AS & A Level Chemistry - 9701 Paper 4 2024 Summer Zone 1

(a) (i) Describe the trend in the solubility of the hydroxides of magnesium, calcium and strontium.
Explain your answer.
........................................ > ........................................ > ........................................
most soluble least soluble
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(ii) Suggest the variation in pH of saturated solutions of the hydroxides of magnesium, calcium and strontium.
Explain your answer.
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(b) Barium hydroxide, Ba(OH)_{2}, is a strong base.
A 250.0 cm^3 solution of Ba(OH)_{2} with a pH of 12.2 is made by dissolving Ba(OH)_{2} in distilled water.
Calculate the mass of Ba(OH)_{2} required to make this solution.
Show your working.
[M_{r}: Ba(OH)_{2}, 171.3]
mass of Ba(OH)_{2} = .............................. g [4]

(c) The solubility of iron(II) hydroxide, Fe(OH)_{2}, is 5.85 \times 10^{-6} mol dm^{-3} at 298 K.
(i) Write the expression for the solubility product, K_{sp}, of Fe(OH)_{2}.
$K_{sp} = $
[1]

(ii) Calculate the value of $K_{sp}$ of Fe(OH)_{2}. Include its units.
$K_{sp} = ..............................$
units = .............................. [2]

(a) (i) Define transition element.
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(a) (ii) Explain why transition elements can form complex ions.
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(b) The 3d orbitals in an isolated $Ag^+$ ion are degenerate.
(i) Define degenerate d orbitals.
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(b) (ii) Sketch the shape of a $3d_{xy}$ orbital in Fig. 2.1.


(c) Tollens’ reagent can be used to distinguish between aldehydes and ketones. Tollens’ reagent contains $[Ag(NH_3)_2]OH$, which can be prepared in a two-step process.

step 1 Aqueous $NaOH$ is added dropwise to aqueous $AgNO_3$ to form $Ag_2O$ as a brown precipitate.
step 2 Aqueous $NH_3$ is added dropwise to $Ag_2O$ to form a colourless solution containing $[Ag(NH_3)_2]OH$.

Construct equations for each of the steps in the preparation of $[Ag(NH_3)_2]OH$.
step 1 ......................................................................................................................................................
step 2 ......................................................................................................................................................

(d) Name the shape of the complex ion $[Ag(NH_3)_2]^+$.
State the bond angle for H-N-Ag and for N-Ag-N.

shape .......................................................................................................................................
bond angle for H-N-Ag = .............
bond angle for N-Ag-N = .............

(e) An electrochemical cell uses $Ag_2O$ as the positive electrode and $Zn$ as the negative electrode immersed in an alkaline electrolyte.

The overall cell reaction is shown.
$$Ag_2O + Zn + H_2O \rightarrow 2Ag + Zn(OH)_2$$

Complete the half-equation for the reaction at each electrode.
at the positive electrode $Ag_2O +$ ..............................................................
at the negative electrode $Zn +$ ..............................................................

(f) Coordination polymers are made when a bidentate ligand acts as a bridge between different metal ions.
Under certain conditions $Ru^{3+}(aq)$ and the bidentate ligand dps can form a coordination polymer containing $([Ru(dps)Cl_4^-])_n$ chains.

The bidentate ligand dps uses each of the nitrogen atoms to bond to a different $Ru^{3+}$.
Complete Fig. 2.3 by drawing the structure for the coordination polymer $([Ru(dps)Cl_4^-])_n$. Show two repeat units.
The dps ligand can be represented using \[ \text{N} \quad \text{N} \].

(a) When a sample of hydrated lithium ethanedioate, $\text{Li}_2\text{C}_2\text{O}_4 \cdot \text{H}_2\text{O}$, is gently heated, two gaseous products are formed and a white solid residue remains.
The residue is added to $\text{HNO}_3(aq)$. A gas is produced that turns limewater milky.
Complete the equation for the decomposition of $\text{Li}_2\text{C}_2\text{O}_4 \cdot \text{H}_2\text{O}$.

$\text{Li}_2\text{C}_2\text{O}_4 \cdot \text{H}_2\text{O} \rightarrow$ .............................. + .............................. + ..............................

