When cobalt(II) chloride dihydrate is dissolved in water or ethanol, what species are present in both cases throughout the solutions in some amount (however, in rather different proportions for the water versus the ethanol)? Group of answer choices: – water – chloride – chlorate – cobalt(II) tetrachloride complex – cobalt(II) hexaaqua complex – sulfate – ethanol – hydroxide
The Correct Answer and Explanation is:
When cobalt(II) chloride dihydrate (CoCl₂·2H₂O) is dissolved in water or ethanol, different species will be present due to the distinct solvation properties of each solvent. Here’s a breakdown of the species that will be present in both solutions:
- Water: When CoCl₂·2H₂O dissolves in water, it dissociates into Co²⁺ ions and chloride (Cl⁻) ions. Additionally, water molecules interact with the Co²⁺ ions to form a cobalt(II) hexaaqua complex (Co(H₂O)₆²⁺), a common coordination complex where six water molecules surround the cobalt ion. This process occurs because water is a highly polar solvent that stabilizes the Co²⁺ ion by forming hydrogen bonds. Thus, in the water solution, the cobalt(II) hexaaqua complex is present along with chloride ions (Cl⁻) and possibly some uncoordinated water molecules.
- Ethanol: Ethanol is less polar than water and has a lower dielectric constant. When CoCl₂·2H₂O is dissolved in ethanol, the Co²⁺ ions dissociate from the chloride ions, but the interaction between the Co²⁺ ion and ethanol molecules is weaker than the interaction with water. As a result, Co²⁺ and Cl⁻ ions will be present in ethanol as well, but ethanol may not stabilize the Co²⁺ ion to the same extent. In this solvent, ethanol molecules could coordinate to the Co²⁺ ion to form some partial complexes, but they are less stable compared to the hexaaqua complex in water. Therefore, the Co²⁺ ion will likely remain as a free ion in greater proportions in ethanol than in water. The chloride ions (Cl⁻) will also be present in the ethanol solution, but without the extensive hydration or complex formation seen in water.
Species present in both solutions:
- Chloride ions (Cl⁻): Present in both solutions, as CoCl₂ dissociates into Co²⁺ and Cl⁻ in both water and ethanol.
- Cobalt(II) hexaaqua complex (Co(H₂O)₆²⁺): Present in the water solution due to the strong hydration of Co²⁺ ions.
- Ethanol: Present in the ethanol solution, but it is a solvent, not a solute species.
In summary, both water and ethanol will have chloride ions (Cl⁻), but water will also feature a cobalt(II) hexaaqua complex. Ethanol will dissolve CoCl₂·2H₂O with less interaction, likely leading to a smaller formation of any cobalt-ethanol complexes.
