Nitric acid, called the Queen of Acids or aqua fortis (strong water) is a vital chemical compound with significant importance in fields such as alchemy, industrial processes, chemistry and laboratory applications. This caustic water is powerful and relentless.
What is Nitric Acid?
Nitric acid (HNO3) is a highly corrosive and strong mineral acid. It is characterized by its potent oxidizing properties, making it a critical reagent in many chemical processes. In its concentrated form, it is a colorless liquid highly soluble in water.
It can take on a yellowish hue due to the presence of nitrogen dioxide (NO2) dissolved in it, especially when stored for long periods. Nitric acid is a key component in the production of fertilizers, explosives, and various chemical compounds.
How to Make Nitric Acid
Nitric acid is initially documented by alchemists in the first century AD and likely exists earlier. Ancient preparation methods involve distilling saltpeter, also known as niter or potassium nitrate, with potent vinegar, or acetic acid.
One of the most common laboratory methods is through oxidation of ammonia. This process occurs in the presence of oxygen, using catalysts like platinum or rhodium. The overall chemical reaction can be summarized as follows:
Ammonia Oxidation: [ 4 NH_3 + 5 O_2 -> 4 NO + 6 H_2O ]
Nitric Oxide Oxidation: [ 2 NO + O_2 -> 2 NO_2 ]
Formation of Nitric Acid: [ 3 NO_2 + H_2O -> 2 HNO_3 + HNO_2 ]
In commercial production of nitric acid a mixture of ammonia and air passes through an oxidation catalyst made of a gauze woven from platinum-rhodium alloy wire. The gas exiting the gauze is between 810°C and 960°C, usually above 850°C.
Chemistry & Properties of Nitric Acid
Nitric acid is known for its strong acidity and powerful oxidizing properties. Here are some of its key properties:
Molecular Weight: 63.01 g/mol
Density: 1.51 g/cm³ (concentrated)
Boiling Point: 83 °C (181 °F)
Melting Point: -42 °C (-44 °F)
When dissolved in water, nitric acid dissociates into hydrogen ions ((H^+)) and nitrate ions ((NO_3^-)). Due to strong oxidative abilities, it reacts vigorously with metals and non-metals, often producing nitrogen oxides. Mishandling the Acid Queen can cause serious burns.
Nitric Acid in Alchemy
Nitric acid is a significant compound in alchemical practices. Alchemists call nitric acid “aqua fortis” or strong water, due to its ability to dissolve metals such as gold and silver when combined with other alchemical compounds.
In alchemy nitric acid is used to make silver nitrate or lunar caustic. Three parts hydrochloric acid to one part nitric acid makes the infamous aqua regia, royal water, the Green Lyon of alchemy. This substance dissolves gold, often part of a purifying process.
In order to extract the (purified) gold from the aqua regia, a reducing agent such as sodium metabisulfite is introduced to specifically convert the gold chloride into solid gold particles, while keeping other metal chlorides unchanged and dissolved in the solution.
Another method to extract the gold is thermal decomposition. One needs a heat source (oven) reaching at least 800 °C. First the solution is boiled down to half, then put in the 800 °C oven for an hour or so, and lo and behold, gold appears in solid form.
Nitric acid also appears in writings after 1300 AD mistakenly credited to Albert the Great and Ramon Llull, both from the 13th century. These writings detail the process of distilling a blend of niter and green vitriol, which they call "eau forte" (aqua fortis).
Green vitriol or ferrous sulfate is also used to make sulfuric acid, known as the Acid King due to its ability of consume almost any metal - but not gold. In the 17th century, Johann Glauber develops a way to produce nitric acid by distillation of potassium nitrate with sulfuric acid.
Compounds of Nitric Acid
Nitric acid can form various salts and compounds, which are useful in different applications. Some notable compounds include:
Ammonium Nitrate (NH4NO3): Used as a fertilizer and in explosive compositions.
Sodium Nitrate (NaNO3): Commonly used as a preservative in food and in the manufacture of glass.
Potassium Nitrate (KNO3): Best known as saltpeter, it has applications in fertilizers, food preservation, and in pyrotechnics.
Calcium Nitrate (Ca(NO3)2): Used as a fertilizer and a dehydrating agent.
Uses of Nitric Acid
The applications of nitric acid are extensive, ranging from industrial to laboratory settings:
Fertilizer Production: A major use of nitric acid is in producing fertilizers, particularly ammonium nitrate, which is a key ingredient in many agricultural fertilizers.
Explosives: It is used in the production of explosives, such as TNT (trinitrotoluene), by nitrating organic compounds.
Metal Processing: Nitric acid is essential in metal etching and cleaning processes, as it removes oxides and impurities from metals before further processing.
Chemical Synthesis: It serves as a vital reagent in various chemical reactions and synthesizing nitric oxides and other nitrogen compounds.
Pharmaceuticals: Nitric acid is used to produce certain pharmaceutical compounds and industrial chemicals.
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