A Level Chemistry 9701 Paper 43, Oct/Nov 2024

Disodium phosphate, $({\mathrm{N}\mathrm{a}}^{+}{)}_2({\mathrm{H}\mathrm{P}\mathrm{O}}_4^{2-})$, reacts with an acid to form monosodium phosphate, ${\mathrm{N}\mathrm{a}}^{+}({\mathrm{H}}_2{\mathrm{P}\mathrm{O}}_4^{-})$. Identify the ions that are a conjugate acid–base pair in this reaction, using the formulae of the species involved. conjugate acid .................................................................... conjugate base ....................................................................

Define buffer solution.

Write two equations to show how a mixture of $({\mathrm{N}\mathrm{a}}^{+}{)}_2({\mathrm{H}\mathrm{P}\mathrm{O}}_4^{2-})$ and ${\mathrm{N}\mathrm{a}}^{+}({\mathrm{H}}_2{\mathrm{P}\mathrm{O}}_4^{-})$ can act as a buffer solution. equation 1 ......................................................................................................................... equation 2 .........................................................................................................................

Identify one inorganic ion that acts as a buffer in blood.

Compound $\mathbf{E}$ is the hydroxide of a Group 2 element. Compound $\mathbf{E}$ is a strong alkali. $2.63\mathrm{g}$ of $\mathbf{E}$ is dissolved in water to make $250{\mathrm{c}\mathrm{m}}^3$ of solution $\mathbf{F}$. Solution $\mathbf{F}$ has a pH of 13.09 at $298\mathrm{K}$. Show that the concentration of hydroxide ions in solution $\mathbf{F}$ is $0.123{\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{d}\mathrm{m}}^{-3}$.

Explain why the concentration of compound $\mathbf{E}$ in solution $\mathbf{F}$ is $0.0615{\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{d}\mathrm{m}}^{-3}$.

Use the concentration given in (ii) to identify compound $\mathbf{E}$. compound $\mathbf{E}$ ................................................................................................................

Compound $\mathbf{E}$ is much more soluble than magnesium hydroxide. A saturated solution of magnesium hydroxide in water has a concentration of $1.40\times {10}^{-4}{\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{d}\mathrm{m}}^{-3}$ at $298\mathrm{K}$. Calculate the solubility product, $K_{\mathrm{s}\mathrm{p}}$, of magnesium hydroxide. Include units. $K_{\mathrm{s}\mathrm{p}}=$ .............................. units ..............................

Explain why compound $\mathbf{E}$ is much more soluble than magnesium hydroxide.

Predict and explain the variation in enthalpy change of hydration for the ions ${\mathrm{F}}^{-}$, ${\mathrm{C}\mathrm{l}}^{-}$, ${\mathrm{B}\mathrm{r}}^{-}$ and ${\mathrm{I}}^{-}$.

Fig. 2.1 shows an incomplete energy cycle involving calcium fluoride, ${\mathrm{C}\mathrm{a}\mathrm{F}}_2$. Complete line D. Include state symbols.

The value of the enthalpy change for process 1 can be calculated using the values of five other enthalpy changes which are not referred to in Fig. 2.1. process 1: $\mathrm{C}\mathrm{a}(\mathrm{s})+{\mathrm{F}}_2(\mathrm{g})\to {\mathrm{C}\mathrm{a}}^{2+}(\mathrm{g})+2{\mathrm{F}}^{-}(\mathrm{g})$ Identify these five other enthalpy changes, using either names or symbols.

Define lattice energy, $\mathrm{\Delta }{H}_{\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{t}}$.

Complete the expression to give the mathematical relationship between $\mathrm{\Delta }{H}_{\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{t}}$ of calcium fluoride and the enthalpy changes for processes 1 and 3. $\mathrm{\Delta }{H}_{\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{t}}=$

Use data from Table 2.1 to calculate a value for the hydration energy, $\mathrm{\Delta }{H}_{\mathrm{h}\mathrm{y}\mathrm{d}}$, of fluoride ions, ${\mathrm{F}}^{-}(\mathrm{g})$. Table 2.1

$\mathrm{\Delta }{H}_{\mathrm{h}\mathrm{y}\mathrm{d}}{\mathrm{F}}^{-}(\mathrm{g})=$ .............................. ${\mathrm{k}\mathrm{J}\mathrm{m}\mathrm{o}\mathrm{l}}^{-1}$

Define entropy.

