AS & A Level Chemistry - 9701 Paper 4 2020 Winter Zone 2

The rate of the reaction $\text{H}_2(\text{g}) + \text{I}_2(\text{g}) \rightleftharpoons 2\text{HI}(\text{g})$ is studied.

(a) A small amount of $\text{H}_2(\text{g})$ is mixed with a large excess of $\text{I}_2(\text{g})$ at a temperature of 400K and the reaction is monitored. The graph obtained is shown.


(i) Suggest why a large excess of $\text{I}_2(\text{g})$ is used in this experiment.
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(ii) The reaction is first order with respect to $\text{H}_2(\text{g})$.
Use data from the graph to confirm this statement.
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(b) Three separate experiments were carried out at 400K with different starting concentrations of $\text{H}_2(\text{g})$ and $\text{I}_2(\text{g})$. The results are shown in the table.
[Table_1]

(i) Use the data, and the order of reaction with respect to $\text{H}_2(\text{g})$ given in (a)(ii), to deduce the order of reaction with respect to $\text{I}_2(\text{g})$.
Explain your answer, giving data in support of your explanation.
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(ii) Use information from (a)(ii) and your answer to (b)(i) to write the rate equation for the forward reaction.
rate = ...................................................................................................................................................................... [1]

(iii) Use your rate equation and data from experiment 1 to calculate the value of the rate constant, $k$, for the forward reaction at 400K. Include units for $k$.
$k = ......................................$ units = ...................................... [2]

(c) At 400K the rate constant for the forward reaction is approximately 1000 times greater than the rate constant for the backward reaction. The overall orders of the forward and backward reactions are the same.

forward reaction \( \text{H}_2(\text{g}) + \text{I}_2(\text{g}) \rightarrow 2\text{HI}(\text{g}) \)
backward reaction \( 2\text{HI}(\text{g}) \rightarrow \text{H}_2(\text{g}) + \text{I}_2(\text{g}) \)

(i) Use this information to explain what will happen if equal concentrations of HI(g), $\text{H}_2(\text{g})$ and $\text{I}_2(\text{g})$ are mixed at 400K.
You should comment on:
• the relative initial rates of the forward and backward reactions
• the position of the equilibrium reached.
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(ii) At 700K the rate constant for the forward reaction is approximately 50 times greater than the rate constant for the backward reaction.
Use this information and the information in (c)(i) to deduce the signs of the $\Delta H$ values of the forward and backward reactions. Explain your answer.
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[Total: 12]

(a) Write an expression for the $K_a$ of the weak acid HA in terms of the concentrations of the species involved.

$K_a = \text{.....................}$ [1]

(b) The hydroxylammonium ion, $HONH_3^+$, is a weak acid. A $1.00 \times 10^{-3}$ moldm$^{-3}$ solution of hydroxylammonium ions has a pH of 4.41.

(i) Calculate the $K_a$ of $HONH_3^+$.
$K_a = \text{............................}$ [2]

(ii) Calculate the p$K_a$ of $HONH_3^+$.
p$K_a = \text{............................}$ [1]

(c) The solubility product of manganese(II) hydroxide, $Mn(OH)_2$, in water is $1.1 \times 10^{-11}$ mol$^3$dm$^{-9}$ at 298K.

Calculate the solubility of $Mn(OH)_2$ in water at 298K.

solubility = ......................... mol dm$^{-3}$ [2]

(a) The energy cycle shown can be used, along with suitable data, to calculate the enthalpy change of hydration of $\text{Ca}^{2+}(g)$. Each arrow indicates a transformation, W, X, Y and Z. Each transformation consists of one or more steps.



The following data and data from the Data Booklet should be used.

electron affinity of $\text{Cl}(g)$ = –349 kJ mol$^{-1}$
enthalpy change of atomisation of Ca(s) = +193 kJ mol$^{-1}$
enthalpy change of formation of CaCl$_2$(s) = –795 kJ mol$^{-1}$
enthalpy change of solution of CaCl$_2$(s) = –83 kJ mol$^{-1}$
enthalpy change of hydration of $\text{Cl}^{-}(g)$ = –364 kJ mol$^{-1}$

(i) Calculate the value of the enthalpy change corresponding to transformation W. Show your working.

enthalpy change W = .......................... kJ mol$^{-1}$ [2]

(ii) Use your answer to (a)(i) and other data to calculate the value of the enthalpy change corresponding to transformation Z.

enthalpy change Z = .......................... kJ mol$^{-1}$ [2]

(iii) Use your answer to (a)(ii) to calculate the enthalpy change of hydration of $\text{Ca}^{2+}(g)$.

enthalpy change of hydration of $\text{Ca}^{2+}(g)$ = .......................... kJ mol$^{-1}$ [2]

(iv) Write an expression, in terms of W, X, Y and/or Z, to show how the enthalpy changes of two of the transformations can be used to calculate the lattice energy of CaCl$_2$(s).

lattice energy of CaCl$_2$(s) = ......................................................................................................... [1]

(v) State whether the lattice energy of CaCl$_2$(s) is more or less exothermic than the lattice energy of MgF$_2$(s).

