A Level Chemistry Paper 4

Define enthalpy change of solution. [1]

enthalpy change when one mole of a solute AND dissolves in water to form a solution of infinite dilution

Suggest the trend in the magnitude of the lattice energies of the Group 1 iodides, LiI, NaI, KI.

Explain your answer. [2]

cationic) charge density decreases Li+ to K+ [1]

so lattice energies become less negative / less exothermic AND because less attraction between ions [1]

The reaction of I^- ions with persulfate ions, S₂O₈^2-, can be catalysed by Fe³⁺ ions.

2I^- + S₂O₈^2- → I₂ + 2SO₄^2-

Write equations to show how Fe3+ catalyses this reaction. [2]

TiO²⁺(aq) is a colourless ion.

Suggest why. [2]

Ti is in +4 oxidation state so no d electrons / d⁰ OR Ti in TiO2+ has no d electrons / d⁰ [1]

cannot absorb photons / light in visible spectrum OR no wavelength / frequency absorbed in visible spectrum [1]

The TiO²⁺ ion forms when TiO₂ reacts with an excess of sulfuric acid. TiO²⁺ can be reduced by zinc metal in acidic conditions to form a purple solution containing Ti³⁺(aq).

Write an ionic equation for the reduction of TiO²⁺ by zinc metal in acidic conditions. [1]

2TiO²⁺ 4H⁺ + Zn → 2Ti³⁺ + 2H₂O + Zn²⁺

Nitrophenol can be produced from benzene in a five-step synthesis route. Outline this multi-step synthesis reaction. [10]

• benzene → nitrobenzene (concentrated HNO₃ + H₂SO₄ @ 25 — 60^oC)

• nitrophenol → phenylamine (hot Sn, concentrated HCl followed by NaOH)

• phenylamine → diazonium salt (HNO₂, <10^oC)

• diazonium salt → phenol (warm with H₂O)

• phenol → nitrophenol (dilute HNO₃ at room temperature)

State the two types of reaction that occur when J reacts with NaOH(aq). [2]

• hydrolysis

• acid-base / neutralisation

Phenol and benzene both react with nitric acid, as shown in the figure.

Explain why the reagents and conditions for these two reactions are different. [3]

p-orbital on oxygen overlaps with ring / π system OR lone pair of e– on oxygen is delocalised into the ring [1]

electron density in ring increases [1]

attracts/polarises electrophile better [1]

Lidocaine is used as an anaesthetic. A synthesis of lidocaine is shown.

W can be formed by reacting HOCH₂COOH with an excess of SOCl₂, PCl₅, or PCl₃.

Write equations for these reactions. [3]

• SOCl₂ by-products: SO₂ + HCl

• PCl₅ by-products: POCl₃ + HCl

• PCl₃ by-products: H₃PO₄

After W and X have reacted together, an excess of CH₃COONa(aq) is added to the reaction mixture. Suggest why. [1]

to remove / neutralise excess H+ / acid produced

OR to react with any acidic by-products / HCl / SO2

OR to react with any unreacted W

The reaction of W with X, reaction 1, follows an addition–elimination mechanism.

Complete the mechanism for the reaction of W with X.

Include all relevant curly arrows, lone pairs of electrons, charges and partial charges.

Use Ar–NH₂ to represent X. [4]

Describe the mode of action of a heterogeneous catalyst in a reaction. [3]

M1 adsorption of reactants to the surface of the catalyst

M2 bonds in the reactants weaken (lowering the activation energy)

M3 reaction occurs and the products are desorbed

Manganese(VII) oxide, Mn₂O₇, can be made by treatment of KMnO₄ with concentrated sulfuric acid (reaction 1).

Mn₂O₇ readily decomposes at room temperature to form manganese(IV) oxide and a colourless diatomic gas (reaction 2).

Construct equations for both the reactions described. [2]

Aqueous manganese(II) ions show similar chemical properties to aqueous copper(II) ions when reacted separately with NaOH(aq) and with concentrated HCl.

1. Write the ionic equation, and state the type of reaction, for the reaction of [Mn(H₂O)₆]²⁺ with NaOH(aq). [2]

2. Write the ionic equation, and state the type of reaction, for the reaction of [Mn(H₂O)₆]²⁺ with concentrated HCl. [2]

Define standard electrode potential, E^o. [1]

voltage / EMF / potential difference when a half-cell is connected to a (standard) hydrogen electrode under standard conditions

A salt bridge is used in an electrochemical cell.

State the function of the salt bridge. Explain your answer [1]

ions move (from the salt bridge) to maintain charge balance / complete the circuit

Benzoyl chloride is hydrolysed by water at room temperature to form benzoic acid.

Complete the diagram to show the mechanism for the reaction between C₆H₅COCl and H₂O.

Include charges, dipoles, lone pairs of electrons and curly arrows as appropriate. [4]

Thin-layer and gas-liquid chromatography can be used to analyse mixtures of substances.

Each type of chromatography makes use of a stationary phase and a mobile phase.

	stationary phase	mobile phase
thin-layer chromatography
gas-liquid chromatography

The solubility of the Group 2 sulfates decreases down the group.

Explain this trend. [3]

The solubility of the Group 2 hydroxides increases down the group.

Explain this trend. [3]

Describe the general trend in first electron affinities for Cl, Br and I. Explain your answer.

The thermal stability of Group 1 hydrogencarbonates increases down the group. Suggest an explanation for the trend in thermal stability of the Group 1 hydrogencarbonates. [2]

M1 ionic radius of M+ / cationic radius increases OR charge density of ion / M+ decreases down Group 1

M2 less distortion / polarisation of the anion / HCO3 – OR CO bond / C-O / C=O less weakened

Complete Table 5.1 to predict the substance liberated at each electrode during electrolysis of the indicated electrolyte with inert electrodes. [3]

Concentrated HNO₃ reacts with concentrated H₂SO₄ to generate the electrophile NO₂⁺ .

