Sodium reacting with water. The sodium metal (Na) is the small ball at center. The acid-base indicator phenolphthalein has been added to the water bath. This shows the production of sodium hydroxide (NaOH) by the reaction. Phenolphthalein turns purple in alkaline solutions, and sodium hydroxide is a strong alkali. The equation for this reaction is: 2Na + 2H2O ---> 2NaOH + H2. The hydrogen (H2) produced is burnt off by the heat of the reaction. Sodium is a very reactive metal that must be stored under oil as it reacts with both water and atmospheric oxygen.