IB Chemistry HL
Topic9 Questions and Answers
1.
2.
Aqueous solutions of AgNO3, Cu(NO3)2 and Cr(NO3)3 are electrolyzed using the same quantity
of electricity. How do the number of moles of metal formed compare?
A.
Ag = Cu = Cr
B.
Ag > Cu > Cr
C.
Ag < Cu < Cr
D.
Cu > Ag > Cr
The standard electrode potentials for two half-cells involving iron are given below.
Fe2+(aq) + 2e– → Fe(s)
Fe3+(aq) + e–→ Fe2+(aq)
Eο = –0.44 V
Eο = +0.77 V
What is the equation and the cell potential for the spontaneous reaction that occurs when the two
half-cells are connected?
3.
A.
3Fe2+(aq) → Fe(s) + 2Fe3+(aq)
Eο = +1.21 V
B.
Fe2+(aq) + Fe3+(aq) → 2Fe(s)
Eο = +0.33 V
C.
Fe(s) + 2Fe3+(aq) → 3Fe2+(aq)
Eο = +0.33 V
D.
Fe(s) + 2Fe3+(aq) → 3Fe2+(aq)
Eο = +1.21 V
Metallic tin can be produced by the electrolysis of a molten salt containing Sn2+ ions. Which
change(s) would double the amount of tin produced?
I.
Doubling the current passed during electrolysis
II.
Doubling the time used for electrolysis
III.
Using Sn4+ ions instead of Sn2+ ions
A.
I only
B.
II only
C.
I and II only
D.
I, II and III
1
4.
5.
Which of the following factors affect the amount of product formed during electrolysis?
I.
The current used
II.
The duration of electrolysis
III.
The charge on the ion
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
The cyanide ion, CN–, can form two complex ions with iron ions. The formulas of these ions are
[Fe(CN)6]4– and [Fe(CN)6]3–. What is the oxidation number of iron in the two complex ions?
4–
[Fe(CN)6]
6.
3–
[Fe(CN)6]
A.
–4
–3
B.
+2
+3
C.
+3
+2
D.
–3
–4
Consider the following reactions.
Cu2+(aq) + 2e–
Cu(s)
Eο = +0.34 V
Mg2+(aq) + 2e–
Mg(s) Eο = –2.36 V
Zn2+(aq) + 2e–
Zn(s)
Eο = –0.76 V
Which statement is correct?
A.
Cu2+(aq) will oxidize both Mg(s) and Zn(s).
B.
Zn(s) will reduce both Cu2+(aq) and Mg2+(aq).
C.
Mg2+(aq) will oxidize both Cu(s) and Zn(s).
D.
Cu(s) will reduce both Mg2+(aq) and Zn2+(aq).
2
7.
Consider the standard electrode potentials of the following reactions.
Cr3+(aq) + 3e– →Cr(s)
–0.75 V
Cd2+(aq) + 2e– → Cd(s)
–0.40 V
What is the value of the cell potential (in V) for the following reaction?
2Cr(s) + 3Cd2+(aq) → 2Cr3+(aq) + 3Cd(s)
8.
9.
10.
A.
–0.35
B.
–1.15
C.
+0.30
D.
+0.35
Aqueous solutions containing different concentrations of NaCl were electrolysed using platinum
electrodes. What is the major product at the positive electrode in each case?
0.001 mol dm–3 NaCl(aq)
1.0 mol dm–3 NaCl(aq)
A.
H2
Na
B.
H2
H2
C.
O2
Cl2
D.
Cl2
O2
Which is a feature of the standard hydrogen electrode?
A.
hydrogen gas at 1.01×105 Pa (1 atm) pressure
B.
1.0 mol dm–3 sulfuric acid
C.
a temperature of 273 K
D.
a magnesium electrode
Which pair of factors both affect the amount (in mol) of chlorine produced in the electrolysis of
aqueous sodium chloride?
A.
current and temperature
B.
temperature and chloride ion concentration
C.
chloride ion concentration and length of time of electrolysis
D.
pressure and length of time of electrolysis
3
11.
From the given standard electrode potentials which statement is correct?