(b) The trend in the decomposition temperatures of the Group 2 ethanedioates is similar to that of the Group 2 nitrates.
Suggest which of $\text{CaC}_2\text{O}_4$ and $\text{BaC}_2\text{O}_4$ will decompose at the \textit{lower} temperature. Explain your answer.
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(c) Potassium iron(III) ethanedioate, $\text{K}_3[\text{Fe}(\text{C}_2\text{O}_4)_3]$, dissolves in water to form a green solution.
Explain why transition elements can form coloured complexes.
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(d) The anhydrous iron(III) compound $\text{K}_3[\text{Fe}(\text{C}_2\text{O}_4)_3]$ decomposes on heating to form a mixture of $\text{K}_2[\text{Fe}(\text{C}_2\text{O}_4)_2]$, $\text{K}_2\text{C}_2\text{O}_4$ and $\text{CO}_2$.
Complete the equation for the decomposition of $\text{K}_3[\text{Fe}(\text{C}_2\text{O}_4)_3]$.
............ $\text{K}_3[\text{Fe}(\text{C}_2\text{O}_4)_3] \rightarrow$ ............ $\text{K}_2[\text{Fe}(\text{C}_2\text{O}_4)_2]$ + ............ $\text{K}_2\text{C}_2\text{O}_4$ + ............ $\text{CO}_2$

(e) The $[\text{Fe}(\text{C}_2\text{O}_4)_3]^{3-}$ complex ion shows stereoisomerism.
Complete the three-dimensional diagrams in Fig. 3.1 to show the \textbf{two} stereoisomers of $[\text{Fe}(\text{C}_2\text{O}_4)_3]^{3-}$.
The $\text{C}_2\text{O}_4^{2-}$ ligand can be represented using $\circ$ $\circ$.

[Image of Fig. 3.1 with isomer 1 and isomer 2]

(f) Buffer solutions are used to regulate pH.
Write \textbf{two} equations to describe how a solution containing $\text{HC}_2\text{O}_4^-$ ions acts as a buffer solution when small amounts of acid or alkali are added.
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(g) A fuel cell is an electrochemical cell that can be used to generate electrical energy by using oxygen to oxidise a fuel.
Ethanedioic acid, $(\text{COOH})_2$, dissolved in an alkaline electrolyte is being investigated as a fuel.
The relevant standard electrode potentials, $E^\circ$, for the cell are shown.

$\text{O}_2(g) + 2\text{H}_2\text{O}(l) + 4e^- \rightleftharpoons 4\text{OH}^-(aq)$ \hspace{10pt} $E^\circ = +0.40 \, \text{V}$
$2\text{CO}_2(g) + 2e^- \rightleftharpoons \text{C}_2\text{O}_4^{2-}(aq)$ \hspace{20pt} $E^\circ = -0.59 \, \text{V}$

Use these equations to deduce the overall cell reaction. Calculate the value of $E_\text{cell}^\circ$.

overall cell reaction ..................................................................................................................

$E_\text{cell}^\circ = .................................... \text{V}$

(a) Define standard electrode potential, $E^\text{o}$, including a description of standard conditions.

(b) (i) An electrochemical cell is set up to measure $E^\text{o}$ of the $\text{Ag}^+\text{(aq)}/\text{Ag(s)}$ electrode.
Draw a labelled diagram of this electrochemical cell. Include all necessary substances. It is not necessary to state conditions used.

(b) (ii) A separate electrochemical cell is set up using a lower concentration of $\text{Ag}^+\text{(aq)}$ than that used in (b)(i).
Suggest how the electrode potential, $E$, for the $\text{Ag}^+\text{(aq)}/\text{Ag(s)}$ electrode would change from its $E^\text{o}$ value. Explain your answer.

(c) Define enthalpy change of solution, $\Delta H^\text{o}_\text{sol}$.

(d) Some relevant energy changes for $\text{AgNO}_3$ are shown in Table 4.1.
[Table_1]
(i) Complete the energy cycle in Fig. 4.1 to show the relationship between the lattice energy, $\Delta H^\text{o}_\text{latt}$, of $\text{AgNO}_3\text{(s)}$ and the energy changes shown in Table 4.1. Include state symbols for all the species.


(d) (ii) Calculate the lattice energy, $\Delta H^\text{o}_\text{latt}$, of $\text{AgNO}_3\text{(s)}$.
$\Delta H^\text{o}_\text{latt}$ = ..................... $\text{kJ mol}^{-1}$

(e) Suggest the trend in the magnitude of the lattice energies of the metal nitrates, $\text{NaNO}_3\text{(s)}$, $\text{Mg(NO}_3)_2\text{(s)}$ and $\text{RbNO}_3\text{(s)}$. Explain your answer.
........................................... most exothermic ............................................. least exothermic

(a) In aqueous solution, persulfate ions, $S_2O_8^{2-}$, react with iodide ions, as shown in reaction 1.

reaction 1 $S_2O_8^{2-} + 2I^- \rightarrow 2SO_4^{2-} + I_2$

The rate of reaction 1 is investigated. A sample of $S_2O_8^{2-}$ is mixed with a large excess of iodide ions of known concentration. The graph in Fig. 5.1 shows the results obtained.



