(a) Describe and explain the variation in the solubilities of the hydroxides of the Group 2 elements. (b) The table lists the standard enthalpy changes of formation, $\Delta H_f^\ominus$, for some compounds and aqueous ions. species $\Delta H_f^\ominus$ / kJ mol$^{-1}$ --- --- Ba$^{2+}$(aq) $-538$ OH$^-$(aq) $-230$ CO$_2$(g) $-394$ BaCO$_3$(s) $-1216$ H$_2$O(l) $-286$ (i) Reaction 1 occurs when CO$_2$(g) is bubbled through an aqueous solution of Ba(OH)$_2$. Use the data in…

Chemistry 9701/43 — May/June 2017

Cambridge A-Level · A Level Structured Questions · worked solutions for every part, with the mark scheme

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Topics Introduction to A Level Organic Chemistry · Nitrogen Compounds · Transition Elements · Analytical Techniques · Group 2 · Chemical Energetics · +6 more

Q1Group 2Chemical EnergeticsFree sample

(a)

Describe and explain the variation in the solubilities of the hydroxides of the Group 2 elements.

(b)

The table lists the standard enthalpy changes of formation, $\Delta H_f^\ominus$ , for some compounds and aqueous ions.

species	$\Delta H_f^\ominus$ / kJ mol $^{-1}$
Ba $^{2+}$ (aq)	$-538$
OH $^-$ (aq)	$-230$
CO $_2$ (g)	$-394$
BaCO $_3$ (s)	$-1216$
H $_2$ O(l)	$-286$

(i)

Reaction 1 occurs when CO $_2$ (g) is bubbled through an aqueous solution of Ba(OH) $_2$ .

Use the data in the table to calculate the standard enthalpy change for reaction 1, $\Delta H_{r1}^\ominus$ .

\text{Ba(OH)}_2\text{(aq)} + \text{CO}_2\text{(g)} \rightarrow \text{BaCO}_3\text{(s)} + \text{H}_2\text{O(l)} \quad \text{reaction 1}

\Delta H_{r1}^\ominus = \text{............................. kJ mol}^{-1}

(ii)

If CO $_2$ (g) is bubbled through an aqueous solution of Ba(OH) $_2$ for a long time, the precipitated BaCO $_3$ (s) dissolves, as shown in reaction 2.

\text{BaCO}_3\text{(s)} + \text{CO}_2\text{(g)} + \text{H}_2\text{O(l)} \rightarrow \text{Ba(HCO}_3)_2\text{(aq)} \quad \text{reaction 2}

The standard enthalpy change for reaction 2, $\Delta H_{r2}^\ominus$ , = $-26$ kJ mol $^{-1}$ .

Use this information and the data in the table to calculate the standard enthalpy change of formation of the HCO $_3^-$ (aq) ion.

\Delta H_f^\ominus \text{ HCO}_3^-\text{(aq)} = \text{.............................. kJ mol}^{-1}

(iii)

The overall process is shown by reaction 3.

Use your answer to (ii), and the data given in the table, to calculate the standard enthalpy change for reaction 3, $\Delta H_{r3}^\ominus$ .

\text{Ba(OH)}_2\text{(aq)} + 2\text{CO}_2\text{(g)} \rightarrow \text{Ba(HCO}_3)_2\text{(aq)} \quad \text{reaction 3}

\Delta H_{r3}^\ominus = \text{.............................. kJ mol}^{-1}

(iv)

How would the value of $\Delta H_{r3}^\ominus$ compare with the value of $\Delta H_{r4}^\ominus$ for the similar reaction with Ca(OH) $_2$ (aq) as shown in reaction 4?
Explain your answer.

\text{Ca(OH)}_2\text{(aq)} + 2\text{CO}_2\text{(g)} \rightarrow \text{Ca(HCO}_3)_2\text{(aq)} \quad \text{reaction 4}

(c)

The standard entropy change for reaction 1 is $\Delta S_{r1}^\ominus$ .

Suggest, with a reason, how the standard entropy change for reaction 3 might compare with $\Delta S_{r1}^\ominus$ .

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