Aqua regia, Latin for “royal water,” is a powerful acidic solution known to dissolve noble metals like gold and platinum. It's used in ancient and medieval alchemy, and is still popular in modern chemistry for various applications.
While the creation of aqua regia is relatively straightforward, it demands strict adherence to safety protocols. During the process of making aqua regia, due to its corrosive nature, precautions must be taken.
What Is Aqua Regia?
Aqua regia is a mix of two strong acids: hydrochloric acid (HCl) and nitric acid (HNO3). In a typical composition, aqua regia is one part nitric acid to three parts hydrochloric acid. These two acids form a corrosive solution able to dissolve gold, platinum and other refractory metals.
Composition:
Hydrochloric Acid (HCl): The primary acid used for metal dissolution.
Nitric Acid (HNO3): Adds oxidizing power to the solution.
How to Make Aqua Regia
Materials Needed:
Hydrochloric Acid (HCl): Concentrated form (usually around 37%).
Nitric Acid (HNO3): Concentrated form (usually around 68%).
Glass container: A beaker or a glass flask resistant to corrosion.
Pipette or measuring cylinder: For accurate measurement of acids.
Safety gear: Gloves, goggles, and a lab coat. This is a fuming liquid and penetrates disposable face masks.
Step-by-Step Instructions:
Prepare the Workspace:
Work in a well-ventilated area, preferably under a fume hood.
Place all materials on a stable surface away from any flammable materials.
Wear Proper Safety Gear:
Always wear gloves, goggles, and a lab coat to protect your skin and eyes from splashes.
Measure the Acids:
Carefully measure the nitric acid (1 part) and hydrochloric acid (3 parts) using a pipette or measuring cylinder.
Mix the Acids:
Always add acid to water, never the other way around. In this case, you will combine the two concentrated acids carefully.
Slowly pour the nitric acid into the hydrochloric acid in the glass container. The reaction produces heat and releases toxic fumes, so do this step cautiously.
Observe the Mixture:
The solution will typically turn yellow, indicating the formation of aqua regia. This is due to the formation of various nitrogen oxides.
Storage:
Aqua regia should be used immediately and not stored, as it loses effectiveness over time.
Uses of Aqua Regia
The applications of aqua regia are extensive, including:
Gold Recovery: Separating gold from electronic waste and refining gold to remove impurities. It's often used in achemy in this capacity.
Analytical Chemistry: Dissolving samples for analysis in various scientific studies.
Metal Etching: Used in microfabrication for etching metals.
Cleaning Glassware: Removing stubborn metal residues from laboratory glassware.
Safety Precautions
Aqua regia is extremely hazardous, and proper safety measures should always be followed:
Ventilation: Always work under a fume hood to eliminate toxic fumes.
Equipment: Use only glass or certain plastics; do not use metal containers as aqua regia is highly corrosive.
In Case of Spills: Neutralize spills with a suitable agent and follow chemical waste disposal protocols.
First Aid: In case of skin or eye contact, wash the affected area with copious amounts of water and seek medical attention immediately.
Labeling: Clearly label containers to avoid accidental misuse.
Aqua regia is a remarkable chemical solution with a range of applications in chemistry and metallurgy. Its ability to dissolve noble metals makes it a practical tool for scientists and jewelers alike, and one of the most important preparations from the alchemical laboratory.
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