Q1. In this question consider the data below. Q2. Use the data in the table below to answer this question. Electrochemical Cell 1 SCT E / V

Q1.

E / V Ag+_{(aq) + e}− _{→ Ag(s) +0.80} 2H+_{(aq) + 2e}− _{→ H2(g) 0.00} Pb2+_{(aq) + 2e}− _{→ Pb(s) −0.13} The e.m.f. of the cell Ag(s) | Ag+_{(aq) || Pb}2+_{(aq) | Pb(s) is}

A 0.93 V B 0.67 V C −0.67 V D −0.93 V

(Total 1 mark)

Q2. Use the data in the table below to answer this question.

E / V

MnO (aq) + 8H+_{(aq) + 5e}− _{→ Mn}2+_{(aq) + 4H}

2O(l) + 1.52 Cr2O (aq) + 14H+(aq) + 6e− → 2Cr3+(aq) + 7H2O(l) + 1.33 Fe3+_{(aq) + e}− _{→ Fe}2+_{(aq) + 0.77} Cr3+_{(aq) + e}− _{→ Cr}2+_(aq) − 0.41 Zn2+_{(aq) + 2e}− _{→ Zn(s) − 0.76} The most powerful oxidising agent in the table is

A Mn2+_(aq)

B Zn(s) C MnO (aq) D Zn2+_(aq)

Q3. Use the data in the table below to answer this question.

E / V

MnO (aq) + 8H+_{(aq) + 5e}− _{→ Mn}2+_{(aq) + 4H}

2O(l) + 1.52 Cr2O (aq) + 14H+(aq) + 6e− → 2Cr3+(aq) + 7H2O(l) + 1.33 Fe3+_{(aq) + e}− _{→ Fe}2+_{(aq) + 0.77} Cr3+_{(aq) + e}− _{→ Cr}2+_(aq) − 0.41 Zn2+_{(aq) + 2e}− _{→ Zn(s) − 0.76} Which one of the following statements is not correct?

A Fe2+_{(aq) can reduce acidified MnO (aq) to Mn}2+_(aq)

B CrO (aq) can oxidise acidified Fe2+_{(aq) to Fe}3+_(aq)

C Zn(s) can reduce acidified Cr2O (aq) to Cr2+(aq)

D Fe2+_{(aq) can reduce acidified Cr}3+_{(aq) to Cr}2+_(aq)

(Total 1 mark)

Q4.

Cr2O (aq) + 14H+(aq) + 6e− → 2Cr3+(aq) + 7H2O(l) E = +1.33 V Br2(aq) + 2e− → 2Br−(aq) E = +1.09 V Fe3+_{(aq) + e}− _{→ Fe}2+_{(aq) E = +0.77 V} VO2+_{(aq) + 2H}+_{(aq) + e}− _{→ V}3+_{(aq) + H2O(l) E = +0.34 V} SO (aq) + 4H+_{(aq) + 2e}− _{→ H2SO3(aq) + H2O(l) E = +0.17 V}

Based on the above data, which one of the following could reduce 0.012 mol of bromine to bromide ions?

A 40 cm3 _{of a 0.10 mol dm}−3 _{solution of Cr2O (aq)}

B 80 cm3 _{of a 0.30 mol dm}−3 _{solution of Fe}3+_(aq)

C 50 cm3 _{of a 0.24 mol dm}−3 _{solution of V}3+_(aq)

(Total 1 mark)

Q5.

Cu Cu2+ _Ag+ _Ag Which statement is correct about the operation of the cell?

A Metallic copper is oxidised by Ag+ _ions.

B The silver electrode has a negative polarity. C The silver electrode gradually dissolves to form Ag+ _ions.

D Electrons flow from the silver electrode to the copper electrode via an external circuit.

(Total 1 mark)

Q6. A disproportionation reaction occurs when a species M

2M+(aq) → M2+_{(aq) + M(s)}

The table below contains E data for copper and mercury species. E / V Cu2+_{(aq) + e}− _{→ Cu}+_{(aq) + 0.15} Cu+_{(aq) + e}− _{→ Cu(s) + 0.52} Hg2+_{(aq) + e}− _{→ Hg}+_{(aq) + 0.91} Hg+_{(aq) + e}− _{→ Hg(l) + 0.80}

Using these data, which one of the following can be predicted? A Both Cu(I) and Hg(I) undergo disproportionation.

B Only Cu(I) undergoes disproportionation. C Only Hg(I) undergoes disproportionation.

D Neither Cu(I) nor Hg(I) undergoes disproportionation.

Q7. Which ion cannot catalyse the reaction between iodide (I

Half-equation EO _{/ V} S2O82– + 2e– → 2SO42– +2.01 Co3+ _{+ e}– _{→ Co}2+ _+1.82 Fe3+ _{+ e}– _{→ Fe}2+ _+0.77 I2 + 2e– → 2I– +0.54 Cr3+ _{+ e}– _{→ Cr}2+ –0.41 A Co2+ B Cr2+ C Fe2+ D Fe3+ (Total 1 mark)

Q8.

E / V Ag+_{(aq) + e}− _{→ Ag(s) +0.80} 2H+_{(aq) + 2e}− _{→ H2(g) 0.00} Pb2+_{(aq) + 2e}− _{→ Pb(s) −0.13}

The e.m.f. of the cell Pt(s) | H2(g) | H+(aq) || Ag+(aq) | Ag(s) would be increased by

A increasing the concentration of H+_(aq).

B increasing the surface area of the Pt electrode. C increasing the concentration of Ag+_(aq).

D decreasing the pressure of H2(g).

