1.
2.
Which statement is correct?
A.
Oxidation involves loss of electrons and a decrease in oxidation state.
B.
Oxidation involves gain of electrons and an increase in oxidation state.
C.
Reduction involves loss of electrons and an increase in oxidation state.
D.
Reduction involves gain of electrons and a decrease in oxidation state.
What occurs during the operation of a voltaic cell based on the following reaction?
Ni(s) + Pb2+(aq) → Ni2+(aq) + Pb(s)
3.
External circuit
Ion movement in solution
A.
electrons move from Ni to Pb
Pb2+(aq) move away from Pb(s)
B.
electrons move from Ni to Pb
Pb2+(aq) move toward Pb(s)
C.
electrons move from Pb to Ni
Ni2+(aq) move away from Ni(s)
D.
electrons move from Pb to Ni
Ni2+(aq) move toward Ni(s)
Which is the strongest reducing agent according to the spontaneous reactions below?
2Cr(s) + 3Fe2+(aq)  2Cr3+(aq) + 3Fe(s)
Fe(s) + Pb2+(aq)  Fe2+(aq) + Pb(s)
A.
4.
Pb2+(aq)
D.
Pb(s)
Ag = Cu = Cr
B. Ag > Cu > Cr
C. Ag < Cu < Cr
D. Cu > Ag > Cr
Cr(OH)3
B.
Cr2O3
C.
Cr2(SO4)3
D.
CrO3
Mg
B.
Mg2+
C.
Cu
D.
Cu2+
Which processes occur during the electrolysis of molten sodium chloride?
A.
8.
C.
Magnesium is a more reactive metal than copper. Which is the strongest oxidizing agent?
A.
7.
Cr3+(aq)
The oxidation number of chromium is the same in all the following compounds except
A.
6.
B.
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.
5.
Cr(s)
I.
Sodium and chloride ions move through the electrolyte.
II.
Electrons move through the external circuit.
III.
Oxidation takes place at the positive electrode (anode).
I and II only
B.
I and III only
C.
II and III only D.
I, II and III
In which reaction does chromium undergo a change in oxidation number?
1
9.
A.
Cr2O3 + 3H2SO4 → Cr2(SO4)3 + 3H2O
B.
Cr2(SO4)3 + 6NaOH → 2Cr(OH)3 + 3Na2SO4
C.
K2Cr2O7 + 4H2SO4 + 6HCl → Cr2(SO4)3 + K2SO4 + 7H2O + 3Cl2
D.
2K2CrO4 + H2SO4 → K2Cr2O7 + K2SO4 + H2O
When the following equation is balanced, what is the coefficient for Ce4+?
_SO32– + _H2O + _Ce4+  _SO42– + _H+ + _Ce3+
A.
10.
1
B.
2
C.
3
D.
4
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?
11.
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?
A.
12.
13.
I.
Doubling the current passed during electrolysis
II.
Doubling the time used for electrolysis
III.
Using Sn4+ ions instead of Sn2+ ions
I only
B.
II only C.
I and II only
D.
I, II and III
What happens to the Cr3+(aq) ion when it is converted to CrO42–(aq)?
A.
Its oxidation number decreases and it undergoes reduction.
B.
Its oxidation number decreases and it undergoes oxidation.
C.
Its oxidation number increases and it undergoes reduction.
D.
Its oxidation number increases and it undergoes oxidation.
The following reactions are spontaneous as written.
Fe(s) + Cd2+(aq) → Fe2+(aq) + Cd(s)
2
Cd(s) + Sn2+(aq) → Cd2+(aq) + Sn(s)
Sn(s) + Pb2+(aq) → Sn2+(aq) + Pb(s)
Which of the following pairs will react spontaneously?
Sn(s) + Fe2+(aq)
I.
A.
14.
I only
B.
II.
II only
III.
Fe(s) + Pb2+(aq)
C.
D.
II and III only
III only
What species are produced at the positive and negative electrodes during the electrolysis of molten sodium
chloride?
