Chloroauric acid H[AuCl4] is a yellow solution created in the 18th century. A gold(III) salt, chloroauric acid is an innovative compound, and the gold can be recovered. Gold salts are used in medicine, for example to treat rheumatoid arthritis, and in science and industry.
Chloroauric acid is first synthesized in the late 18th century by chemists exploring the chemistry of gold. By this time alchemy has fallen out of favor and is demonized by new generations of scientists.
"Chrysotherapy" and "aurotherapy" are the applications of gold compounds to medicine. The medicinal effects of gold come under the microscope at the end of the 19th century, when it's discovered gold cyanide defeats the tuberculosis pathogen Mycobacterium tuberculosis.
This compound is primarily used in organic synthesis and is important to the production and recovery of gold. This era marks the beginning of understanding gold's complex behaviors when combined with halogens.
Early chemists such as Sir Humphry Davy (1778-1829) begin to look further into the complexities of gold chemistry. Davy is also credited with discovering clathrate hydrates. These are chunks of solids resembling ice with holes usually containing gasses.
In 1799, Davy experiments with nitrous oxide and is astonished at how it makes him laugh. He nicknames it "laughing gas" and writes about its potential as an anesthetic to relieve pain during surgery.
Danish chemist Hans Christian Ørsted also significantly contributes to the study of gold compounds. Over time, his research helps clarify the properties and applications of chloroauric acid.
Properties of Chloroauric Acid
Chloroauric acid exhibits several notable properties:
Chemical Formula: H[AuCl₄]
Appearance: Bright yellow to orange crystalline solid in its anhydrous form, and a yellow solution in water.
Melting Point: Approximately 230 °C for the anhydrous form.
Solubility: Highly soluble in water, forming an acidic solution
Acidity: Acts as a strong acid, releasing protons in aqueous solutions
Stability: Generally stable, but can decompose under extreme conditions such as high temperatures or significant reductions.
Oxidation State: Gold is in the +3 oxidation state, essential for many reactions.
How To Recover Gold from Chloroauric Acid
The recovery of gold from chloroauric acid involves several steps, most commonly through a reduction process. Here’s an outline of the procedure:
Introduce a Reducing Agent: Sodium borohydride (NaBH₄) or another reducing agent like zinc powder is added to the chloroauric acid solution.
Formation of Gold Precipitate: The reducing agent converts the gold ions back to metallic gold, which precipitates out of the solution as a metallic solid. This produces about 90% of the gold available in the solution.
Filtration: The solid gold is then filtered out from the liquid.
Washing and Drying: The precipitates must be thoroughly washed to remove any residual chemicals and dried.
Melting: Finally, the recovered gold can be melted down for further use.
Electrochemical Methods of Gold Extraction: In this technique, an electric current is applied to the solution, causing gold ions to deposit onto an electrode. This method can achieve a gold recovery rate of over 95%.
Each method requires careful handling due to the potential toxicity of some reagents.
Facts About Chloroauric Acid
Toxicity: Chloroauric acid can be toxic and must be handled with care, using appropriate safety equipment and procedures.
Color Indicator: The intensity of the yellow color in chloroauric acid solutions is indicative of gold concentration; deeper shades often suggest higher concentrations.
Synthetic Uses: Researchers are exploring synthetic pathways using chloroauric acid for creating novel materials and catalysts.
Symbolic Use: Gold has long been associated with wealth and luxury, which enriches the allure of chloroauric acid in various cultures.
Color Variation: The bright yellow hue of concentrated solutions is often utilized as a visual cue in many chemical processes.
Research Impact: The study of chloroauric acid has initiated exploration into gold-based pharmaceuticals, influencing a deeper understanding of the unique properties of gold.
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