• A. blue to pink ✓
  • B. white to red
  • C. white to green
  • D. blue to white


The answer to the question is: A. blue to pink

Anhydrous cobalt (II) chloride, also known as cobaltous chloride or cobalt dichloride, is a chemical compound with the formula CoCl2. It is a crystalline solid that is widely used in various industrial and laboratory applications. One of the most interesting properties of anhydrous cobalt (II) chloride is its ability to change color based on its hydration state.

When anhydrous cobalt (II) chloride is exposed to steam or water vapor, it undergoes a reversible hydration reaction, which causes a change in its color. The original color of anhydrous cobalt (II) chloride is blue. However, when it reacts with steam or water vapor, it turns pink due to the formation of the hydrated form of cobalt (II) chloride, known as cobalt (II) chloride hexahydrate (CoCl2·6H2O).

The change in color is attributed to the alteration in the electronic structure of the cobalt ions upon hydration. In the anhydrous form, the cobalt ions are coordinated with four chloride ions in a tetrahedral geometry, resulting in a blue color due to the absorption of certain wavelengths of light. Upon hydration, the coordination sphere around the cobalt ions changes, leading to a different electronic configuration and a corresponding change in color to pink.

This phenomenon has practical applications in moisture detection and as a humidity indicator. Anhydrous cobalt (II) chloride can be used in desiccants and humidity indicator cards due to its ability to reversibly change color in response to changes in humidity levels.

In summary, anhydrous cobalt (II) chloride changes from blue to pink when exposed to steam or water vapor due to its reversible hydration reaction, resulting in the formation of cobalt (II) chloride hexahydrate.

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