NH₃ — Ammonia

Ammonia (NH₃) is a colorless, pungent gas composed of nitrogen and hydrogen. It is one of the most important industrial chemicals, widely used in fertilizers, explosives, and cleaning agents. Ammonia occurs naturally in the atmosphere in trace amounts and is produced during the decomposition of organic matter containing nitrogen compounds such as proteins and urea.

The molecule has a trigonal pyramidal structure with a lone pair of electrons on nitrogen, giving it a distinct shape and high polarity. It is highly soluble in water and forms an alkaline solution known as ammonium hydroxide (NH₄OH).

Ammonia is found both naturally and synthetically:

• Natural Occurrence: Produced by the bacterial decomposition of nitrogenous organic matter in plants and animals.
• Atmosphere: Found in minute traces, especially near animal habitats and decaying organic material.
• In Soil: Formed during the nitrogen cycle by microorganisms that break down organic waste.
• In Space: Detected in the atmospheres of gas giant planets like Jupiter and Saturn.

Physical Properties:

• Ammonia is a colorless gas with a sharp, pungent smell.
• It is lighter than air and can be liquefied easily under pressure.
• It is highly soluble in water, forming a basic solution (ammonium hydroxide).
• Liquid ammonia boils at -33°C and solidifies at -78°C.
• Its aqueous solution turns red litmus paper blue due to its basic nature.

Chemical Properties:

• 1. Basic Nature: Ammonia dissolves in water to form ammonium hydroxide:
  

  \(NH_3 + H_2O \rightleftharpoons NH_4^+ + OH^-\)

• 2. Reaction with Acids: It reacts with acids to form ammonium salts:
  

  \(NH_3 + HCl \rightarrow NH_4Cl\)

• 3. Reaction with Oxygen: When burned in excess oxygen, it forms nitrogen and water:
  

  \(4NH_3 + 3O_2 \rightarrow 2N_2 + 6H_2O\)

  In the presence of platinum catalyst, it produces nitric oxide:
  

  \(4NH_3 + 5O_2 \xrightarrow{Pt,\ 800°C} 4NO + 6H_2O\)

• 4. Reaction with Chlorine: With excess chlorine, it forms nitrogen trichloride (explosive):
  

  \(8NH_3 + 3Cl_2 \rightarrow 6NH_4Cl + N_2\)

  \(NH_3 + 3Cl_2 \rightarrow NCl_3 + 3HCl\)

• 5. Reducing Property: Ammonia acts as a reducing agent:
  

  \(3CuO + 2NH_3 \rightarrow 3Cu + 3H_2O + N_2\)

In the laboratory, ammonia is prepared by heating an ammonium salt with a strong base such as calcium hydroxide:

• From Ammonium Chloride and Slaked Lime:
  

  \(2NH_4Cl + Ca(OH)_2 \rightarrow 2NH_3\uparrow + 2H_2O + CaCl_2\)

  The gas is collected by the downward displacement of air as it is lighter than air.

Test for Ammonia: It turns moist red litmus paper blue and forms white fumes of ammonium chloride when exposed to hydrochloric acid vapors:

The Haber Process is the primary industrial method of producing ammonia by combining nitrogen and hydrogen gases directly:

Conditions:

• Catalyst: Finely divided iron with molybdenum as promoter
• Temperature: 450°C
• Pressure: 200 atm
• Raw Materials: Nitrogen (from fractional distillation of air) and hydrogen (from natural gas or water gas)

The ammonia produced is condensed and collected as a liquid under pressure. The process is exothermic and reversible, so optimized conditions are used for maximum yield.

• Fertilizer Production: Used in the manufacture of ammonium nitrate, ammonium sulfate, and urea which are essential fertilizers for agriculture.
• Refrigeration: Liquid ammonia is used as a refrigerant due to its high latent heat of vaporization.
• Cleaning Agent: Used in household and industrial cleaning solutions.
• Manufacture of Chemicals: Ammonia is a raw material for nitric acid, hydrazine, and explosives.
• Textile and Paper Industry: Used in dyeing, bleaching, and neutralizing acidic residues.
• Medicinal Use: Aqueous ammonia acts as a mild antiseptic and stimulant.

Although ammonia is essential industrially, it must be handled carefully due to its corrosive and toxic properties:

• Health Hazards: Inhalation causes irritation of the eyes, throat, and lungs. High concentrations can be fatal.
• Environmental Impact: Excess ammonia in soil or water causes eutrophication, disrupting aquatic ecosystems.
• Safety Precautions: Proper ventilation, protective equipment, and storage in sealed containers are essential to avoid accidents.