Chemistry 9701 · AS & A Level · Group 2

Group 2 — practice question

The atomic number of calcium is $20$.
(a)[1]

Complete the electronic structures of a calcium atom, $\text{1s}^2\text{2s}^2\text{2p}^6\,\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots$ and of a calcium ion with a $+2$ oxidation state, $\text{1s}^2\text{2s}^2\text{2p}^6\,\ldots\ldots\ldots\ldots\ldots\ldots$.

(b)[1]

Calcium nitrate, $\text{Ca(NO}_3)_2$, is used in fertilisers and can be made by an acid-base reaction. Write an equation showing the preparation of calcium nitrate by an acid-base reaction.

(c(i))[1]

When anhydrous calcium nitrate is heated strongly, it decomposes and leaves a white solid. Identify this solid and suggest one additional observation for the reaction.

(c(ii))[2]

The ease with which the Group II nitrates undergo thermal decomposition falls down the group. Explain this trend.

(d(i))[2]

What does the term standard enthalpy change of hydration, $\Delta H^{\theta}_{\text{hyd}}$, mean?

(d(ii))[3]

Use the data below to calculate the lattice energy, $\Delta H^{\theta}_{\text{latt}}$, of calcium nitrate, $\text{Ca(NO}_3)_2\text{(s)}$. It may help to draw an energy cycle.

(e)[2]

The standard enthalpy change of hydration for $\text{Ba}^{2+}$, $\Delta H^{\theta}_{\text{hyd}}(\text{Ba}^{2+}\text{(g)})$, is $-1305\,\text{kJ mol}^{-1}$. Suggest an explanation for why the $\Delta H^{\theta}_{\text{hyd}}$ of the $\text{Ba}^{2+}$ ion is less exothermic than the $\Delta H^{\theta}_{\text{hyd}}$ of the $\text{Ca}^{2+}$ ion.

Worked solution & mark scheme

This 12-mark question has a full step-by-step worked solution and mark scheme. One marking point: Electron configurations: Ca $=3s^23p^64s^2$; $\text{Ca}^{2+}=3s^23p^6$

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