Properties of Sodium Hydroxide
It is hygroscopic and readily combines with carbon dioxide from the air (forming a coating of sodium carbonate), so it should be stored in tightly sealed vessels. In water it dissolves very well, giving off considerable amounts of heat and forming highly corrosive sodium lye – a colorless, odorless and non-flammable liquid that reacts with acids, non-metal oxides and amphoteric hydroxides to form sodium salts, is slippery to the touch, causes burns.
It has a corrosive effect on metals, especially in the presence of moisture. It easily reacts with metals of amphoteric properties giving off hydrogen, e.g. with aluminium and zirconium, forming aluminates and zirconates, respectively. It forms salts with weak organic acids, e.g. phenols and nitromethane. Non-metals under the influence of NaOH become disproportionated, e.g. white phosphorus boiled with NaOH solution gives phosphoric and phosphate, and sulfur dissolves in NaOH solution to form sulfide and sulfite.