Question

Explain the composition of aqua regia as a mixture.

Answer 1

Hint: Aqua regia is a mixture of concentrated nitric and hydrochloric acids, usually one part nitric acid to three parts hydrochloric acid by volume. Because of its ability to dissolve gold, alchemists gave this mixture its name (literally, "royal water"). It's a bright red or yellowish liquid.

Complete answer:
Gold and platinum are frequently dissolved in aqua regia. It is extremely corrosive and can burn the skin. It and other similar mixtures are used in analytical procedures to dissolve certain iron ores, phosphate rocks, slags, nickel-chromium alloys, antimony, selenium, and some of the less-soluble sulfides such as mercury, arsenic, cobalt, and lead.

Aqua regia must be prepared in a fume hood and used in one. In a glass container, combine three parts hydrochloric acid to one part nitric acid. First, the hydrochloric acid must be measured into the glassware, followed by the nitric acid, which is slowly added. Never use more than 38% nitric acid.

Aqua regia quickly loses its effectiveness (yet remains a strong acid) due to the reaction between its components, so its components are usually only mixed immediately before use. While local regulations may vary, aqua regia can be safely disposed of by carefully neutralizing it before pouring it down the sink. If there is dissolved metal contamination, the neutralized.

Note: Aqua regia is also used in etching and certain analytical procedures. In some laboratories, it is also used to clean glassware of organic compounds and metal particles. Most people prefer this method over the more traditional chromic acid bath for cleaning NMR tubes because no traces of paramagnetic chromium can remain to contaminate spectra.