Cobalt chloride is widely used as an indicator of silica gel activity. The dried state is shown by a — Physical Chemistry — Kinetics Chemistry Question
Cobalt(II) complexes
Cobalt chloride is widely used as an indicator of silica gel activity. The dried state is shown by a blue color and the red color indicates the absorption of water. In the case of pure compounds, cobalt(II) chloride anhydrate is blue and the hexahydrate is red. The aqueous solutions of both compounds are shown by a red color. On the other hand, the ethanol solution of cobalt(II) chloride anhydrate is shown by a blue color. The color changes to red with the addition of water.
Write the coordination number and the coordination structure of the cobalt complex in the ethanol solution of cobalt(II) chloride anhydrate.
Model Answer
Coordination number: 4
Coordination structure: tetrahedral
The blue colour remains when an amount of water double than that of the cobalt chloride was added to the ethanol solution of cobalt(II) chloride. Write the chemical formula of the major cobalt complex in the solution.
Model Answer
[CoCl2(H2O)2]
Write the chemical reaction when a large amount of water is added to the solution.
Model Answer
[CoCl2(H2O)2] + 4 H2O → [Co(H2O)6]2+ + 2 Cl–
Write the coordination number and the coordination structure of the cobalt complex in the aqueous solution.
Model Answer
Coordination number: 6
Coordination structure: octahedral
If a certain amount of water is added to the ethanol solution, the solution becomes violet. Explain the color change if a small amount of concentrated hydrochloric acid is added to the violet solution.
Model Answer
It becomes blue due to the formation of tetrahedral chlorocomplexes of Co(II).
Explain the color change if the temperature of the violet solution decreases.
Model Answer
Heating causes a change in the structure of the complex. The solution becomes blue.
Write the chemical formula of the cobalt complex in cobalt(II) chloride hexahydrate.
Model Answer
[Co(H2O)6]Cl2