CBSE Class 9 Answered

Carbon cycle

The various processes by which the percentage proportion of carbon dioxide, CO₂ in the atmosphere is kept constant constitute the carbon cycle. About 0.03% to 0.04% of carbon dioxide is present in the atmosphere.

• Carbon dioxide is produced in industries by heating of carbonates and bicarbonates and also by reacting carbonates and bicarbonates with acids.

Carbonates:

CaCO_3(s) CaO_(s) + CO_2(g)

Bicarbonates:

2KHCO_3(s) K₂CO_3(s) + H₂O_(g) + CO_2(g)

Removal of carbon dioxide:

Carbon dioxide is used in the process of photosynthesis and is also absorbed by water, alkalis and limewater.

2KOH + CO₂ → K₂CO₃ + H₂O
Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
                                 (Milky)

Ca CO₃ + CO₂ + H₂O → Ca(HCO₃)₂