A Level Chemistry 9701 Paper 41, May/June 2023

Group 2 nitrates decompose when heated. Describe how the thermal stability of Group 2 nitrates changes with increasing proton number. Explain your answer.

Copper(II) nitrate decomposes in a similar manner to Group 2 nitrates. Write an equation for the decomposition of $\mathrm{C}\mathrm{u}(\mathrm{N}{\mathrm{O}}_3{)}_2$.

$\mathrm{C}\mathrm{u}(\mathrm{N}{\mathrm{O}}_3{)}_2$ is added to water to form solution A. Fig. 1.1 shows some reactions of solution A. Complete Table 1.1 to show the formula and colour of each of the copper-containing species present in A, B, C and D.

${\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}}^{4-}$ is a polydentate ligand. Explain what is meant by a polydentate ligand.

Group 2 metal ions can form complexes similar to those of transition elements. A solution of ${\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}}^{4-}$ is added to water containing $[\mathrm{C}\mathrm{a}({\mathrm{H}}_2\mathrm{O}{)}_6{]}^{2+}$ to form a new complex, $[\mathrm{C}\mathrm{a}\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}{]}^{2-}$, as shown. equilibrium 1 $[\mathrm{C}\mathrm{a}({\mathrm{H}}_2\mathrm{O}{)}_6{]}^{2+}+{\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}}^{4-}\rightleftharpoons [\mathrm{C}\mathrm{a}\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}{]}^{2-}+6{\mathrm{H}}_2\mathrm{O}$ Circle on the structure of ${\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}}^{4-}$ in Fig. 1.2 the six atoms that form bonds with the metal ion.

The calcium ions in $[\mathrm{C}\mathrm{a}({\mathrm{H}}_2\mathrm{O}{)}_6{]}^{2+}$ and $[\mathrm{C}\mathrm{a}\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}{]}^{2-}$ have a coordination number of 6. Explain what is meant by coordination number.

The complex $[\mathrm{C}\mathrm{a}\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}{]}^{2-}$ can be used to remove toxic metals from the body. Table 1.2 shows the numerical values for the stability constants, $K_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{b}}$, for some metal ions with ${\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}}^{4-}$. An aqueous solution containing $[\mathrm{C}\mathrm{a}\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}{]}^{2-}$ is added to a solution containing equal concentrations of $\mathrm{C}{\mathrm{r}}^{3+}(\mathrm{a}\mathrm{q})$, $\mathrm{F}{\mathrm{e}}^{3+}(\mathrm{a}\mathrm{q})$ and $\mathrm{P}{\mathrm{b}}^{2+}(\mathrm{a}\mathrm{q})$. The resulting mixture is left to reach a state of equilibrium. State the type of reaction when $[\mathrm{C}\mathrm{a}\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}{]}^{2-}$ reacts with $\mathrm{C}{\mathrm{r}}^{3+}(\mathrm{a}\mathrm{q})$, $\mathrm{F}{\mathrm{e}}^{3+}(\mathrm{a}\mathrm{q})$ and $\mathrm{P}{\mathrm{b}}^{2+}(\mathrm{a}\mathrm{q})$.

Deduce the relative concentrations of $[\mathrm{C}\mathrm{r}\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}{]}^{-}$, $[\mathrm{F}\mathrm{e}\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}{]}^{-}$ and $[\mathrm{P}\mathrm{b}\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}{]}^{2-}$ present in the resulting mixture. Explain your answer. .......................................... > .......................................... > .......................................... highest concentration lowest concentration