Explain your answer.

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(b) The sulfates of the Group 2 elements vary in solubility down Group 2.

(i) Give the names of two solutions that could be mixed to form barium sulfate.

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(ii) State and explain how the solubilities of the sulfates of the Group 2 elements vary down Group 2.

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(a) Identify the substances liberated at the anode and at the cathode during the electrolysis of saturated KCl(aq).
at the anode ........................................................................................................
at the cathode .......................................................................................................

(b) When dilute sulfuric acid is electrolysed, oxygen is liberated at the anode.
  Dilute sulfuric acid is electrolysed for 15.0 minutes using a current of 0.750A.
  Calculate the volume of oxygen that is liberated under room conditions.

volume of oxygen = .............................. cm³

(c) The halogens chlorine, bromine and iodine differ in their strengths as oxidising agents. These strengths are indicated by the $E^{\circ}$ values for these halogens.

(i) Give the $E^{\circ}$ values for chlorine, bromine and iodine acting as oxidising agents.
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[1]

(ii) Deduce which of chlorine, bromine and iodine will react with a solution of Sn²⁺(aq) under standard conditions.
  Explain your answer. Include a relevant equation in your explanation.
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[3]

(iii) An excess of chlorine is added to a solution of acidified Mn²⁺(aq) under standard conditions.
  Give the formula of the product of this reaction that contains manganese.
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[1]

(d) An electrochemical cell can be made by connecting an Fe³⁺/Fe²⁺ half-cell to an $S_{2}O_{8}^{2-}$/$SO_{4}^{2-}$ half-cell under standard conditions.

(i) Calculate the standard cell potential of this electrochemical cell.
$E^{\circ}_{cell} = ..............................$ V
[1]

(ii) State the material that should be used as the electrode in each half-cell.
  in the Fe³⁺/Fe²⁺ half-cell .............................................................
  in the $S_{2}O_{8}^{2-}$/$SO_{4}^{2-}$ half-cell ........................................................
[1]

(iii) Describe one change to each half-cell that would increase the value of the cell potential. The temperature should remain at 298K.
  Fe³⁺/Fe²⁺ half-cell ................................................................................
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  $S_{2}O_{8}^{2-}$/$SO_{4}^{2-}$ half-cell ........................................................................
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[1]

(a) Define the term transition element.
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(b) (i) Complete the electronic configuration of an isolated gaseous Fe³⁺ ion.
1s² ...................................................................................................................... [1]
(ii) Name two transition elements whose isolated gaseous atoms have the same number of electrons in the 3d subshell as an isolated gaseous Fe³⁺ ion.
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(c) Cobalt(II) sulfate is added to water to form a pink solution containing complex ion P. An excess of concentrated hydrochloric acid is added to this solution to form a blue solution containing complex ion Q.
(i) Complete the diagram to show the three-dimensional structure of Q. State the charge on this complex ion.
charge ...............
[2]
(ii) Name the type of reaction in which P forms Q.
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(iii) Explain why solutions that contain transition element ions are often coloured.
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(iv) Explain why the colours of P and Q are different.
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(d) A solution of the bidentate ligand 1,2-diaminoethane, H₂NCH₂CH₂NH₂, is added to an aqueous solution of cobalt(II) sulfate. Oxygen is then bubbled into the mixture forming a complex ion with the formula [Co(H₂NCH₂CH₂NH₂)₃]³⁺.
This complex ion exists as a mixture of two isomers. The geometry of both of these isomeric complexes is octahedral.
(i) In this reaction, cobalt undergoes two types of reaction. One type of reaction is the same as that described in (c)(ii).
Name the other type of reaction that cobalt undergoes.
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(ii) Draw the three-dimensional structures of the two isomeric complexes in the boxes.
You may use N—N to represent a molecule of H₂NCH₂CH₂NH₂.

[2]
(iii) Name the type of stereoisomerism shown by these two isomeric complexes.
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(iv) State the co-ordination number of cobalt in these two isomeric complexes.
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(e) The stability constants, K_stab, of three complexes of mercury(II) are given in the table.
[Table_1]

(i) Write an expression for the K_stab of [Hg(CN)₄]^2-.
K_stab = ...................................................................................................................... [1]
(ii) An aqueous solution containing Hg²⁺ is added to a solution containing equal concentrations of CN^-(aq), Cl^-(aq) and I^-(aq). The mixture is left to reach equilibrium.
Predict which of the complexes [Hg(CN)₄]^2-, [HgCl₄]^2- and [HgI₄]^2- is present in the resulting mixture in the highest concentration and which is present in the lowest concentration. Explain your answer.
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(a) Ethanoic acid, $\text{CH}_3\text{CO}_2\text{H}$ and trichloroethanoic acid, $\text{CCl}_3\text{CO}_2\text{H}$, are both carboxylic acids. Ethanoic acid can be used to make ethanamide, $\text{CH}_3\text{CONH}_2$.

