Potassium reacting with water. Potassium (symbol K) is a highly reactive metallic element of group one of the periodic table. It reacts with water to produce soluble potassium hydroxide (KOH) and hydrogen gas (H2). The reaction produces enough heat to ignite the hydrogen, which burns with a pink flame due to the presence of the potassium. The equation for the reaction is: 2K + 2H2O ---> 2KOH + H2. The heat of the reaction also melts the potassium metal, which forms a molten ball that floats on the water's surface.