Sodium metabisulfite Na2S2O5 can be thought of as a chemical container for sulfur dioxide. When added to water 1 mole reacts with 1 mole of water to form two moles of sodium hydrogen sulfite (sodium bisulfite). It is used because it is more stable as a solid than sodium bisulfite. The most common form of sodium bisulfite is therefore a near saturated solution known commonly as bisulfite lye.