The rate of reaction between 2-chloro-2-methylpropane, (CH₃)₃CCl, and methanol is investigated. When a large excess of methanol is used, the overall reaction is first order. (CH₃)₃CCl + CH₃OH → (CH₃)₃COCH₃ + HCl Fig. 3.1 shows the results obtained. [Figure 3.1] (c) (i) Define standard electrode potential, E®. (ii) A salt bridge is used in an electrochemical cell. State the function of the salt bridge. Explain your answer. (iii) Complete the diagram of the apparatus that can be used to measure the Eº of the Cr2O72-(aq), H+(aq)/Cr3+(aq) electrode against the standard hydrogen electrode. Your diagram should be fully labelled to identify all apparatus, substances and conditions. [Figure with salt bridge] (iv) The E® of the Cr2O72-(aq), H+(aq)/Cr³+(aq) electrode is +1.33V. Label the negative electrode and the direction of electron flow in the external circuit when the current flows in your diagram in (c)(iii). (d) Table 3.1 lists relevant electrode potentials for some electrode reactions for use in (d)(i) and (d)(ii). Table 3.1 electrode reaction E/V Cr2O72- + 14H+ + 6e¯ = 2Cr3+ + 7H2O +1.33 CH3CHO + 2H+ + 2e¯ = CH3CH2OH -0.61 CH3COOH + 2H+ + 2e¯ = CH3CHO + H₂O -0.94 O2 + 4H+ + 4e¯ ⇌ 2H₂O +1.23

1. (a)(i)Use the graph to determine the rate of reaction at 40s. Show all your working. rate ... moldm-³s-1[1]
2. (a)(ii)Use the graph to show that the overall reaction is first order. Explain your answer.[2]
3. (b)In a different reaction, which is also a first order reaction, 75% of the reactant is consumed in 320 s. Calculate the rate constant, k, for this reaction. State the units for k. k = ... units = ...[2]
4. (c)(i)Define standard electrode potential, E®.[1]
5. (c)(ii)A salt bridge is used in an electrochemical cell. State the function of the salt bridge. Explain your answer.[1]
6. (c)(iii)Complete the diagram of the apparatus that can be used to measure the Eº of the Cr2O72-(aq), H+(aq)/Cr3+(aq) electrode against the standard hydrogen electrode. Your diagram should be fully labelled to identify all apparatus, substances and conditions.[3]
7. (c)(iv)The E® of the Cr2O72-(aq), H+(aq)/Cr³+(aq) electrode is +1.33V. Label the negative electrode and the direction of electron flow in the external circuit when the current flows in your diagram in (c)(iii).[1]
8. (d)(i)Ethanal is oxidised to ethanoic acid in the presence of Cr2O72- ions. Construct the ionic equation for the oxidation of ethanal to ethanoic acid using dichromate(VI) in acid conditions. Calculate the Ecell for this reaction. ionic equation Ecell = ... V[2]
9. (d)(ii)In an ethanol-oxygen fuel cell, CH3CH2OH(I) and O2(g) are in contact with two inert electrodes immersed in an acidic solution. The cell reaction for the oxidation of ethanol by oxygen is shown. 2CH3CH2OH + O2 → 2CH3COOH + 2H2O Ecell = +2.01 V Calculate AG, in kJ mol⁻¹, for the oxidation of ethanol by oxygen. AG = ... kJ mol-1[2]

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