What is the test and observation used to identify carbonate ions (CO32-)?

The identification of carbonate ions (CO32-) involves a chemical reaction that produces carbon dioxide when the carbonate is treated with an acid. When carbon dioxide is bubbled through limewater (a solution of calcium hydroxide), it reacts to form calcium carbonate, which is insoluble in water. This reaction causes the limewater to turn milky as precipitated calcium carbonate forms.

Therefore, the correct answer highlights that the presence of carbonate ions can be confirmed by the observable change of limewater turning milky upon the addition of carbon dioxide. This characteristic reaction is a key indicator used in laboratory settings to identify carbonate ions effectively.