Combustibility
Hydrogen chloride gas is neither combustible, nor does it support combustion.
Action of Heat
When heated to above 500oC hydrogen chloride gas dissociates into hydrogen and chlorine.
Reaction with Ammonia
When ammonia is mixed with hydrogen chloride, thick white fumes of ammonium chloride are formed, i.e., 
Activity
In a transparent combustion tube, cotton wool dipped in concentrated hydrochloric acid and liquor ammonia is introduced separately from the two ends of the tube. Both the ends of the combustion tube are then closed with rubber stoppers (Fig.5.6).
Thick white fumes of ammonium chloride (NH4Cl) are seen in the combustion tube. The white fumes are more dense and closer to the cotton containing hydrochloric acid. This is because, ammonia is lighter than hydrogen chloride gas, and hence can move faster than the heavier hydrogen chloride molecules.
Activity
Take about 1 ml each of concentrated hydrochloric acid and liquor ammonia in two different test tubes (Fig.5.7).
Warm them gently and bring the mouths of the test tubes together. Thick white fumes of ammonium chloride will be seen at the mouth of the test tubes.
Action on Indicators (Acidic Properties)
a) With Litmus
If the gas and litmus paper are both absolutely dry, then hydrogen chloride gas does not affect litmus paper. If the litmus paper is wet, the gas dissolves in the moisture to form hydrochloric acid and the blue litmus paper turns red.
b) With Methyl Orange
Methyl orange solution turns pink in the presence of hydrogen chloride.
c) With Phenolphthalein
Alkaline phenolphthalein turns from deep pink to a colourless solution, if an aqueous solution of hydrogen chloride is added to it.
The above reactions show the acidic behavior of hydrogen chloride.Action on
- Metals
When hydrogen chloride gas is passed over heated metals such as sodium, magnesium, zinc etc. the metal combines with the chlorine to form their respective metal chlorides, and liberates hydrogen (Fig.5.8).
Action on Silver Nitrate Solution
When a glass rod dipped in silver nitrate solution, is introduced into a test tube containing hydrogen chloride gas, a white precipitate is seen on the glass rod.
Action with Lead Nitrate Solution
Pour about 1 ml of lead nitrate solution into a test tube containing hydrogen chloride gas. A white precipitate of lead chloride is formed.