(i) Use Fig. 5.1 to determine the initial rate of reaction 1. Show your working.

$\text{rate} = \text{.......................... moldm}^{-3}\text{min}^{-1}$ [1]

(ii) The rate equation for reaction 1 is rate = $k [S_2O_8^{2-}] [I^-]$.

Suggest why a large excess of iodide ions allows the rate constant to be determined from the half-life in this investigation.

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[1]

(b) The reaction of persulfate ions, $S_2O_8^{2-}$, with iodide ions is catalysed by $Fe^{2+}$ ions.

Write two equations to show how $Fe^{2+}$ catalyses reaction 1.

equation 1 .........................................................................................................................................
equation 2 ..........................................................................................................................................
[2]

(c) Describe the effect of an increase in temperature on the rate constant and the rate of reaction 1.

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[1]

(d) In aqueous solution, thiosulfate ions, $S_2O_3^{2-}$, react with hydrogen ions, as shown in reaction 2.

reaction 2 $S_2O_3^{2-} + 2H^+ \rightarrow SO_2 + S + H_2O$

The rate of reaction is first order with respect to $[S_2O_3^{2-}]$ and zero order with respect to $[H^+]$ under certain conditions.

The rate constant, $k$, for this reaction is $1.58 \times 10^{-2} s^{-1}$.

Calculate the half-life, $t_{\frac{1}{2}}$, for reaction 2.

$t_{\frac{1}{2}}$ = .............................. s [1]

(e) The compound nitrosyl bromide, NOBr, can be formed as shown in reaction 3.

reaction 3 $2NO(g) + Br_2(g) \rightarrow 2NOBr(g)$

The rate is first order with respect to $[NO]$ and first order with respect to $[Br_2]$.

The reaction mechanism has two steps.

Suggest equations for the two steps of this mechanism. State which is the rate-determining step.

step 1 ...........................................................................................................................................................
step 2 ...........................................................................................................................................................
rate-determining step = ..................................
[2]

(a) (i) State what is meant by partition coefficient, $K_{pc}$.
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(ii) The partition coefficient, $K_{pc}$, for a compound, $X$, between carbon disulfide, CS$_2$, and water is 10.5.
1.85 g of $X$ is dissolved in water and made up to 100.0 cm$^3$ in a volumetric flask.
40.0 cm$^3$ of this aqueous solution is shaken with 25.0 cm$^3$ of CS$_2$.
The mixture is left to reach equilibrium.
Calculate the mass of $X$, in g, extracted into the CS$_2$ layer.
mass of $X$ = .............................. g [2]

(b) The compound C$_6$H$_6$ has many structural isomers. Four suggested structures of C$_6$H$_6$ are shown in Fig. 6.1.

Kekulé benzene Dewar benzene Ladenburg benzene delocalised benzene


Using Fig. 6.1, complete Table 6.1 to predict the number of carbon atoms that have sp, sp$^2$ and sp$^3$ hybridisation in Kekulé benzene, Dewar benzene and Ladenburg benzene.

[Table_1]

Table 6.1
C$_6$H$_6$ structure | sp hybridised | sp$^2$ hybridised | sp$^3$ hybridised
Kekulé benzene
Dewar benzene
Ladenburg benzene
[2]

(c) Describe the shape of delocalised benzene.
Include the geometry of each carbon, the C-C-H bond angle and the type of bond(s) between the carbon atoms and between the carbon and hydrogen atoms.
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(d) Suggest why Dewar benzene and Ladenburg benzene are unstable isomers of C$_6$H$_6$.
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(e) Complete Table 6.2 to predict the number of peaks in the proton (¹H) NMR spectrum for Dewar benzene, Ladenburg benzene and delocalised benzene.
[Table_2]

Table 6.2
number of peaks
Dewar benzene
Ladenburg benzene
delocalised benzene
[1]

(f) The reaction of phenylethanone with 1,4-dibromobutane, BrCH$_2$CH$_2$CH$_2$CH$_2$Br, in the presence of FeBr$_3$ is shown in Fig. 6.2.



The mechanism of this reaction is similar to that of the alkylation of benzene.