The number of moles of water of crystallisation in a hydrated ionic salt can be determined by titration using aqueous ${\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}}^{4-}$ ions with a suitable indicator. • 0.255 g of hydrated chromium(III) sulfate, $\mathrm{C}{\mathrm{r}}_2(\mathrm{S}{\mathrm{O}}_4{)}_3\cdot n{\mathrm{H}}_2\mathrm{O}$, is dissolved in water and made up to $100{\mathrm{c}\mathrm{m}}^3$ in a volumetric flask. • $25.0{\mathrm{c}\mathrm{m}}^3$ of this solution requires $26.2{\mathrm{c}\mathrm{m}}^3$ of $0.00800\mathrm{m}\mathrm{o}\mathrm{l}{\mathrm{d}\mathrm{m}}^{-3}$ aqueous ${\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}}^{4-}$ ions to reach the end-point. The reaction occurs as shown. $[\mathrm{C}\mathrm{r}({\mathrm{H}}_2\mathrm{O}{)}_6{]}^{3+}+{\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}}^{4-}\to [\mathrm{C}\mathrm{r}\mathrm{E}\mathrm{D}\mathrm{T}\mathrm{A}{]}^{-}+6{\mathrm{H}}_2\mathrm{O}$ Use the data to calculate the value of $n$ in the formula of $\mathrm{C}{\mathrm{r}}_2(\mathrm{S}{\mathrm{O}}_4{)}_3\cdot n{\mathrm{H}}_2\mathrm{O}$. Show your working.

A solution of $\mathrm{C}{\mathrm{r}}^{3+}(\mathrm{a}\mathrm{q})$ and a solution of $\mathrm{F}{\mathrm{e}}^{3+}(\mathrm{a}\mathrm{q})$ have different colours. Explain why the two complexes have different colours.

Some transition element complexes can show stereoisomerism. State two types of stereoisomerism shown by transition element complexes. 1 ................................................................................................................................ 2 ................................................................................................................................

The complexes $[\mathrm{P}\mathrm{t}(\mathrm{N}{\mathrm{H}}_3{)}_2\mathrm{C}{\mathrm{l}}_2]$ and $[\mathrm{P}\mathrm{t}(\mathrm{e}\mathrm{n}{)}_2{]}^{2+}$ have the same geometry (shape) around the metal ion. $[\mathrm{P}\mathrm{t}(\mathrm{N}{\mathrm{H}}_3{)}_2\mathrm{C}{\mathrm{l}}_2]$ exists as two stereoisomers whereas $[\mathrm{P}\mathrm{t}(\mathrm{e}\mathrm{n}{)}_2{]}^{2+}$ only has one possible structure. State the geometry around the metal ion.

The complex $[\mathrm{C}\mathrm{r}(\mathrm{e}\mathrm{n}{)}_3{]}^{2+}$ exists as two stereoisomers whereas the complex $[\mathrm{C}\mathrm{r}(\mathrm{O}\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_2\mathrm{N}{\mathrm{H}}_2{)}_3{]}^{-}$ exists as four stereoisomers. Complete the three-dimensional diagrams in Fig. 2.1 to show the four stereoisomers of $[\mathrm{C}\mathrm{r}(\mathrm{O}\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_2\mathrm{N}{\mathrm{H}}_2{)}_3{]}^{-}$. Represent the ligand ${}^{-}\mathrm{O}\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_2\mathrm{N}{\mathrm{H}}_2$ by using O—N.

The complex $[\mathrm{C}\mathrm{r}(\mathrm{O}\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_2\mathrm{N}{\mathrm{H}}_2{)}_3{]}^{-}$ is formed by reacting $\mathrm{C}{\mathrm{r}}^{2+}(\mathrm{a}\mathrm{q})$ with the conjugate base of 2-aminoethanol. A synthesis of 2-aminoethanol is shown in Fig. 2.2. Suggest the mechanism for step 1 of the reaction of oxirane with ammonia in Fig. 2.3. Include all relevant curly arrows, lone pairs of electrons, charges and partial charges. Draw the structure of the organic intermediate.

A small amount of by-product E, shown in Fig. 2.4, is produced during the reaction shown in Fig. 2.2. Suggest how the formation of by-product E can be minimised.

