Explain why transition elements can exhibit more than one oxidation state.
The ion $[\mathrm{Fe(H_2O)_6}]^{2+}$ is found in aqueous solutions of iron(II) salts. Define complex ion.
The ion $[\mathrm{Fe(H_2O)_6}]^{2+}$ may be converted into $[\mathrm{Fe(H_2O)_4(OH)_2}]$. Suggest a suitable reagent for this conversion. State the type of reaction.
The green precipitate $[\mathrm{Fe(H_2O)_4(OH)_2}]$ becomes brown if it is left standing in air. Use the information in Table 2.1 to explain why $[\mathrm{Fe(H_2O)_4(OH)_2}]$ turns brown on standing in air. Include an equation for this reaction.
The complex $[\mathrm{Co(NH_3)_6}]^{2+}$ reacts with hydrogen peroxide according to the following equation. Reaction 1: $\mathrm{2[Co(NH_3)_6]^{2+} + H_2O_2 \rightarrow 2[Co(NH_3)_6]^{3+} + 2OH^-}$, $E^{\circ}_{\mathrm{cell}} = +1.67\ \mathrm{V}$. Calculate $\Delta G^{\circ}$, in kJ mol$^{-1}$, for reaction 1.