Sodium Carbonate (washing soda) Na2CO3.10H2O

Sodium carbonate, familiar as washing soda, Na2CO3.10H2O, is manufactured commercially by the Solvay process. In the first stage, CO2 gas is passed into a concentrated NaCl solution that has been saturated with NH3; this proceeds through two reactions — 2NH3(aq) + H2O + CO2(g) → (NH4)2CO3(aq), then (NH4)2CO3(aq) + H2O + CO2(aq) → 2NH4HCO3(aq) — and the ammonium bicarbonate formed then undergoes a double-decomposition reaction with the dissolved sodium chloride, NH4HCO3(aq) + NaCl(aq) → NH4Cl(aq) + NaHCO3(s). Because sodium bicarbonate has comparatively low solubility, its crystals precipitate straight out of solution. In the second stage, these separated sodium bicarbonate crystals are heated to give sodium carbonate, 2NaHCO3(s) →(Δ) Na2CO3(s) + H2O(g) + CO2(g). The process also recovers its ammonia: the NH4Cl solution left over is treated with slaked lime, Ca(OH)2, regenerating NH3 for reuse and producing calcium chloride as a byproduct, 2NH4Cl(aq) + Ca(OH)2(s) → 2NH3(g) + CaCl2(aq) + H2O(l). (Potassium carbonate cannot be made this same way, because potassium hydrogen carbonate is too water-soluble to precipitate out when potassium chloride solution is used in place of sodium chloride.)

Properties: sodium carbonate is a white crystalline solid, formula Na2CO3.10H2O, highly soluble in water. On heating, the decahydrate first loses water to become the monohydrate, and above 373 K the monohydrate loses its remaining water to give anhydrous Na2CO3, a white powder called soda-ash: Na2CO3.10H2O(s) →(373 K) Na2CO3.H2O(s) + 9H2O(g), then Na2CO3.H2O(s) →(>373 K) Na2CO3(s) + H2O(g). An aqueous solution of sodium carbonate is alkaline because the carbonate ion hydrolyses, Na2CO3 + H2O → NaHCO3 + NaOH. …