Nitric acid holds an extremely important position in the world of chemical substances, and its Chemical Abstracts Service (CAS) Registry Number is 7697 - 37 - 2. This unique number is like the identification card of a chemical substance, ensuring its accurate identification and tracking worldwide. Whether in scientific research literature, chemical production records, or safety supervision documents, relevant information about nitric acid can be precisely located using this number.
In terms of its chemical structure, the chemical formula of nitric acid is HNO₃, which is formed by the ingenious combination of one hydrogen atom (H), one nitrogen atom (N), and three oxygen atoms (O). This structure endows nitric acid with strong chemical reactivity. Pure nitric acid is a colorless liquid with a pungent odor, and it is volatile in the air. The nitric acid vapor that volatilizes will form an acid mist when it encounters water vapor.
Nitric acid has strong oxidizing properties, which is one of its most remarkable chemical characteristics. It can react with many metals. For example, when it reacts with copper, it will produce copper nitrate, nitrogen dioxide, and water. During this reaction process, the nitrogen element in nitric acid is reduced from the +5 valence state to the +4 valence state, demonstrating a strong ability to gain electrons and oxidizing copper into copper ions. When reacting with metals, the reduction products of nitric acid will vary depending on the concentration of nitric acid. Concentrated nitric acid usually produces nitrogen dioxide, while dilute nitric acid may produce nitrogen oxides with lower valence states such as nitric oxide. This makes nitric acid widely used in fields such as metal processing and etching. In the electronics industry, the oxidizing property of nitric acid is utilized to etch the unwanted copper foil on circuit boards, precisely constructing the circuit pattern.
In the field of organic chemistry, nitric acid also plays a crucial role. It is often used as a nitrating agent in organic synthesis reactions to introduce the nitro group (-NO₂) into organic compound molecules. Taking the nitration reaction of benzene as an example, under the catalytic action of concentrated sulfuric acid, nitric acid reacts with benzene to produce nitrobenzene. Nitrobenzene is an important intermediate for the preparation of various dyes, pharmaceuticals, and fragrances. Such nitration reactions greatly enrich the variety of organic compounds, providing a powerful tool for the development of organic synthetic chemistry and promoting the progress of many related industries such as the pharmaceutical and materials science industries.
In terms of industrial preparation, nitric acid is mainly produced by the ammonia oxidation method. First, a mixed gas of ammonia and air is passed through a platinum-rhodium alloy mesh catalyst, and ammonia is oxidized to nitric oxide at high temperature. Then, nitric oxide reacts with the oxygen in the air to form nitrogen dioxide. Finally, nitrogen dioxide is absorbed by water to produce nitric acid. In this complex industrial process, the precise control of the reaction conditions at each step is of vital importance, determining the yield and quality of nitric acid.
The agricultural field also cannot do without the contribution of nitric acid. Nitric acid is an important raw material for the production of nitrate fertilizers, such as ammonium nitrate. These fertilizers can provide nitrogen elements for crops, promoting the growth and development of plants and increasing crop yields. Both the ammonium nitrogen and nitrate nitrogen in ammonium nitrate can be effectively absorbed and utilized by plants. In the soil, nitrate nitrogen can be quickly absorbed by the roots of plants to meet the large demand for nitrogen in the early growth stage of plants, while ammonium nitrogen can gradually be converted into nitrate nitrogen in the soil, continuously providing nutrients for plants.
However, the strong oxidizing and corrosive properties of nitric acid also pose certain safety risks. It has a strong irritating and corrosive effect on the skin, eyes, and respiratory tract. Once it comes into contact with human tissues, it will rapidly react with proteins, leading to tissue burns and ulcers. During industrial production and storage, if the operation is improper, the leakage of nitric acid may cause serious environmental pollution, corroding the soil and water bodies and affecting the ecological balance. Therefore, when using nitric acid, it is necessary to strictly follow the safety operation procedures and be equipped with professional protective equipment, such as acid and alkali resistant protective clothing, protective goggles, and gloves. The containers for storing nitric acid need to be made of corrosion-resistant materials, such as stainless steel or special plastics, and should be placed in a well-ventilated, cool, dry place, far away from fire sources and flammable materials. At the same time, a complete leakage emergency treatment plan should be in place.
Nitric acid plays an indispensable role in many fields such as the chemical industry, pharmaceuticals, electronics, and agriculture. Its unique chemical properties not only bring great application value but also come with safety challenges that need to be carefully addressed. Through reasonable utilization and strict control, nitric acid continues to drive the development of modern industry and technology.
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