The real chemical name for aqua regia is nitro-hydrochloric acid. This powerful substance is most renowned for its unique ability to dissolve noble metals, including gold.
The Chemical Identity: Nitro-hydrochloric Acid
Aqua regia, famously known for its highly corrosive nature, is scientifically identified as nitro-hydrochloric acid. This nomenclature directly reflects its composition: it is a fuming mixture of nitric acid and hydrochloric acid. The specific combination of these two strong acids gives aqua regia its extraordinary chemical properties, allowing it to react with and dissolve substances that neither acid could dissolve on its own.
Historical Context and Other Names
The term "aqua regia" itself is Latin for "royal water," a name bestowed upon it due to its remarkable capacity to dissolve gold, often referred to as the "royal metal." The reference also notes that it is sometimes known as aqua regis, which similarly translates to "king's water." These historical names highlight the awe and significance chemists and alchemists attributed to this unique solution.
Composition and Unique Properties
Aqua regia is not a single compound but a meticulously balanced mixture of acids, optimally in a specific ratio for maximum effectiveness.
- Optimal Ratio: The most effective form of aqua regia is a mixture of nitric acid and hydrochloric acid, typically in a volume ratio of 1:3. This precise ratio is crucial for its unparalleled reactivity.
- Highly Corrosive: As a "highly corrosive fuming mixture," aqua regia produces noxious fumes and can cause severe chemical burns upon contact.
- Dissolving Gold: Its most celebrated property is its ability to dissolve gold. While nitric acid can oxidize gold, it forms an insoluble layer that prevents further reaction. Hydrochloric acid then reacts with the oxidized gold ions to form soluble tetrachloroaurate(III) anions, effectively removing the insoluble layer and allowing the reaction to proceed continuously.
Key Characteristics of Aqua Regia
| Feature | Description |
|---|---|
| Real Name | Nitro-hydrochloric acid |
| Other Names | Aqua regia, Aqua regis, Royal water, King's water |
| Composition | Mixture of Nitric Acid (HNO₃) and Hydrochloric Acid (HCl) |
| Optimal Ratio | 1 volume part Nitric Acid : 3 volume parts Hydrochloric Acid |
| Key Property | Highly corrosive; famously dissolves gold and platinum |
| Appearance | Fuming liquid, often yellow or reddish-orange |
Significance and Applications
The unique dissolving power of nitro-hydrochloric acid makes it indispensable in various fields, particularly in:
- Gold Refining: It is extensively used in the purification of gold, separating it from other metals.
- Analytical Chemistry: For dissolving samples containing noble metals prior to analysis.
- Etching and Cleaning: In certain specialized applications, it's used for etching metals or cleaning glassware in laboratories, though its extreme corrosiveness necessitates careful handling.
