Free, 20% in air, and 0.04% dissolved in water
1. By heating a metal carbonate
CaCO3 Δ→ CaO + CO2↑
ZnCO3 Δ→ ZnO + CO2↑
CuCO3 Δ→ CuO + 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 Δ→ Na2CO3 + H2O + CO2↑
Ca(HCO3)2 Δ→ Ca2CO3 + H2O + CO2↑
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.