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Study of Compounds

Hydrogen Chloride

Hydrogen chloride (HCl)



Evolved gas (i.e., hydrogen chloride gas) can be dried by passing through concentrated H2SO4. The dry hydrogen chloride gas is collected by upward displacement of water since it is heavier than air.







The composition of ammonia was determined by Claude Berthollet in 1785.

Occurrence

In the free state, ammonia is found in air and natural water.

In the combined state, it is obtained by destructive distillation of coal or wood. Also, it is found on the sides of craters and fissures of lava of volcanoes.

Structure

  • It has a trigonal pyramidal structure with nitrogen atom at the apex.

  • It has three bond pairs and one lone pair of electrons.
Forms
  • Dry ammonia gas (gaseous ammonia)
  • Liquid ammonia (liquified ammonia)
  • Liquor ammonia fortis (saturated solution of ammonia in water)
  • Laboratory bench reagent (dilute solution of liquor ammonia)

Preparation of ammonia

Ammonia can be prepared by the following methods.
 

  • Ammonium salts on warming with caustic alkali produce salt, water and ammonia gas as shown in the reactions below:
2 NH4Cl + CaOH2     Δ      CaCl2 + 2 H2O + 2 NH3NH42SO4 + 2 NaOH      Δ      Na2SO4 + 2 H2O + 2 NH3
  • Ammonia is formed by the decay of nitrogenous organic matter such as urea.

  • On a small scale, ammonia is obtained from ammonium salts, which decompose when treated with caustic soda or lime. It forms a metal salt, water, and ammonia gas.

In this method, the mixture of ammonium chloride and dry calcium hydroxide is placed in a round-bottomed flask. It is clamped to an iron stand so that its neck is tilting downwards. This stops water vapours formed by condensation to trickle back into the hot flask.

The ammonia gas contains water vapours as impurities. The water vapour has to be removed as the ammonia gas is extremely soluble in water. Thus, it is passed through drier containing quicklime.

The vapour density of ammonia is 8.5. Therefore, it is lighter than air. Thus, it is collected by downward displacement of the air. Also, since ammonia gas is extremely soluble in water, it cannot be collected over water.

  • Ammonia can also be prepared by treating metal nitrides like magnesium, sodium and aluminium with warm water.

In this method, magnesium nitride is placed in a conical flask. Warm water is allowed to trickle on it. This evolves moist ammonia gas.

The ammonia gas contains water vapours as impurities. The water vapour has to be removed as ammonia gas is extremely soluble in water. Hence, it is passed through drier containing quicklime.

The vapour density of ammonia is 8.5. Therefore, it is lighter than air. Thus, it is collected by downward displacement of air. Also, since ammonia gas is extremely soluble in water, it cannot be collected over water.

The following reactions take place when water reacts with sodium and magnesium nitride.

  • Preparation of Aqueous ammonia

By dissolving ammonia in water, an aqueous solution of ammonia is obtained. Take water in a container and dip a small portion of the mouth of the funnel in water.

The level of the water decreases when ammonia dissolves in water at a higher rate than that of its production.

The water rushes into the funnel due to the decrease in the pressure above water level and t…

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