Give the preparation and uses of sodium hydrogen carbonate (Baking soda - $NaHCO_3$).

(N/A) Preparation: Sodium hydrogen carbonate is prepared by saturating a solution of sodium carbonate with carbon dioxide. The white crystalline powder of sodium hydrogen carbonate,being less soluble,precipitates out.
$Na_2CO_3 + H_2O + CO_2 \rightarrow 2NaHCO_3$
Uses:
$(i)$ It is used as a mild antiseptic for skin infections.
$(ii)$ It is used in fire extinguishers.
$(iii)$ It is used as an ingredient in baking powder to make cakes and pastries light and fluffy due to the release of $CO_2$ gas upon heating.