Positive electrode
15.
Cd(s) + Pb2+(aq)
A.
Na (l)
Negative electrode
Cl2(g)
B.
Cl–(l)
Na+(l)
C.
Na(l)
Cl2(g)
D.
Cl2(g)
Na(l)
+
What is the coefficient for H+ when the equation below is balanced?
__Pb(s) + __NO3–(aq) + __H+(aq) → __Pb2+(aq) + __NO(g) + __H2O(l)
A.
16.
2
B.
4
6
D.
8
Which of the following factors affect the amount of product formed during electrolysis?
I. The current used
A.
17.
C.
I and II only
II. The duration of electrolysis
B.
I and III only
C.
III. The charge on the ion
II and III only D.
I, II and III
Consider the following reaction.
H2SO3(aq) + Sn4+(aq) + H2O(l) → Sn2+(aq) + HSO4–(aq) + 3H+(aq)
Which statement is correct?
18.
19.
A.
H2SO3 is the reducing agent because it undergoes reduction.
B.
H2SO3 is the reducing agent because it undergoes oxidation.
C.
Sn4+ is the oxidizing agent because it undergoes oxidation.
D.
Sn4+ is the reducing agent because it undergoes oxidation.
In which change does oxidation occur?
A.
CH3CHO → CH3CH2OH
B.
CrO42–→ Cr2O72–
C.
SO42–→ SO32–
D.
NO2– → NO3–
What happens at the positive electrode in a voltaic cell and in an electrolytic cell?
3
Voltaic cell
Oxidation
Reduction
Oxidation
Reduction
A.
B.
C.
D.
20.
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–
3–
[Fe(CN)6]
21.
Electrolytic cell
Reduction
Oxidation
Oxidation
Reduction
[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?
22.
A.
Cu2+(aq) will oxidize both Mg(s) and Zn(s).
C.
Mg2+(aq) will oxidize both Cu(s) and Zn(s).
B. Zn(s) will reduce both Cu2+(aq) and Mg2+(aq).
D. Cu(s) will reduce both Mg2+(aq) and Zn2+(aq).
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)
A.
23.
–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
4
24.
25.
C.
O2
Cl2
D.
Cl2
O2
What are the oxidation numbers of the elements in sulfuric acid, H2SO4?
Hydrogen
Sulfur
Oxygen
A.
+1
+6
–2
B.
+1
+4
–2
C.
+2
+1
+4
D.
+2
+6
–8
A voltaic cell is made from copper and zinc half-cells. The equation for the reaction occurring in the cell is
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
Which statement is correct when the cell produces electricity?
26.
27.
A.
Electrons are lost from zinc atoms.
B.
The mass of the copper electrode decreases.
C.
Electrons flow from the copper half-cell to the zinc half-cell.
D.
Negative ions flow through the salt bridge from the zinc half-cell to the copper half-cell.
What happens when molten sodium chloride is electrolysed in an electrolytic cell?
A.
Chlorine is produced at the positive electrode.
B.
Sodium ions lose electrons at the negative electrode.
C.
Electrons flow through the liquid from the negative electrode to the positive electrode.
D.
Oxidation occurs at the negative electrode and reduction at the positive electrode.
The unbalanced equation for the conversion of sulfur dioxide to sulfuric acid is given below.
___SO2 + ___H2O → ___ H2SO4
Which other species are used, and on which side of the equation, to balance it?
28.
29.
A.
H+ and e– on the left
B.
H+ on the left and e– on the right
C.
H+ on the right and e– on the left
D.
H+ and e– on the right
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
5
sodium chloride?
30.
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
Which equations represent reactions that occur at room temperature?
A.
31.
32.
I.
2Br–(aq) + Cl2(aq)  2Cl–(aq) + Br2(aq)
II.
2Br–(aq) + I2(aq)  2I–(aq) + Br2(aq)
III.
2I–(aq) + Cl2(aq)  2Cl–(aq) + I2(aq)
I and II only
B.
