Exam code: YCH11
The standard hydrogen electrode uses an electrode of platinum coated in a finely divided form of the metal called platinum black.
What is the purpose of this coating?
to increase the rate of the equilibrium between the hydrogen gas and the hydrogen ions
to provide an inert protective coating for the electrode
to increase the electrical conductivity of the electrode
to ensure that the conditions remain standard
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The apparatus shown was used to measure the standard electrode potential for the reduction of Cr2 ions to Cr3+ ions in acid solution:
Cr2(aq) + 14H+(aq) + 6e–→ 2Cr3+(aq) + 7H2O(l)
Which material should be used for each electrode?
| Electrode 1 | Electrode 2 | |
☐ | A | Na2Cr2O7 | Cr2O3 |
☐ | B | H2 | Cr |
☐ | C | Pt | Cr |
☐ | D | Pt | Pt |
Solution 1 is
0.33 mol dm–3 H3PO4 (aq)
0.50 mol dm–3 H2SO4 (aq)
1.00 mol dm–3 HCl (aq)
1.00 mol dm–3 CH3COOH (aq)
Solution 2 contains 14.71g of K2Cr2O7 .
What mass of Cr2(SO4)3⋅18H2O should also be used?
[Mr values: K2Cr2O7 = 294.2 Cr2(SO4)3⋅18H2O = 716.3]
8.95 g
17.91 g
19.62 g
35.82 g
Solution 2 is best acidified with
H2SO4
HCl
HBr
H2CrO4
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A hydrogen‐oxygen fuel cell is used to provide electrical energy for an electric motor in a car.
The electrolyte in the fuel cell is acidic. What is the half‐equation at the anode?
1⁄2O2 (g) + 2H+ (aq) + 2e−→ H2O (l)
H2O (l) → 1⁄2O2 (g) + 2H+ (aq) + 2e−
H2 (g) → 2H+ (aq) + 2e−
2H+ (aq) + 2e−→ H2 (g)
Hydrogen‐oxygen fuel cells have advantages over methanol‐oxygen fuel cells in vehicles.
Which of these is an advantage of the hydrogen‐oxygen fuel cell?
more energy is released per mole of fuel used
emissions do not contribute to climate change
hydrogen is easier to store than methanol
only hydrogen can be obtained from renewable resources
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The equation for a redox reaction is
5Fe2+(aq) + Mn(aq) + 8H+(aq) → 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)
Which is the correct cell diagram to measure Eθcell for this reaction?
Fe | Fe2+, Fe3+ || [MnO4– + 8H+], [Mn2+ + 4H2O] | Mn
Fe | Fe2+, Fe3+ || [Mn2+ + 4H2O], [MnO4– + 8H+] | Mn
Pt | Fe2+, Fe3+ || [MnO4– + 8H+], [Mn2+ + 4H2O] | Pt
Pt | Fe2+, Fe3+ || [Mn2+ + 4H2O], [Mn+ 8H+] | Pt
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This question is about the reaction
2Fe3+ (aq) + Ti (s) → 2Fe2+ (aq) + Ti2+ (aq)
The electrode potential for the Fe3+/ Fe2+ electrode system is +0.77 V.
What is the electrode potential for the Ti2+/Ti electrode system?
−3.17V
−1.63V
+1.63V
+3.17V
What metals should be used for the electrodes in the cell for this reaction?
|
| Metals used for the electrode | |
|
| Fe3+/ Fe2+ electrode system | Ti2+/ Ti electrode system |
□ | A | iron | titanium |
□ | B | iron | platinum |
□ | C | platinum | titanium |
□ | D | platinum | platinum |
The half-cell for the Fe3+/ Fe2+ electrode system is prepared by mixing equal volumes of solutions of iron(II) sulfate, FeSO4, and iron(III) sulfate, Fe2(SO4)3.
What concentrations of the original solutions are needed for the resulting mixture to be standard?
|
| Concentration of the original solution | |
|
| FeSO4 | Fe2(SO4)3 |
□ | A | 1 mol dm–3 | 0.5 mol dm–3 |
□ | B | 1 mol dm–3 | 1 mol dm–3 |
□ | C | 2 mol dm–3 | 1 mol dm–3 |
□ | D | 2 mol dm–3 | 2 mol dm–3 |
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An electrochemical cell is set up to measure for the reaction
Fe (s) + Sn2+ (aq) → Fe2+ (aq) + Sn (s)
What is the cell diagram for this cell?
Fe(s) | Fe2+(aq) || Sn(s) | Sn2+(aq)
Fe2+(aq) | Fe(s) || Sn2+(aq) | Sn(s)
Fe(s) | Fe2+(aq) || Sn2+(aq) | Sn(s)
Fe2+(aq) | Fe(s) || Sn(s) | Sn2+(aq)
The standard electrode potential for the Fe / Fe2+ electrode system is −0.44 V and for the reaction is +0.30 V.
What is the standard electrode potential for the Sn / Sn2+ electrode system?
