Electrochemical Exam Questions Bank | 2026/2027 |
Answers Correct | With Complete Solutions
A disproportionation reaction occurs when a species M+
spontaneously undergoes simultaneous oxidation and reduction.
below contains E data for copper and mercury species.
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
( Correct Answers b
A lead-acid cell can be recharged.
Write an equation for the overall reaction that occurs when the
cell is being recharged?
PbO2(s) + 3H+(aq) + HSO4-(aq) + 2e- → PbSO4(s) + 2H2O
(I) +1.69
,PbSO4(s) + H+(aq) + 2e- → Pb(s) + HSO4-(aq)
to be calculated Correct Answers Opposite for reduction
(PbS04) --> Same side = add 2 together
2PbS04 ==> for HS04-
2PbSO4 + 2H2O → Pb +PbO2 + 2HSO4- + 2H+
A rechargeable nickel-cadmium cell is an alternative
Cd(OH)2(s) + 2e- ----> Cd(s) + 2OH-(aq) -0.88
NiO(OH)(s) + H2O(I) + e- ---> Ni(OH)2(s) + OH- 0.52
Deduce the oxidation state of the nickel in this cell after
recharging is complete. Write an equation for the overall
reaction that occurs when the cell is recharged. Correct
Answers usually nickel will be reduced
in recharging = opposite reaction = so oxidation will happen
hence O.S = +3 in NiO(OH)
eq=
opposite
(+ve) = oxidised
acidification,
, 25.0 cm3 of a solution of hydrogen peroxide
reacted exactly with 16.2 cm3 of a 0.0200 mol dm-3 solution of
potassium manganate(VII).
overall equation for the reaction is given below.
2Mn04- + 6H+ + 5H2O2 → 2Mn2+ + 8H2O + 5O2
(i) Use eq for reaction to determine
conc, in g dm-3, of hydrogen peroxide solution? Correct
Answers moles of h202 = reacting ratio
concentration = moles / volume * 1000
(moldm-3)
gdm-3 = mol dm-3 × Mr
Ag+(aq) + e− --> Ag(s) (+0.80)
Fe3+(aq) + e− --> Fe2+(aq) (+0.77)
Fe2+(aq) + 2e− ---> Fe(s) (-0.44)
Use data from table to predict +
explain redox reactions
occur when iron powder (s) added to excess of aqueous silver
nitrate Correct Answers Eϴ Ag+ > Eϴ Fe2+
Eϴ Ag+ > Eϴ Fe3+ --> (careful)
silver ions oxidise iron (to iron(II) ions /
Answers Correct | With Complete Solutions
A disproportionation reaction occurs when a species M+
spontaneously undergoes simultaneous oxidation and reduction.
below contains E data for copper and mercury species.
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
( Correct Answers b
A lead-acid cell can be recharged.
Write an equation for the overall reaction that occurs when the
cell is being recharged?
PbO2(s) + 3H+(aq) + HSO4-(aq) + 2e- → PbSO4(s) + 2H2O
(I) +1.69
,PbSO4(s) + H+(aq) + 2e- → Pb(s) + HSO4-(aq)
to be calculated Correct Answers Opposite for reduction
(PbS04) --> Same side = add 2 together
2PbS04 ==> for HS04-
2PbSO4 + 2H2O → Pb +PbO2 + 2HSO4- + 2H+
A rechargeable nickel-cadmium cell is an alternative
Cd(OH)2(s) + 2e- ----> Cd(s) + 2OH-(aq) -0.88
NiO(OH)(s) + H2O(I) + e- ---> Ni(OH)2(s) + OH- 0.52
Deduce the oxidation state of the nickel in this cell after
recharging is complete. Write an equation for the overall
reaction that occurs when the cell is recharged. Correct
Answers usually nickel will be reduced
in recharging = opposite reaction = so oxidation will happen
hence O.S = +3 in NiO(OH)
eq=
opposite
(+ve) = oxidised
acidification,
, 25.0 cm3 of a solution of hydrogen peroxide
reacted exactly with 16.2 cm3 of a 0.0200 mol dm-3 solution of
potassium manganate(VII).
overall equation for the reaction is given below.
2Mn04- + 6H+ + 5H2O2 → 2Mn2+ + 8H2O + 5O2
(i) Use eq for reaction to determine
conc, in g dm-3, of hydrogen peroxide solution? Correct
Answers moles of h202 = reacting ratio
concentration = moles / volume * 1000
(moldm-3)
gdm-3 = mol dm-3 × Mr
Ag+(aq) + e− --> Ag(s) (+0.80)
Fe3+(aq) + e− --> Fe2+(aq) (+0.77)
Fe2+(aq) + 2e− ---> Fe(s) (-0.44)
Use data from table to predict +
explain redox reactions
occur when iron powder (s) added to excess of aqueous silver
nitrate Correct Answers Eϴ Ag+ > Eϴ Fe2+
Eϴ Ag+ > Eϴ Fe3+ --> (careful)
silver ions oxidise iron (to iron(II) ions /
