Carbon Dioxide


Free, 20% in air, and 0.04% dissolved in water


Lab method

1.        By heating a metal carbonate
CaCO3 ΔCaO + CO2
ZnCO3 ΔZnO + CO2
CuCO3 ΔCuO + CO2(bluish-green to black)

Sodium and potassium carbonates do not decompose on heating. Sodium carbonate may give off water vapor.
               Na2CO3 · 10H2O Na2CO3 + 10H2O
2.        By adding hydrochloric acid to calcium carbonate
CaCO3 + 2HCl   CaCl2 + H2O + CO2
(Other acids, like sulphuric acid are not preferred because calcium carbonate gets coated by another calcium salt, rendering it passive)

The gas is collected under air.

               NaHCO3 + HCl   NaCl + H2O + CO2
               2NaHCO3 ΔNa2CO3 + H2O + CO2
               Ca(HCO3)2 ΔCa2CO3 + H2O + CO2

Industrial method

Steam is passed over heated coke. The reaction produces hydrogen and carbon monoxide. This water gas, if passed with excess steam over a catalyst, iron (III) oxide, forms carbon dioxide and hydrogen.
C + H2O CO + H2
CO + H2 + H2O CO2 + 2H2



1.        It is a colorless, odorless, tasteless acidic gas.
2.        It is slightly soluble in water. (It can be dried using P2O5)


1.        It does not support combustion, and it does not burn. However, magnesium burns in CO2 to form its oxide and carbon.
2Mg + CO2 2MgO + C
               Sodium and potassium also burn, but later form carbonates.
4Na + CO2 2Na2O + C
4K + CO2 2K2O + C
Na2O + CO2 Na2CO3
K2O + CO2 K2CO3
2.        It neutralizes alkalies.
CO2 + 2KOH K2CO3 + H2O
CO2 + 2NaOH Na2CO3 + H2O
CO2 + Ca(OH)2 CaCO3 + H2O


1.        In fire extinguishers – formed by the action of sulphuric acid on sodium hydrogen carbonate.
2.        Used as a refrigerant – dry ice.
3.         Is a leavening agent – baking soda, sodium bicarbonate and an acid in dry form react.
4.        In soft drinks, dissolved and under pressure.