Ca2+(aq) + 2e–
Ni2+(aq) + 2e–
Fe3+(aq) + e–
12.
13.
14.
A.
Ca2+(aq) can oxidize Ni(s)
B.
Ni2+(aq) can reduce Ca2+(aq)
C.
Fe3+(aq) can oxidize Ni(s)
D.
Fe3+(aq) can reduce Ca2+(aq)
Ca(s)
Ni(s)
Fe2+(aq)
EӨ = –2.87 V
EӨ = –0.23 V
EӨ = +0.77 V
Which statement is correct about the electrolysis of copper(II) sulfate solution using graphite
electrodes?
A.
A colourless gas is produced at the negative electrode.
B.
The electrolyte does not change colour.
C.
The negative electrode decreases in mass.
D.
A colourless gas is produced at the positive electrode.
A metallic object is electroplated with copper using a solution of copper(II) sulfate. Which
statement is correct?
A.
The positive electrode increases in mass.
B.
The concentration of Cu2+ ions in the solution decreases.
C.
Reduction occurs at the positive electrode.
D.
The reaction occurring at the negative electrode is Cu2+ + 2e–  Cu.
Two half-equations and their standard electrode potentials are shown in the table.
EӨ / V
Half-equation
Pb2+(aq) + 2e–
Pb(s)
–0.13
Ag2+(aq) + e–
Ag(s)
+0.80
What is the cell potential, in V, for the reaction below?
Pb(s) + 2Ag+(aq)  Pb2+(aq) + 2Ag(s)
A.
0.67
B.
0.93
C.
1.47
D.
1.73
4
15.
Two electrolytic cells are connected in series so that the same current flows through both cells
for the same length of time.
SnSO4(aq)
-
+
-
+
CuSO4 (aq)
The amount of tin deposited is 0.01 mol. How much copper is deposited?
16.
17.
A.
0.005 mol
B.
0.01 mol
C.
0.02 mol
D.
0.05 mol
Which are used for the electroplating of a metal spoon with copper?
I.
an electrolyte containing aqueous copper(II) ions
II.
a copper anode (positive electrode)
III.
a copper cathode (negative electrode)
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
Consider these standard electrode potentials.
Cu2+(aq) + e–  Cu+(aq)
EӨ = +0.15 V
Cu+(aq) + e–  Cu(s)
EӨ = +0.52 V
What is the standard cell potential when the two half-cells are connected?
A.
– 0.67 V
B.
– 0.37 V
C.
+ 0.37 V
D.
+ 0.67 V
5
18.
Consider the standard electrode potentials of the following reactions:
Sn4+(aq) + 2e–  Sn2+(aq)
+0.15 V
Fe3+(aq) + e–  Fe2+(aq)
+0.77 V
What is the value of the cell potential (in volts) for the spontaneous reaction?
19.
20.
A.
+1.69
B.
+1.39
C.
+0.92
D.
+0.62
In the electrolysis of acidified water, if 8.4 cm3 of hydrogen gas is evolved, what volume of
oxygen gas is evolved?
A.
4.2 cm3
B.
8.4 cm3
C.
12.6 cm3
D.
16.8 cm3
Which factors affect the amount of metal formed during electrolysis?
I.
II.
III.
Charge on the metal ion
Current
Time
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
6
21.
22.
23.
Which changes lead to the production of more moles of metal during the electrolysis of a
molten salt?
I.
using a metal ion with a higher charge
II.
increasing the current
III.
using a longer time
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
Which equation represents the reduction process occurring in the standard hydrogen electrode?
A.
H2(g) → 2H+(aq) + 2e–
B.
H+(aq) + OH–(aq) → H2O(l)
C.
2H+(aq) + 2e– → H2(g)
D.
O2(g) + 4H+(aq) + 4e– → 2H2O(l)
Which statement is correct about the value of Eο?
A.
The more positive the value of Eο, the greater the driving force for reduction.
B.
The more negative the value of Eο, the greater the driving force for reduction.
C.
The more positive the value of Eο, the greater the rate of reaction.
D.
The more negative the value of Eο, the greater the rate of reaction.
24.
