Group 2 (AS)：練習問題

Which statement correctly describes the trend in the thermal stability of Group 2 carbonates as the atomic number of the metal increases?

When a Group 2 metal, \(M\), reacts with an excess of dilute sulfuric acid, a gas is evolved and a white precipitate is formed.

Which metal is most likely to be \(M\)?

A 0.10 mol sample of a Group 2 anhydrous carbonate, \(XCO_3\), was heated to constant mass. The resulting solid residue was then added to an excess of water. The final mixture was filtered, and the filtrate required 100 \(cm^3\) of 2.0 \(mol\,dm^{-3}\) \(HCl\) for complete neutralisation.

Which metal is \(X\)?

Equal amounts of magnesium nitrate and barium nitrate are heated strongly in separate test-tubes until they completely decompose.

Which statement correctly compares the observations or products of these reactions?

The solubility of Group 2 sulfates and hydroxides follows distinct trends down the group from magnesium to barium.

Which row in the table correctly identifies these trends and a contributing factor?

(a) Describe and explain the trend in thermal stability of the Group 2 nitrates, from magnesium nitrate to barium nitrate.

(b) Describe and explain the trend in the solubility of Group 2 hydroxides, from magnesium hydroxide to barium hydroxide.

(a) The thermal stability of Group 2 carbonates increases down the group from magnesium to barium. Explain this trend in terms of the properties of the Group 2 cations and their effect on the carbonate ion, \(\text{CO}_3^{2-}\).

(b) The solubility of Group 2 sulfates decreases down the group. This variation can be explained by considering the relative magnitudes of the standard lattice energy, \(\Delta H_{latt}^{\ominus}\), and the standard enthalpy change of hydration, \(\Delta H_{hyd}^{\ominus}\). Explain why the solubility of sulfates decreases down the group, specifically discussing how both energy terms change and which change is more significant.

(c) Write a balanced chemical equation for the thermal decomposition of magnesium nitrate, \(\text{Mg(NO}_3)_2\).

(d) State and explain whether barium nitrate would require a higher or lower temperature than magnesium nitrate to undergo decomposition, referring to the ionic radius of the \(\text{Ba}^{2+}\) ion.