Q9. Use the standard electrode potential data in the table below to answer the questions which

E/ V _________________________________________________________ Ce4+_{(aq) + e}– _Ce3+_{(aq) +1.70} MnO–_{(aq) + 8H}+_{(aq)+ 5e}– _Mn2+_{(aq) + 4H2O(l) +1.51} Cl2(g) + 2e– 2Cl–(aq) +1.36 VO2+(aq) +2H+(aq) + e– VO2+(aq) + H2O(l) +1.00 Fe3+_{(aq) + e}– _Fe2+_{(aq) +0.77} SO42–(aq) + 4H+(aq) + 2e– H2SO3(aq) + H2O(l) +0.17 _________________________________________________________

(a) Name the standard reference electrode against which all other electrode potentials are measured.

___________________________________________________________________

(1)

(b) When the standard electrode potential for Fe3+_{(aq) / Fe}2+_{(aq) is measured, a} platinum electrode is required.

(i) What is the function of the platinum electrode?

______________________________________________________________ (ii) What are the standard conditions which apply to Fe3+_(aq)/Fe2+_{(aq) when}

measuring this potential?

______________________________________________________________ ______________________________________________________________ ______________________________________________________________

(c) The cell represented below was set up under standard conditions. Pt|H2SO3(aq), SO42–(aq)||MnO4–(aq), Mn2+(aq)|Pt

Calculate the e.m.f. of this cell and write an equation for the spontaneous cell reaction.

Cell e.m.f. __________________________________________________________ Equation __________________________________________________________

___________________________________________________________________

(3)

(d) (i) Which one of the species given in the table is the strongest oxidising agent? ______________________________________________________________ (ii) Which of the species in the table could convert Fe2+_{(aq) into Fe}3+_{(aq) but}

could not convert Mn2+_{(aq) into MnO4}–_(aq)?

______________________________________________________________

(3)

(e) Use data from the table of standard electrode potentials to deduce the cell which would have a standard e.m.f. of 0.93 V. Represent this cell using the convention shown in part (c).

___________________________________________________________________

(2) (Total 12 marks)

Q10. This question is about vanadium compounds and ions.

(a) Use data from Table 4 to identify the species that can be used to reduce VO2+ ions to VO2+ _{in aqueous solution and no further.}

Explain your answer.

Electrode half-equation EƟ / V VO2+(aq) + 2H+(aq) + e− → VO2+(aq) + H2O(l) +1.00 VO2+_{(aq) + 2H}+_{(aq) + e}− _{→ V}3+_{(aq) + H2O(l) +0.34} Cl2(aq) + 2e− → 2Cl−(aq) +1.36 Fe3+_{(aq) + e}− _{→ Fe}2+_{(aq) +0.77} Zn2+_{(aq) + 2e}− _{→ Zn(s) –0.76} Reagent ___________________________________________________________ Justification _________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ (2)

(b) Give the oxidation state of vanadium in [VO(H2O)5]2+

___________________________________________________________________

(c) The [V(H2O)4Cl2]+ ion exists as two isomers. One isomer is shown. Draw the structure of the other isomer and state the type of isomerism.

Type of isomerism ____________________________________________________

(2)

(d) Heating NH4VO3 produces vanadium(V) oxide, water and one other product. Give an equation for the reaction.

___________________________________________________________________

(1)

(e) Vanadium(V) oxide is the catalyst used in the manufacture of sulfur trioxide. Give two equations to show how the catalyst is used and regenerated.

___________________________________________________________________ ___________________________________________________________________

(1) (Total 7 marks)

Mark schemes

Q1.

Q2.

Q3.

Q4.

Q5.

Q6.

Q7.

Q8.

Q9.

(a) (Standard) hydrogen (electrode) (1)

1 (b) (i) To allow transfer of electrons / provide a reaction surface (1)

(ii) 298 K (1)

Both F3+ _{(aq) and Fe}2+ _{(aq) have a concentration of 1} mol dm–3 _{(1) (QoL)}

OR [H+_{] = 1 mol dm}–3

NOT zero current or 100 kPa

3 (c) +1.34 V (1)

2 MnO4– + 5 H2SO3 → 2 Mn2+ + 5 SO42– + 3 H2O +4 H+ Correct species / order (1)

Balanced and cancelled (1)

Allow one for 2 MnO4– + 5 H2SO3 → 2 Mn2+ + 5 SO42–

3 (d) (i) Ce4+ _{(aq) (1)}

(ii) VO2+ (aq) (1); Cl2 (1)

Penalise additional answers to zero

3 (e) Pt | Fe2+ _{(aq), Fe}3+ _{(aq) || Ce}4+_{(aq), Ce}3+ _{(aq) | Pt}

Correct species (1) Correct order (1)

Deduct one mark for each error

2

[12]

Q10.

(a) Fe2+

Accept any Fe(II) compound – correct formula or name

1

EƟ _VO2+_{(/ VO}2+_{) > E}Ɵ _Fe3+_(/Fe2+_{) > E}Ɵ _VO2+_(/V3+₎

If calculations of EMF are provided producing EMFs = 0.23(V) and -0.43(V), with a comment, allow M2

allow EƟ _Fe3+ _(/Fe2+_{) value of +0.77 is between the E}Ɵ _values

for the electrode half-equations containing the V species or wtte 1 (b) (+) 4 IV or four 1 (c)

Ignore absence of charge

Wedges, dotted lines and [ ] not required

Do not penalise bond from H to V (in water ligands)

Cis/trans

allow E/Z, geometric and stereo(isomerism)

1 (d) 2 NH4VO3 → V2O5 + H2O + 2NH3

Accept multiples Ignore state symbols

1 (e) V2O5 + SO2 → V2O4 + SO3

V2O4 + ½ O2 → V2O5

Both equations needed for 1 mark in this order Allow multiples

1