AS & A Level Chemistry - 9701 Paper 4 2020 Winter Zone 1

Nitrogen monoxide, NO, reacts with oxygen to form nitrogen dioxide, NO_2.
2NO(g) + O_2(g) ⇌ 2NO_2(g)
The rate equation for the forward reaction is shown.
rate = k[NO]^2[O_2]

(a) Complete the following table.

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°C to determine the rate of the forward reaction.

experiment	[NO]/mol dm^-3	[O_2]/mol dm^-3	rate / mol dm^-3 s^-1
1	0.00300	0.00200	1.51 × 10^-4
2	0.00500	_______	6.05 × 10^-5

(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_2O_8^2-, react with iodide ions, I^-.
S_2O_8^2- + 2I^- → 2SO_4^2- + I_2
The rate equation for the reaction in the absence of any catalyst is shown.
rate = k[S_2O_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]

[Total: 8]

(a) The lattice energies of three ionic compounds are given.

[Table_1]

(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.
$$ \Delta H_{latt} \text{MgO(s)} = \text{.....................} \text{ kJ mol}^{-1} $$
$$ \Delta H_{latt} \text{BaO(s)} = \text{.....................} \text{ kJ mol}^{-1} $$
[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.

electron affinity of F(g) = -348 kJ mol$^{-1}$
enthalpy change of atomisation of Mg(s) = +147 kJ mol$^{-1}$
enthalpy change of formation of MgF$_2$(s) = -1102 kJ mol$^{-1}$

$$ \Delta H_{latt} \text{MgF}_2\text{(s)} = \text{.....................} \text{[3]} $$

(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]
Total: 15

(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 .........................................

(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
(c) The equation representing the standard electrode potential, $\text{E}^∘$, 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) + 5$e^− \rightleftarrows \text{Mn}^{2+}$ (aq) + 4$\text{H}_2\text{O}$ (l) $\text{E}^∘ = +1.52 \text{V}$

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

(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.
...........................................................
...........................................................
...........................................................

(a) (i) Give the mathematical expression for each of the terms pH and $K_w$.

pH = ......................................................

$K_w$ = ......................................................

(a) (ii) Calculate the pH of $0.027 \, \text{mol dm}^{-3}$ NaOH(aq).

pH = ..............................................

(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 = ..............................................

(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 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 g of ethanamide at equilibrium.

(i) Calculate the partition coefficient, $K_{pc}$, for ethanamide in water and octan-1-ol.

$K_{pc}$ = ..............................................

(c) (ii) The $50.0 \, \text{cm}^3$ of water containing 0.935 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

A solution is made by dissolving CuSO$_4$·5H$_2$O in an excess of aqueous ammonia. This solution contains the copper complex [Cu(NH$_3$)$_4$]$^{2+}$.

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

$$K_{stab} = \text{.....................}$$

[1]

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

.................................................................................................................................

[1]

The solution of [Cu(NH$_3$)$_4$]$^{2+}$ is heated gently in a fume cupboard so that NH$_3$ is released. Some NH$_3$ remains in solution and some forms 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.

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

(b) Suggest an equation for the reaction of [Cu(NH$_3$)$_4$]$^{2+}$ to form Cu(OH)$_2$ as the aqueous solution of [Cu(NH$_3$)$_4$]$^{2+}$ 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]

[2]

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

.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................

[5]

(a) When 1.0 mol dm^-3 Na₂S₂O₃(aq) is added to a solution containing Ag⁺(aq) ions, a linear complex, P, is formed. S₂O₃^2- 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)₂Cl₂]^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)₂Cl₂]^2-.
.............................................................................................................................................................. [1]
(iii) Name the type of stereoisomerism shown by [Pt(CN)₂Cl₂]^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 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 most acidic.
Explain your answer.
........................................ > ........................................ > ........................................
most acidic                    least acidic
.................................................................................................................................................
.................................................................................................................................................
.................................................................................................................................................
.................................................................................................................................................
................................................................................................................................................. [3]

Benzene, C₆H₆, 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 Br⁺.

Complete the mechanism by which benzene reacts with 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, C₆H₁₁CH₂OH, 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_10O_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]
[Total: 9]

(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 | type of polymerisation
HOCH$_2$CH$_2$OH and HO$_2$CCH$_2$CO$_2$H
and \,\, \quad \text{HO}\qquad \qquad \text{OH} \quad \quad \quad \qquad \qquad \, \quad \qquad \, \qquad \begin{align}\quad & & \begin{matrix} \qquad & \qquad \qquad \qquad \quad \, \quad \qquad \qquad \text{Cl} \qquad- \qquad & \quad \qquad \qquad \text{Cl} \qquad \,\qquad \, \quad\qquad \qquad & \end{matrix} \quad \quad \qquad \qquad \quad \end{align}\,\begin{align}\quad CH_3CH_2CF_2 \quad & \quad \text{and} \quad \quad \ \space \quad CH_3\qquad CHCH_2 \quad & \end{align}

(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.

[3]

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


(c) The skeletal formula of compound W is shown.

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

(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.
[1]

[Total: 8]