AS & A Level Chemistry - 9701 Paper 4 2020 Winter Zone 3

Nitrogen monoxide, NO, reacts with oxygen to form nitrogen dioxide, NO$_2$.

2NO(g) + O$_2$(g) $\rightleftharpoons$ 2NO$_2$(g)

The rate equation for the forward reaction is shown.

rate = k[NO]$^2$[O$_2$]

(a) Complete the following table.

[Table_1]

the order of reaction with respect to [NO]
the order of reaction with respect to [O$_2$]
the overall order of reaction
[1]

(b) Two separate experiments are carried out at 30$^\circ$C to determine the rate of the forward reaction.


[Table_2]

(i) Use the data for experiment 1 to calculate the value of the rate constant, k. State the units of k.

k = .......................................... units = ..........................................
[2]

(ii) Calculate the value of [NO] in experiment 2.

[NO] = .......................................... mol dm$^{-3}$
[1]

(c) Define the term rate-determining step.

..................................................................................................................
..................................................................................................................
[1]

(d) Peroxodisulfate ions, S$_2$O$_8^{2-}$, react with iodide ions, I$^-$.

S$_2$O$_8^{2-}$ + 2I$^-$ $\rightarrow$ 2SO$_4^{2-}$ + I$_2$

The rate equation for the reaction in the absence of any catalyst is shown.

rate = k[S$_2$O$_8^{2-}$][I$^-$]

(i) Suggest equations for a two-step mechanism for this reaction, stating which of the two steps is the rate-determining step.

step 1 ..........................................
step 2 ..........................................
rate-determining step = ..........................................
[2]

(ii) A large excess of peroxodisulfate ions is mixed with iodide ions. Immediately after mixing, [I$^-$] = 0.00780 mol dm$^{-3}$. Under the conditions used, the half-life of [I$^-$] is 48 seconds.

Calculate the iodide ion concentration 192 seconds after the peroxodisulfate and iodide ions are mixed.

iodide ion concentration = .......................................... mol dm$^{-3}$
[1]

The lattice energies of three ionic compounds are given.
[Table_1]
(a) (i) Define the term lattice energy.
.................................................. ...........................................................................................................
...................................................................................................................................... [2]
(ii) Explain why the lattice energy of CaO is more exothermic than the lattice energy of LiF.
.......................................................................................................................... ................................................................................................................................................ [1]
(iii) Use the data in the table to estimate approximate values for the lattice energies of magnesium oxide and barium oxide.
$$\Delta H_{\text{latt}} \text{MgO(s)} = \text{............................... kJ mol}^{-1}$$
$$\Delta H_{\text{latt}} \text{BaO(s)} = \text{............................... kJ mol}^{-1}$$ [1]
(b) (i) Write an equation for the reaction between BaO and H$_2$O.
Include state symbols.
.......................................................................................................................................... [1]
(ii) State and explain how the solubilities of the hydroxides of the Group 2 elements vary down the group.
................................................................................................. .................................................................................................................................................................................
................................................................................................................................................................................................................................ [4]
(c) Use the following data and relevant data from the Data Booklet to calculate a value for the lattice energy of magnesium fluoride, MgF$_2$(s).
You might find it helpful to construct an energy cycle.
Show your working.
$$\text{electron affinity of F(g)} = -348 \text{kJ mol}^{-1}$$
$$\text{enthalpy change of atomisation of Mg(s)} = +147 \text{kJ mol}^{-1}$$
$$\text{enthalpy change of formation of MgF}_2\text{(s)} = -1102 \text{kJ mol}^{-1}$$
$$\Delta H_{\text{latt}} \text{MgF}_2\text{(s)} = \text{...............................}$$ [3]
(d) (i) Define the term electron affinity.
................................................................................................................................................................................................................................... [2]
(ii) The electron affinity of carbon, C(g), is -120 kJ mol$^{-1}$.
Suggest an explanation for the difference between the electron affinity of fluorine and the electron affinity of carbon.
................................................................................................................................................... ................................................................................................................................................... [1]

(a) Identify the substances liberated at the anode and at the cathode during the electrolysis of aqueous sodium sulfate, $\text{Na}_2\text{SO}_4$(aq).

anode .................................................................
cathode .............................................................. [1]

(b) When molten sodium chloride is electrolysed, chlorine is liberated at the anode and sodium is liberated at the cathode.

