Magnesium has a melting point of $650\,^{\circ}\text{C}$ and a high electrical conductivity. When magnesium is heated in air, magnesium oxide, $\text{MgO}$, is formed as the main product. Smaller quantities of magnesium nitride, $\text{Mg}_3\text{N}_2$, are also produced.
(a)[2]
Explain these properties of magnesium in terms of its structure and bonding.
(b(i))[1]
Calculate the oxidation number for magnesium and for the nitrogen species in $\text{Mg}_3\text{N}_2$ to fill in Table 1.1.
(b(ii))[1]
Identify the type of reaction that occurs between magnesium and nitrogen. Explain your answer.
(b(iii))[2]
Define the enthalpy change of formation.
(b(iv))[3]
When $3.645\,\text{g}$ of $\text{Mg}(s)$ burns in excess $\text{N}_2(g)$ to make $\text{Mg}_3\text{N}_2(s)$, $23.05\,\text{kJ}$ of energy is released. Determine the enthalpy change of formation, $\Delta H_f$, of $\text{Mg}_3\text{N}_2$. Show your working.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “High melting point of Mg because of many strong metallic bonds / strong electrostatic attractions between Mg$^{2+}$ cations and delocalised electrons / strong bonds in giant metallic structure” …