Chemistry 9701/42 — May/June 2012

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

questions

100

marks

120

minutes

Topics Chemical Energetics · Introduction to A Level Organic Chemistry · Carboxylic Acids and Derivatives · Nitrogen Compounds · Hydrocarbons · Transition Elements · +7 more

Q1Chemical EnergeticsGroup 2Free sample

(a)

(i)

What is meant by the term enthalpy change of hydration, $\Delta H^\ominus_{\text{hyd}}$ ?

(ii)

Write an equation that represents the $\Delta H^\ominus_{\text{hyd}}$ of the $\text{Mg}^{2+}$ ion.

(iii)

Suggest a reason why $\Delta H^\ominus_{\text{hyd}}$ of the $\text{Mg}^{2+}$ ion is greater than $\Delta H^\ominus_{\text{hyd}}$ of the $\text{Ca}^{2+}$ ion.

(iv)

Suggest why it is impossible to determine the enthalpy change of hydration of the oxide ion, $\text{O}^{2-}$ .

(b)

The enthalpy change of solution for $\text{MgCl}_2$ , $\Delta H^\ominus_{\text{sol}}(\text{MgCl}_2(\text{s}))$ , is represented by the following equation.

\text{MgCl}_2(\text{s}) + \text{aq} \rightarrow \text{Mg}^{2+}(\text{aq}) + 2\text{Cl}^-(\text{aq})

Describe the simple apparatus you could use, and the measurements you would make, in order to determine a value for $\Delta H^\ominus_{\text{sol}}(\text{MgCl}_2(\text{s}))$ in the laboratory.

(c)

The table below lists data relevant to the formation of $\text{MgCl}_2(\text{aq})$ .

enthalpy change	value / $\text{kJ mol}^{-1}$
$\Delta H^\ominus_{\text{f}}(\text{MgCl}_2(\text{s}))$	$-641$
$\Delta H^\ominus_{\text{f}}(\text{MgCl}_2(\text{aq}))$	$-801$
lattice energy of $\text{MgCl}_2(\text{s})$	$-2526$
$\Delta H^\ominus_{\text{hyd}}(\text{Mg}^{2+}(\text{g}))$	$-1890$

By constructing relevant thermochemical cycles, use the above data to calculate a value for

(i)

$\Delta H^\ominus_{\text{sol}}(\text{MgCl}_2(\text{s}))$ ,

$\Delta H^\ominus_{\text{sol}} =$ ....................................... $\text{kJ mol}^{-1}$

(ii)

$\Delta H^\ominus_{\text{hyd}}(\text{Cl}^-(\text{g}))$ .

$\Delta H^\ominus_{\text{hyd}} =$ ....................................... $\text{kJ mol}^{-1}$

(d)

Describe and explain how the solubility of magnesium sulfate compares to that of barium sulfate.

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7 more questions

Q2Introduction to A Level Organic Chemistry · Hydrocarbons · Transition Elements · Chemical Energetics · Reaction Kinetics15M
Q3Introduction to A Level Organic Chemistry · Hydroxy Compounds · Electrochemistry · Hydrocarbons · Carboxylic Acids and Derivatives14M
Q4Chemical Energetics9M
Q5Carboxylic Acids and Derivatives · Nitrogen Compounds · Halogen Compounds · Introduction to A Level Organic Chemistry · Polymerisation16M
Q6Nitrogen Compounds · Transition Elements · Chemical Energetics10M
Q7Analytical Techniques10M
Q8Introduction to A Level Organic Chemistry · Carboxylic Acids and Derivatives · Nitrogen Compounds · Hydroxy Compounds10M

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