The cobalt chloride and limewater tests are used to detect the presence of two different substances:

* Cobalt chloride test: This test is used to detect the presence of water. Anhydrous cobalt chloride (CoCl₂) is blue in color. When exposed to water, it changes color to pink due to the formation of hydrated cobalt chloride (CoCl₂·6H₂O).

* Limewater test: This test is used to detect the presence of carbon dioxide (CO₂). Limewater is a solution of calcium hydroxide (Ca(OH)₂). When CO₂ is bubbled through limewater, it reacts with the calcium hydroxide to form calcium carbonate (CaCO₃), which is insoluble in water and appears as a milky white precipitate.

Therefore, the cobalt chloride test indicates the presence of water, while the limewater test indicates the presence of carbon dioxide.