A sample of molten sodium chloride is electrolysed for 1.50 hours using a current of 4.50A.

Calculate the volume of chlorine and the mass of sodium that are liberated under room conditions.

volume of chlorine = ....................................... dm$^3$
mass of sodium = ....................................... g [4]

(c) The equation representing the standard electrode potential, $E^\circ$, for the reduction of $\text{MnO}_4^−$(aq) to $\text{Mn}^{2+}$(aq) in acid solution is given.

$\text{MnO}_4^−$(aq) + 8$\text{H}^+$(aq) + 5e$^− \rightleftharpoons$ $\text{Mn}^{2+}$(aq) + 4$\text{H}_2\text{O}$(l) $E^\circ$ = +1.52 V

(i) Draw a diagram of the apparatus that would be used to measure the $E^\circ$ value of this half-cell. Your diagram should be fully labelled to identify all apparatus, substances and conditions. [4]

(ii) Use the Data Booklet to identify a substance that could be used to oxidise $\text{Mn}^{2+}$ ions to $\text{MnO}_4^{-}$ ions under standard conditions.

Write an equation for the reaction.

.......................................................................................................................................
.......................................................................................................................................
....................................................................................................................................... [2]

[Total: 11]

(a) (i) Give the mathematical expression for each of the terms pH and $K_w$.
pH = .................................................................
$K_w$ = ................................................................. [2]
(ii) Calculate the pH of $0.027 \text{ mol dm}^{-3}$ NaOH(aq).
pH = .............................................. [1]

(b) The $K_a$ value of chloric(I) acid, $HClO$, is $3.72 \times 10^{-8} \text{ mol dm}^{-3}$.
Calculate the pH of $0.010 \text{ mol dm}^{-3}$ $HClO(aq)$.
pH = ......................................... [1]

(c) Water and octan-1-ol form two layers when mixed.
Ethanamide is more soluble in water than it is in octan-1-ol. When $1.00 \text{ g}$ of ethanamide is added to $50.0 \text{ cm}^3$ of water and this is then shaken with $50.0 \text{ cm}^3$ of octan-1-ol, it is found that the water layer contains $0.935 \text{ g}$ of ethanamide at equilibrium.
(i) Calculate the partition coefficient, $K_{pc}$, for ethanamide in water and octan-1-ol.
$K_{pc}$ = .............................................. [1]
(ii) The $50.0 \text{ cm}^3$ of water containing $0.935 \text{ g}$ of ethanamide is then shaken with $100.0 \text{ cm}^3$ of pure octan-1-ol under the same conditions.
Calculate the mass of ethanamide that is dissolved in the $100.0 \text{ cm}^3$ of octan-1-ol at equilibrium.
mass of ethanamide = .............................................. g [2]
[Total: 7]

A solution is made by dissolving CuSO₄·5H₂O in an excess of aqueous ammonia. This solution contains the copper complex $[\text{Cu(NH}_3\text{)}_4]^{2+}$.

(a) (i) Write an expression for the $K_{\text{stab}}$ of $[\text{Cu(NH}_3\text{)}_4]^{2+}$.

$K_{\text{stab}} =$ \\\\\\\\\\\\\\\\\\[1]

(ii) State the colour of the solution of $[\text{Cu(NH}_3\text{)}_4]^{2+}$.
.................................................................................................................. [1]

The solution of $[\text{Cu(NH}_3\text{)}_4]^{2+}$ is heated gently in a fume cupboard so that $\text{NH}_3$ is released. Some $\text{NH}_3$ remains in solution and some forms $\text{NH}_3$ gas. The colour of the solution changes; a precipitate of Cu(OH)₂ forms and is collected.

A sample of Cu(OH)₂ is added to concentrated hydrochloric acid. A reaction takes place forming a coloured copper complex, Y.

