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C20.1 Electrode potentials and the electrochemical seriesAQA A2 Chemistry C20 Electrode And Electrochemical Cells: Page No. 51
1 a
Ni(s)INi
2+(aq) II Ag+(aq)IAg(s)
E =+ 1.05 V
b Electrons would flow from the nickel electrode to the silver electrode.
Ni(s) -+ Ni
2+(aq) + 2e
Ag~(aq) + c–+ Ag(s)
Overall: Ni(s) + 2Ag+(aq) -+ Ni
2+(aq) + 2Ag(s)
2 @
a +0.63 V
b -0.63 V.
20.2 Predicting the direction of redox reactions AQA A2 Chemistry C20 Electrode And Electrochemical Cells : Page No. 55
1 0.90 V zinc electrode positive
2 @
a +0.93 v
b -0.53 v
c +0.97 v
d +0.26 v
3 Chlorine and bromine, but not iodine.
4.a no
b no
20.3 Electrochemical cells AQA A2 Chemistry C20 Electrode And Electrochemical Cells : Page No. 59
1 List the advantages and disadvantages of each cell, described with regard to cost, practicaiity, safety, and the environment.
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Practice questions: Page No. 60-61
1
(a)
(b) 1.23 V
(c) Pt|H
2(g)|OH–(aq),H
2O(l)||O
2(g)|H
2O(l),OH–(aq)|Pt
Correct but with Pt missing
Includes Pt with correct representation
(d) © Uses O
2 + 2H
2O + 4e
– → 4OH
And (2x) 2OH− + H2 → 2H2O + 2e
–
2H
2 + O
2 → 2H
2O
(e) Increases the surface area (so reaction faster)
(f)
Overall reaction is the same (2H
2 + O
2 → 2H
2O)
(g)
Hydrogen and oxygen supplied continuously
OR
Can be operated without stopping to recharge
(h)
Hydrogen may need to be made using an energy source that is not ‘carbon neutral’
2
(a) Zn
(b) From the table above select
(i)
Fe
2+
(ii))
Cl
2
(c) .
(i)
The standard electrode potential:
1.25 V
(ii)
Tl
3+ + 2Fe
2+ → 2Fe
3++ Tl
+
3
(a)
Pt|H
2|H
+||Fe2
+|Fe
Note, allow one mark only for correct symbol in reverse:
Fe|Fe
2+||H
+|H
2|Pt
(b)
Electron donor
(c) Cl
2 / chlorine
(Species on RHS / electron donor) has most positive / largest Eo / has highest potential
(d)
(i) Cl / chlorine
(ii) Chlorine +1 to chlorine 0
(e)
| 4HOCl + 4H+ + 4OH–→ 2Cl2 + O2 + 6H2O
OR
4HOCl → 2Cl2 + O2 + 2H2O |
f ©
e.m.f. = 0.40 – (–1.25) = 1.65 V / +1.65 V.
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