At $298\mathrm{K}$, the Gibbs free energy change, $\mathrm{\Delta }G$, for the solution of compound $\mathbf{T}$ is $+6.00{\mathrm{k}\mathrm{J}\mathrm{m}\mathrm{o}\mathrm{l}}^{-1}$. The enthalpy change of solution, $\mathrm{\Delta }{H}_{\mathrm{s}\mathrm{o}\mathrm{l}}$, of compound $\mathbf{T}$ is $+30.0{\mathrm{k}\mathrm{J}\mathrm{m}\mathrm{o}\mathrm{l}}^{-1}$ at $298\mathrm{K}$. Calculate the value of the entropy change, $\mathrm{\Delta }S$, for the solution of compound $\mathbf{T}$ at $298\mathrm{K}$. $\mathrm{\Delta }S=$ .............................. ${\mathrm{J}\mathrm{K}}^{-1}{\mathrm{m}\mathrm{o}\mathrm{l}}^{-1}$

Predict whether compound $\mathbf{T}$ becomes more or less soluble as the water is heated from $298\mathrm{K}$ to $360\mathrm{K}$. Explain your answer.

$\mathbf{A}$ and $\mathbf{B}$ react together to give product $\mathrm{A}\mathrm{B}$. $$\mathrm{A}+\mathrm{B}\to \mathrm{A}\mathrm{B}$$ When the concentrations of $\mathbf{A}$ and $\mathbf{B}$ are both $0.0100{\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{d}\mathrm{m}}^{-3}$, the rate of formation of $\mathrm{A}\mathrm{B}$ is $7.62\times {10}^{-4}{\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{d}\mathrm{m}}^{-3}{\mathrm{s}}^{-1}$. When the concentrations of $\mathbf{A}$ and $\mathbf{B}$ are both $0.0200{\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{d}\mathrm{m}}^{-3}$, the rate of formation of $\mathrm{A}\mathrm{B}$ is $3.05\times {10}^{-3}{\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{d}\mathrm{m}}^{-3}{\mathrm{s}}^{-1}$. Complete the three possible rate equations that are consistent with these data. rate = ................................................................................................................................. rate = ................................................................................................................................. rate = .................................................................................................................................

Choose one of the rate equations you have written in (i), and calculate the value of the rate constant, $k$. Include the units of $k$. $k=$ .............................. units ..............................

Explain why it is not possible to calculate a value for the half-life, $t_{\frac{1}{2}}$, of this reaction using the value of the rate constant $k$ calculated in (ii) and the equation $k=0.693\mathrm{/}{t}_{\frac{1}{2}}$.

Catalysts may be homogeneous or heterogeneous. Identify two metals that act as heterogeneous catalysts in the removal of ${\mathrm{N}\mathrm{O}}_2$ from the exhaust gases of car engines. ............................................................... and ..............................................................

Iron acts as a heterogeneous catalyst in the Haber process. Describe the mode of action of this iron catalyst.

${\mathrm{F}\mathrm{e}}^{2+}$ ions act as a homogeneous catalyst in the reaction between ${\mathrm{I}}^{-}(\mathrm{a}\mathrm{q})$ and ${\mathrm{S}}_2{\mathrm{O}}_8^{2-}(\mathrm{a}\mathrm{q})$. Write equations for the two reactions that occur when ${\mathrm{F}\mathrm{e}}^{2+}(\mathrm{a}\mathrm{q})$ is added to a mixture of ${\mathrm{I}}^{-}(\mathrm{a}\mathrm{q})$ and ${\mathrm{S}}_2{\mathrm{O}}_8^{2-}(\mathrm{a}\mathrm{q})$. equation 1 ${\mathrm{S}}_2{\mathrm{O}}_8^{2-}+$ ........................................................................................................ equation 2 .......................................................................................................................

Explain the difference between a homogeneous catalyst and a heterogeneous catalyst.

${\mathrm{F}\mathrm{e}}^{2+}$ ions can be oxidised to ${\mathrm{F}\mathrm{e}}^{3+}$ ions under alkaline conditions by suitable oxidising agents. Iron is a transition element. Explain why iron forms stable compounds in both the +2 and the +3 oxidation states.