A sample of Cu(OH)₂ is added to dilute sulfuric acid. A reaction takes place forming a coloured copper complex Z.

$[\text{Cu(NH}_3\text{)}_4]^{2+}$, Y and Z are different colours.

(b) Suggest an equation for the reaction of $[\text{Cu(NH}_3\text{)}_4]^{2+}$ to form Cu(OH)₂ as the aqueous solution of $[\text{Cu(NH}_3\text{)}_4]^{2+}$ is heated.
.................................................................................................................. [1]

(c) Suggest an equation for the reaction of Cu(OH)₂ with concentrated hydrochloric acid, forming Y.
.................................................................................................................. [2]

(d) Complete the table with the colour and geometry of complex Y and the colour, geometry and formula of complex Z.

[Table_1]

.................................................................................................................. [2]

(e) Explain why complexes Y and Z are coloured and why their colours are different.
.................................................................................................................. [5]

(a) When 1.0 mol dm$^{-3}$ Na$_2$S$_2$O$_3$(aq) is added to a solution containing Ag$^{+}$(aq) ions, a linear complex, P, is formed. S$_2$O$_3^{2-}$ ions are present in P as monodentate ligands.

(i) Define the term monodentate ligand.
.................................................................................................................................
................................................................................................................................. [2]

(ii) Give the formula of P, including its charge.
................................................................................................................................. [1]

(b) When 1.0 mol dm$^{-3}$ NaCN(aq) is added to a solution of P, a mixture which includes a second linear complex, Q, is formed. In this mixture the concentration of Q is much greater than the concentration of P.

(i) Write an equation for the reaction that occurs when NaCN(aq) is added to a solution of P.
................................................................................................................................. [1]

(ii) Suggest a reason why the concentration of Q is much greater than the concentration of P in the mixture.
.................................................................................................................................
.................................................................................................................................
................................................................................................................................. [1]

(iii) Name the type of reaction in which P forms Q.
................................................................................................................................. [1]

(c) Platinum forms a complex ion with the formula [Pt(CN)$_2$Cl$_2$]$^{2-}$. In this complex ion the carbon atom of each CN$^{-}$ ligand bonds to the platinum ion. This complex shows stereoisomerism.

(i) There are only two isomers of this complex.
Draw structures of these two isomers in the boxes below.

[1]

(ii) Describe the geometry of [Pt(CN)$_2$Cl$_2$]$^{2-}$.
................................................................................................................................. [1]

(iii) Name the type of stereoisomerism shown by [Pt(CN)$_2$Cl$_2$]$^{2-}$.
................................................................................................................................. [1]

Phenol, $C_6H_5OH$, is a weak acid.

(a) Phenol can be made from phenylamine, $C_6H_5NH_2$.
Give the reagents and conditions for this reaction.
.......................................................................................................................................................................................
....................................................................................................................................................................................... [2]

(b) Phenol reacts with dilute aqueous nitric acid under room conditions to give a mixture of two
isomeric products with molecular formula $C_6H_5NO_3$.
Use the \textit{Data Booklet} to draw the structural formulae of these two products in the boxes and
name each product.


name
name ............................................................................................ [2]

(c) Phenol reacts with an excess of aqueous bromine.

(i) Draw and name the organic product of this reaction in the box.

name ............................................... [2]

(ii) Describe two visual observations that can be made when phenol reacts with an excess of
aqueous bromine.
observation 1 ...............................................
observation 2 ............................................... [1]

(d) Write an equation for a neutralisation reaction in which phenol behaves as an acid.
............................................................................................................................................................................. [1]

(e) Water, phenol and ethanol can all behave as acids.
Place these three compounds in order of acidity, starting with the \textbf{most} acidic.
Explain your answer.
................................ > ................................. > ..................................
most acidic
least acidic
.............................................................................................................................................................................
.............................................................................................................................................................................
.............................................................................................................................................................................
.............................................................................................................................................................................
............................................................................................................................................................................. [3]

Benzene, $C_6H_6$, can be obtained from crude oil.
(a) Benzene reacts with bromine, in the presence of a suitable catalyst, forming bromobenzene as one product.
(i) Give the name or formula of the other product of this reaction.
.............................................................................................................................. [1]
(ii) In the presence of the catalyst, bromine can be considered to form the electrophile $\text{Br}^+$.
Complete the mechanism by which benzene reacts with $\text{Br}^+$, using curly arrows to show the movement of electron pairs.

