Sodium sulfate Salt cake Na2SO4

Superiority:

Physical and chemical properties

Na₂SO₄ is chemically very stable, being unreactive toward most oxidising or reducing agents at normal temperatures. At high temperatures, it can be reduced to sodium sulfide. It is a neutral salt, which forms aqueous solutions with pH of 7. The neutrality such solutions reflects the fact that Na₂SO₄ is derived, formally speaking, from a strong acid (sulfuric acid) and a strong base (sodium hydroxide). Sodium sulfate reacts with an equivalent amount of sulfuric acid to give an equilibrium concentration o the acid salt sodium hydrogen sulfate:

Na₂SO₄( aq) + H₂SO₄(aq) → 2 NaHSO₄(aq)

In fact the equilibrium is very complex and dependent on concentration and temperature, with other acid salts being present.

Na₂SO₄ is a typical ionic sulfate, containing Na⁺ ions and SO₄²⁻ ions. Aqueous solutions can produce precipitates when combined with salts of Ba²⁺ or Pb²⁺, which form insoluble sulfates:

Na₂SO₄(aq) + BaCl₂(aq) → 2 NaCl(aq) + BaSO₄( s)

Sodium sulfate has unusual solubility characteristics in water, ³ as shown in the graph below. Its solubility rises more than tenfold between 0 °C to 32.4 °C, where it reaches a maximum of 49.7 g Na₂SO₄ per 100 g water. At this point the solubility curve changes slope, and the solubility becomes almost independent of temperature. In the presence of NaCl, the solubility of Na₂SO₄ is markedly diminished. Such changes provide the basis for the use of sodium sulfate in passive solar heating systems, as well is in the preparation and purification of sodium sulfate.

This nonconformity can be explained in terms of hydration, since 32.4 °C corresponds with the temperature at which the crystalline decahydrate (Glauber's salt) changes to give a sulfate liquid phase and an anhydrous solid phase.