# Question #e5ea0

Oct 31, 2015

Yes. Hydrated copper(II) sulfate is always blue.

#### Explanation:

Hydrated copper(II) sulfate is copper(II) sulfate pentahydrate, or $\text{CuSO"_4·5"H"_2"O}$.

The water attaches to the copper(II) ion, forming a water/ion complex that absorbs red or yellow light. The absorption of light energy excites an electron from water which is promoted to the copper(II) ion. This causes blue light to be emitted, giving the copper(II) sulfate pentahydrate its blue color.

http://antoine.frostburg.edu/chem/senese/101/inorganic/faq/blue-vitriol.shtmll

In the lab you can heat a sample of copper sulfate to dry it, forming anhydrous copper sulfate. You will notice the compound becoming more white in appearance as it dries. Adding water will cause the color to change back to a blue color is the compound switches back to the hydrated version.