A Level Chemistry 9701 Paper 42, May/June 2024

Describe the trend in the solubility of the sulfates of magnesium, calcium and strontium. Explain your answer. ........................................... > ........................................... > ........................................... most soluble least soluble

Define lattice energy, $\mathrm{\Delta }{H}_{\text{latt}}$.

State and explain the main factors that affect the magnitude of lattice energies.

Table 1.1 shows some energy changes. Table 1.1

Born–Haber cycles can be used to determine the lattice energies of ionic compounds. Complete the Born–Haber cycle in Fig. 1.1 for potassium sulfide, ${\text{K}}_2\text{S(s)}$. Include state symbols for all of the species.

Calculate the lattice energy, $\mathrm{\Delta }{H}_{\text{latt}}^{\ominus }$, of ${\text{K}}_2\text{S(s)}$ using relevant data from Table 1.1. Show your working.

Lithium nitrate, ${\text{LiNO}}_3$, decomposes on heating in a similar way to Group 2 nitrates to give the metal oxide, a brown gas and oxygen. Write an equation for the decomposition of ${\text{LiNO}}_3$.

The other Group 1 nitrates, ${\text{MNO}}_3$, decompose on heating to form the metal nitrite, ${\text{MNO}}_2$, and oxygen. The thermal stability of these nitrates increases down the group. Suggest why the thermal stability of ${\text{MNO}}_3$ increases down the group.

Acidified manganate(VII) ions, ${\text{MnO}}_4^{-}$, can be used to analyse solutions containing nitrite ions, ${\text{NO}}_2^{-}$, by titration. $\mathbf{X}$ is a solution of ${\text{NaNO}}_2$. $250.0{\text{cm}}^3$ of $\mathbf{X}$ is added to $50.0{\text{cm}}^3$ of $0.125\text{mol}{\text{dm}}^{-3}$ acidified ${\text{MnO}}_4^{-}(\text{aq})$. The ${\text{MnO}}_4^{-}(\text{aq})$ ions are in excess; all the ${\text{NO}}_2^{-}$ ions are oxidised in the reaction. The unreacted ${\text{MnO}}_4^{-}(\text{aq})$ required $22.50{\text{cm}}^3$ of $0.0400\text{mol}{\text{dm}}^{-3}$ ${\text{Fe}}^{2+}(\text{aq})$ to reach the end-point. The relevant half-equations are shown. $${\text{NO}}_2^{-}+{\text{H}}_2\text{O}\rightleftharpoons {\text{NO}}_3^{-}+2{\text{H}}^{+}+2{\text{e}}^{-}$$ $${\text{MnO}}_4^{-}+8{\text{H}}^{+}+5{\text{e}}^{-}\rightleftharpoons {\text{Mn}}^{2+}+4{\text{H}}_2\text{O}$$ $${\text{Fe}}^{2+}\rightleftharpoons {\text{Fe}}^{3+}+{\text{e}}^{-}$$ Calculate the concentration, in $\text{mol}{\text{dm}}^{-3}$, of ${\text{NaNO}}_2$ in $\mathbf{X}$.

Table 2.1 shows electrode potentials for some electrode reactions involving manganese compounds. Table 2.1

Aqueous manganate(VI) ions, ${\text{MnO}}_4^{2-}$, are unstable in acidic conditions and undergo a disproportionation reaction. The $E_{\text{cell}}^{\ominus }$ for this reaction is $+1.14\text{V}$. Construct an overall ionic equation for this disproportionation reaction.

Suggest and explain how the $E_{\text{cell}}$ value of the disproportionation reaction changes with an increase in pH.

Carbon disulfide, ${\text{CS}}_2$, is flammable and reacts readily with oxygen, as shown in reaction 1. $$\text{reaction 1}{\text{CS}}_2(\text{g})+3{\text{O}}_2(\text{g})\to {\text{CO}}_2(\text{g})+2{\text{SO}}_2(\text{g})$$ Table 3.1 shows the standard enthalpy of formation, $\mathrm{\Delta }{H}_{\text{f}}^{\ominus }$, and the standard entropy, $S^{\ominus }$, for some substances. Table 3.1

Calculate the standard Gibbs free energy change, $\mathrm{\Delta }{G}^{\ominus }$, in $\text{kJ}{\text{mol}}^{-1}$, for reaction 1 at $25{}^{\circ }\text{C}$.

