80% A
70% B
60%
50%
40%
Below
C
D
E
U
%
1

1.
Use the data below to answer the following questions
Reaction at 298 K E /V
Ag+(aq) + e– Ag(s)
+0.80
AgF(s) + e– Ag(s) + F–(aq)
+0.78
AgCl(s) + e– Ag(s) + Cl–(aq)
+0.22
AgBr(s) + e–
H+(aq) + e–
D+ (aq) + e–
Ag(s) + Br–(aq)
½ H2(g)
½ D2(g)
+0.07
0.00
–0.004
AgI(s) + e– Ag(s) + I–(aq)
–0.15
The symbol D denotes deuterium which is heavy hydrogen
1
2
H.
(a) By considering electron transfer, state what is meant by the term oxidising agent.
……………………………………………………………………………………
(1)
(b) State which of the two ions H
+
(aq)
or D
+
(aq)
, is more powerful oxidising agent.
Write an equation for the spontaneous reaction which occurs when a mixture of aqueous H
+
ions and D
+
ions are in contact with a mixture of hydrogen and deuterium gas. Deduce the e.m.f. of the cell in which this reaction would occur spontaneously.
Stronger oxidising agent …………………………………………………………
Equation ………………………………………………………………………….
……………………………………………………………………………………
…………………………………………………………………………………….
2

e.m.f ……………………………………………………………………………...
……………………………………………………………………………………
(3)
(c) Write an equation for the spontaneous reaction which occurs when aqueous F
ions and Cl
-
ions are in contact with a mixture of solid AgF and solid AgCl.
Deduce the e.m.f. of the cell in which this reaction would occur spontaneously.
Equation
………………………………………………………………………..
…………………………………………………………………………………….
e.m.f ………………………………………………………………………………
…………………………………………………………………………………….
(2)
(d) Silver does not usually react with dilute solutions of strong acids to liberate hydrogen.
(i) State why this is so.
…………………………………………………………………………….
(ii) Suggest a hydrogen halide that might react with silver to liberate hydrogen in aqueous solution. Write an equation for the reaction and deduce the e.m.f. of the cell in which this reaction would occur spontaneously.
Hydrogen halide ………………………………………………………….
Equation ………………………………………………………………….
……………………………………………………………………………
…………………………………………………………………………….
3

2.
e.m.f. ……………………………………………………………………..
…………………………………………………………………………….
(4)
TOTAL 10 marks
Use the data given below, where appropriate, to answer the questions, which follow.
Standard electrode potentials in acid solution
Mg2+ (aq) + 2e–

Mg(s)
Zn2+ (aq) + 2e–

Zn(s)
Sn4+(aq) + 2e–

Sn2+(aq)
VO2+(aq) + 2H+(aq) + e–

V3+(aq) + H2O(l)
VO (aq) + 2H
+(aq) + e– 
VO2+(aq) + H2O(l)
Ce4+(aq) + e–

Ce3+(aq)
E /V
–2.37
–0.76
+0.15
+0.34
+1.02
+1.70
(a) Give the components of the standard reference electrode used in determining the standard electrode potentials above. State the conditions under which this standard reference electrode has a potential of 0.00 V.
Components ………………………………………………………………………
……………………………………………………………………………………
…………………………………………………………………………………….
Conditions ………………………………………………………………………..
……………………………………………………………………………………
……………………………………………………………………………………
(6)
4

(b) A diagram of a cell is shown below.
Zinc
V
Salt bridge
Magnesium
(i) Calculate the overall standard potential of this cell.
…………………………………………………………………………….
(ii) State the polarity of the zinc electrode
…………………………………………………………………………….
(2)
(c) A diagram of a cell is shown below
Inert electrode
V
Salt bridge
Inert electrode
Solution 1.0 M with Solution 1.0 M with
(i) Calculate the overall standard potential of the cell
…………………………………………………………………………….
(ii) Deduce the direction of the electron flow in the external circuit when the inert electrodes are connected together
…………………………………………………………………………….
(2)
5

3.
(d) Using the data form the table, derive an equation for the overall redox process which occurs when a solution containing Ce 4+
(aq)
is added to a solution containing V
3+
(aq)
.
……………………………………………………………………………………
……………………………………………………………………………………
…………………………………………………………………………………….
(3)
(e) Which, if any, of the four vanadium-containing species, V
2+
(aq)
, V
3+
(aq)
, VO
2+
(aq) and VO
2
2+
(aq), will convert Sn
2+
(aq)
into Sn
4+
(aq)
in acid solution?
…………………………………………………………………………………….
(2)
TOTAL 15 marks
Use the table of the standard electrode potential to answer the following questions
Cl2(g) + 2e–

