AS & A Level Chemistry - 9701 Paper 2 2024 Winter Zone 3

Cobalt, rhodium and iridium are metals in the same group of the Periodic Table.
(a) The shorthand electronic configuration of cobalt is [Ar]3d^7 4s^2.
(i) Identify what is meant by [Ar] by giving its full electronic configuration.
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(ii) The lowest-energy electrons in cobalt are in the 1s orbital.
Draw the shape of a 1s orbital. [1]
(iii) Deduce the number of unpaired electrons in a cobalt atom.
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(b) Table 1.1 gives some details of the stable naturally occurring isotopes of rhodium and iridium.

Table 1.1
| isotope | number of protons | number of neutrons | total number of electron shells |
| --- | --- | --- | --- |
| ^{103}_{45}Rh | 58 | | |
| ^{191}_{77}Ir | | | 6 |
| ^{193}_{77}Ir | | | 6 |

Complete Table 1.1. [3]

(c) Table 1.2 shows the relative abundances of isotopes in a sample of an alloy containing rhodium and iridium only.

Table 1.2
| isotope | relative isotopic mass | relative abundance in alloy |
| --- | --- | --- |
| ^{103}_{45}Rh | 102.91 | 50.00 |
| ^{191}_{77}Ir | 190.96 | 15.18 |
| ^{193}_{77}Ir | 192.96 | 34.82 |

(i) Define relative isotopic mass.
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(ii) Use Table 1.2 to calculate the relative atomic mass, A_r, of iridium in the alloy.
Give your answer to two decimal places.
relative atomic mass of iridium = ...................................... [2]

(d) Hydrated rhodium(III) chloride, RhCl_3·xH_2O, catalyses the conversion of ethene to but-2-ene.
Both stereoisomers of but-2-ene are formed in the reaction.
(i) Hydrated rhodium(III) chloride contains 20.5% by mass of water of crystallisation.
Deduce the integer value of x in RhCl_3·xH_2O.
Show your working.
x = ............................................. [2]
(ii) Define stereoisomers.
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(iii) Explain how the conversion of ethene to but-2-ene can be described as an addition reaction.
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(iv) Draw the two stereoisomers of but-2-ene.

[2]

Chlorine is one of the elements in Group 17 of the Periodic Table.

(a) (i) Describe the colours of the Group 17 elements, chlorine to iodine, at room temperature.
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(ii) Describe the relative reactivity of the elements chlorine to iodine as oxidising agents.
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(iii) State what is observed when chlorine reacts with hydrogen.
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(iv) Explain why the thermal stability of the hydrogen halides decreases down the group.
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(b) The halogenoalkane CH$_3$CH$_2$Cl forms when chlorine reacts with C$_2$H$_6$ via a free-radical substitution mechanism.

(i) Define free radical.
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(ii) State the essential condition for chlorine to react with C$_2$H$_6$ at room temperature.
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(iii) Write two equations to show the propagation steps in this reaction.
1 ..................................................................................................................................................................
2 .................................................................................................................................................................. [2]

(c) CHCl$_3$ is another halogenoalkane. CHCl$_3$ forms when propanone reacts with NaClO. NaClO is made from chlorine in a disproportionation reaction.

(i) Identify a reagent and conditions that can be used to convert chlorine to NaClO.
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(ii) Define disproportionation.
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(iii) Write numbers in the boxes to balance the equation showing the reaction of propanone with NaClO.
$$\text{CH}_3\text{COCH}_3 + \square \text{NaClO} \rightarrow \square \text{CHCl}_3 + \square \text{CH}_3\text{COONa} + \square \text{NaOH}$$ [1]

(iv) Aqueous AgNO$_3$ dissolved in ethanol reacts with an aqueous solution of CHCl$_3$. State what is observed in this reaction. Explain your answer.
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(a) Table 3.1 shows some properties of two Group 14 elements, C and Sn, in their standard states. The table is incomplete.

\begin{center} Table 3.1 \end{center}
\begin{tabular}{|c|c|c|} \hline & \textbf{C (graphite)} & \textbf{Sn} \\ \hline \textbf{state and appearance in standard state} & grey shiny solid & silvery solid \\ \hline \textbf{electrical conductivity} & & good \\ \hline \textbf{type of bonding} & & metallic \\ \hline \textbf{type of structure} & giant & \\ \hline \end{tabular}

(i) Complete Table 3.1. [3]
(ii) Identify the lattice structure shown by graphite. [1]
(iii) Explain why Sn has good electrical conductivity. [1]

(b) Carbon is found in inorganic compounds such as carbonates.
(i) Write an equation for the reaction of magnesium carbonate with dilute HCl(aq). [1]
(ii) Describe the thermal stability of the carbonates down Group 2. [1]
(iii) Ammonium carbonate undergoes an acid–base reaction with NaOH(aq). Explain this statement. [2]

(c) Fig. 3.1 shows a sketch of some of the ionisation energies of silicon, Si.

(i) Complete the graph in Fig. 3.1 to show the third to sixth ionisation energies of Si. [2]
(ii) Construct an equation to represent the second ionisation energy of Si. [1]

(d) Fig. 3.2 shows the boiling points of the simplest hydrides of the Group 14 elements, C to Pb.

(i) Explain the trend in the boiling points of the Group 14 hydrides shown in Fig. 3.2. [2]
(ii) Deduce the shape of a molecule of SiH₄. [1]

(e) Silicon readily reacts with elements of high electronegativity.
(i) Write an equation for the formation of SiCl₄ from its constituent elements. [1]
(ii) Describe what is observed when a small sample of SiCl₄ is added to water. [1]
(iii) SiO₂ is a white solid that melts above 1700°C. SiCl₄ is a colourless liquid at room temperature. Explain the difference in the melting points of these two compounds with reference to their structure and bonding. [2]

(f) Tin forms an amphoteric oxide, SnO₂. Suggest the formula of the tin compound that forms when SnO₂ reacts with H₂SO₄ in an acid–base reaction. [1]

Propanone, $\text{CH}_3\text{COCH}_3$, is an important organic reagent. Fig. 4.1 shows some reactions of propanone and its derivatives.


(a) Reaction 1 is a nucleophilic addition reaction.
(i) Complete Fig. 4.2 to show the mechanism for the formation of A from propanone.
Include charges, dipoles, lone pairs of electrons and curly arrows as appropriate.

[3]
(ii) Explain why A does not show optical isomerism.
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(b) Suggest the reagents and conditions for reaction 2.
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(c) Reaction 3 is a reduction reaction.
(i) Construct an equation to represent reaction 3.
Use [H] to represent one atom of hydrogen from the reducing agent.
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(ii) Name C.
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(d) State what is observed in reaction 4.
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(e) Explain why Fehling’s reagent does not react with propanone.
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(f) Compounds A, B and C can be distinguished using infrared spectroscopy.

Fig. 4.3 shows the infrared spectrum of one of the compounds.

[Table_1]

(i) Explain why the absorptions at 2850–2950 $\text{cm}^{–1}$ are not useful to help determine which of the compounds A, B or C produces the infrared spectrum in Fig. 4.3.
Use Table 4.1 to answer this question.
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(ii) Identify which of compounds A, B or C produces the infrared spectrum in Fig. 4.3. Explain your answer.
compound ......................................
explanation ......................................
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