Sodium reacting with water. Flames during a chemical reaction caused by water being dripped onto sodium from a burette (at upper centre). Water molecules (H20) are made of hydrogen (H) and oxygen (O) atoms. The sodium (Na) metal is more reactive than hydrogen and replaces one of them in the water molecules to make sodium hydroxide or caustic soda (NaOH). Each hydrogen atom combines with another to form hydrogen gas (H2). The equation for this reaction is: 2Na + 2H20 -----> 2NaOH + H2. Sodium hydroxide is a strongly alkaline substance used to manufacture other chemicals, paper, rayon, aluminium, detergents, petrochemicals and textiles.