Compound F, ${\mathrm{C}}_4{\mathrm{H}}_9\mathrm{N}\mathrm{O}$, can be formed from the reaction of by-product E, ${\mathrm{C}}_4{\mathrm{H}}_{11}\mathrm{N}{\mathrm{O}}_2$, with concentrated ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$. Compound F is a saturated and basic organic compound. Suggest a structure for compound F. State the type of reaction undergone by E to form F.

Aqueous acidified iodate(V) ions, $\mathrm{I}{\mathrm{O}}_3^{-}$, react with iodide ions, as shown. $\mathrm{I}{\mathrm{O}}_3^{-}+6{\mathrm{H}}^{+}+5{\mathrm{I}}^{-}\to 3{\mathrm{I}}_2+3{\mathrm{H}}_2\mathrm{O}$ The initial rate of this reaction is investigated. Table 3.1 shows the results obtained. The rate equation for this reaction is $\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{e}=k[\mathrm{I}{\mathrm{O}}_3^{-}][{\mathrm{H}}^{+}{]}^2[{\mathrm{I}}^{-}{]}^2$. Explain what is meant by order of reaction.

Complete Table 3.2.

Use your answer to (a)(ii) to sketch lines in Fig. 3.1 to show the relationship between the initial rates and the concentrations of $[\mathrm{I}{\mathrm{O}}_3^{-}]$ and $[{\mathrm{I}}^{-}]$.

Use data from Table 3.1 to calculate the rate constant, $k$, for this reaction. Include the units of $k$.

Use data from Table 3.1 to calculate the concentration of hydrogen ions, $[{\mathrm{H}}^{+}]$, in experiment 2.

This reaction is repeated in two separate experiments. The experiments are carried out at the same temperature and with the same concentrations of ${\mathrm{I}}^{-}$ and $\mathrm{I}{\mathrm{O}}_3^{-}$. One experiment takes place at pH 1.0 and the other experiment takes place at pH 2.0. Calculate the value of $\frac{\text{rate at pH 1.0}}{\text{rate at pH 2.0}}$.

In aqueous solution, iron(III) ions react with iodide ions, as shown. $2\mathrm{F}{\mathrm{e}}^{3+}+2{\mathrm{I}}^{-}\to 2\mathrm{F}{\mathrm{e}}^{2+}+{\mathrm{I}}_2$ The initial rate of reaction is first order with respect to $\mathrm{F}{\mathrm{e}}^{3+}$ and second order with respect to ${\mathrm{I}}^{-}$. The mechanism for this reaction has three steps. Each step involves only two ions reacting together. Suggest equations for the three steps of this mechanism. Identify the rate-determining step.

State the hybridisation of the carbon atoms and the C–C–H bond angle in benzene, ${\mathrm{C}}_6{\mathrm{H}}_6$. Explain how orbital overlap leads to the formation of $\sigma$ and $\pi$ bonds in benzene.

Compound Z can be synthesised from benzene in three steps by the route shown in Fig. 4.1. Draw structures for X and Y in Fig. 4.1.

Give the reagents and conditions for steps 1, 2 and 3. step 1 ................................................................................................................................ step 2 ................................................................................................................................ step 3 ................................................................................................................................

Compound W is an isomer of Z. Give the systematic name of W.

Complete Table 4.1 to show the number of peaks observed in the carbon-13 NMR spectrum for W and Z.

The exhaust systems of most modern gasoline-fuelled cars contain a catalytic converter with three metal catalysts. These metals act as heterogeneous catalysts. Name three metal catalysts used in catalytic converters.

Explain what is meant by a heterogeneous catalyst.

