How will you show that exhaled air contains carbon dioxide gas?

Hi Rushikesh,

Perform the following experimant in order to prove that the exhaled air contains carbon dioxide.

Take freshly prepared lime water in two test tubes and label them as A and B. Use a syringe to pass air in test tube A, and blow air in test tube B through a straw.

You will observe that limewater turns milky in both test tubes. However, it was faster in test tube B.

 Explanation:

Limewater is the common name for saturated calcium hydroxide solution.

Its chemical formula is Ca (OH) ₂.

When CO₂ is passed through lime water, it turns milky due to the formation of calcium carbonate. This reaction can be denoted as:

 In test tube B, lime water turned milky faster because the air we exhale is CO₂. In comparison, the introduced air is atmospheric air in test tube A, which contains only 0.03% CO₂.

 Hope it is clear to you now,

Cheers!!