Determining the equilibrium constant of cobalt chloride spectroscopically method
Answers
Explanation:
The two different coloured Co(II) complex ions, [Co(H2O)6]2+ and [CoCl4]2-, exist together in equilibrium in solution in the presence of chloride ions:
[Co(H2O)6]2+(aq)(pink) + 4Cl-(aq) ⇌ [CoCl4]2-(aq)(blue) + 6H2O(l)
This equilibrium can be disturbed by changing the chloride ion concentration or by changing the temperature. The colour changes accompanying the changes in equilibrium position are as predicted by Le Chatelier’s principle.
Lesson organisation
The distinctive colours of the two cobalt(II) species in solution produce an attractive visual demonstration of a reversible reaction and the effect of concentration and temperature on the position of equilibrium.
The demonstration can be used to introduce reversible reactions and chemical equilibrium or to illustrate Le Chatelier’s principle once these concepts have been established. If students are unfamiliar with the formulae of complex ions this may confuse the issue. For the purposes of this discussion the equilibrium could adequately be represented by:
Pink cobalt species + chloride ions ⇌ Blue cobalt species + water molecules