AS & A Level Chemistry - 9701 Paper 2 2022 Summer Zone 2

(a) Magnesium has a melting point of 650°C and high electrical conductivity.
Explain these properties of magnesium by referring to its structure and bonding.
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(b) When magnesium is heated in air, magnesium oxide, MgO, is the major product. Smaller amounts of magnesium nitride, Mg_{3}N_{2}, are also made.

(i) Calculate the oxidation number for magnesium and for the nitrogen species in Mg_{3}N_{2} to complete Table 1.1.

Table 1.1

| species | magnesium in Mg_{3}N_{2} | nitrogen in Mg_{3}N_{2} |
|-----------------------|--------------------------|------------------------|
| oxidation number | | |
[1]

(ii) Identify the type of reaction which takes place between magnesium and nitrogen. Explain your answer.
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(iii) Define enthalpy change of formation.
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(iv) When 3.645 g of Mg(s) burns in excess N_{2}(g) to form Mg_{3}N_{2}(s), 23.05 kJ of energy is released.
Calculate the enthalpy change of formation, ΔH_{f}, of Mg_{3}N_{2}. Show your working.

ΔH_{f} (Mg_{3}N_{2}) = .................................................. [3] [Total: 9]

Radium, Ra, is an element found in Group 2 of the Periodic Table. It is a crystalline solid at room temperature and conducts electricity.
Radium chloride, RaCl₂, has a melting point of 900°C and is soluble in water.
(a) Predict the lattice structure of RaCl₂(s) based on the properties described.
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(b) Draw a dot-and-cross diagram to show the arrangement of outer electrons in RaCl₂.
[1]
(c) Solid Ra and Ca show similar reactions with H₂O, but the reactions occur at different rates.
Separate samples, each containing a single piece of solid Ra or Ca, are added to equal volumes of cold water.
Each sample contains equal numbers of moles of solid and the H₂O is in excess.
(i) Construct an equation for the reaction of Ra with H₂O.
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(ii) Identify which element, Ra or Ca, reacts with H₂O at a faster rate. Suggest how the observations of each reaction would differ.
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(iii) Suggest why these reactions occur at different rates.
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(iv) One of the solutions is cloudy when the reaction has finished.
At the end of each reaction, universal indicator is added to each reaction mixture.
Suggest pH values of the solutions made in both reactions. Explain your answer.
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(d) A sample of aqueous calcium halide, CaX₂(aq), contains either chloride, bromide or iodide ions.
Complete Table 2.1 to describe a two-step process that could be used to identify the halide ion present.
[Table_1]
[3]
[Total: 11]

(a) 0.025 mol of HI(g) is added to a closed vessel and left to reach dynamic equilibrium. The total pressure of the vessel is 100 kPa.
equation 1 $2\text{HI}(g) \rightleftharpoons \text{H}_2(g) + \text{I}_2(g)$
(i) Explain what is meant by dynamic equilibrium.
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(ii) Describe one difference in the initial appearance of the reaction mixture compared to the mixture at equilibrium.
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(iii) Write an expression for $K_p$ for the reaction described in equation 1.
$K_p =$ .............................................................................................................................. [1]
(iv) At equilibrium the partial pressure of HI(g) is 86.4 kPa.
Calculate the amount of HI(g) present in the mixture at equilibrium. Show your working.
amount of HI(g) = ext{............................} mol [2]

(b) Use equation 1 and the bond energy values in Table 3.1 to calculate the change in enthalpy, $\Delta H$, for the thermal decomposition of 1 mole of HI(g). Show your working.
[Table_1]
$\Delta H = \text{............................} \text{kJ mol}^{-1}$ [2]