Direction of electron flow
A
Salt bridge
Zn(s)
Cu(s)
Zn 2+(aq)
Cu 2+ (aq)
7
(a)
The apparatus shown above may be used to carry out a redox reaction.
(i)
State the function of the salt bridge.
……………………………………………………………………………………
……………………………………………………………………………………
(1)
(ii)
Write a half-equation for the oxidation reaction.
……………………………………………………………………………………
……………………………………………………………………………………
(1)
(iii)
The above reactions are carried out under standard conditions.
State what the standard conditions are for the cell.
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(2)
(iv)
Using the Data Booklet, calculate the cell potential for the above cell.
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(2)
(v)
State and explain what happens to the concentration of the copper(II) ions when the
cell is producing an electric current.
……………………………………………………………………………………
……………………………………………………………………………………
(2)
(vi)
State two observations that could be made if the zinc rod were placed in a solution
of copper(II) ions.
……………………………………………………………………………………
……………………………………………………………………………………
(2)
8
(b)
The standard electrode potentials for three electrode systems are given below.
(i)
Ti3+(aq) + e–  Ti2+(aq)
Eο = –0.37 V
Fe3+ (aq) + e–  Fe2+(aq)
Eο = +0.77 V
Ce4+(aq) + e–  Ce3+(aq)
Eο = +1.45 V
Using the data above, deduce which species is the best reducing agent, giving a
reason in terms of electrons for your answer.
……………………………………………………………………………………
……………………………………………………………………………………
(2)
(ii)
Write an equation, including state symbols, for the overall reaction with the
greatest cell potential.
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(2)
(iii)
State and explain the sign of Gο for the reaction in (b) (ii).
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(2)
(c)
(i)
State the name of a solution that would produce only hydrogen and oxygen when
electrolyzed using platinum electrodes.
……………………………………………………………………………………
(1)
(ii)
Draw a diagram of apparatus that would allow the gases produced in the reaction in
(c) (i) to be collected separately. Annotate your diagram to show the polarity of
each electrode and the names and relative volumes of each gas.
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
(3)
(Total 20 marks)
9
25.
– +
A
X
Y
CuSO 4 (aq)
Two copper strips X and Y are placed in an aqueous solution of copper(II) sulfate and
electrolyzed for a certain time. X was then dried and weighed.
(i)
State and explain what would happen to the mass of X.
…………………………………………………………………………………………..
…………………………………………………………………………………………..
(3)
(ii)
State two ways in which the change in the mass of X could be increased.
…………………………………………………………………………………………..
(2)
(Total 5 marks)
26.
(a)
Some standard electrode potentials are shown in Table 15 of the Data Booklet.
(i)
State three conditions under which the hydrogen electrode is assigned a potential of
zero.
………………………………………………………………………………………
………………………………………………………………………………………
(3)
(ii)
Calculate the cell potential of a cell made by connecting standard copper and zinc
electrodes. State the direction of electron flow in the external circuit when the cell
produces current. Outline the changes occurring at the electrodes and in the
solutions during the process.
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
(5)
10
(b)
Using information from Table 15, determine whether or not there is a spontaneous
reaction between copper metal and a solution containing hydrogen ions.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(2)
(c)
Using information from Table 15, identify a substance that will oxidize bromide ions but
not chloride ions. Explain your choice, and write an equation for the redox reaction you
have chosen.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(5)
(Total 15 marks)
27.
(a)
In one experiment involving the electrolysis of molten sodium chloride, 0.1 mol of
chlorine was formed. Deduce, giving a reason, the amount of sodium formed at the same
time.
(2)
(b)
In another experiment involving the electrolysis of molten sodium chloride, the time of
the electrolysis was halved and the current increased from 1 amp to 5 amp, compared to
the experiment in (a). Deduce the amount of chlorine formed, showing your working.
(2)
(c)
If dilute aqueous sodium chloride is electrolyzed, a different product is obtained at each
electrode. Identify the product formed at each electrode and write an equation showing its
formation.
(4)
(Total 8 marks)
28.
Define the term standard electrode potential of an element. Table 15 of the Data Booklet
contains EӨ values for two reactions involving O2(g). Identify the EӨ value of the reaction that
could be used to oxidize bromide ions and explain your reasoning. Construct a balanced
equation for the oxidation of bromide ions using this reaction and calculate the cell potential.
