Question

What is observed when carbon dioxide gas is passed through lime water. (i) for a short duration (ii) for a long duration? Also write the chemical equation for the reaction involved.
(class 10 CBSE SAMPLE PAPER 2017-18 SCIENCE)

Answer 1

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.

HOPE THIS WILL HELP YOU....

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.

HOPE THIS WILL HELP YOU....