Write the equation(s) to show how this happens. [2]

Compare the relative ease of nitration of benzene, benzoic acid and phenol. Explain your reasoning; include reference to the structures of the three compounds in your answer. [4]

Compare the relative acidities of ethanol, ethanoic acid, chloroethanoic acid and phenol. Explain your reasoning. [4]

Compare the relative basicities of ammonia, cyclohexylamine and phenylamine. Explain your reasoning. [3]

Complete the mechanism of the reaction between cyclohexylamine and CH₃COCl.

R–NH₂ is used to represent cyclohexylamine. Include all relevant lone pairs of electrons, curly arrows, charges and partial charges. [4]

Explain the reasons why the lattice energy of MgCl₂ is more exothermic than the lattice energy of KCl. [2]

Mg2+ is smaller (than K+ )

Mg2+ is greater charge (than K+ )

greater attraction between Mg2+ and Cl – /between the ions (in MgCl2) OR stronger ionic bonds (in MgCl2)

Describe the standard conditions used in a half-cell. [1]

• ion concentration of 1 mol dm^-3

• 298K

Equal volumes of 1.0mol dm^–3 Sn²⁺(aq) and 1.0mol dm^–3 Cl^- (aq) are mixed.

Use relevant E^o values to explain whether a reaction occurs between these two ions. [2]

Equal volumes of 1.0mol dm^–3 of Sn²⁺(aq) and acidified 1.0mol dm^–3 VO²⁺(aq) are mixed.

Write an equation for the reaction that takes place in the resulting mixture. [2]

State what is meant by partition coefficient. [1]

ratio of concentration of the solute in two solvents at equilibrium [1]

The partition coefficient, K_pc, for butanoic acid between ethoxyethane and water is 3.50.

A solution of 2.00g of butanoic acid in 100cm³ ethoxyethane is added to water. This mixture is left until there is no further change in the concentration of butanoic acid in either solvent. The mass of butanoic acid dissolved in the ethoxyethane layer is now 1.62g.

Calculate the volume of water used. [2]

A is a pale green salt containing Fe²⁺ ions. A sample of 2.62g of A is dissolved in water and the solution is made up to exactly 100cm³ with water. 25.0cm³ samples of this solution are placed in conical flasks and titrated against 0.0100mol dm^–3 acidified potassium manganate(VII).

The equation for the only reaction that occurs is shown.

5Fe²⁺ + MnO4^– + 8H⁺ → 5Fe³⁺ + Mn²⁺ + 4H₂O

The average titre value is 35.0cm³ of 0.0100mol dm^–3 acidified potassium manganate(VII).

1. Describe the colour change that is seen in the conical flask at the end-point of this titration. [1]

2. Calculate the percentage by mass of iron in A. [Ar : Fe, 55.8] [2]

1. colourless / pale green to pink / purple

Define stability constant. [1]

the equilibrium (constant) for the formation of the complex ion in a solvent from its constituent ions or molecules

Chlorobenzene and chloroethane have different reactivities in nucleophilic substitution reactions.

1. Identify a suitable reagent to illustrate this difference in reactivity. The reagent chosen should give visibly different results with chlorobenzene and chloroethane. [1]

2. Write equations to describe any reactions that occur. [1]

3. Explain the difference in the reactivities of chlorobenzene and chloroethane in nucleophilic substitution reactions. [1]

Complete Table 9.1 to give the number of peaks in the carbon-13 NMR spectrum of each of the five isomers of C₅H₁₀O₂ that has an ester group. [2]

5 5 5 4 4

State the number of peaks that would be seen in the proton (1 H) NMR spectrum of methyl butanoate, CH₃CH₂CH₂CO₂CH₃. Name all the splitting patterns seen in this spectrum. [2]

H₂PO₂^- is a strong reducing agent. It can be used to reduce metal cations without the need for electrolysis.

HPO₃^2- + 2H₂O + 2e^- ⇌ H₂PO₂^- + 3OH^- E^o= –1.57V

In an experiment, an alkaline HPO₃^2-/H₂PO₂^- half-cell is constructed with [H₂PO₂^-] = 0.050 mol dm^-3. All other ions are at their standard concentration.

Predict how the value of E of this half-cell differs from its E^o value. Explain your answer. [2]

The Cr³⁺/Cr half-cell has a standard electrode potential of –0.74V. An electrochemical cell consists of an alkaline HPO₃^2-/H₂PO₂^- half-cell and a Cr³⁺/Cr half-cell.

Calculate the standard cell potential, E^o_cell^.

+0.83V

Complete the diagram in Fig. 2.1 to show how the standard electrode potential of the Cr³⁺/Cr half-cell can be measured relative to that of the standard hydrogen electrode.

1. Identify the chemicals, conditions and relevant pieces of apparatus. [3]

2. Label Fig. 2.1 to show: [1]
   which is the positive electrode
   the direction of electron flow in the external circuit

3. H₂PO₂^- reduces Ni²⁺ to Ni in alkaline conditions. Use equation 1 to construct the ionic equation for this reaction.
   equation 1 HPO₃^2- + 2H₂O + 2e^- ⇌ H₂PO₂^- + 3OH^- [1]

State and explain the relative ease of hydrolysis of acyl chlorides, alkyl chlorides and aryl chlorides. [3]

Tulobuterol is produced from Q as shown in Fig. 5.5.

Suggest reagents and conditions for steps 3 and 4.

Draw the structure of Z.

Define enSuggest one disadvantage of producing two enantiomers in this synthesis. Suggest a method of adapting the synthesis to produce a single enantiomer.