(Total 8 marks)
11
29.
Use information from Table 15 of the Data Booklet, where relevant, in answering this part.
(i)
The diagram shows the apparatus used in an experiment involving half-cells.
Voltmeter
Nickel
Solution containing
Ni 2+ (aq)
Lead
Solution containing
Pb 2 (aq)
The reading on the voltmeter is 0.10 V. State two standard conditions that apply for this
reading to be obtained.
(2)
(ii)
The voltmeter is replaced by a 2 volt power supply, so that non-spontaneous reactions
occur. Deduce the half-equations for these reactions.
(2)
(iii)
Chlorine gas is formed when potassium manganate(VII) is added to concentrated
hydrochloric acid. Calculate the cell potential for this reaction and deduce the equation
for the reaction.
(3)
(iv)
Explain why potassium dichromate(VI) does not react with concentrated hydrochloric
acid.
(1)
(Total 8 marks)
30.
(a)
When a concentrated aqueous solution of sodium chloride is electrolyzed using inert
electrodes, a different gas is produced at each electrode.
(i)
Write equations for the oxidation and reduction half-reactions.
Oxidation half-reaction: ...................................................................................
...........................................................................................................................
Reduction half-reaction: ...................................................................................
...........................................................................................................................
(2)
(ii)
Explain why sodium is not formed during the electrolysis of aqueous NaCl
solution.
...........................................................................................................................
...........................................................................................................................
(1)
12
(b)
Deduce the products formed during the electrolysis of an aqueous solution of sodium
fluoride. Write an equation for the reaction at the positive electrode (the anode) and give
your reasoning.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
(4)
(Total 7 marks)
31.
The following are standard electrode potentials.
Half-equation
Zn2+(aq) + 2e–
Cr3+(aq) + 3e–
Fe2+(aq) + 2e–
Sn2+(aq) + 2e–
Cu2+(aq) + 2e–
Fe3+(aq) + e–
(a)
Zn(s)
Cr(s)
Fe(s)
Sn(s)
Cu(s)
Fe2+(aq)
Eο / V
–0.76
–0.74
–0.44
–0.14
+0.34
+0.77
These values were obtained using a standard hydrogen electrode. Describe the
materials and conditions used in the standard hydrogen electrode. (A suitably
labelled diagram is acceptable.)
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(5)
13
(b)
Define the term oxidizing agent in terms of electron transfer and identify the strongest
oxidizing agent in the list above.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(2)
(c)
A cell was set up using zinc in zinc sulfate solution and copper in copper(II) sulfate
solution, both solutions being under standard conditions.
(i)
Calculate the cell potential.
……………………………………………………………………………………
……………………………………………………………………………………
(1)
(ii)
Write an equation for the spontaneous cell reaction.
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(2)
(d)
Both zinc and tin are used to coat iron to prevent it from rusting. Once the surface is
scratched, oxygen and water containing dissolved ions come into contact with the iron
and the coating metal.
(i)
State and explain whether zinc or tin would be more effective in preventing iron
from rusting under these conditions.
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(2)
(ii)
Electroplating may be used to coat one metal with another metal. Identify the three
factors affecting the amount of metal discharged during electroplating.
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(3)
14
(iii)
Explain why electrolysis of aqueous zinc sulfate is not used for coating with zinc
metal.
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(2)
(e)
Another cell was set up as shown below.
V
Pt(s)
Cr(s)
Y
Cr3+ (aq)
Fe 3+(aq), Fe 2+(aq)
half-cell A
(i)
half-cell B
Identify the part of the cell labelled Y and outline its function.
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(2)
(ii)
Write an equation for the initial reactions at each electrode and hence write an
equation for the cell reaction.
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(4)
(iii)
Describe the direction of electron flow in the external circuit.
15
……………………………………………………………………………………
(1)
(iv)
Calculate the cell potential.
……………………………………………………………………………………
……………………………………………………………………………………
(1)
(Total 25 marks)
32.