The half-equation for the reduction of ${\mathrm{F}\mathrm{e}}^{3+}$ under alkaline conditions, and its $E^{\circ }$ value, are shown. $${\mathrm{F}\mathrm{e}(\mathrm{O}\mathrm{H})}_3+{\mathrm{e}}^{-}\rightleftharpoons {\mathrm{F}\mathrm{e}(\mathrm{O}\mathrm{H})}_2+{\mathrm{O}\mathrm{H}}^{-}{E}^{\circ }=-0.56\mathrm{V}$$ Four more half-equations for reactions under alkaline conditions, and their $E^{\circ }$ values, are shown. $${\mathrm{A}\mathrm{l}(\mathrm{O}\mathrm{H})}_4^{-}+3{\mathrm{e}}^{-}\rightleftharpoons \mathrm{A}\mathrm{l}+4{\mathrm{O}\mathrm{H}}^{-}{E}^{\circ }=-2.35\mathrm{V}$$ $${\mathrm{C}\mathrm{l}\mathrm{O}}^{-}+{\mathrm{H}}_2\mathrm{O}+2{\mathrm{e}}^{-}\rightleftharpoons {\mathrm{C}\mathrm{l}}^{-}+2{\mathrm{O}\mathrm{H}}^{-}{E}^{\circ }=+0.89\mathrm{V}$$ $${\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{O}+4{\mathrm{e}}^{-}\rightleftharpoons 4{\mathrm{O}\mathrm{H}}^{-}{E}^{\circ }=+0.40\mathrm{V}$$ $${\mathrm{Z}\mathrm{n}(\mathrm{O}\mathrm{H})}_4^{2-}+2{\mathrm{e}}^{-}\rightleftharpoons \mathrm{Z}\mathrm{n}+4{\mathrm{O}\mathrm{H}}^{-}{E}^{\circ }=-1.22\mathrm{V}$$ Select two oxidising agents that can oxidise ${\mathrm{F}\mathrm{e}}^{2+}$ ions to ${\mathrm{F}\mathrm{e}}^{3+}$ ions under alkaline conditions. Write an equation, and give the $E_{\mathrm{c}\mathrm{e}\mathrm{l}\mathrm{l}}^{\circ }$ value, for each of the two reactions that occur. oxidising agent 1: .............................. equation: ........................................................................................................................... $E_{\mathrm{c}\mathrm{e}\mathrm{l}\mathrm{l}}^{\circ }=$ .............................. V oxidising agent 2: .............................. equation: ........................................................................................................................... $E_{\mathrm{c}\mathrm{e}\mathrm{l}\mathrm{l}}^{\circ }=$ .............................. V

Explain why transition elements form complex ions.

${\mathrm{C}\mathrm{o}}^{2+}$ ions form complex ion $\mathbf{G}$. Each $\mathbf{G}$ ion contains two ${\mathrm{C}\mathrm{o}}^{2+}$ ions, both of which are octahedrally coordinated. Each $\mathbf{G}$ ion contains one ${\mathrm{O}}_2$ molecule, which donates one pair of electrons to each ${\mathrm{C}\mathrm{o}}^{2+}$ ion, and one ${\mathrm{N}\mathrm{H}}_2^{-}$ ion, which donates one pair of electrons to each ${\mathrm{C}\mathrm{o}}^{2+}$ ion. The remaining ligands are ${\mathrm{N}\mathrm{H}}_3$ molecules. Deduce the formula of complex ion $\mathbf{G}$. Include its overall charge. formula of $\mathbf{G}$ .........................................................

The d-orbitals of the ${\mathrm{C}\mathrm{o}}^{2+}$ ions present in complex ion $\mathbf{G}$ are split. State the number of d-orbitals that are at a higher energy level and the number of d-orbitals that are at a lower energy level in each ${\mathrm{C}\mathrm{o}}^{2+}$ ion. | number of d-orbitals at a higher energy level | | | number of d-orbitals at a lower energy level | |

${\mathrm{C}\mathrm{o}}^{2+}$ ions form a different complex ion, $\mathbf{M}$. Each $\mathbf{M}$ ion contains two ${\mathrm{C}\mathrm{o}}^{2+}$ ions, both of which are octahedrally coordinated, but the ligands are different from the ligands in $\mathbf{G}$. Explain why $\mathbf{G}$ and $\mathbf{M}$ have different colours.

Cadmium forms complex ion $\mathbf{X}$, $[\mathrm{C}\mathrm{d}({\mathrm{N}\mathrm{H}}_3{)}_4{]}^{2+}$. When a solution containing ${\mathrm{C}\mathrm{N}}^{-}$ ions is added to an aqueous solution of $\mathbf{X}$, a ligand exchange reaction takes place, forming complex ion $\mathbf{Y}$. $\mathbf{Y}$ contains no ${\mathrm{N}\mathrm{H}}_3$ ligands and no ${\mathrm{H}}_2\mathrm{O}$ ligands. $\mathbf{Y}$ is in a much higher concentration in the mixture than $\mathbf{X}$. The oxidation state and coordination number of cadmium do not change in this reaction. Write an ionic equation for this reaction, using the formulae of the complex ions.

