Chemistry 9701 · AS & A Level · 4.2

4.2 — practice question

On heating, solutions of Group 2 hydrogencarbonates, $\text{M(HCO}_3\text{)}_2$, break down to produce the matching metal carbonate, carbon dioxide and water.
(a(i))[1]

Write an equation for the thermal decomposition of strontium hydrogencarbonate, $\text{Sr(HCO}_3\text{)}_2$.

(a(ii))[2]

Explain why the thermal stability of Group 2 carbonates rises down the group.

(b)[4]

The hydroxides and fluorides of Group 2 elements show similar solubility patterns. Describe the pattern in the solubility of the fluorides of calcium, strontium and barium. Explain your answer.

(c(i))[1]

Define $\Delta H_{\mathrm{hyd}}$, the enthalpy change of hydration.

(c(ii))[2]

State the main factors that influence the size of enthalpy change of hydration. Explain your answer.

(d)[2]

Table 1.1 gives several energy changes. Use data from Table 1.1 to calculate the enthalpy change of solution, $\Delta H_{\mathrm{sol}}$, for $\text{MgF}_2$(s). Drawing a labelled energy cycle may help. Show your working.

(e(i))[2]

Mercury(I) fluoride, Hg$_2$F$_2$, is only sparingly soluble in water. In Hg$_2$F$_2$, the cation is the diatomic ion Hg$_2^{2+}$ with a covalent Hg-Hg bond. Write the solubility product expression, $K_{\mathrm{sp}}$, for Hg$_2$F$_2$. Include the units.

(e(ii))[1]

At 298 K, the solubility of Hg$_2$F$_2$ is $9.20 \times 10^{-3}\ \mathrm{mol\ dm^{-3}}$. Calculate $K_{\mathrm{sp}}$ for Hg$_2$F$_2$ at 298 K.

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