(c) Describe the effect of increasing pressure on the value of $K_p$ for the decomposition of HI(g).
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(d) HCl(g) is prepared by adding NaCl(s) to concentrated $\text{H}_2\text{SO}_4$.
HI(g) is \textit{not} prepared by adding NaI(s) to concentrated $\text{H}_2\text{SO}_4$ because the HI(g) produced also reacts with concentrated $\text{H}_2\text{SO}_4$.
(i) Identify the type of reaction that occurs when NaI(s) reacts with concentrated $\text{H}_2\text{SO}_4$ to form HI(g).
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(ii) Write an equation for the reaction of HI(g) and concentrated $\text{H}_2\text{SO}_4$.
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(iii) Explain why HI(g) reacts with concentrated $\text{H}_2\text{SO}_4$ whereas HCl does not.
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(a) Bromine reacts with butane in the presence of ultraviolet light to form bromobutane.
Two structural isomers with the molecular formula $C_4H_9Br$ are produced during this reaction.
(i) Draw the two structural isomers and state the systematic name of each isomer.
[Image_1: structural isomer 1]
name ................................................
[Image_2: structural isomer 2]
name ................................................ [2]
(ii) Identify the type of structural isomerism shown in (a)(i).
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(b) Halothane is an anaesthetic.
[Image_3: halothane diagram]
Fig. 4.1
(i) Identify the chiral centre in halothane and mark it with an asterisk (*). [1]
When halothane reacts in ultraviolet light, homolytic fission occurs and the $\text{C}−\text{Br}$ bond is broken.
(ii) Construct an equation to show the homolytic fission of halothane, $CF_3CHBrCl$.
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(b) (iii) Complete Fig. 4.2 to show the arrangement of electrons in a bromine atom using the electrons in boxes notation.
[Image_4: electron configuration diagram]
Fig. 4.2 [1]

(c) X is an addition polymer.
[Image_5: polymer diagram]
Fig. 4.3
(i) Draw the monomer of X.
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(ii) Suggest one reason why the disposal of items made from X is difficult.
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(a) Complete Table 5.1 for each reaction, by:
• stating the reagent and conditions used
• identifying the type of reaction that occurs.

Table 5.1
[Table_1]

(b) A sample of 2-iodopropane, CH₃CH(I)CH₃, reacts under the same conditions as reaction 1 to produce CH₃CH(OH)CH₃.

Explain why 2-iodopropane reacts at a faster rate than 2-bromopropane.
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(c) Fig. 5.2 shows how butan-1-ol can be made from 1-bromopropane in three steps.

(i) In step 1, 1-bromopropane reacts with CN\textsuperscript{-} to form butanenitrile.
Complete Fig. 5.3 to show the mechanism for step 1. Include charges, dipoles, lone pairs of electrons and curly arrows as appropriate.


(ii) In step 2, butanenitrile is heated with HCl(aq). A hydrolysis reaction occurs.
Construct an equation for the reaction in step 2.
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(iii) Step 3 is a reduction reaction.
Construct an equation for the reduction reaction in step 3. Use [H] to represent one atom of hydrogen from the reducing agent.
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(iv) State the identity of a suitable reducing agent in step 3.
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Z is a molecule which contains the elements carbon, hydrogen and oxygen only.
Z contains only alkene and carboxyl functional groups.

(a) Complete Table 6.1 by describing the observations that occur when two different reagents are added to separate samples of Z(aq).

Table 6.1
\[\begin{array}{|c|c|}\hline \text{reagent added to Z(aq)} & \text{observation} \\ \hline Br_2(aq) & \\ \hline Na_2CO_3(s) & \\ \hline \end{array}\]
[2]

(b) Table 6.2 shows the percentage by mass of each element present in Z.

Table 6.2
\[\begin{array}{|c|c|}\hline \text{element} & \text{percentage by mass / %} \\ \hline \text{carbon} & 41.38 \\ \hline \text{hydrogen} & 3.45 \\ \hline \text{oxygen} & 55.17 \\ \hline \end{array}\]
Using the data in Table 6.2, demonstrate that the empirical formula of Z is CHO. Show your working.
[1]

(c) Fig. 6.1 shows the mass spectrum of Z.



Fig. 6.1
(i) Deduce the molecular formula of Z. Explain your answer by referring to the molecular ion peak in Fig. 6.1 and the empirical formula of Z.
[1]

(ii) Use Fig. 6.1 to suggest the formulae of the fragments with \(m/e\) peaks at 45 and at 71.
\(m/e\) 45 ..........................................................................................................................
\(m/e\) 71 ..........................................................................................................................
[2]

(iii) Suggest the structure of Z using relevant information from Table 6.1, (b) and (c).
[1]

[Total: 7]