The reaction between alkali and CO2(g) is slow. Because -
inter conversions of hydrated CO2 to various species are slower
pH < 8, CO2 reacts as follows
CO2+H2O⇌H2CO3 (slow)H2CO3+OH−→HCO−3+H2O (fast)At pH>8, CO2 reacts as followsCO2+OH−→HCO−3 (slow)HCO−3+OH−→CO−3+H2O (fast)
×CO−3↔CO2−3