Subject Chemistry IGCSE (0620/5070)
Exam Board Cambridge International Examinations (CIE)
Topic Redox Reactions
Sub-Topic Oxidation-Reduction Reactions /Tests for oxidant and reluctant
Time Allowed: 60 minutes Score: /58 Percentage: /100
1. When magnesium is heated with zinc oxide a reaction occurs.
The equation is shown.
Mg + ZnO MgO + Zn
Which substance is oxidised?
A magnesium
B magnesium oxide
C zinc
D zinc oxide
2. In which equation is carbon both oxidised and reduced?
A C + O2 CO2
B CO2 + C 2CO
C 3CO + Fe2O3 3CO2 + 2Fe
D 2CO + O2 2CO2
3. Some reactions of element M are shown.
burn add water
element M oxide of M solution
add to purple acidified add blue litmus
potassium manganate(VII)
goes colourless goes red
What is element M?
A carbon
B iron
C magnesium
D sulfur
4. Copper(II) oxide reacts with iron. The equation for the reaction is shown.
3CuO + 2Fe 3Cu + Fe2O3
Why can this reaction be described as the reduction of copper(II) oxide?
A Iron gains oxygen.
B The copper(II) oxide loses oxygen.
C The copper(II) oxide weighs less after the reaction than before.
D There are fewer substances on the right of the equation.
5. Carbon reacts with carbon dioxide as shown.
CO2 + C → 2CO Which
statement about this reaction is correct?
A Carbon dioxide and carbon are both oxidised.
B Carbon dioxide and carbon are both reduced.
C Carbon dioxide is reduced and carbon is oxidised.
D Carbon dioxide is oxidised and carbon is reduced.
6. `What happens to a chemical substance when it is reduced?
A It burns.
B It decomposes.
C It loses oxygen.
D It gains mass.
7. In which change is the sulfur, S, in sulfur(I) oxide, S2O, reduced?
During the manufacture of sulfuric acid, sulfur dioxide is converted to sulfur trioxide.
2SO2 + O2 2SO3
Which type of reaction is this?
A displacement B neutralization C oxidation D thermal decomposition
8. When heated strongly, silicon(IV) oxide reacts with carbon.
SiO2 + 2C → Si + 2CO Which
term describes what happens to silicon(IV) oxide?
A thermal decomposition
B neutralisation
C oxidation
D reduction
9. Which equation shows an oxidation reaction?
A C + O2 → CO2
B CaCO3 → CaO + CO2
C CaO + 2HCl → CaCl 2 + H2O
D N2O4 → 2NO2
10. Which equation shows reduction of an iron compound?
A 4Fe + 3O2 → 2Fe2O3
B Fe + 2HCl → FeCl 2 + H2
C 4FeO + O2 → 2Fe2O3
11. Fe2O The results of some experiments with sulfur dioxide are shown.
Which results are correct?
A 1, 2 and 4 B 2, 3 and 4 C 1 and 2 only D 3 and 4 only
12. In a blast furnace, iron is extracted when iron(III) oxide reacts with carbon monoxide.
The equation is shown.
Fe2O3 + 3CO → 2Fe + 3CO2
Which substance is oxidised and which is reduced?
13. The thermite reaction can be used to produce iron from iron(III) oxide.
The equation for the reaction is shown.
2Al + Fe2O3 → 2Fe + Al 2O3
Which statements about this reaction are correct?
1 Aluminium is the oxidising agent.
2 Aluminium is less reactive than iron.
3 Electrons are transferred from aluminium to iron.
4 The iron in the iron(III) oxide is reduced.
A 1 and 3 B 1 and 4 C 2 and 3 D 3 and 4
14 . Heating copper(II) carbonate produces copper(II) oxide and carbon dioxide.
Heating the copper(II) oxide formed with carbon produces copper.
Which processes are involved in this conversion of copper(II) carbonate to copper?
A sublimation followed by oxidation
B sublimation followed by reduction
C thermal decomposition followed by oxidation
D thermal decomposition followed by reduction
15.. When aqueous iron(III) chloride is added to aqueous potassium iodide a chemical reaction occurs
and iodine is formed.
Which statement is correct?
A Iodide ions are oxidised, they gain electrons in this reaction.
B Iodide ions are oxidised, they lose electrons in this reaction
C Iron(III) chloride is oxidised in this reaction.
D Neither iodide ions nor iron(III) chloride is oxidised in this reaction.