−0.74 V
−0.14 V
+0.14 V
+0.74 V
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Hydrogen-oxygen fuel cells can operate in acidic or alkaline conditions.
What is the reaction at the anode in an alkaline hydrogen-oxygen fuel cell?
O2 (g) + 2H2O (l) + 4e− → 4OH− (aq)
4OH− (aq) → O2 (g) + 2H2O (l) + 4e−
2H2O (l) + 2e− → H2 (g) + 2OH− (aq)
H2 (g) + 2OH− (aq) → 2H2O (l) + 2e−
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Which of these species is the strongest oxidising agent?
Half-equation | E° / V |
|---|---|
Cu2+ (aq) + 2e- → Cu (s) | +0.34 |
Fe3+ (aq) + e- → Fe2+ (aq) | +0.77 |
I2 (aq) + 2e- → 2I- (aq) | +0.54 |
Zn2+ (aq) + 2e- → Zn (s) | −0.76 |
Fe2+
Fe3+
Zn
Zn2+
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Which of these is the correctly balanced half-equation for the reduction of MnO4- (aq) to Mn2+ (aq) in acidic solution?
MnO4- + 4H+ + 3e- → Mn2+ + 2H2O
MnO4- + 8H+ + 5e- → Mn2+ + 4H2O
MnO4- + 8H+ + 7e- → Mn2+ + 4H2O
MnO4- + 14H+ + 5e- → Mn2+ + 7H2O
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An electrochemical cell is made from the electrode systems shown by these half‐equations.
Ag+ (aq) + e− ⇌ Ag (s) = +0.80V
V (aq) + 2H+ (aq) + e− ⇌ VO2+ (aq) + H2O (l) = +1.00V
The apparatus used to measure the value for under standard conditions is shown.
Which silver compound could be used as the electrolyte in the left‐hand half‐cell?
silver nitrate
silver hydroxide
silver chloride
silver carbonate
The electrolyte in the right‐hand half‐cell is prepared using equal volumes of
1 mol dm−3 acidified VO2+ (aq) and 1 mol dm−3 acidified VO2+ (aq)
2 mol dm−3 acidified VO2+ (aq) and 2 mol dm−3 acidified VO2+ (aq)
1 mol dm−3 VO2+ (aq) and 1 mol dm−3 HCl (aq)
1 mol dm−3 VO2+ (aq) and 1 mol dm−3 HCl (aq)
Which is the equation for the overall cell reaction under standard conditions?
VO2+(aq) + Ag+(aq) + H2O(l) + Ag(s) + 2H+(aq)
+ Ag(s) + 2H+(aq) VO2+(aq) + Ag+(aq) + H2O(l)
VO2+(aq) + 3Ag(s) + 2H+(aq) + 3Ag+(aq) + H2O(l)
+ 3Ag+(aq) + H2O(l) VO2+(aq) + 3Ag(s) + 2H+(aq)
Which is the value of in volts?
−1.80
−0.20
+0.20
+1.80
Which is the cell diagram for this cell, using the conventional representation of half‐cells?
Ag(s) | Ag+(aq) || [ + 2H+(aq)] | [VO2+(aq) + H2O(l)] | Pt(s)
Ag(s) | Ag+(aq) || [ + 2H+(aq)] , [VO2+(aq) + H2O(l)] | Pt(s)
Ag(s) | Ag+(aq) || [ VO2+(aq) + H2O(l)] | [ + 2H+(aq)] | Pt(s)
Ag(s) | Ag+(aq) || [ VO2+(aq) + H2O(l)] , [ + 2H+(aq)] | Pt(s)
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Some standard electrode potentials are shown.
Electrode system | / V |
Bk3+ + e– ⇌ Bk2+ | –2.80 |
Cu2+ + e– ⇌ Cu+ | +0.15 |
Bk4+ + e– ⇌ Bk3+ | +1.67 |
Au+ + e– ⇌ Au | +1.69 |
Au2+ + e– ⇌ Au+ | +1.80 |
Ag3+ + e– ⇌ Ag2+ | +1.80 |
Ag2+ + e– ⇌ Ag+ | +1.98 |
Cu3+ + e– ⇌ Cu2+ | +2.40 |
Which of these disproportionation reactions is thermodynamically feasible under standard conditions?
2Bk3+ → Bk2+ + Bk4+
2Cu2+ → Cu++ Cu3+
2Au+ → Au + Au2+
2Ag2+ → Ag++ Ag3+
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Which is true of a hydrogen‐oxygen fuel cell?
the cathode has a more positive potential than the anode
hydrogen is oxidised at the cathode
oxygen is reduced at the negative electrode
the cell potential is different when operating under alkaline or acidic conditions
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Which half-equation correctly represents the reaction occurring at the anode of an alkaline hydrogen–oxygen fuel cell?
H2 (g) + 2OH- (aq) → 2H2O (l) + 2e-
O2 (g) + 2H2O (l) + 4e- → 4OH- (aq)
H2 (g) → 2H+ (aq) + 2e-
O2 (g) + 4H+ (aq) + 4e- → 2H2O (l)
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