The following diagram shows a voltaic cell.
voltmeter
V
salt bridge
iron electrode
silver electrode
Fe 2+(aq)
(a)
Ag +(aq)
State an equation to represent the spontaneous reaction occurring in the cell.
....................................................................................................................................
....................................................................................................................................
(1)
(b)
Define the term standard electrode potential.
....................................................................................................................................
....................................................................................................................................
(1)
(c)
Use Table 15 from the Data Booklet to calculate the standard cell potential for the
spontaneous reaction in (a).
....................................................................................................................................
....................................................................................................................................
(1)
16
(d)
Draw arrows on the above diagram to indicate the direction of electron flow.
(1)
(Total 4 marks)
33.
(a)
Iodide ions, I–(aq), react with iodate ions, IO3–(aq), in an acidic solution to form
molecular iodine and water.
(i)
Determine the oxidation number of iodine in I– and in IO3–.
.........................................................................................................................
(1)
(ii)
Identify, with a reason, the species that undergoes:
oxidation ..........................................................................................................
..........................................................................................................................
reduction ..........................................................................................................
..........................................................................................................................
(2)
(iii)
Write an ionic equation for the reaction of I– with IO3– in an acidic solution.
..........................................................................................................................
..........................................................................................................................
(2)
(b)
Use information from Table 15 of the Data Booklet to calculate the cell potential for the
following reaction and state whether or not the reaction is spontaneous.
Cu(s) + Cu2+(aq)  2Cu+(aq)
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
(Total 8 marks)
34.
A table of standard electrode potentials can be found in Table 14 of the Data Booklet.
(a)
Describe the materials and conditions used in the standard hydrogen electrode.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(5)
17
(b)
Define the term oxidizing agent in terms of electron transfer and identify the strongest
oxidizing agent in Table 14 of the Data Booklet.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(c)
A cell was set up using tin in tin(II) sulfate solution and copper in copper(II) sulfate
solution, with both solutions under standard conditions.
(i)
Calculate the cell potential.
...........................................................................................................................
...........................................................................................................................
(1)
(ii)
Write an equation for the spontaneous cell reaction.
...........................................................................................................................
...........................................................................................................................
(2)
(Total 10 marks)
18
1.
B
[1]
2.
D
[1]
3.
C
4.
D
[1]
[1]
5.
B
[1]
6.
A
[1]
7.
D
[1]
8.
C
[1]
9.
A
[1]
10.
C
[1]
11.
C
12.
D
[1]
[1]
13.
D
[1]
14.
B
[1]
15.
B
[1]
16.
A
[1]
17.
C
[1]
18.
D
[1]
19.
A
[1]
19
20.
D
[1]
21.
C
[1]
22.
C
[1]
23.
A
[1]
24.
(a)
(i)
(c)
1
(ii)
Zn(s)  Zn2+(aq) + 2e– (state symbols not needed);
1
(iii)
298 K/25°C, 1 atm/1.01×105Pa, 1 mol dm–3 solutions;
(all 3 for [2], 2 for [1])
2
(iv)
0.34 – (–0.76) = 1.10 V;
[1] for finding correct data, [1] for answer with unit (ECF).
2
(v)
decreases;
Cu2+ ions are converted to Cu metal/Cu deposited on electrode;
Allow ECF from (iv).
2
(vi)
(b)
ionic conductor/allows movement of ions between electrolytes
/completes circuit;
(i)
Cu deposited on Zn rod/rod goes pink/brown;
blue colour of solution  paler;
gets hotter/temperature increase/exothermic;
Ti2+ (no ECF to explanation);
Ti2+ has greatest tendency to lose electrons/Ti3+ has least tendency
to gain electrons;
(ii)
Ce4+(aq) + Ti2+(aq)  Ce3+(aq) + Ti3+(aq)
[1] for equation, [1] for state symbols. If wrong equation is
given, award [1]
for state symbols.
(iii)
Gο negative;
reaction spontaneous/corresponds to positive cell potential;
Positive [0], non-spontaneous [1].
(i)
(aqueous) sodium hydroxide/dilute sulfuric acid/sodium sulfate;
Accept correct formulas.
Any combination of K+/Na+/H+ and NO3–/SO42–.
