Chemistry 9701/41 — May/June 2017

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

questions

100

marks

120

minutes

Topics Introduction to A Level Organic Chemistry · Nitrogen Compounds · Transition Elements · Group 2 · Chemical Energetics · Equilibria · +5 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	$\Delta H_f^\ominus / \text{ kJ mol}^{-1}$
$\text{Ba}^{2+}(\text{aq})$	$-538$
$\text{OH}^-(\text{aq})$	$-230$
$\text{CO}_2(\text{g})$	$-394$
$\text{BaCO}_3(\text{s})$	$-1216$
$\text{H}_2\text{O}(\text{l})$	$-286$

(i)

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

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}(\text{l}) \quad \text{reaction 1}

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

(ii)

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

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

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

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

\Delta H_f^\ominus \text{ HCO}_3^-(\text{aq}) = \text{.............................. } \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{.............................. } \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 $\text{Ca(OH)}_2(\text{aq})$ 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 $\Delta S_{r1}^\ominus$ .

The rest of this paper

5 more questions

Q2Introduction to A Level Organic Chemistry · Nitrogen Compounds · Equilibria · Transition Elements23M
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Q4Introduction to A Level Organic Chemistry · Hydrocarbons · Nitrogen Compounds15M
Q5Introduction to A Level Organic Chemistry · Carboxylic Acids and Derivatives · Nitrogen Compounds14M
Q6Reaction Kinetics · Halogen Compounds · Introduction to A Level Organic Chemistry · Analytical Techniques16M

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