Cadmium forms complex ion $\mathbf{Z}$ in the same oxidation state and with the same coordination number as in $\mathbf{X}$. All the ligands in $\mathbf{Z}$ are ${\mathrm{C}\mathrm{l}}^{-}$ ions. When $\mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}(\mathrm{a}\mathrm{q})$ is added to a solution of $\mathbf{X}$, very little $\mathbf{Z}$ forms. Write the three cadmium complexes, $\mathbf{X}$, $\mathbf{Y}$ and $\mathbf{Z}$, in order of increasing stability constant, $K_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{b}}$. .......................................... .......................................... .......................................... smallest value of $K_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{b}}$ largest value of $K_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{b}}$

Ethanedioate ions, ${\mathrm{C}}_2{\mathrm{O}}_4^{2-}$, form complexes with transition element ions. The concentration of ${\mathrm{C}}_2{\mathrm{O}}_4^{2-}$ ions can be found by reaction with acidified ${\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_7^{2-}$ ions. ${\mathrm{C}}_2{\mathrm{O}}_4^{2-}$ ions are protonated and form $\mathrm{H}\mathrm{O}\mathrm{O}\mathrm{C}\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$ molecules which are oxidised by ${\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_7^{2-}$. The half-equations are shown. $${\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_7^{2-}+14{\mathrm{H}}^{+}+6{\mathrm{e}}^{-}\rightleftharpoons 2{\mathrm{C}\mathrm{r}}^{3+}+7{\mathrm{H}}_2\mathrm{O}$$ $$2{\mathrm{C}\mathrm{O}}_2+2{\mathrm{H}}^{+}+2{\mathrm{e}}^{-}\rightleftharpoons \mathrm{H}\mathrm{O}\mathrm{O}\mathrm{C}\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$$ Construct an equation for the reaction between acidified ${\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_7^{2-}$ and $\mathrm{H}\mathrm{O}\mathrm{O}\mathrm{C}\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$.

A $25.0{\mathrm{c}\mathrm{m}}^3$ sample of a solution of ${\mathrm{N}\mathrm{a}}_2{\mathrm{C}}_2{\mathrm{O}}_4$ reacts with exactly $16.20{\mathrm{c}\mathrm{m}}^3$ of an acidified solution of $0.0500{\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{d}\mathrm{m}}^{-3}{\mathrm{K}}_2{\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_7$. Calculate the concentration of the solution of ${\mathrm{N}\mathrm{a}}_2{\mathrm{C}}_2{\mathrm{O}}_4$. $[{\mathrm{N}\mathrm{a}}_2{\mathrm{C}}_2{\mathrm{O}}_4]=$ .......................................... ${\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{d}\mathrm{m}}^{-3}$

Label one bond angle on each of complexes $\mathbf{P}$, $\mathbf{Q}$, $\mathbf{R}$ and $\mathbf{S}$, and identify the size of the angle in degrees.

Identify the shapes of complexes $\mathbf{P}$, $\mathbf{Q}$, $\mathbf{R}$ and $\mathbf{S}$. $\mathbf{P}$ ............................................................................................................................... $\mathbf{Q}$ ............................................................................................................................... $\mathbf{R}$ ............................................................................................................................... $\mathbf{S}$ ...............................................................................................................................

Two $\mathbf{L}$ ligands are exchanged with two different monodentate ligands $\mathbf{X}$ and $\mathbf{Y}$ in each of complexes $\mathbf{P}$, $\mathbf{Q}$, $\mathbf{R}$ and $\mathbf{S}$. Identify all the complexes which form new complexes that show geometrical isomerism.

Three $\mathbf{L}$ ligands are exchanged with three different monodentate ligands $\mathbf{X}$, $\mathbf{Y}$ and $\mathbf{Z}$ in each of complexes $\mathbf{P}$, $\mathbf{Q}$ and $\mathbf{R}$. Identify all the complexes which form new complexes that show optical isomerism.

Complete the equation for the reaction of ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{C}\mathrm{l}$ with this catalyst to form ${\mathrm{C}}_2{\mathrm{H}}_5^{+}$ as one product. $${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{C}\mathrm{l}+\text{.......................................}\to {\mathrm{C}}_2{\mathrm{H}}_5^{+}+\text{.......................................}$$

Ethylbenzene reacts with more ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{C}\mathrm{l}$, forming a mixture containing 1,2-diethylbenzene and 1,4-diethylbenzene. Draw the structures of 1,2-diethylbenzene and 1,4-diethylbenzene.