Halides not acceptable. (“water” is not a solution)
2 max
2
2
2
1
(ii)
20
hydrogen / H 2
oxygen / O 2
–
+
Or similar suitable diagram.
gas collection method;
names of gases correct way round at electrodes;
2:1 volume ratio correct way round;
3
[20]
25.
(i)
(ii)
mass increases;
copper deposited;
because X is negative and attracts Cu2+ ions/reduction occurs at X/
Cu2+ + 2e–  Cu;
3
increase time;
increase current;
2
[5]
26.
(a)
(i)
(ii)
(b)
(c)
([H+]=)1 mol dm–3;
298 K/25°C;
1 atm/101.3 or 101 kPa
Accept 100 kPa;
3
Eο(=0.76 +0.34) = (+)1.1(0)(V);
from zinc/Zn to copper/Cu;
copper/Cu deposited/electrode becomes larger/thicker/heavier;
zinc/Zn electrode becomes smaller/thinner/lighter;
Cu2+ solution becomes paler/colourless;
Allow ECF for –1.1 V, all answers must be consistent with
the error.
no (spontaneous) reaction;
appropriate use of Table 15/Eο = –0.34 + 0.00 = –0.34 V/Eο value for
the reaction would be negative;
5
2
O2/Cr2O72–;
Accept names.
Eο value for the reaction with Br– is positive/suitable calculation to show this;
Eο value for the reaction with Cl– is negative/Cl2 stronger oxidizing agent than
O2/Cr2O72–;
5
4Br– + O2 + 4H+ → 2Br2 + 2H2O/Cr2O72– + 14H + 6Br– → 2Cr3+ + 7H2O + 3Br2;
Award [1] for all formulas correct, [1] if coefficients correct.
[15]
21
27.
(a)
(b)
0.2 mol;
the Na:Cl2 mol ratio is 2 : 1;
0.1 12 5;
= 0.25 mol;
(c)
2
2
negative electrode
hydrogen/H2;
2H+ + 2e  H2/2H2O + 2e  H2 + 2OH;
positive electrode
oxygen/O2;
4OH  2H2O + O2 + 4e/2H2O  O2 + 4H+ + 4e.
4
[8]
28.
the potential/voltage difference between the element and its ions;
(and) a hydrogen electrode;
under standard conditions/ion concentration at 1 mol dm3/298 K/25C;
(+)1.23 (V);
EӨ value more positive or less negative than bromine/bromide system/
EӨ value of combined half-cells is positive/OWTTE;
2Br +
1
2
O2 + 2H+  Br2 + H2O;
Award [1] for all formulas correct, [1] for correct balancing.
Award [1] for correct equation reversed.
EӨ (= 1.23  1.09) = (+)0.14 (V);
Ignore state symbols.
8
[8]
29.
(i)
(ii)
(iii)
(iv)
(metal ions at) 1 mol dm3 concentration;
25C/298 K;
Do not accept 1 atm pressure.
Ni2+ + 2e–Ni;
Pb  Pb2+ + 2e;
No penalty for using e instead of e.
No penalty for
instead of .
0.15 V;
10Cl + 2Mn O 4 + 16H +  5Cl2 + 2Mn2+ + 8H2O;
Ignore state symbols.
Correct reactants and products = [1]
Correct balancing = [1]
not sufficiently good oxidizing agent/cell potential would have
negative EӨ value;
2
2
3
1
[8]
22
30.
(a)
(i)
(ii)
(b)
oxidation half-reaction: 2Cl– → Cl2 + 2e–;
reduction half-reaction: 2H2O + 2e– → H2 + 2OH–/2H+ + 2e– → H2
Award [1] only if equations are interchanged.
States not required.
2
Na has high Eοred / Na+ not readily reduced (in comparison to H2O)/if
formed, Na would (immediately) react with water to form Na+
H(g) and O2(g)/accept names;
2H2O → O2 + 4H+ + 4e–/4OH–→ 2H2O + O2 + 4e–;
water is oxidized (instead of the halide);
since EοOX for F– is very negative/Eοred for F2 is very high;
Accept answer based on oxidizing/reducing strengths.
1
4
[7}
31.
