Test for carbon dioxide which observation is expected?

Test for carbon dioxide which observation is expected?

• A. Squeaky pop with a lit splint
• B. Relights a glowing splint
• C. Turns limewater cloudy
• D. Damp red litmus turns blue

Answer: (C)

The key idea is that carbon dioxide changes limewater. Limewater is a solution of calcium hydroxide. When CO2 passes into it, a reaction occurs to form calcium carbonate, which is insoluble and appears as a milky, cloudy suspension. Chemically, CO2 dissolves in water to form carbonic acid, which reacts with the hydroxide ions to give carbonate ions that combine with calcium to make CaCO3 precipitate. That milky cloudiness is the telltale sign of carbon dioxide. Others are different: a squeaky pop with a lit splint signals hydrogen, a glowing splint being rekindled signals oxygen, and a damp red litmus turning blue indicates a basic gas. Since CO2 is acidic, it would not turn damp red litmus blue; in water it would make an acidic solution and would turn blue litmus red. So the observed cloudy limewater best identifies carbon dioxide.

The key idea is that carbon dioxide changes limewater. Limewater is a solution of calcium hydroxide. When CO2 passes into it, a reaction occurs to form calcium carbonate, which is insoluble and appears as a milky, cloudy suspension. Chemically, CO2 dissolves in water to form carbonic acid, which reacts with the hydroxide ions to give carbonate ions that combine with calcium to make CaCO3 precipitate. That milky cloudiness is the telltale sign of carbon dioxide.

Others are different: a squeaky pop with a lit splint signals hydrogen, a glowing splint being rekindled signals oxygen, and a damp red litmus turning blue indicates a basic gas. Since CO2 is acidic, it would not turn damp red litmus blue; in water it would make an acidic solution and would turn blue litmus red. So the observed cloudy limewater best identifies carbon dioxide.