Q.Discuss the various reactions that occur in the Solvay process.

Step 1: Ammoniation and carbonation of brine

CO$_2$ is passed into a saturated, ammoniated brine (NaCl saturated with NH$_3$):

Step 2: Precipitation of sodium bicarbonate

Ammonium bicarbonate then reacts with the sodium chloride present:

Sodium bicarbonate has comparatively low solubility and crystallises out of the cold, saturated solution, and is filtered off.

Step 3: Conversion to sodium carbonate

The filtered NaHCO$_3$ is heated (calcined) to give sodium carbonate (soda ash):

The CO$_2$ released is recycled back into Step 1.

Step 4: Recovery/regeneration of ammonia

The NH$_4$Cl left in the filtrate is treated with slaked lime to recover ammonia for reuse, so that NH$_3$ acts only as a recyclable catalyst-like reagent, not a consumed raw material:

$2NH_4Cl + Ca(OH)_2 \rightarrow 2NH_3\uparrow + CaCl_2 + 2H_2O$ …

Walk through the Solvay process in its logical sequence: ammoniation + carbonation of brine → precipitation of the less-soluble NaHCO$_3$ → calcination to Na$_2$CO$_3$ (recycling CO$_2$) → regeneration …

• Omitting the ammonia-regeneration step and treating NH$_3$ as if it were consumed rather than recycled.
• Writing NaHCO$_3$ as the final product instead of showing its calcination to Na$_2$CO$_3$. …