Carbon disulfide reacts with chlorine to form tetrachloromethane, as shown in reaction 2. $$\text{reaction 2}{\text{CS}}_2+3{\text{Cl}}_2\to {\text{CCl}}_4+{\text{S}}_2{\text{Cl}}_2\mathrm{\Delta }{H}^{\ominus }=-261.6\text{kJ}{\text{mol}}^{-1}$$ $$\mathrm{\Delta }{S}^{\ominus }=-365.5\text{J}{\text{K}}^{-1}{\text{mol}}^{-1}$$ Calculate the maximum temperature, in $\text{K}$, for reaction 2 to be feasible.

Explain why transition elements have variable oxidation states.

Sketch the shape of a $3{\text{d}}_{z^2}$ orbital in Fig. 4.1.

Samples of $[\text{Cu}({\text{H}}_2\text{O}{)}_6{]}^{2+}(\text{aq})$ are reacted separately with an excess of solution $\mathbf{A}$ and with an excess of solution $\mathbf{B}$. The reaction of $[\text{Cu}({\text{H}}_2\text{O}{)}_6{]}^{2+}(\text{aq})$ with solution $\mathbf{A}$ is a precipitation reaction. The reaction of $[\text{Cu}({\text{H}}_2\text{O}{)}_6{]}^{2+}(\text{aq})$ with solution $\mathbf{B}$ is a ligand substitution reaction. Suggest a possible identity for solution $\mathbf{A}$ and for solution $\mathbf{B}$. Give relevant observations and the formula of the copper-containing product for each reaction. solution $\mathbf{A}$ .................................................................................................................................. observations ............................................................................................................................. formula of the copper-containing product ................................................................................. solution $\mathbf{B}$ .................................................................................................................................. observations ............................................................................................................................. formula of the copper-containing product .................................................................................

Solutions containing the $[\text{Ag}({\text{NH}}_3{)}_2{]}^{+}$ complex are colourless. Explain why this complex is colourless.

Two bidentate ligands are shown in Fig. 4.2. Explain what is meant by a bidentate ligand.

Ruthenium(III) ions, ${\text{Ru}}^{3+}$, form an octahedral complex, $[\text{Ru}(\text{dpys}{)}_2{\text{Cl}}_2{]}^{+}$, with the ligands dpys and chloride ions. This complex shows the same kind of stereoisomerism as $[\text{Ru}({\text{NH}}_3{)}_4{\text{Cl}}_2{]}^{+}$ but also shows a different type of stereoisomerism. Complete the three-dimensional diagrams in Fig. 4.3 to show the three different stereoisomers of $[\text{Ru}(\text{dpys}{)}_2{\text{Cl}}_2{]}^{+}$. The dpys ligand can be represented using N~N.

State the different types of stereoisomerism shown by $[\text{Ru}(\text{dpys}{)}_2{\text{Cl}}_2{]}^{+}$.

Deduce which stereoisomers in (e)(i) are non-polar. Explain your answer.

Nitrosyl chloride, $\text{NOCl}$, can be formed by the reaction between nitrogen monoxide and chlorine, as shown. $$2\text{NO}+{\text{Cl}}_2\to 2\text{NOCl}$$ The initial rate of this reaction is investigated, starting with different concentrations of $\text{NO}$ and ${\text{Cl}}_2$. The results obtained are shown in Table 5.1. Table 5.1

Use the data in Table 5.1 to deduce the rate equation for this reaction. Explain your reasoning.

Use your rate equation from (a)(i) and the data from experiment 1 to calculate the rate constant, $k$, for this reaction. Include the units of $k$.

${\text{NO}}_2\text{Cl}$ is another compound containing nitrogen, oxygen and chlorine. In sunlight, ${\text{NO}}_2\text{Cl}$ can undergo homolytic fission to release chlorine radicals which can catalyse the conversion of ozone, ${\text{O}}_3$, into oxygen. Complete the mechanism for this process.

Ozone reacts with nitrogen dioxide, as shown. $${\text{O}}_3+2{\text{NO}}_2\to {\text{N}}_2{\text{O}}_5+{\text{O}}_2$$ The rate of reaction is first order with respect to ${\text{O}}_3$ and first order with respect to ${\text{NO}}_2$. Suggest equations for a two-step mechanism for this reaction. step 1 ........................................................................................................................................ step 2 ........................................................................................................................................

