Question

The most commonly used experiment to detect release of CO${}_2$ is

• A. Exhaling test
• B. Lime water test
• C. Mercury test
  
• D. None of the above

Answer 1

The correct option is B Lime water test

Limewater reacts with carbon dioxide (CO2) in a two-step process. Limewater is calcium hydroxide dissolved in water.

Ca(OH)2 + H2O -> Ca++ + 2OH-

Then, the Ca++ reacts with the CO2 to give calcium carbonate which is very insoluble in water:

Ca(OH)2 + CO2 -> CaCO3 + H2O (CaCO3 will precipitate, creating a milky solution)

In the presence of more, or excess, CO2, the CaCO3 reacts with more Co2 to give calcium bicarbonate, which is water soluble:

CaCO3 + CO2 -> Ca(HCO3) + H2O

So the milky appearance goes away as the insoluble CaCO3 reacts forming the soluble Ca(HCO3)2. Hence, the most commonly used experiment to detect the release of co2 is the lime water test.

So, the correct answer is 'lime water test'.