[2]
(iii) Name this mechanism.
.............................................................................................................................. [1]

(b) Benzene can be used as a starting material in the synthesis of cyclohexylmethanol, $C_6H_{11}CH_2OH$, as outlined below.

(i) Identify a suitable reagent and a suitable catalyst for step 1.
reagent .......................................................................................................................................
catalyst ....................................................................................................................................... [2]
(ii) Draw the structure of A.

[1]
(iii) Identify suitable reagents for steps 3 and 4.
step 3 ...................................................................................................................................
step 4 ................................................................................................................................... [2]
(iv) Deduce the number of peaks in the carbon-13 NMR spectrum of cyclohexylmethanol.
.............................................................................................................................. [1]
[Total: 10]

The proton NMR spectrum of compound E in the solvent $CDCl_3$ is shown. The molecular formula of compound E is $C_9H_{10}O_2$.

(a) Explain why $CDCl_3$ is used as a solvent instead of $CHCl_3$. [1]
(b) Explain why TMS is added to give the small peak at chemical shift $\delta = 0$. [1]
(c) Compound E is hydrolysed by hot $NaOH(aq)$, giving two organic products only. One of these products is ethanol.
Name the functional group in compound E that is hydrolysed by hot $NaOH(aq)$. [1]
(d) (i) Describe and explain the splitting patterns of the peaks at $\delta = 1.4$ and $\delta = 4.3$.
splitting pattern at $\delta = 1.4$ .................................................................................................. reason for splitting pattern at $\delta = 1.4$ ..................................................................
splitting pattern at $\delta = 4.3$ .................................................................................................. reason for splitting pattern at $\delta = 4.3$ ..................................................................
[2]
(ii) Each molecule of compound E contains five protons which give rise to the peaks between $\delta = 7.0$ and $\delta = 8.5$.
Identify the functional group in compound E which contains these protons. [1]
(iii) Give the structural formula of compound E. [1]
(e) The mass spectrum of compound E includes fragment ions with $m/e$ values of 29 and 77.
Give the formulae of these fragment ions.
fragment ion with $m/e = 29$ .............................................................................................
fragment ion with $m/e = 77$ .............................................................................................
[2]

(a) The table shows three pairs of monomers that are capable of polymerisation.

Complete the table by identifying each type of polymerisation.

[Table_1: pair of monomers and type of polymerisation]
pair of monomers | type of polymerisation
HOCH_{2}CH_{2}OH and HO_{2}CCH_{2}CO_{2}H
[Image_1: structure]
CH_{3}CHCF_{2} and CH_{3}CHCH_{2}

(b) 2-aminopropanoic acid, CH_{3}CH(NH_{2})CO_{2}H, can polymerise under suitable conditions. No other monomer is involved in this reaction.

(i) Draw a section of the polymer chain formed including three monomer residues. Clearly identify one repeat unit on your diagram.

(ii) 2-aminopropanoic acid, CH_{3}CH(NH_{2})CO_{2}H, exists as two stereoisomers.

Draw three-dimensional diagrams to show the two stereoisomers of 2-aminopropanoic acid. State the type of stereoisomerism shown.

type of stereoisomerism .................................................................

(c) The skeletal formula of compound W is shown.
[Image_2: skeletal formula of compound W]
When W is mixed with a second compound, called a hardener, a polymerisation reaction occurs, producing a non-solvent-based adhesive.

(i) Give the name of this type of non-solvent-based adhesive.

(ii) The hardener is a diamine. A diamine has an alkyl chain with two amine groups which are not bonded to the same carbon atom.

Draw the structural formula of a compound that would make a suitable hardener.