Page 14 - Curriculum Visions Dynamic Book

Soluble alkaline ammonia
Ammonia is an alkaline substance, so it will cause a colour change in a chemical indicator. Ammonia is also extremely soluble and one volume of water will dissolve four hundred times its own volume of ammonia. The density of the solution falls to 0.880 grams per millilitre as it becomes saturated and the solution is known as “880 ammonia”.
Both of these properties of ammonia can be demonstrated in a dramatic way, as shown on this page, in a classic laboratory experiment.
Preparing dry ammonia
in the laboratory
Ammonium sulphate and calcium hydroxide are ground up and mixed using a pestle and mortar. The mixture is put into a long-necked, round-bottomed flask, and the neck clamped so that it points downwards.
The mixture is heated.
The heat energy causes a reaction and ammonia and water vapour are given off.
The (wet) ammonia gas is passed through a vertical column (called a drying tower) containing calcium oxide (another base, so no reaction occurs). The calcium oxide (lime) takes up the water from the ammonia (to make calcium hydroxide, slaked lime) and the dry ammonia gas now passes to an inverted collecting flask. Here it displaces air from the flask because ammonia has a lower density than air.
Short exit tube
Long entry tube
 Laboratory apparatus for preparing dry ammonia.
Ammonium sulphate and calcium hydroxide mixture.
Calcium oxide drying tower.
EQUATION: Producing ammonia in the laboratory
Ammonium sulphate + calcium hydroxide ➪ ammonia + water + calcium sulphate (NH4)2SO4(s) + Ca(OH)2(s) ➪ 2NH3(g) + 2H2O(l) + CaSO4(s)
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