ \text{Au} + 4 \text{HCl} + \text{HNO}_3 \rightarrow \text{H[AuCl}_4] + 2 \text{H}_2\text{O} + \text{NO}. \] The complex ion formed is \( [\text{AuCl}_4]^- \), where chlorido ions (Cl-) are coordinated to the central metal ion (gold, Au). This is a typical coordination compound.
Step 1: Identify the Oxidation State of Gold. To determine the oxidation state of gold (Au) in the complex ion \( [\text{AuCl}_4]^- \), we can use the following steps: Let the oxidation state of gold be \( x \). In the chloride ligands, chlorine has an oxidation state of \( -1 \). So, for the complex ion: \[ x + 4(-1) = -1. \] Simplifying: \[ x - 4 = -1 \quad \Rightarrow \quad x = +3. \] Thus, the oxidation state of gold in this complex is \( +3 \).
Step 2: Determine the IUPAC Name. The complex ion formed is \( [\text{AuCl}_4]^- \). According to **IUPAC naming conventions: - The prefix tetra- is used for four chloride (Cl) ligands. - The central metal, gold (Au), is named as aurate. - The oxidation state of the metal, which is \( +3 \), is indicated in Roman numerals as (III). Therefore, the correct IUPAC name of the complex ion \( [\text{AuCl}_4]^- \) is **Tetrachloridoaurate (III)**.
Conclusion: The correct IUPAC name of the complex ion formed when gold dissolves in aqua regia is \( \mathbf{Tetrachloridoaurate (III)} \). Thus, the correct answer is \( \mathbf{(C)} \).