2Cl–(aq)
Br2(l) + 2e–

2Br–(aq)
+1.36
+1.07
NO (aq) + 3H +(aq) + 2e– 
Fe3+(aq) + e–

Fe2+(aq)
HNO2(aq) + H2O(1) +0.94
+0.77
I2(aq) + 2e–

2I–(aq)
VO2+(aq) + 2H+(aq) + e–

V3+(aq) + H2O(1)
V3+(aq) + e–

V2+(aq)
Fe2+(aq) + 2e–

Fe(s)
+0.54
+0.34
–0.26
–0.44
E /V
(a) In terms of electron transfer, define the term oxidising agent.
…………………………………………………………………………………….
(1)
6

(b) (i) Give the conditions under which the electrode potential for Cl
2 (g)
/ 2Cl
(aq) is +1.36 V
……………………………………………………………………………
……………………………………………………………………………
…………………………………………………………………………….
(ii) Give a change in one of these conditions which would result in the electrode potential becoming more positive. Explain your answer.
Change in conditions ……………………………………………………..
Explanation ………………………………………………………………
…………………………………………………………………………….
(5)
(c) (i) Which of the reducing agents in the table is the weakest?
…………………………………………………………………………….
(ii) Identify all the species in the table which could convert I
-
(aq)
into I
2 (aq) which could not convert Br
-
(aq)
into Br
2 (l)
…………………………………………………………………………….
(iii) Identify the metal ions which could be left in solution if an excess of powered iron metal was added to an acidified solution containing
VO
2+
(aq)
ions.
…………………………………………………………………………….
(5)
TOTAL 11 marks
7

4. Large block of magnesium are bolted onto the hulls of iron ships in an attempt to prevent iron being converted into iron (II), one of the steps in the rusting process.
Use the data below, where appropriate, to answer the questions which follow
Mg2+(aq) + 2e–
Fe2+(aq) + 2e–
O2(g) + 2H2O(l) + 4e–
Mg(s)
Fe(s)
4OH–(aq)
E / V
–2.37
–0.44
+0.40
(a) Calculate the e.m.f. of the cell represented by Mg
(s)
Mg
2+
(aq)
Fe
2+
(aq)
Fe
(s) under standard conditions. Write an half equation for the reaction occurring at the negative electrode of this cell when a current is drawn
Cell e.m.f. ………………………………………………………………………..
Half equation ……………………………………………………………………..
…………………………………………………………………………………….
(2)
(b) Deduce how the e.m.f. of the cell Mg
(s)
Mg
2+
(aq)
Fe
2+
(aq)
Fe
(s)
changes when the concentration of Mg
2+ is decreased. Explain your answer.
Change in e.m.f. ………………………………………………………………….
Explanation ………………………………………………………………………
…………………………………………………………………………………….
(3)
8

5.
(c) Calculate a value for the e.m.f. of the cell represented by Pt
(s)
OH
-
(aq)
O
2 (g)
Fe
2+
(aq)
Fe
(s)
and use it to explain why iron corrodes when in contact with water which contains dissolved oxygen
Change in e.m.f. …………………………………………………………………………
Explanation………………………………………………………………………………
…..……………………………………………………………………………………….
(2)
TOTAL 7 marks
(a) The following reaction occurs in aqueous solution
5S
2
O
8
2-
+ Br
2
+ 6H
2
O
→
2BrO
3
-
+ 12H
+
+ 10SO
4
2-
Identify the reducing agent and write a half equation for its reaction
Reducing agent ……………………………………………………………….
Half-equation …………………………………………………………………
(2)
(b) The electrode potential for the half equation
Co 2+
(aq)
+ 2e → Co
(s) is measured by reference to a standard hydrogen electrode.
(i) State the temperature at which the standard electrode potential E
θ
Must be is measured and give the concentration of Co
2+
(aq)
that must be used
Temperature.……………………………………………………...
Concentration …………………………………………………….
9

(ii) Electrode potentials are usually measured by reference to a secondary electrode. Identify a secondary electrode and give a reason why it is used rather than a secondary electrode.
Secondary electrode potential ……………………………………
Reason ……………………………………………………………
(4)
(c) Cobalt in oxidation states +2 and+3 forms complex ions with water, ammonia and cyanide ligands. Use where appropriate the data given below to answer the questions which follow
[Co(H2O)6]3+(aq) + e–

[Co(H2O)6]2+(aq) E = +1.81 V
1
2
O2(g) + 2H+(aq) + 2e–
[Co(NH3)6]3+(aq) + e–
2H+(aq) + 2e–


H2O(l)

[Co(NH3)6]2+(aq) E = +0.10 V
H2(g)
E
E
= +1.23 V
= 0.00 V
[Co(CN)6]3–(aq) + e–

[Co(CN)6]4–(aq) E = –0.80 V
(i) Which of the six cobalt species shown above is the most powerful oxidising agent?
...................................................................................................................
(ii) Identify a cobalt (II) species which cannot be oxidised by gaseous oxygen.
....................................................................................................................
10

(iii) Hydrogen is evolved when a salt containing the species [Co(CN)
6
]
4-
(aq)
is reacted with dilute acid. Use the electrode potentials to explain the formation of the hydrogen gas.
.....................................................................................................................
.....................................................................................................................
.....................................................................................................................
(4)
TOTAL 10 marks
11