I and III only
C.
II and III only D.
I, II and III
Which equation represents a redox reaction?
A.
KOH(aq) + HCl(aq)  KCl(aq) + H2O(l)
C.
CuO(s) + 2HCl(aq)  CuCl2(aq) + H2O(l)
D.
ZnCO3(s) + 2HCl(aq)  ZnCl2(aq) + CO2(g) + H2O(l)
B.
Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
The following information is given about reactions involving the metals X, Y and Z and solutions of their
sulfates.
X(s) + YSO4(aq)  no reaction
Z(s) + YSO4(aq)  Y(s) + ZSO4(aq)
When the metals are listed in decreasing order of reactivity (most reactive first), what is the correct order?
A.
33.
ZYX
B.
XYZ
YXZ
D.
YZX
From the given standard electrode potentials which statement is correct?
Ca2+(aq) + 2e–
Ni2+(aq) + 2e–
Fe3+(aq) + e–
34.
C.
EӨ = –2.87 V
EӨ = –0.23 V
EӨ = +0.77 V
Ca(s)
Ni(s)
Fe2+(aq)
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)
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.
6
D.
35.
36.
37.
38.
A colourless gas is produced at the positive electrode.
What are the oxidation numbers of the elements in the compound phosphoric acid, H3PO4?
Hydrogen
Phosphorus
Oxygen
A.
+1
+1
–2
B.
+1
+5
–2
C.
+3
+1
–4
D.
+3
+5
–8
A voltaic cell is made from magnesium and iron half-cells. Magnesium is a more reactive metal than iron.
Which statement is correct when the cell produces electricity?
The concentration of Fe2+ ions increases.
A.
Electrons are lost from magnesium atoms.
B.
C.
Electrons flow from the iron half-cell to the magnesium half-cell.
D.
Negative ions flow through the salt bridge from the magnesium half-cell to the iron half-cell.
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
Ag+(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.
39.
0.67
B.
0.93
C.
1.47
D.
1.73
Two electrolytic cells are connected in series so that the same current flows through both cells for the same
length of time.
7
SnSO4(aq)
-
-
+
+
CuSO4 (aq)
The amount of tin deposited is 0.01 mol. How much copper is deposited?
A.
40.
0.005 mol
A.
C.
0.02 mol
D.
0.05 mol
Fe3+ becomes Fe2+
I and II only
B.
II.
Cl– becomes Cl2
I and III only
C.
III.
CrO3 becomes Cr3+
II and III only D.
I, II and III
Which statement is correct for the electrolysis of a molten salt?
A.
Positive ions move toward the positive electrode.
C.
Only electrons move in the electrolyte.
D.
42.
0.01 mol
Which are examples of reduction?
I.
41.
B.
B. A gas is produced at the negative electrode.
Both positive and negative ions move toward electrodes.
Which statement about the following reaction is correct?
2Br–(aq) + Cl2(aq)  Br2(aq) + 2Cl–(aq)
43.
A.
Br–(aq) is reduced and gains electrons.
B.
Cl2(aq) is reduced and loses electrons.
C.
Br–(aq) is oxidized and loses electrons.
D.
Cl2(aq) is oxidized and gains electrons.
Which are used for the electroplating of a metal spoon with copper?
A.
44.
I.
an electrolyte containing aqueous copper(II) ions
II.
a copper anode (positive electrode)
III.
a copper cathode (negative electrode)
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.
45.
– 0.67 V
B.
– 0.37 V
C.
+ 0.37 V
D.
+ 0.67 V
Consider the following spontaneous reactions.
8
Fe(s) + Cu2+(aq)  Fe2+(aq) + Cu(s)
Cu(s) + 2Ag+(aq)  Cu2+(aq) + 2Ag(s)
Zn(s) + Fe2+(aq)  Zn2+(aq) + Fe(s)
Which is the correct combination of strongest oxidizing agent and strongest reducing agent?
46.
48.
49.
Strongest reducing agent
A.
