Describe a chemical test for water. Give the test and the result

Pure copper(II) sulfate is white. It is also known as anhydrous copper(II) sulfate because it has no water in it.

When water is present in a sample of copper(II) sulfate it turns blue. It is still a dry solid, because the individual water molecules are trapped within the ionic lattice surrounding the copper(II) ions. Solutions of copper(II) sulfate are also blue.

This colour change can be used to detect the presence of water (or water vapour).

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.