 In the single displacement reaction of a reactive metal with water, we will react calcium metal with water. The reaction is very rapid and exothermic. Hydrogen gas has evolved and calcium hydroxide is formed. Calcium hydroxide is not very water soluble, so we get the formation of a large amount of white solid in the flask. The hydrogen gas can be tested for by using a burning splint. The hydrogen gas is flammable and ignites. We can test for the fact that calcium hydroxide is produced by adding phenethylene. The phenethylene is colorless in acid solution and pink in basic solution. The fact that the phenethylene turns pink tells us that we have produced the metal hydroxide.