Suggest a mechanism for the decomposition of the carbonate ion by adding two curly arrows in Fig. 1.1.
Describe how the thermal stability of Group 2 carbonates changes down the group. Explain your answer.
Define lattice energy.
The lattice energy of the Group 2 carbonates, $\Delta H^{\circ}_{\text{latt}}(\text{MCO}_3)$, becomes less exothermic down the group. The lattice energy of the Group 2 oxides, $\Delta H^{\circ}_{\text{latt}}(\text{MO})$, also becomes less exothermic down the group. $\Delta H^{\circ}_{\text{latt}}(\text{MCO}_3)$ and $\Delta H^{\circ}_{\text{latt}}(\text{MO})$ change by different amounts going down the group. Suggest how the standard enthalpy change of the decomposition reaction for Group 2 carbonates changes down the group. Explain your reasoning in terms of the relative sizes of the anions and the relative changes in lattice energy down the group.
Give the ionic equation for the reaction between $\text{SO}_3^{2-}$ and acidified $\text{MnO}_4^-$. The half-equations are: $\text{H}_2\text{O} + \text{SO}_3^{2-} \rightarrow \text{SO}_4^{2-} + 2\text{H}^+ + 2\text{e}^-$ and $\text{MnO}_4^- + 8\text{H}^+ + 5\text{e}^- \rightarrow \text{Mn}^{2+} + 4\text{H}_2\text{O}.$
Calculate the percentage purity of the sample of $\text{K}_2\text{SO}_3$. Show your working.
Potassium disulfite, $\text{K}_2\text{S}_2\text{O}_5$, is another food additive. The disulfite ion, $\text{S}_2\text{O}_5^{2-}$, has the displayed formula shown in Fig. 1.2. Deduce the geometry (shape) around the $\text{S}(\alpha)$ atom in $\text{S}_2\text{O}_5^{2-}$.