Un 2031 Nitric Acid

Nitric acid (HNO_₃), classified under UN 2031 as a corrosive liquid, is a highly reactive and versatile inorganic compound with significant industrial, agricultural, and laboratory applications. Its chemical and physical properties make it both useful and hazardous, requiring strict handling and storage protocols.

Appearance and State:
1.Pure nitric acid is a colorless, fuming liquid with a pungent, suffocating odor. However, commercial grades often appear yellow or brown due to the presence of dissolved nitrogen oxides (e.g., NO_₂), a result of decomposition under light or heat.
2.At higher concentrations (e.g., "concentrated" nitric acid), it emits dense white or yellowish fumes when exposed to air, a characteristic of its volatility.

Density and Solubility:
1.Density: Approximately 1.51 g/cm³ for concentrated nitric acid (68–70% HNO_₃ by weight).
2.Solubility: Miscible with water in all proportions, forming highly exothermic solutions. Dilution requires caution due to heat release and potential splashing.

Boiling and Melting Points:
1.Boiling Point: 83°C (181°F) at atmospheric pressure (pure HNO₃). However, concentrated solutions may form azeotropes (e.g., 68% HNO₃ boils at ~120.5°C).
2.Melting Point: -42°C (-43.6°F), allowing it to remain liquid under most ambient conditions.

Viscosity and Surface Tension:
Low viscosity and high surface tension, similar to water, contributing to its  (flow properties).

Volatility and Fuming:
Highly volatile, releasing toxic NO₂ and NO gases (collectively "nitrogen oxides") into the air. This "fuming" property is more pronounced in concentrated solutions ("fuming nitric acid," ≥95% HNO_₃).

Strong Acidic Nature:
1.Nitric acid is a strong monoprotic acid, dissociating completely in water to release H⁺ ions and nitrate (NO₃⁻) ions:\(\text{HNO₃} + \text{H_₂O} \rightarrow \text{H_₃O⁺} + \text{NO_₃⁻}\)
2.Exhibits typical acid reactions, such as neutralizing bases to form nitrates (e.g., reacting with NaOH to form NaNO₃ and water).

Oxidizing Agent:
1.One of its most notable properties is its strong oxidizing behavior, driven by the nitrate ion (NO_₃⁻) under acidic conditions. It can oxidize metals, nonmetals, and organic compounds, often with the release of nitrogen oxides (NO, NO_₂, N_₂O, etc.) depending on concentration and temperature.
2.Reactions with Metals:
1.Active metals (e.g., Fe, Zn, Al) react vigorously, producing metal nitrates, water, and reduced nitrogen species. For example:\(\text{4Zn} + \text{10HNO₃ (dilute)} \rightarrow \text{4Zn(NO_₃)_₂} + \text{NH_₄NO_₃} + \text{3H_₂O}\)
2.Noble metals (e.g., Cu, Ag) dissolve in concentrated HNO₃:\(\text{Cu} + \text{4HNO₃ (concentrated)} \rightarrow \text{Cu(NO₃)₂} + \text{2NO_₂↑} + \text{2H_₂O}\)
3.Passivation: Some metals (e.g., Al, Fe) form a protective oxide layer in concentrated HNO_₃, preventing further reaction ("passivation").

Decomposition:
1.Unstable under heat, light, or prolonged storage, decomposing into water, nitrogen dioxide (NO_₂), and oxygen (O_₂):\(\text{4HNO_₃} \rightarrow \text{4NO_₂↑} + \text{O_₂↑} + \text{2H_₂O}\)
2.This decomposition accelerates with concentration, temperature, and exposure to light, explaining why nitric acid is often stored in dark, cool containers.

Reactions with Organic Materials:
1.Highly corrosive to organic tissues (e.g., skin, wood, fabrics) due to its oxidizing and acidic properties. It can nitrate organic compounds, such as cellulose in wood or proteins in skin, leading to charring and severe burns.
2.In the synthesis of organic nitro compounds (e.g., TNT, nitrobenzene), nitric acid acts as a nitrating agent in combination with sulfuric acid (e.g., "mixed acid" for nitration reactions).

Azeotrope Formation:
Forms a constant-boiling mixture (azeotrope) with water at ~68% HNO_₃ by weight, boiling at 120.5°C. This limits purification by simple distillation.

• Corrosivity: Causes severe burns to skin, eyes, and mucous membranes.
• Toxic Fumes: Releases NO₂ and other nitrogen oxides, which are toxic and irritate the respiratory system.
• Reactivity: Explosive reactions may occur with reducing agents, organic materials, metals, and cyanides.
• Environmental Risks: Harmful to aquatic life; can acidify soils and waterways if improperly discharged.

• Industrial: Production of fertilizers (e.g., ammonium nitrate), explosives, dyes, and pharmaceuticals.
• Laboratory: As a reagent in analytical chemistry (e.g., digesting samples for metal analysis) and acid-base reactions.
• Metal Processing: Etching, pickling, and cleaning of metals.
• Agriculture: Limited use in fertilizers (as a source of nitrate) and pest control, though strictly regulated.

• Personal Protective Equipment (PPE): Wear acid-resistant gloves, goggles, and lab coats; use fume hoods to avoid inhalation of fumes.
• Storage: Store in tightly sealed, corrosion-resistant containers (e.g., HDPE or glass) in a cool, dark place, away from organic materials and reducing agents.
• Spill Response: Neutralize spills with alkaline agents (e.g., sodium bicarbonate) and flush with copious water, following strict environmental protocols.

In summary, nitric acid's unique physical and chemical properties-particularly its strong acidity and oxidizing power-make it indispensable in various industries, but its hazardous nature demands strict safety measures to prevent accidents and environmental harm.

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