How can carbon dioxide gas be tested?

Carbon dioxide gas can be tested effectively by bubbling it through limewater. The key reaction involved is that when carbon dioxide is passed into limewater, which is a solution of calcium hydroxide, it reacts to form calcium carbonate. This calcium carbonate is only slightly soluble in water, and as it forms, it creates a precipitate that appears milky or cloudy. This change in appearance indicates the presence of carbon dioxide.

The other methods mentioned do not provide a reliable indication of carbon dioxide. For instance, using a glowing splint checks for oxygen, as a glowing splint will relight in the presence of oxygen, but it is not a test for carbon dioxide. Observing effects on litmus paper is typically used to determine acidity or alkalinity; carbon dioxide forms a weak acid when dissolved in water, but this method is not definitive for detecting the gas itself. Collecting carbon dioxide in a gas syringe and measuring its volume is useful for quantitative analysis but does not serve as a specific test for the presence of carbon dioxide.

Therefore, bubbling carbon dioxide through limewater is the most straightforward and immediate test for this gas.