 In the double displacement reaction of an ammonium compound with a hydroxide, we will place a small amount of solid ammonium chloride in the test tube. We will add some 6-molar sodium hydroxide solution. The test tube is warmed. The ammonium ion will react with the hydroxide ion to produce ammonia, gas, and water. The ammonia gas escapes from the solution. We can test for the presence of the ammonia gas by bringing in a piece of wet red litmus paper. The ammonia gas dissolves in the water making a basic solution which turns the red litmus paper blue.