Lawrie Ryan and Roger Norris Solutions for Chapter: Transition Elements, Exercise 8: Question

Blue cobalt chloride paper gets its blue colour from ${\left[{\mathrm{CoCl}}_4\right]}^{2-}$ ions. Give the oxidation number of the cobalt in this complex.

Blue cobalt chloride paper is used to test for water. If water is present, the paper turns pink as a complex forms between the cobalt ion and six water ligands. Write an equation to show the ligand substitution reaction that takes place in a positive test for water.

Which of the following equations correctly describes the reaction of hydrated copper $\left(\mathrm{II}\right)$ ions with concentrated hydrochloric acid? Also Identify the oxidation number of the central metal atom formed in the reaction.