Sodium sulfate is an important compound of sodium, when anhydrous, it is a white crystalline solid of formula Na2SO4. Na2SO4 is chemically very stable, being unreactive toward most oxidising or reducing agents at normal temperatures. It is a neutral salt, which forms aqueous solutions with pH of 7. Sodium sulfate has unusual solubility characteristics in water, in the presence of NaCl, the solubility of Na2SO4 is markedly diminished.