Preparation
Sodium carbonate is generally prepared by Solvay Process. In this process, the advantage is taken of the low solubility of sodium hydrogen carbonate whereby it gets precipitated in the reaction of sodium chloride with ammonium hydrogen carbonate. The latter is prepared by passing CO2 to a concentrated solution of sodium chloride saturated with ammonia, where ammonium carbonate followed by ammonium hydrogen carbonate is formed. The equations for the complete process may be written as:

$\begin{array}{l}{2 \mathrm{NH}_{3}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2} \rightarrow\left(\mathrm{NH}_{4}\right)_{2} \mathrm{CO}_{3}} \\\\ {\left(\mathrm{NH}_{4}\right)_{2} \mathrm{CO}_{3}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2} \rightarrow 2 \mathrm{NH}_{4} \mathrm{HCO}_{3}} \\\\ {\mathrm{NH}_{4} \mathrm{HCO}_{3}+\mathrm{NaCl} \rightarrow \mathrm{NH}_{4} \mathrm{Cl}+\mathrm{NaHCO}_{3}}\end{array}$

Sodium hydrogen carbonate crystal separates. These are heated to give sodium carbonate.

$2 \mathrm{NaHCO}_{3} \rightarrow \mathrm{Na}_{2} \mathrm{CO}_{3}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}$

Properties

Sodium carbonate is a white crystalline solid which exists as a decahydrate,Na₂CO₃·10H₂O. This is also called washing soda.
It is readily soluble in water.
On heating, the decahydrate loses its water of crystallisation to form monohydrate.
Above 373K, the monohydrate becomes completely anhydrous and changes to a white powder called soda ash.

Uses

It is used in water softening, laundering and cleaning.
It is used in the manufacture of glass, soap, borax and caustic soda.
It is used in paper, paints and textile industries.
It is an important laboratory reagent both in qualitative and quantitative analysis.

Sodium Bicarbonate
It is also known as baking soda.

Preparation
It is prepared by passing carbon dioxide through a saturated solution of sodium carbonate as follows:

$\mathrm{N} \mathrm{a}_{2} \mathrm{CO}_{3}+\mathrm{CO}_{2}+\mathrm{H_{2}} \mathrm{O} \rightarrow \mathrm{2NaHCO}_{3}$
Sodium bicarbonate can be easily precipitated from here as it is less soluble in water.

Properties

It is a white crystalline solid partially soluble in water and its aqueous solution is basic. NaHCO₃ gives yellow colour with methyl red or methyl orange bur no colour with HPH i.e., phenolphthalein.
On heating ar 100^oC, it decomposes into Na₂CO₃ with the evolution of CO₂.
With zinc sulphate, it forms normal zinc carbonate.

$\begin{array}{r}{\mathrm{ZnSO}_{2}+2 \mathrm{NaHCO}_{3} \longrightarrow \mathrm{ZnCO}_{3}+\mathrm{Na}_{2} \mathrm{SO_{4}\: +\: H_{2}} \mathrm{O}+\mathrm{CO}_{2}}\end{array}$
It reacts with dilute acids as follows:

$\mathrm{NaHCO}_{3}+\mathrm{HCl} \longrightarrow \mathrm{NaCl}+\mathrm{H_{2}} \mathrm{O}+\mathrm{CO}_{2}$

Uses

It is used to remove acidity in the stomach and in the making of baking powder (Sodium bicarbonare+potassium hydrogen tartatare).
It is used in fire extinguishers.
It is used in medicines as a mild antiseptic for skin infections.
It is used in making effervescent drinks.