Ag(s)
Zn(s)
B.
Ag+(aq)
Zn(s)
C.
Zn2+(aq)
Ag(s)
D.
Zn(s)
Ag+(aq)
In which change does nitrogen undergo oxidation?
A.
47.
Strongest oxidizing agent
NO2  N2O4
B.
NO3–  NO2
C.
N2O5 NO3– D.
NH3  N2
Which statement is correct?
A.
Spontaneous redox reactions produce electricity in an electrolytic cell.
B.
Electricity is used to carry out a non-spontaneous redox reaction in a voltaic cell.
C.
Oxidation takes place at the negative electrode in a voltaic cell and the positive electrode in an
electrolytic cell.
D.
Oxidation takes place at the negative electrode in a voltaic cell and reduction takes place at the positive
electrode in an electrolytic cell.
The compound [Co(NH3)5Br]SO4 is isomeric with the compound [Co(NH3)5SO4]Br. What is the oxidation
state of cobalt in these compounds?
[Co(NH3)5Br]SO4
[Co(NH3)5SO4]Br
A.
+3
+3
B.
+2
+1
C.
+3
+2
D.
+2
+3
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?
A.
50.
+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?
9
A.
51.
4.2 cm3
A.
53.
54.
55.
56.
8.4 cm3
C.
12.6 cm3
D.
16.8 cm3
Which factors affect the amount of metal formed during electrolysis?
I.
52.
B.
Charge on the metal ion
I and II only
B.
II.
I and III only
Current
C.
III.
Time
II and III only D.
I, II and III
What happens to vanadium during the reaction VO2+(aq)  VO3–(aq)?
A.
It undergoes oxidation and its oxidation number changes from +4 to +5.
B.
It undergoes oxidation and its oxidation number changes from +2 to +4.
C.
It undergoes reduction and its oxidation number changes from +2 to –1.
D.
It undergoes reduction and its oxidation number changes from +4 to +2.
What occurs during the electrolysis of a molten salt?
A.
Electricity is produced by a spontaneous redox reaction.
B.
Electricity is used to cause a non-spontaneous redox reaction to occur.
C.
Electrons flow through the molten salt.
D.
Electrons are removed from both ions of the molten salt.
Which statement is correct about an oxidizing agent in a chemical reaction?
A.
It reacts with oxygen.
B.
It reacts with H+ ions.
C.
It loses electrons.
D.
It undergoes reduction.
Which formula represents an aldehyde?
A.
CH3CH2CHO
B.
CH3COCH3
C.
CH3CH2COOH
D.
CH3COOCH3
The standard electrode potentials for two half reactions are
V2+(aq) + 2e–  V(s)
Tl+(aq) + e–  Tl(s)
–1.19 V
–0.34 V
What is the EӨ value (in volts) for the following reaction?
V(s) + 2Tl+(aq)  V2+(aq) + 2Tl(s)
A.
+0.85
B.
+0.51 C.
–1.53
D.
–1.87
10
57.
Which changes lead to the production of more moles of metal during the electrolysis of a molten salt?
A.
58.
I.
using a metal ion with a higher charge
II.
increasing the current
III.
using a longer time
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
What is the reducing agent in this reaction?
Cu(s) + 2 NO 3 (aq) + 4H+(aq) → Cu2+(aq) + 2NO2(g) + 2H2O(l)
A.
59.
Cu(s)
B.
NO 3 (aq)
C.
Cu2+(aq)
D.
H+(aq)
A particular voltaic cell is made from magnesium and iron half-cells. The overall equation for the reaction
occurring in the cell is
Mg(s) + Fe2+(aq) → Mg2+(aq) + Fe(s)
Which statement is correct when the cell produces electricity?
60.
61.
A.
Magnesium atoms lose electrons.
B.
The mass of the iron electrode decreases.
C.
Electrons flow from the iron half-cell to the magnesium half-cell.
D.
Negative ions flow through the salt bridge from the magnesium half-cell to the iron half-cell.