Explain why there is very little 1,3-diethylbenzene in the product mixture.

1,2-diethylbenzene can be oxidised to benzene-1,2-dioic acid, ${\mathrm{C}}_6{\mathrm{H}}_4(\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}{)}_2$. State the reagent and conditions used for this reaction.

Complete the overall equation for this reaction. An atom of oxygen from the oxidising agent is represented as $[\mathrm{O}]$. All of the atoms in the two ethyl groups are fully oxidised in this reaction. $$\text{.................................}+\text{.................}[\mathrm{O}]\to {\mathrm{C}}_6{\mathrm{H}}_4(\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}{)}_2+\text{................................}+\text{................................}$$ (1,2-diethylbenzene)

Predict the number of peaks in the carbon-13 NMR spectrum of benzene-1,2-dioic acid.

The proton (${}^1\mathrm{H}$) NMR spectra of ethylbenzene, ${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{C}}_2{\mathrm{H}}_5$, in ${\mathrm{C}\mathrm{D}\mathrm{C}\mathrm{l}}_3$ and of benzene-1,2-dioic acid, ${\mathrm{C}}_6{\mathrm{H}}_4(\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}{)}_2$, in ${\mathrm{C}\mathrm{D}\mathrm{C}\mathrm{l}}_3$ are shown. They have not been identified. Explain the use of ${\mathrm{C}\mathrm{D}\mathrm{C}\mathrm{l}}_3$, instead of ${\mathrm{C}\mathrm{H}\mathrm{C}\mathrm{l}}_3$, as the solvent when obtaining these spectra.

Identify the substance shown by the spectrum in Fig. 6.1, and complete Table 6.1. substance .......................................................................................................................... Table 6.1

Identify the substance shown by the spectrum in Fig. 6.2, and complete Table 6.2. substance .......................................................................................................................... Table 6.2

When ${\mathrm{D}}_2\mathrm{O}$ is used as a solvent, the spectrum obtained is different from the spectrum in Fig. 6.2. Describe this difference and explain your answer.

Benzene-1,2-dioic acid can be used to produce $\mathbf{K}$. Suggest the name of this type of reaction.

Identify compound $\mathbf{U}$ which contains only three elements.

Describe the reagents and conditions for reaction 1.

Identify compound $\mathbf{V}$.

Complete the equation for reaction 3. $${\mathrm{C}\mathrm{H}}_3\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}+{\mathrm{S}\mathrm{O}\mathrm{C}\mathrm{l}}_2\to \text{......................................................................................................}$$

Identify compound $\mathbf{W}$.

Describe the conditions for reaction 4.

Suggest the reagent needed for reaction 6.

Complete Table 7.1 by adding the reaction numbers, 1, 2, 3, 4, 5 and 6, to the right-hand column. Use the reaction numbers given in Fig. 7.1. Each of the numbers 1, 2, 3, 4, 5 and 6 should be used once only. Table 7.1

Compare the basicities of ${\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{N}\mathrm{H}\mathrm{C}\mathrm{O}\mathrm{C}\mathrm{H}}_3$, ${\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{N}\mathrm{H}\mathrm{C}}_2{\mathrm{H}}_5$ and ${\mathrm{N}\mathrm{H}}_3$. Explain your answer. ............................................ ............................................ ............................................ most basic least basic

An aqueous solution of phenol, ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{O}\mathrm{H}$, is acidic at $298\mathrm{K}$. Explain why phenol is more acidic than water.

Name the two products formed when phenol reacts with an excess of ${\mathrm{B}\mathrm{r}}_2(\mathrm{a}\mathrm{q})$. ............................................................... and ...............................................................

Draw the structures of the two isomeric organic products, with $M_r=139$, that are formed when phenol reacts with ${\mathrm{H}\mathrm{N}\mathrm{O}}_3(\mathrm{a}\mathrm{q})$ at room temperature.

Write the equation for the reaction between phenol, ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{O}\mathrm{H}$, and sodium metal.

Phenol can be produced from phenylamine in a two-step synthesis. $$\text{phenylamine}\stackrel{\text{step one}}{\to }\text{intermediate compound}\stackrel{\text{step two}}{\to }\text{phenol}$$ Describe the reagents and conditions needed in each step. step one: reagents .................................................................................................................................... conditions ................................................................................................................................. step two: reagents .................................................................................................................................... conditions .................................................................................................................................