Color Changes in Hydration Tests for Water

Steps:

• Recall anhydrous cobalt(II) chloride (CoCl₂) is blue and turns pink upon absorbing water to form the hexahydrate.
• Recall anhydrous copper(II) sulfate (CuSO₄) is white and turns blue upon absorbing water to form the pentahydrate.
• Compare options: A and B describe CoCl₂ changes; C and D describe CuSO₄ changes.
• Match correct observation: only D aligns with white to blue for CuSO₄.

Why D is correct:

• Anhydrous CuSO₄ is white; hydration forms [Cu(H₂O)₆]²⁺ complex, producing blue color.

Why the others are wrong:

• A: Anhydrous CoCl₂ is blue, not white; it turns pink, not white.
• B: Anhydrous CoCl₂ is blue and turns pink, not from pink to blue.
• C: Anhydrous CuSO₄ is white and turns blue, not from blue to pink.

Final answer: D