Question

What is observed when carbon dioxide gas is passed through lime water. (a) for a short duration? (b) for long duration? also write the chemical equations for the reactions involved?

Answer 1

1) When carbon dioxide is passed through lime water for a short time, the solution turns milky. This is due to the formation of calcium carbonate.

ie Ca(OH) 2 + CO2 = CaCO3 + H2O

2) When carbon dioxide is passed through lime water for a longer time, the milkiness disappears because calcium carbonate turns into calcium hydrogen carbonate which is colorless in nature.

CaCO3 + H2O + CO2 = Ca(HCO3) 2

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Answer 2

Solution:

i) For short duration:

When calcium hydroxide(lime water) solution reacts with carbon dioxide gas,the Limewater turns milky due to the formation of a white precipitate of calcium carbonate (CaCO3) which is insoluble in water.

Ca(OH)2(aq) + CO2(g) ------> CaCO3 (s) + H2O(l)

ii) for long duration:

When excess of carbon dioxide gas is passed through lime water then the white precipitate calcium carbonate formed first dissolves due  to the formation of a soluble salt calcium hydrogen carbonate (Ca(HCO3)2, and the Solution becomes clear again.

CaCO3 (s) + H2O(l) + CO2(g) ------> Ca(HCO3)2.

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