Combustibility
Ammonia is neither combustible in air nor does it support combustion. However it burns in oxygen with a greenish-yellowish flame producing water and nitrogen.
a) Burning of Ammonia in Oxygen
Activity
Set the apparatus as shown in figure 6.7.
Firstly, when ammonia is passed through the longer tube and is made to ignite, it does not catch fire. Then oxygen is sent through the shorter tube. Now when ammonia is ignited, it catches fire and the following reaction takes place:
Although the products formed in the above reaction are insignificant, it is an extremely important reaction from viewpoint of industry. This is because in the presence of platinum, catalytic oxidation of ammonia can take place to give various important products.
b) Catalytic Oxidation of Ammonia
Activity
Set the apparatus as shown in figure 6.8.
The platinum coil is heated at 800oC in a combustion tube till it becomes white hot. Then ammonia and oxygen are passed through the tube. Under these conditions and in the presence of the catalyst, ammonia combines with free oxygen or oxygen of the air, to form nitric oxide and water vapour.
As colourless nitric oxide comes out into the air, it cools down and combines with the oxygen of the air to form reddish brown fumes of nitrogen dioxide.
The formed nitrogen dioxide is converted into nitric acid in the presence of water and oxygen.
The importance of the above reactions lies in the production of nitric acid, which is a very important industrial product.
Basic Nature
Absolutely dry ammonia or pure liquefied ammonia is neutral. In the presence of water however, it forms ammonium hydroxide, which yields hydroxyl ions. As a result of this reaction, it exhibits basic nature. It is a weak base and is perhaps the only gas that is alkaline in nature.
Action on Indicators
Ammonia acts upon indicators as mentioned in below table.
Action of Ammonia on Various Indicators
Action with Acids
Ammonia reacts with the acids to form their respective ammonium salts.
Action with Water
Ammonia is highly soluble in water and forms ammonium hydroxide.
