Ammonia |Structure, Properties, Preparation, Uses

Ammonia (NH₃) is a colorless gas with a sharp, pungent odor. It is a compound of nitrogen and hydrogen and plays a crucial role in both the industrial sector and biological processes.

Let's learn about ammonia in detail, including its structure, properties and uses.

Ammonia

Ammonia is nitrogen and hydrogen-based chemical. It is made up of one nitrogen and three hydrogen atoms. NH₃ is its chemical formula.

Formation of ammonia by the decomposition of nitrogenous organic matter urea (NH₂CONH₂).

NH₂CONH₂ + 2H₂O → (NH₄)₂CO₃ ⇌ 2NH₃ + CO₂ + H₂O

The natural breakdown of animal and plant bodies produces ammonia because the nitrogen compounds present in them decompose as they die or decay, resulting in ammonia. Ammonia can also be found in the soil as an ammonium salt.

Ammonia Structure- NH₃

The ammonia molecule is produced when three sp³ hybrid orbitals of nitrogen and three s orbitals of hydrogens collide. A lone pair of electrons occupy the 4^th sp³ hybrid orbital of nitrogen. The ammonia molecule has a trigonal pyramidal structure as a result of this.

The H-N-H angle is 107.8^∘ , while the N-H bond length is 101.7 pm. Due to lone pair-bond pair repulsion, which tends to push the N-H bond slightly inwards, the H-N-H bond angle is somewhat less than the tetrahedral angle of 109^∘28′. Ammonia is linked in liquid and solid forms due to hydrogen bonding.

👁 Ammonia Structure

👁 Structure of Ammonia

Physical Properties of Ammonia

Property	Description
Physical State	Colourless gas
Odour	Distinct pungent odour, known as ammoniacal odour
Density Relative to Air	Lighter than air, gathered via air displacement downward
Effect on Inhalation	Causes tears to well up in the eyes when inhaled quickly
Liquefaction Conditions	Easily liquefies at room temperature under a pressure of 8 to 10 atmospheres
Boiling Point under 1 atm	–33.5°C (239.6K)
Enthalpy of Vaporization	High (1370J/g), used in ice-making equipment and refrigeration systems
Freezing Point	Freezes into a white crystalline solid at –77.8°C (195.3K)
Water Solubility	Extremely high; one volume of water dissolves about 1300 volumes of ammonia gas
Collection Method	Cannot be collected in water due to its high water solubility

Chemical Properties of Ammonia

• Ammonia is very soluble in water due to its basic composition. Due to the production of OH^– ions, its aqueous solution is weakly basic.

NH₃(g)+H₂O(I) ⇋ NH₄OH(aq) ⇋ NH₄⁺(aq)+OH^–(aq)

Because it is basic, it turns moist red litmus blue and neutralises acids in both dry and wet states, generating their corresponding salts.

NH₃+HCl → NH₄Cl

2NH₄OH+H₂SO₄ → (NH₄)₂SO₄+2H₂O

• Ammonia functions as a Lewis base due to the existence of a lone pair of electrons on the nitrogen atom. Consequently, it can easily donate its electron pair to establish a coordinate bond with electron-deficient compounds such as BF₃ or transition metal cations possessing unoccupied d-orbitals to form complexes. As an example,

Ag⁺(aq)+2NH₃(aq) → [Ag(NH₃)₂]⁺(aq)

Cu²⁺(aq)+4NH₃(aq) → [Cu(NH₃)₄]²⁺(aq)

Thus, ammonia acts as a ligand.

• Ammonia is neither a fuel nor a fuel supporter when it comes to combustion. In the presence of oxygen, however, it produces dinitrogen and water.

4NH₃+3O₂→2 N₂+6H₂O

• Ammonia is oxidised to dinitrogen gas when it passes through a solution of calcium hypochlorite (bleaching powder), bromine water, or heated copper oxide.

4NH₃+3Ca(OCl)₂ → 2 N₂+3CaCl₂+6H₂O

8NH₃+3Br₂ → N₂+6NH₄Br

2NH₃+3CuO+Heat → 3Cu+N₂+3H₂O

Ammonia is oxidised to nitric oxide when it is passed through Pt/Rh gauze at 500 K under a pressure of 9 bar with an excess of air. Ostwald's technique uses this reaction as the starting point for making nitric acid.

Preparation of Ammonia

• Using a strong base to heat ammonium salts: Ammonia is made on a small scale by heating ammonium salts with a strong base.

(NH₄)₂SO₄ + 2NaOH + Heat→2NH₃ + 2H₂O + Na₂SO₄  

NH₄Cl+KOH+Heat→NH₃+H₂O+KCl

• Ammonia is made in the lab by heating a mixture of slaked lime and ammonium chloride.

2NH₄Cl+Ca(OH)₂+Heat→2NH₃+2H₂O+CaCl₂

• The hydrolysis of metal nitrides, such as magnesium and aluminium nitride, with water or alkalis, can also yield ammonia gas.

Mg₃ N₂+6H₂O→2NH₃+3Mg(OH)₂

AlN+3H₂O→NH₃+Al(OH)₃

By passing ammonia gas over quicklime, it is dried (CaO). Because ammonia is a basic gas, it cannot be dried by passing it through concentrated sulphuric acid or phosphorus pentoxide, as it will react with them to generate ammonium sulphate or ammonium phosphate. Calcium chloride cannot be used to dry ammonia gas because calcium chloride creates ammoniates.

Preparation of Ammonia by Haber Process

On a commercial scale, ammonia is manufactured by Haber’s process.

N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ; ΔH^∘=–92.4kJ/mol

This is a reversible, exothermic reaction that occurs when the volume decreases. As a result, according to Le Chatelier's principle, the best conditions for producing ammonia are:

1. Low temperature: Because the forward process is exothermic, the generation of ammonia is favoured at low temperatures. The rate of reaction, however, will be slow at low temperatures. The reaction's optimal temperature has been determined to be around 700K.
2. High pressure will favour the creation of ammonia since the forward reaction happens with a decrease in volume. At a pressure of 200x10⁵Pa (200 atmospheres), the reaction is normally carried out.
3. Catalyst: The reaction rate is relatively slow, at roughly 700K. Iron oxide is used as a catalyst, along with a minor amount of K₂O and Al₂O₃. The addition of molybdenum as a promoter improves the efficiency of the catalyst.

Haber's technique compresses a mixture of N₂ and H₂ in a 1:3 molar ratio to roughly 200-atmosphere pressure. After cooling, the compressed gases are transported through a soda-lime tower to remove moisture and carbon dioxide. These are then fed into a catalyst chamber containing iron oxide, a small amount of k₂O, and Al₂O₃. When the two gases combine to make ammonia, the chamber is heated electrically to a temperature of 700K. Because the process is exothermic, the heat generated keeps the temperature at the desired level, and no additional electrical heating is necessary.

The gases seeping from the chamber contain around 15–20 % ammonia, with the rest being nitrogen and hydrogen with no reaction. They pass via the condensing pipe, which liquefies the ammonia in the receptor and collects it. The unreacted gases are pumped back to the compression pump, where they are mixed with a new gas combination.

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Uses of Ammonia

The following are some of the many uses for ammonia:

• In Ostwald's nitric acid synthesis process.
• In the manufacturing of sodium carbonate, the Solvay process is used.
• It's used in the production of rayon and urea.
• Ammonium sulphate, ammonium nitrate, urea, diammonium phosphate, and other fertilizers are produced.
• In ice plants as a refrigerant.
• Furniture and glass surfaces can be cleaned with it.
• In the laboratory, it is employed as a solvent and as a reagent.