Ammonia Gas: Preparation, Properties, uses

Ammonia gas was first obtained by Joseph Priestley in 1771 by heating the ammonium and lime together and named it Alkaline Air.

In some quantities it is found in the atmosphere. In places where animals rot, its quantity is more than expected in the air. In nature it is also found as its salts.

Example:

In nature, it is found as ammonium chloride (NH4Cl) and ammonium sulphate [(NH4)2SO4].

Preparation in Laboratory

In the laboratory, ammonia is made by heating the ammonium chloride with a quenched lime.

2NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + 2NH3

In a rigid glass tube, a mixture of ammonium and quenched lime is heated. The received ammonia gas is collected from the gas jar by downward displacement of air.

Before being collected in a gas jar, it is passed onto CaO, which removes the moisture of this gas.

Haber’s Process

In this method, nitrogen and hydrogen combine to form ammonia gas.

N2 + 3H2 ⇌ 2NH3 + 24,000 calorie

In this activity, heat is generated and heat is increased. This is an exothermic reversible reaction. In this reaction the volume of the reactants decreases.

According to the principle of le-chatelier, it is necessary to have low temperature and high pressure in this action. In this way more ammonia can be obtained and the action
velocity can be increased.

The presence of suitable catalysts also helps in increasing the velocity of action. But the optimum temperature of the reaction is about 500°C in the presence of the catalyst used in the reaction.

Therefore, in this reaction the temperature is kept at around 500°C. The pressure value is kept equal to about 200 atmospheres.

In this method any of the following catalysts can be used –

  • · Iron granular powder containing a small amount of malibdanam
  • · Ferric oxide containing soda, silica and potassium
  • · Fine powder of nickel

Read more about Ammonia Gas

Physical Properties

It is a colorless and intensely smelling gas. Due to this, tears start coming out of the eyes. This can also be fatal due to an overdose.

The molecular weight of ammonia is 17 and density is 8.5. Hence it is lighter than air. This is why in the laboratory it is collected by downward displacement of air.

It is soluble in water. It also dissolves in large quantities in water. At normal temperature, its water content is 89.9 grams per 100 ml. Like other gases, its solubility in water decreases at higher temperatures.

Ammonia dissolves in water to form ammonium hydrosidae –

NH3 + H2O → NH4OH ⇌ NH4+ + OH–

Ammonium hydrosidae is a valid additive. Hence, aqueous solution of ammonia is alkaline and conductor of electricity.

Ammonia gas does not burn itself nor is it helpful in burning other substances. It does not burn when ammonia gas is ignited in the air. But it starts burning due to excess of oxygen. She extinguishes when a burning candle is carried in a jar of ammonia gas.

The critical temperature of ammonia is 133°C. Therefore, it keeps on increasing pressure at normal temperature.

The boiling point of liquid ammonia is -33.4°C and freezing point -77.7°C. Ammonia has a higher boiling point than phosphine(PH3). The reason for this is that the negative efficiency of nitrogen is higher than the negative efficiency of phosphorus. Hence intermolecular hydrogen bonding occurs in ammonia. And more energy is required to separate its molecules.

Chemical Properties

Reaction with water: Ammonia dissolves in water to form ammonium hydroxide-

NH3 + H2O → NH4OH ⇌ NH4+ + OH–

Alkaline properties: It reacts with acids to form salts.

2NH3 + H2SO4 → (NH4)2SO4

NH3 + HCl → NH4Cl

NH3 + HNO3 → NH4NO3

Combustion: Ammonia does not burn itself or helps in the burning of other substances. It burns with yellow flame in excess of oxygen.

4NH3 + 3O2 → 6H2O + 2N2

Nitric oxide and water are obtained when a mixture of ammonia and oxygen gas flows through a hot plate of platinum.

4NH3 + 5O2 → 6H2O + 4NO

Thermal Decomposition: Ammonia is a permanent additive but dissociates into components at high temperatures or when electric sparks flow.

2NH3 → N2 + 3H2

Action with halogens: If more amount of ammonia is taken with less amount of chlorine, nitrogen gas is obtained.

2NH3 + 3Cl2 → N2 + 6HCl

Uses of Ammonia

  • It is used as a reagent in the laboratory.
  • In the industrial manufacture of nitric acid
  • In making urea, ammonium salts and fertilizers.
  • Artificial silk tear gas is also used in making explosive material, ice, etc.

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