Alkali + carbon dioxide

Carbon dioxide is an acidic gas. When carbon dioxide gas is passed through an alkali solution, neutralization occurs to give a carbonate and water.
When excess carbon dioxide gas is passed through the reaction mixture, a hydrogencarbonate is formed.

Example 1 : KOH solution and CO2 gas.
2KOH(aq) + CO2(g) → K2CO3(aq)+ H2O(l)
K2CO3(aq) + CO2(g) + H2O(l) →2KHCO3(aq)
There is no observable change.

Example 2 : Ca(OH)2 solution (lime water) and CO2 gas.
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
CaCO3(s) + CO2(g) + H2O(l) → Ca(HCO3)(aq)
The solution turns milky firstly. When excess CO2 gas is passed through the reaction mixture, the solution turns clear again.

alkali + carbon dioxide -----> carbonate + water
e.g.
limewater
CO2 + Ca(OH)2 ---------> CaCO3 + H2O


e.g 2KOH + CO2 → K2CO3 + H2O
it is the production process of K2CO3 too

KOH+CO2 ->>>>> K+(aq) + HCO3- (aq)