Aqueous solutions of methanoic acid, $\text{HCOOH}$, and propanoic acid, ${\text{CH}}_3{\text{CH}}_2\text{COOH}$, are mixed together. An equilibrium is set up between two conjugate acid–base pairs. Define conjugate acid–base pair.

The $\text{p}{K}_{\text{a}}$ of $\text{HCOOH}$ is 3.75 and of ${\text{CH}}_3{\text{CH}}_2\text{COOH}$ is 4.87. Complete the equation for the Brønsted–Lowry equilibrium between the stronger of these two acids and water. ..................................... + ${\text{H}}_2\text{O}$ $\rightleftharpoons$ ..................................... + .....................................

Write an expression for the acid dissociation constant, $K_{\text{a}}$, for butanoic acid, ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{COOH}$. $K_{\text{a}}=$

The $\text{p}{K}_{\text{a}}$ of ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{COOH}$ is 4.82. A solution of ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{COOH}(\text{aq})$ has a pH of 3.25. Calculate the concentration, in $\text{mol}{\text{dm}}^{-3}$, of ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{COOH}$ in this solution.

Define buffer solution.

A buffer solution containing a mixture of ${\text{CH}}_3\text{COOH}$ and ${\text{CH}}_3\text{COONa}$ is prepared as follows. A solution of $600{\text{cm}}^3$ of ${\text{CH}}_3\text{COOH}$ is mixed with $400{\text{cm}}^3$ of $0.125\text{mol}{\text{dm}}^{-3}$ ${\text{CH}}_3\text{COONa}$. The buffer solution has pH 5.70. The $K_{\text{a}}$ of ${\text{CH}}_3\text{COOH}$ is $1.78\times {10}^{-5}\text{mol}{\text{dm}}^{-3}$. Calculate the initial concentration, in $\text{mol}{\text{dm}}^{-3}$, of ${\text{CH}}_3\text{COOH}$ used.

A fuel cell is an electrochemical cell that can be used to generate electrical energy by using oxygen to oxidise a fuel. Methanoic acid, $\text{HCOOH}$, is being investigated as a fuel in fuel cells. When the cell operates, $\text{HCOOH}$ is oxidised to carbon dioxide. The half-equation for the reaction at the cathode is: ${\text{O}}_2+4{\text{H}}^{+}+4{\text{e}}^{-}\to 2{\text{H}}_2\text{O}$. In this fuel cell, the overall cell reaction is the same as that for the complete combustion of $\text{HCOOH}$. Deduce the half-equation for the reaction at the anode.

Calculate the volume, in ${\text{cm}}^3$, of oxygen used when a current of $3.75\text{A}$ is delivered by the cell for $40.0\text{minutes}$. Assume the cell operates at room conditions.

Give the systematic name of $\mathbf{P}$.

$\mathbf{P}$ can be synthesised as shown in Fig. 7.2. Suggest reagents and conditions for this reaction.

A student attempts to synthesise $\mathbf{P}$ by an alternative route, as shown in Fig. 7.3. Compound $\mathbf{T}$ is the major product in this reaction rather than $\mathbf{P}$. Explain why $\mathbf{T}$ is the major product in this reaction.

$\mathbf{S}$ reacts in a similar way to phenol in step 3. Draw the structures of $\mathbf{Q}$, $\mathbf{R}$ and $\mathbf{S}$ in the boxes in Fig. 7.1.

Suggest reagents and conditions for steps 1 and 2 in Fig. 7.1. step 1 ................................................................................................................................ step 2 ................................................................................................................................

State the relative basicities of phenylamine, ${\text{C}}_6{\text{H}}_5{\text{NH}}_2$, benzylamine, ${\text{C}}_6{\text{H}}_5{\text{CH}}_2{\text{NH}}_2$, and ammonia, ${\text{NH}}_3$, in aqueous solution. Explain your answer. ........................................... > ........................................... > ........................................... most basic least basic

An excess of ${\text{Br}}_2(\text{aq})$ is added to separate samples of ${\text{C}}_6{\text{H}}_5{\text{NH}}_2$ and benzene, ${\text{C}}_6{\text{H}}_6$. ${\text{C}}_6{\text{H}}_5{\text{NH}}_2$ reacts readily with ${\text{Br}}_2(\text{aq})$ to form organic product $\mathbf{M}$. State the expected observations for this reaction. Draw the structure of $\mathbf{M}$. observations ...................................................................................................................... structure of $\mathbf{M}$

${\text{C}}_6{\text{H}}_6$ does not react with ${\text{Br}}_2(\text{aq})$. Suggest why ${\text{Br}}_2(\text{aq})$ reacts with ${\text{C}}_6{\text{H}}_5{\text{NH}}_2$ but not with ${\text{C}}_6{\text{H}}_6$.