What process occurs at the cathode in a voltaic cell and at the anode in an electrolytic cell?
A.
Cathode of
voltaic cell
Oxidation
Anode of
Electrolytic cell
Reduction
B.
Oxidation
Oxidation
C.
Reduction
Oxidation
D.
Reduction
Reduction
Consider the following reaction:
H2SO3(aq) + Sn4+(aq) + H2O(l) → Sn2+(aq) + HSO4–(aq) + 3H+(aq)
Which statement is correct?
62.
A.
H2SO3 is the reducing agent because it undergoes reduction.
B.
H2SO3 is the reducing agent because it undergoes oxidation.
C.
Sn4+ is the oxidizing agent because it undergoes oxidation.
D.
Sn4+ is the reducing agent because it undergoes oxidation.
Which processes occur during the electrolysis of molten sodium chloride?
11
I.
II.
III.
A.
63.
64.
Sodium and chloride ions move through the electrolyte.
Electrons move through the external circuit.
Oxidation takes place at the anode.
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.
65.
Direction of electron flow
A
Salt bridge
Zn(s)
Cu(s)
Zn 2+(aq)
Cu 2+ (aq)
(a)
The apparatus shown above may be used to carry out a redox reaction.
(i)
State the function of the salt bridge.
……………………………………………………………………………………
12
……………………………………………………………………………………
(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.
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(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)
(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.
13
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
(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.
……………………………………………………………………………………
(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)
14
66.
– +
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)
67.
Consider the following redox equation.
5Fe2+(aq) +MnO4–(aq) +8H+(aq) → 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)
(i)
Determine the oxidation numbers for Fe and Mn in the reactants and in the products.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(2)
(ii)
Based on your answer to (i), deduce which substance is oxidized.
……………………………………………………………………………………………
(1)
15
(iii)
The compounds CH3OH and CH2O contain carbon atoms with different oxidation numbers. Deduce
the oxidation numbers and state the kind of chemical change needed to make CH2O from CH3OH.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(3)
(Total 6 marks)
68.
A part of the reactivity series of metals, in order of decreasing reactivity, is shown below.
magnesium
zinc
iron
lead
copper
silver
If a piece of copper metal were placed in separate solutions of silver nitrate and zinc nitrate
(i)
determine which solution would undergo reaction.
……………………………………………………………………………………………
(1)
(ii)
identify the type of chemical change taking place in the copper and write the
half-equation for this change.
……………………………………………………………………………………………
……………………………………………………………………………………………
(2)
(iii)
state, giving a reason, what visible change would take place in the solutions.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(2)
(Total 5 marks)
69.
(i)
Solid sodium chloride does not conduct electricity but molten sodium chloride does. Explain this
difference, and outline what happens in an electrolytic cell during the electrolysis of molten sodium
chloride using carbon electrodes.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
16
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(4)
(ii)
State the products formed and give equations showing the reactions at each electrode.
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(4)
(iii)
State what practical use is made of this process.
……………………………………………………………………………………………
……………………………………………………………………………………………
(1)
(Total 9 marks)
70.
(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.
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
17
………………………………………………………………………………………
………………………………………………………………………………………
(5)
(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)
71.
A current is passed through molten sodium chloride. Identify the substance formed at each electrode and
write an equation to represent the formation of each substance. Determine the mole ratio in which the
substances are formed.
……………………………………………………………………………………………………
……………………………………………………………………………………………………
……………………………………………………………………………………………………
……………………………………………………………………………………………………
……………………………………………………………………………………………………
……………………………………………………………………………………………………
(Total 5 marks)
72.
Electrolysis can be used to obtain chlorine from molten sodium chloride. Write an equation for the reaction
occurring at each electrode and describe the two different ways in which electricity is conducted when the
cell is in operation.
(Total 4 marks)
73.
(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)
18
(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)
74.
