Question

how is CO2 gas tested in laboratory

Answer 1

CO2. There are two tests for CO2. ... Lime water turns milky as the Calcium hydroxide (chemical name for limewater) reacts with CO2to form Calcium Carbonate which is insoluble in water and thus forms a milky white precipitate.

Answer 2

There are two tests for carbon dioxide. Firstly it will extinguish a flame, however, as any oxygen free gas will also extinguish a flame this is a poor gas test and may result in misidentification.

The best way of testing for Carbon dioxide is to bubble it through lime water. A positive test will result in the lime water turning milky. Lime water turns milky as the Calcium hydroxide (chemical name for limewater) reacts with carbon dioxide to form Calcium Carbonate which is insoluble in water and thus forms a milky white precipitate.