AP BIOLOGY

Detailed explanation-1: -This carbon dioxide is present in the air that we exhale. When we blow into a test tube containing limewater (calcium hydroxide), the carbon dioxide reacts with it and turns it milky. This milky appearance is due to the formation of calcium carbonate.

Detailed explanation-2: -Limewater can be used to detect carbon dioxide. If carbon dioxide is bubbled through limewater then it turns from clear to cloudy/milky in colour. This is why limewater used in a simple respirometer can show that more carbon dioxide is present in exhaled air compared to inhaled air.

Detailed explanation-3: -Lime Water is also known as calcium hydroxide. When exhaled air is blown through lime Water, it turns milky. The carbon dioxide present in the exhaled air reacts with the lime water and turns it into a milky solution.

Detailed explanation-4: -Reaction with limewater Carbon dioxide reacts with limewater (a solution of calcium hydroxide, Ca(OH) 2), to form a white precipitate (appears milky) of calcium carbonate, CaCO 3.