Ammonia – Structure, Properties, Preparation, Uses

The p-block, which is located on the right side of the normal periodic table, contains elements in groups 13 to 18. They have a ns² np^1–6 electrical configuration. The p-block does not include helium, despite it being the first element in group 18. With the exception of the first row, every row in the table has six p-elements (which has none).

Metals, nonmetals, and metalloids are all present in this block, which makes it unique. Group 13, the icosagens; 14, the crystallogens; 15, the pnictogens; 16, the chalcogens; 17, the halogens; and 18, the helium group, which consists of noble gases (except helium) and oganesson.

What is Ammonia?

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

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

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

Structure of Ammonia

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.

Formation of the ammonia molecule

Physical Properties of Ammonia

1. Ammonia is a colourless gas with a distinct pungent odour known as ammoniacal odour.
2. Because it is lighter than air, it is gathered via air displacement downward.
3. When inhaled quickly, it causes tears to well up in the eyes.
4. It can easily liquefy at room temperature if a pressure of 8 to 10 atmospheres is applied.
5. Under one atmosphere pressure, liquid ammonia boils at –33.5^∘C(239.6K). It has a high enthalpy of vaporization (1370J/g) and is hence employed in ice-making equipment and refrigeration systems.
6. At –77.8°C (195.3°K), liquid ammonia freezes into a white crystalline solid.
7. It has high water solubility. One volume of water dissolves about 1300 ammonia gas volumes. Because of its high water solubility, ammonia gas cannot be collected in water.

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.

Manufacture 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 200×10⁵Pa (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.

The Haber Process

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.

Uses of Ammonia

The following are some of the many uses for ammonia:

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

Sample Questions

Question 1: What are the properties of ammonia?

Answer:

Ammonia is a colourless gas with a distinctive pungent ammoniacal odour. It is lighter than air and may easily liquefy at room temperature when subjected to a pressure of 8 to 10 atmospheres. Under one atmosphere pressure, its boiling point is –33.5^∘C(239.6K). It serves as a Lewis foundation.

Question 2: What is the method of preparation of ammonia?

Answer:

Haber’s technology is used to produce ammonia on a commercial basis.

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

This reaction is carried out in the presence of iron oxide as a catalyst with a little amount of K₂O and Al₂O₃ at a temperature of 700K and a pressure of 200×10⁵Pa or 200 atmospheres. Molybdenum is utilised as a promoter to improve the catalyst’s efficiency.

Question 3: What are the uses of ammonia synthesis?

Answer:

Synthetic ammonia is mostly used to make fertilizers including ammonium sulphate, ammonium nitrate, urea, and diammonium phosphate. Apart from that, it’s employed in the production of nitric acid via Ostwald’s process, sodium carbonate via Solvay’s process, and rayon and urea via Solvay’s process.

Question 4: What are the uses of ammonia?

Answer:

Ammonia is used as:

1. In the production of nitric acid by Ostwald’s process, sodium carbonate by Solvay’s process, and rayon and urea by Solvay’s process.
2. In the production of fertilizers such ammonium sulphate, ammonium nitrate, urea, and diammonium phosphate, among others.
3. In ice plants as a refrigerant.
4. As a surface cleaner for furniture and glass.
5. In the laboratory, it is utilised as a solvent and as a reagent.

Question 5: What type of reaction is the synthesis of ammonia by Haber’s process?

Answer:

Haber’s technique produces ammonia through a reversible, exothermic reaction that results in a drop in volume. We hope you found this ammonia post useful. If you have any questions, please leave a comment below and we will respond as soon as possible.