(i) Construct an equation for the formation of the electrophile, BrCH$_2$CH$_2$CH$_2$CH$_2^+$.
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(ii) Complete the mechanism in Fig. 6.3 for the reaction of phenylethanone with BrCH$_2$CH$_2$CH$_2$CH$_2^+$ ions.
Include all relevant curly arrows and charges.
Draw the structure of the organic intermediate.


+ ............... [3]

(iii) The reaction shown in Fig. 6.2 forms small amounts of two by-products, $Y$ (C$_{20}$H$_{22}$O$_2$) and $Z$ (C$_{12}$H$_{14}$O).
Suggest structures for $Y$ and $Z$ in the boxes in Fig. 6.4.

[2]

Four esters, A, B, C and D, with the molecular formula C$_6$H$_{12}$O$_2$, are shown in Fig. 7.1.


(a) Give the systematic name of ester A.
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(b) A mixture of these esters, A, B, C and D, is analysed by gas–liquid chromatography.
The chromatogram produced is shown in Fig. 7.2. The number above each peak represents the area under the peak.
The area under each peak is proportional to the mass of the respective ester in the mixture.


(i) State what is meant by retention time.
.............................................................................................................................................. [1]

(ii) Calculate the percentage by mass of ester D in the original mixture.

percentage by mass of ester D = ................................. % [1]

(c) Separate samples of the esters, A, B, C and D, are analysed using proton ($^1$H) NMR and carbon-13 NMR spectroscopy.

(i) Complete Table 7.1 to show the number of peaks in each NMR spectrum for esters B and C.
[Table_1]

| ester | number of peaks in proton ($^1$H) NMR spectrum | number of peaks in carbon-13 NMR spectrum |
|-------|----------------------------------------------|------------------------------------------|
| B | | |
| C | | |

[2]

(ii) Identify all of the esters from A, B, C and D that have at least one triplet peak in their proton ($^1$H) NMR spectrum.
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(d) Compound F, C$_6$H$_8$O$_3$, shows stereoisomerism and effervesces with Na$_2$CO$_3$(aq).
Compound F reacts with alkaline I$_2$(aq) to form yellow precipitate G and compound H.
Compound F reacts with LiAlH$_4$ to form compound J, C$_6$H$_{12}$O$_2$.
Compound F reacts with SOCl$_2$ to form compound K, C$_6$H$_7$O$_2$Cl.
Compound K reacts with propan-2-ol to form compound L.
Draw the structures of compounds F, G, H, J, K and L in the boxes in Fig. 7.3.

[6]

Neotame is an artificial sweetener added to some foods.
[Image_1: Neotame structure]
(a) (i) State the number of chiral carbon atoms in a molecule of neotame.
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(ii) Neotame contains the arene functional group.
Identify all the other functional groups present in neotame.
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(b) Neotame reacts with an excess of hot NaOH(aq) to form three organic products.
(i) State the two types of reaction that occur when neotame reacts with hot NaOH(aq).
1 ..................................................................................................................................................
2 .................................................................................................................................................. [2]
(ii) Draw the structures of the three organic products formed from the reaction of neotame with an excess of hot NaOH(aq).
[Image placeholders for product structures] [3]

(a) Samples of phenol, $C_6H_5OH$, are reacted separately with sodium and with dilute nitric acid.
[Image_1: phenol structure]
Fig. 9.1
(i) Write the equation for the reaction of $C_6H_5OH$ with Na.
......................................................................................................................... [1]
(ii) Draw the structures of the two major isomeric organic products formed in the reaction of phenol with dilute $HNO_3$.
[Two boxes for drawing structures] [1]

(b) Salicylic acid can be synthesised from phenol.
[Image_2: salicylic acid structure]
Fig. 9.2
One of the steps in this synthesis is the electrophilic substitution reaction of carbon dioxide with the phenoxide ion, $C_6H_5O^-$.
Complete the mechanism in Fig. 9.3 for the reaction of $C_6H_5O^-$ with $CO_2$.
Include all relevant curly arrows, dipoles and charges. Draw the structure of the organic intermediate.
[Image_3: reaction diagram with organic intermediate box] [3]

(c) Some syntheses use Diels–Alder reactions, which normally involve a diene and an alkene reacting together to form a cyclohexene.
(i) Draw three curly arrows in Fig. 9.4 to complete the mechanism for the Diels–Alder reaction between buta-1,3-diene and ethene.
[Image_4: reaction diagram for cyclohexene] Fig. 9.4 [1]
(ii) Another Diels–Alder reaction of buta-1,3-diene is shown in Fig. 9.5.
Predict the product formed in this reaction.
[Image_5: reaction with product prediction box] Fig. 9.5 [1]