In the test for water, what observation indicates water is present when using anhydrous copper sulfate?

• A. Blue turns white
• B. White turns blue
• C. Green turns blue
• D. Blue remains blue

Answer: (B)

Hydration changes color. Anhydrous copper sulfate is white when dry, but it forms copper sulfate pentahydrate, which is blue, as soon as it absorbs water. So seeing white powder turn blue is the clear sign that water is present. If there’s no water, the material stays white. The other possibilities don’t fit this test because they would involve different processes (like dehydration turning blue back to white) or starting from a hydrated form, which isn’t the setup of the test.