(a)
Hydrogen gas at 1 atm
1 mol dm–3 [H +(aq)]
Platinum (coated
with platinum black)
Accept suitable diagram with the following indicated:
Pt electrode;
1 mol dm–3 [H+(aq)];
H2 gas;
at 1 atm/1.01×105 Pa;
298 K/25°C;
(b)
(c)
(d)
5
electron acceptor;
Fe3+(aq)/iron(III) ions/Fe3+;
Do not accept iron/Fe2+/iron ion.
(i)
(+)1.10;
(ii)
Cu2+(aq) + Zn(s) → Zn2+(aq) + Cu(s);
Award [1] for correct reactants and products from (c)(i),
and [1] for state symbols.
(i)
zinc;
zinc is more readily oxidised than iron and so protects it by reacting
preferentially/OWTTE or tin is less readily oxidised than iron and
so iron reacts preferentially/OWTTE;
2
1
2
2
23
(ii)
(e)
charge on the ion discharged;
size/magnitude of the current;
time/duration of the electrolysis;
3
(iii)
positive ions/cations in solution = H+(aq), Zn2+(aq);
H+(aq) discharged preferentially;
(i)
salt bridge;
allows movement of ions between the solutions/to complete
the circuit/to maintain electrical neutrality;
(ii)
2
A: Fe3+(aq) + e– → Fe2+(aq);
B: Cr(s) → Cr3+(aq) + 3e–;
Allow [2] for correct equation for the cell reaction if
equations for A and B are reversed.
3 Fe3+(aq) + Cr(s) → 3 Fe2+(aq) + Cr3+(aq);
Award [1] for correct reactants and products, with state
symbols, and [1] for correct balancing.
4
(iii)
from B to A/from Cr to Pt/from right to left;
Allow ECF from (ii).
1
(iv)
(+)1.51;
Allow ECF from (ii).
1
[25]
32.
(a)
Fe + 2Ag+  Fe2+ + 2Ag;
Ignore state symbols.
1
Accept Fe + 3Ag+  Fe3+ + 3Ag
(b)
(c)
the potential difference/EMF/Voltage between a standard half-cell and
standard hydrogen electrode/OWTTE;
1
(+) 1.24 (V);
1
ECF from (a).
(d)
electron flow indicated on wires;
ECF from (a).
1
voltmeter
V
salt bridge
iron electrode
silver electrode
Fe 2+(aq)
Ag +(aq)
24
[4]
33.
(a)
(i)
(ii)
I = 1/1 and IO3 = +5/5+;
Both answers needed for [1] mark,
Signs must be included
Do not accept Roman numerals
1
oxidation
I (to I2), increase in oxidation number/loss of electron(s);
reduction
IO3– (to I2), decrease in oxidation number/gain of electron(s);
(iii)
5I(aq) + IO3–(aq) + 6H+(aq)  3I2(aq) + 3H2O(l);
Award [2] if correctly balanced
Award [1] for correct reactants and products.
States not required for mark.
2
2
[1 max] if HCl on left and Cl on right side
(b)
Cu2+(aq) + e
Cu+(aq) : EӨ = (+) 0.15(V), Cu(s)
Cu+(aq) + e :
EӨ =  0.52(V)/(+) 0.15 and  0.52(V);
No mark if 0.34 or 0.52 quoted, but then ECF
(Cu2+(aq) + Cu(aq)
2 Cu+(aq)) EӨ value for reaction =  0.37(V);
Award [2] for correct ErxnӨ even if equations are not given,
states not required.
(negative value means) not spontaneous;
Allow ECF: if positive value, can score third mark for
‘spontaneous’.
3
[8]
34.
(a)
(b)
(c)
Pt electrode;
1 mol dm–3 [H+(aq)];
H2 gas;
at 1 atm/1.01×105 Pa;
298 K/25°C;
Accept suitable labelled diagram with the above.
5
electron acceptor;
F2/fluorine;
2
(i)
(+)0.48 (V);
1
(ii)
Cu2+(aq) + Sn(s)  Sn2+(aq) + Cu(s)
Award [1] for correct reactants and products from (c)(i), and
[1] for state symbols.
2
[10]
25