Place these three compounds in order of acidity, starting with the least acidic. Explain your answer.

\( \text{...............................} < \text{...............................} < \text{...............................} \)
least acidic & emsp;               most acidic

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(b) Methanoic acid, $\text{HCO}_2\text{H}$, and ethanedioic acid, $\text{HO}_2\text{CCO}_2\text{H}$, are two other carboxylic acids.

(i) State which, if any, of ethanoic acid, methanoic acid and ethanedioic acid will react with Fehling's reagent.
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(ii) State which, if any, of ethanoic acid, methanoic acid and ethanedioic acid will react with warm acidified manganate(VII) ions.
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(c) Ethanamide can be made from ethanoic acid in a two-step synthesis.

\[ \begin{array}{c} \text{ethanoic acid} \longrightarrow \text{A} \longrightarrow \text{ethanamide} \\ \text{step 1} \quad \text{step 2} \end{array} \]

(i) Compound A contains chlorine.
Give the structural formula and name of A.
structural formula .................................................................................................................................
name .................................................................................................................................... [2]

(ii) Suggest suitable reagents for steps 1 and 2.
step 1 ...................................................................................................................
step 2 ................................................................................................................... [2]

(d) Compound A can also be used to make the amide $\text{CH}_3\text{CONHCH}_2\text{CH}_3$.

The proton NMR spectrum of the amide $\text{CH}_3\text{CONHCH}_2\text{CH}_3$ in the solvent $\text{CDCl}_3$ is shown.



(i) Explain why $\text{CDCl}_3$ is used as a solvent instead of $\text{CHCl}_3$.
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(ii) Complete the diagram with the chemical shifts, $\delta$, of the protons labelled in the $\text{CH}_3\text{CONHCH}_2\text{CH}_3$ molecule.

\(\.\.\.\text{H}\quad \/\delta = \text{..........}\.\.\.\. \)
\(.\.\\text{N}\.\.\.\. \/ \delta = \text{..........}\)
\($/.\.\.\.\.\\text{O}\quad \/ \delta = \text{..........}\/\$\)

(iii) State and explain how the proton NMR spectrum of the amide $\text{CH}_3\text{CONHCH}_2\text{CH}_3$ differs when dissolved in $\text{D}_2\text{O}$ rather than $\text{CDCl}_3$.
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(e) The mass spectrum of the amide $\text{CH}_3\text{CONHCH}_2\text{CH}_3$ includes a fragment ion with $m/e$ value of 58.
Give the molecular formula of this fragment ion.
fragment ion with $m/e$ value of 58 is .......................................................... [1]

(f) The amide undergoes the following reaction to produce diethylamine.

\[ \text{CH}_3\text{CONHCH}_2\text{CH}_3 \xrightarrow{\text{reagent B}} \text{C}_2\text{H}_5\text{NHCH}_2\text{CH}_3 \quad \text{diethylamine} \]

(i) Identify reagent B.
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(ii) State the number of different absorptions in the carbon-13 NMR spectrum of diethylamine.
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(a) Describe the structure of a benzene molecule, $C_6H_6$.

Your answer should include:
• the shape of the molecule
• the relative lengths of the C–C bonds
• bond angles
• the hybridisation of the carbon atoms
• the overlap between orbitals that produces each type of bond present.

(b) Benzene can be used as a starting material to produce phenylamine by a two-step synthesis.

Step 1 is the reaction of benzene with $NO_2^+$ ions.

Complete the mechanism and draw the intermediate of step 1.
Include all relevant charges and curly arrows to show the movement of electron pairs.
(ii) State the name of the mechanism in (b)(i).
(iii) Identify the reagents needed to produce $NO_2^+$ ions.
Write an equation to explain how these reagents produce $NO_2^+$ ions.
(iv) Give reagents and conditions for the production of phenylamine from nitrobenzene in step 2.

(c) Phenylamine reacts with $Br_2$(aq).
(i) Write an equation for this reaction. You may use structural or displayed formulae.
(ii) Name the organic product of this reaction.
(iii) Describe two observations that can be seen when phenylamine reacts with $Br_2$(aq).
observation 1 .........................................
observation 2 .........................................

(d) Describe the relative basicities of ammonia, ethylamine and phenylamine, starting with the least basic.
Explain your answer in terms of their structures.
.............................. < .............................. < ..............................
least basic most basic

(e) 1,3-diaminopropane, $H_2NCH_2CH_2CH_2NH_2$, can be used to make polyamides.
(i) Identify one compound that would react with 1,3-diaminopropane to form a polyamide.
(ii) Draw a section of the polymer chain formed from 1,3-diaminopropane and the compound you chose in (e)(i).
Your answer should include four monomer residues (two of each type of monomer) and show the amide link fully displayed. Clearly identify one repeat unit of this polymer.