Physical Properties of Ammonia

Color

Ammonia is a colorless gas.

Odor

It has a characteristic pungent odor.

Taste

It is bitter to taste.

Vapor Density

Its vapor density is 8.5. Hence it is lighter than air (vapor density of air = 14.4).

Liquefaction

When cooled under pressure ammonia condenses to a colorless liquid, which boils at -33.4^oC. When further cooled, it freezes to a white crystalline snow-like solid, which melts at -77.7^oC.

Solubility

Ammonia is one of the most soluble gases in water. At 0^oC and 760 mm of Hg pressure one volume of water can dissolve nearly 1200 volumes of ammonia. This high solubility of ammonia can be demonstrated by the fountain experiment.

Fountain experiment

Fill a clean dry round-bottomed flask with dry ammonia, close it by a one holed stopper, through which a long jet tube is introduced. The free end of the tube is dipped into a trough of water as shown in figure 6.5.

Add two or three drops of an acid and a small quantity of phenolphthalein to the water in the trough. This water is colorless. Pour a small quantity of spirit or ether on a layer of cotton and place it over the inverted flask.

Due to the cooling effect produced by the process of evaporation of spirit or ether, the ammonia gas contracts a little and as a result, small quantity of the water gets sucked up. As soon as this water enters the flask, the ammonia dissolves in it, forming a partial vacuum. As a result of it, water rushes in and comes out of the tube as a jet of fountain. The color of the water turns deep pink.

Dissolving Ammonia in Water

Due to its high solubility, ammonia cannot be passed through water like many other gases. Ammonia is dissolved in water, as shown in figure 6.6.

This arrangement is called funnel arrangement and its principle is the same as that discussed for HCl gas.

The funnel arrangement prevents back suction of water, which can cause damage to the apparatus used.

It provides larger surface area for dissolution of ammonia.

Remember:-

A very strong solution of ammonia in water is called liquor ammonia. Ammonia can be obtained from it by boiling.

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