Question

The solid anhydrous solid CoCl₂ is blue in color. Because it readily absorbs water from the air, it is used as a humidity indicator to monitor if equipment (such as a cell phone) has been exposed to excessive levels of moisture. Predict what product is formed by this reaction, and how many unpaired electrons this complex will have.

a. [Co(H₂O)₆]²⁺, 3 unpaired electrons
b. [Co(H₂O)₄Cl₂], 2 unpaired electrons
c. [Co(H₂O)₃Cl₃], 1 unpaired electron
d. [Co(H₂O)₆]³⁺, 0 unpaired electrons

Answer 1

The hydration of anhydrous cobalt (II) chloride results in cobalt (II) chloride hexahydrate [Co(H₂O)₆]2+, which includes three unpaired electrons in its electronic structure. The correct option is a.

Step-by-step explanation:

When the solid anhydrous cobalt (II) chloride, CoCl₂, absorbs water from the air, it forms a hydrated complex. The correct product of this hydration reaction is cobalt (II) chloride hexahydrate, whose formula is CoCl₂ · 6H₂O.

This indicates that six water molecules coordinate with each cobalt ion. Looking at the options provided, option (a), which is [Co(H₂O)₆]2+, closely represents the hydrated form of CoCl₂.

To determine the number of unpaired electrons, we should consider the electronic configuration of cobalt (II), which is 3d7. In an octahedral field created by six water molecules, there are indeed three unpaired electrons, following Hund's rule for electron filling in degenerate orbitals.

Thus, the correct prediction for the product formed by the reaction of CoCl₂ with water is [Co(H₂O)₆]2+ with three unpaired electrons, corresponding to option (a).