Explain why benzamide, ${\text{C}}_6{\text{H}}_5{\text{CONH}}_2$, is a much weaker base than ammonia, ${\text{NH}}_3$.

${\text{C}}_6{\text{H}}_5{\text{CONH}}_2$ is formed by reacting benzoyl chloride, ${\text{C}}_6{\text{H}}_5\text{COCl}$, with ${\text{NH}}_3$. Complete the mechanism in Fig. 8.1 for the reaction of ${\text{C}}_6{\text{H}}_5\text{COCl}$ with ${\text{NH}}_3$. Include all relevant lone pairs of electrons, curly arrows, charges and dipoles. Draw the structure of the organic intermediate.

Phenylalanine, ${\text{C}}_6{\text{H}}_5{\text{CH}}_2\text{CH}({\text{NH}}_2)\text{COOH}$, is an amino acid with an isoelectric point of 5.5. State what is meant by isoelectric point.

Draw the structure of ${\text{C}}_6{\text{H}}_5{\text{CH}}_2\text{CH}({\text{NH}}_2)\text{COOH}$ at pH 10.

${\text{C}}_6{\text{H}}_5{\text{CH}}_2\text{CH}({\text{NH}}_2)\text{COOH}$ and alanine, ${\text{CH}}_3\text{CH}({\text{NH}}_2)\text{COOH}$, react to form a dipeptide containing both amino acid residues. Draw the structure of this dipeptide. The peptide functional group formed should be displayed.

Explain why trichloroethanoic acid, ${\text{CCl}}_3\text{COOH}$, is more acidic than ethanoic acid, ${\text{CH}}_3\text{COOH}$.

Acyl chlorides are formed by reacting carboxylic acids with thionyl chloride, ${\text{SOCl}}_2$. Ethanedioyl chloride, $(\text{COCl}{)}_2$, can be prepared by reacting ethanedioic acid, $(\text{COOH}{)}_2$, with an excess of ${\text{SOCl}}_2$. Write an equation for this reaction.

Samples of $(\text{COCl}{)}_2$ are reacted separately with an excess of warm acidified ${\text{KMnO}}_4(\text{aq})$ and with ${\text{H}}_2{\text{NCH}}_2{\text{CH}}_2{\text{NH}}_2$. The carbon-containing product from the reaction with ${\text{H}}_2{\text{NCH}}_2{\text{CH}}_2{\text{NH}}_2$ has the molecular formula ${\text{C}}_4{\text{H}}_6{\text{N}}_2{\text{O}}_2$. Complete the boxes in Fig. 9.1 to suggest the structure of the carbon-containing product in each reaction.

A polyester can be synthesised from the reaction of $(\text{COCl}{)}_2$ with ethane-1,2-diol, ${\text{HOCH}}_2{\text{CH}}_2\text{OH}$. Draw two repeat units of the polymer formed. Any functional groups should be displayed.

Compound $\mathbf{H}$, ${\text{C}}_6{\text{H}}_{10}{\text{O}}_3$, reacts with alkaline ${\text{I}}_2(\text{aq})$ to form yellow precipitate $\mathbf{J}$ but does not react with ${\text{Na}}_2{\text{CO}}_3(\text{aq})$. The proton (${}^1\text{H}$) NMR spectrum of $\mathbf{H}$ in ${\text{CDCl}}_3$ is shown in Fig. 9.2. Identify yellow precipitate $\mathbf{J}$.

Complete Table 9.2 for the proton (${}^1\text{H}$) NMR spectrum of $\mathbf{H}$, ${\text{C}}_6{\text{H}}_{10}{\text{O}}_3$. Table 9.2

Suggest a structure for $\mathbf{H}$, ${\text{C}}_6{\text{H}}_{10}{\text{O}}_3$.