Two reactions occurring in the manufacture of bromine from sea water are
I
II
(i)
Cl2(g) + 2Br–(aq)  2Cl–(aq) + Br2(g)
Br2(g) + SO2(g) + 2H2O(l)  2HBr(g) + H2SO4(g)
Explain, by reference to electrons, why reaction I is referred to as a redox reaction.
(2)
(ii)
State and explain whether SO2 is reduced or oxidized in reaction II by referring to the oxidation
numbers of sulfur in this reaction.
(3)
(Total 5 marks)
75.
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)
76.
In terms of electron transfer define:
(i)
oxidation
....................................................................................................................................
....................................................................................................................................
(1)
(ii)
oxidizing agent
....................................................................................................................................
....................................................................................................................................
(1)
(Total 2 marks)
77.
Deduce the change in oxidation number of chromium in the below reaction. State with a reason whether the
chromium has been oxidized or reduced.
CrO72 + 14H+ + 6Fe2+  2Cr3+ + 6Fe3+ + 7H2O
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
19
..............................................................................................................................................
(Total 2 marks)
78.
(a)
(i)
Define oxidizing agent in terms of electron transfer.
.........................................................................................................................
.........................................................................................................................
(1)
(ii)
Deduce the change in oxidation number of chromium in the reaction below. State with a reason
whether the chromium has been oxidized or reduced.
Cr2O7 2 + 14H+ + 6Fe2+  2Cr3+ + 7H2O
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
(2)
(Total 3 marks)
79.
Iron in food, in the form of Fe3+, reacts with ascorbic acid (vitamin C), C6H8O6, to form dehydroascorbic
acid, C6H6O6.
(i)
Write an ionic half-equation to show the conversion of ascorbic acid to dehydroascorbic acid in
aqueous solution.
.........................................................................................................................
.........................................................................................................................
(1)
(ii)
In the other ionic half-equation Fe3+ is converted to Fe2+. Deduce the overall equation for the
reaction between C6H8O6 and Fe3+.
.........................................................................................................................
.........................................................................................................................
(1)
(Total 2 marks)
80.
(i)
Draw a diagram of apparatus that could be used to electrolyse molten potassium bromide. Label the
diagram to show the polarity of each electrode and the product formed.
(3)
(ii)
Describe the two different ways in which electricity is conducted in the apparatus.
(2)
(iii)
Write an equation to show the formation of the product at each electrode.
(2)
(Total 7 marks)
20
81.
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)
82.
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 each iodine-containing species in the reaction.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(ii)
Identify, with a reason, the species that undergoes:
oxidation ....................................................................................................................
....................................................................................................................................
reduction ....................................................................................................................
....................................................................................................................................
(2)
(Total 4 marks)
83.
(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: ...................................................................................
21
...........................................................................................................................
Reduction half-reaction: ...................................................................................
...........................................................................................................................
(2)
(ii) Explain why sodium is not formed during the electrolysis of aqueous NaCl solution.
...........................................................................................................................
...........................................................................................................................
(1)
(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)
84.
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.)
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
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22
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
(5)
(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.
……………………………………………………………………………………
……………………………………………………………………………………
23
……………………………………………………………………………………
(3)
(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.
……………………………………………………………………………………
(1)
24
(iv)
Calculate the cell potential.
……………………………………………………………………………………
……………………………………………………………………………………
(1)
(Total 25 marks)
85.
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)
(d)
Draw arrows on the above diagram to indicate the direction of electron flow.
(1)
(Total 4 marks)
86.
Tin(II) ions can be oxidized to tin(IV) ions by acidified potassium permanganate(VII) solution according to
the following unbalanced equation.
__ Sn2+ + __MnO4– + __ H+ __ Sn4+ + __Mn2+ + __ H2O
25
(a)
Identify the oxidizing agent and the reducing agent.
Oxidizing agent .........................................................................................................
Reducing agent ..........................................................................................................
(1)
(b)
Balance the equation above.
....................................................................................................................................
....................................................................................................................................
(1)
(Total 2 marks)
87.
(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)
26
(Total 8 marks)
88.
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)
(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)
27