The exhaust systems of many diesel-fuelled cars contain an additional system to reduce vehicle emissions. This uses a liquid that is added to the exhaust system. This liquid contains urea, $(\mathrm{N}{\mathrm{H}}_2{)}_2\mathrm{C}\mathrm{O}$, which decomposes on heating to isocyanic acid, $\mathrm{H}\mathrm{N}\mathrm{C}\mathrm{O}$, and ammonia. reaction 1 $(\mathrm{N}{\mathrm{H}}_2{)}_2\mathrm{C}\mathrm{O}\to \mathrm{H}\mathrm{N}\mathrm{C}\mathrm{O}+\mathrm{N}{\mathrm{H}}_3$ Isocyanic acid reacts with water vapour to form ammonia and carbon dioxide. reaction 2 $\mathrm{H}\mathrm{N}\mathrm{C}\mathrm{O}(\mathrm{g})+{\mathrm{H}}_2\mathrm{O}(\mathrm{g})\to \mathrm{N}{\mathrm{H}}_3(\mathrm{g})+\mathrm{C}{\mathrm{O}}_2(\mathrm{g})$ Some values for standard enthalpy changes of formation, $\mathrm{\Delta }{H}_{\mathrm{f}}^{\ominus }$, and standard entropies, $S^{\ominus }$, are given in Table 5.1. Explain what is meant by the term entropy of a system.

Use the data in Table 5.1 to calculate $\mathrm{\Delta }{G}^{\ominus }$ for reaction 2 at $25{}^{\circ }\mathrm{C}$. Show your working.

The ammonia formed in reactions 1 and 2 can be used to remove nitrogen dioxide from exhaust emissions, as shown. reaction 3 $8\mathrm{N}{\mathrm{H}}_3+6\mathrm{N}{\mathrm{O}}_2\to 7{\mathrm{N}}_2+12{\mathrm{H}}_2\mathrm{O}$ Use the equations for reactions 1, 2 and 3 to construct an overall equation for the reduction of $\mathrm{N}{\mathrm{O}}_2$ by $(\mathrm{N}{\mathrm{H}}_2{)}_2\mathrm{C}\mathrm{O}$.

Isocyanic acid, $\mathrm{H}\mathrm{N}\mathrm{C}\mathrm{O}$, can form cyanuric acid, ${\mathrm{C}}_3{\mathrm{H}}_3{\mathrm{N}}_3{\mathrm{O}}_3$, under certain conditions. ${\mathrm{C}}_3{\mathrm{H}}_3{\mathrm{N}}_3{\mathrm{O}}_3$ has a cyclic structure containing alternating carbon and nitrogen atoms in the ring system. Suggest a structure for cyanuric acid.

Isocyanic acid, $\mathrm{H}\mathrm{N}\mathrm{C}\mathrm{O}$, is a weak acid. $\mathrm{H}\mathrm{N}\mathrm{C}\mathrm{O}+{\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\mathrm{H}}_3{\mathrm{O}}^{+}+\mathrm{N}\mathrm{C}{\mathrm{O}}^{-}\mathrm{p}{K}_{\mathrm{a}}=3.70\text{ at }25{}^{\circ }\mathrm{C}$ Write the mathematical expressions for $\mathrm{p}{K}_{\mathrm{a}}$ and pH. $\mathrm{p}{K}_{\mathrm{a}}=$ ................................................................................................................................. $\mathrm{p}\mathrm{H}=$ ...................................................................................................................................

Calculate the pH of $0.120\mathrm{m}\mathrm{o}\mathrm{l}{\mathrm{d}\mathrm{m}}^{-3}\mathrm{H}\mathrm{N}\mathrm{C}\mathrm{O}(\mathrm{a}\mathrm{q})$. Give your answer to three significant figures.

Calculate the percentage of $\mathrm{H}\mathrm{N}\mathrm{C}\mathrm{O}$ molecules that are ionised in $0.120\mathrm{m}\mathrm{o}\mathrm{l}{\mathrm{d}\mathrm{m}}^{-3}\mathrm{H}\mathrm{N}\mathrm{C}\mathrm{O}$.

Compound H has the structural formula $\mathrm{C}{\mathrm{H}}_2=\mathrm{C}\mathrm{H}\mathrm{C}\mathrm{H}(\mathrm{N}{\mathrm{H}}_2)\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$. Name all the functional groups in H.

Compound H exhibits stereoisomerism. Draw three-dimensional structures for the two stereoisomers of H. Name this type of stereoisomerism.

