What substance is commonly used as a chemical test for the presence of water?

Anhydrous copper sulfate is commonly used as a chemical test for the presence of water due to its unique behavior when it comes into contact with moisture. In its anhydrous form, copper sulfate is a white powder, but when it absorbs water, it undergoes a significant color change to a bright blue, forming hydrated copper sulfate. This property makes it an effective indicator for detecting even small amounts of water in various samples.

Calcium chloride and magnesium sulfate are also hygroscopic materials that absorb water, but they do not exhibit a vivid color change that can be easily observed. Sodium bicarbonate is not used as a moisture indicator and is unrelated to the qualitative detection of water. The distinctive blue color of anhydrous copper sulfate upon hydration not only provides clear visual evidence of the presence of water but also allows for straightforward qualitative assessment in laboratory settings.