Compound H can be prepared from the reaction of J with an excess of hot aqueous acid. Complete Fig. 6.2 to show the equation for this reaction.

Name the type of reaction in (b)(i).

Polymers consist of monomers joined together by undergoing either addition or condensation polymerisation. Compound H can react to form an addition polymer, K, or a condensation polymer, L, depending on the conditions. Draw one repeat unit of addition polymer K.

Draw two repeat units of condensation polymer L. The new functional group formed should be displayed.

Explain why condensation polymers can normally biodegrade more readily than addition polymers.

State the relative basicities of ethanamide, diethylamine and ethylamine in aqueous solution. Explain your answer. ............................................. > ............................................. > ............................................. most basic least basic

The amino acid alanine, ${\mathrm{H}}_2\mathrm{N}\mathrm{C}\mathrm{H}(\mathrm{C}{\mathrm{H}}_3)\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$, can act as a buffer. Define a buffer solution.

Write two equations to show how an aqueous solution of alanine can act as a buffer solution.

Glutamic acid is another amino acid that acts as a buffer. Draw the skeletal formula for glutamic acid.

Draw the structure for the dipeptide, ala-glu, formed from one molecule of alanine and one molecule of glutamic acid. The peptide bond formed should be displayed.

The isoelectric point of alanine is 6.0 and of glutamic acid is 3.2. A mixture of the dipeptide, ala-glu, and its two constituent amino acids, alanine and glutamic acid, is analysed by electrophoresis using a buffer at pH 6.0. Draw and label three spots on Fig. 7.2 to indicate the predicted position of each of these three species after electrophoresis. Explain your answer.

Alanine, ${\mathrm{H}}_2\mathrm{N}\mathrm{C}\mathrm{H}(\mathrm{C}{\mathrm{H}}_3)\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$, reacts with methanol to form the ester G under certain conditions. The proton (${}^1\mathrm{H}$) NMR spectrum of G dissolved in ${\mathrm{D}}_2\mathrm{O}$ is shown in Fig. 7.3. Complete Table 7.2 for the proton (${}^1\mathrm{H}$) NMR spectrum of G.

The proton (${}^1\mathrm{H}$) NMR spectrum of G dissolved in $\mathrm{C}\mathrm{D}\mathrm{C}{\mathrm{l}}_3$ is obtained. Describe the difference observed between this spectrum and the proton NMR spectrum in ${\mathrm{D}}_2\mathrm{O}$ shown in Fig 7.3. Explain your answer.

Complete Table 8.1 by placing one tick (✓) in each row to indicate the sign of each type of energy change under standard conditions.

Define enthalpy change of hydration.

Table 8.2 shows various energy changes which can be used in the following questions. Select and use relevant data from Table 8.2 to calculate the lattice energy, $\mathrm{\Delta }{H}_{\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{t}}^{\ominus }$, of $\mathrm{C}\mathrm{a}\mathrm{B}{\mathrm{r}}_2(\mathrm{s})$. It may be helpful to draw a labelled energy cycle. Show your working.

Select and use relevant data from Table 8.2 and your answer to (c)(i) to calculate the standard enthalpy change of hydration, $\mathrm{\Delta }{H}_{\mathrm{h}\mathrm{y}\mathrm{d}}^{\ominus }$, of $\mathrm{B}{\mathrm{r}}^{-}$. It may be helpful to draw a labelled energy cycle. If you were not able to answer (c)(i), use $-2500\mathrm{k}\mathrm{J}{\mathrm{m}\mathrm{o}\mathrm{l}}^{-1}$ as your value for $\mathrm{\Delta }{H}_{\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{t}}^{\ominus }$ of $\mathrm{C}\mathrm{a}\mathrm{B}{\mathrm{r}}_2(\mathrm{s})$. This is not the correct value. Show your working.

The enthalpy change of hydration of the $\mathrm{B}{\mathrm{r}}^{-}$ ion is more negative than the enthalpy change of hydration of the ${\mathrm{I}}^{-}$ ion. Explain why.