16.. The equations for two reactions of iodide ions are shown.
– –
reaction 1 2I (aq) + H2O2(aq) → I2(aq) + 2OH (aq)
– +
reaction 2 I (aq) + Ag (aq) → AgI(s)
Which statement is correct?
A Both reactions are redox reactions.
B Neither reaction is a redox reaction.
C Only reaction 1 is a redox reaction.
D Only reaction 2 is a redox reaction.
17. The equation for the reaction between zinc and aqueous copper(II) sulfate is shown.
Zn + CuSO4 → ZnSO4 + Cu
Which statement is correct?
A The oxidation state of the oxidising agent has changed from 0 to +2.
B The oxidation state of the reducing agent has changed from 0 to +2.
C The oxidation state of the reducing agent has changed from +2 to 0.
D This is not a redox reaction. The solution changes from colourless to blue.
18. In which equation is the underlined substance acting as a reducing agent?
A 3CO + Fe2O3 → 2Fe + 3CO2
B CO2 + C → 2CO
C CuO + H2 → Cu + H2O
D CaO + H2O → Ca(OH)2
19. Gaseous compound X is an oxidising agent. X is bubbled through separate solutions of aqueous
potassium iodide and acidified potassium manganate(VII).
X X
aqueous potassium iodide
potassium manganate(VII).
Which row shows the colour changes when X is bubbled through these two solutions?
aqueous acidified potassium
potassium iodide manganate(VII)
A brown to colourless no change
B brown to colourless purple to colourless
C colourless to brown no change
D colourless to brown purple to colourless
20. In which reaction is nitric acid acting as an oxidising agent?
A Cu + 4HNO3 → Cu(NO3)2 + 2H2O + 2NO2
B CuO + 2HNO3 → Cu(NO3)2 + H2O
C Na2CO3 + 2HNO3 → 2NaNO3 + H2O + CO2
D NaOH + HNO3 → NaNO3 + H2O
21. An example of a redox reaction is shown.
2+ 2+
Zn + Cu Zn + Cu
Which statement about the reaction is correct?
2+
A Zn is the oxidising agent and it oxidises Cu .
2+
B Zn is the oxidising agent and it reduces Cu .
2+
C Zn is the reducing agent and it oxidises Cu .
2+
D Zn is the reducing agent and it reduces Cu .
22. Equations for reactions of iron and iron compounds are shown.
Fe + 2HCl → FeCl 2 +H2
2FeCl 2 + Cl 2 → 2FeCl 3
FeSO4 + Mg → Fe + MgSO4
FeSO4 + 2NaOH → Fe(OH)2 + Na2SO4
How many of these are redox reactions?
A 1 B 2 C 3 D 4
23. Aqueous potassium iodide, KI(aq), can be used as a test reagent in redox reactions.
Iodide ions are readily ……X…… . A positive result for the test is when the solution changes
colour from ……Y…… to ……Z…… .Which words correctly complete gaps X, Y and Z?
X Y Z
A oxidised brown colourless
B oxidised colourless brown
C reduced brown colourless
D reduced colourless brown
24. A colourless gas is passed into each of three different solutions. The results for each solution are
shown in the table.
solution result
potassium iodide stays colourless
acidified potassium dichromate(VI) orange to green
acidified potassium manganate(VII) purple to colourless
What is the colourless gas?
A an acid
B an alkali
C an oxidising agent
D a reducing agent
25. Which ionic equation represents a redox reaction?
+ –
A Ag + Cl → AgCl
2+
B Ba + SO4 2−→ BaSO4
+ –
C H + OH → H2O
2+ 2+
D Zn + Cu → Zn + Cu
26. The equation for the reaction between aluminium and copper(II) oxide is shown.
27. Which equation represents a redox reaction?
28. Which of the reactions show the underlined substance being reduced?
29. Which equation represents an oxidation reaction?
30. In which substance does the nitrogen atom have the same oxidation number as the nitrogen atom in HNO 3
1 (a) Displacement reactions occur between metals and metal ions. 0620/42/M/J/19/Q7
Displacement reactions can be used to determine the order of reactivity of metals such as lead
(Pb), nickel (Ni), and silver (Ag).
The ionic equation for a displacement reaction is shown.
Ni(s) + Pb2+(aq) Pb(s) + Ni2+(aq) The
ionic half-equations for this reaction are shown.
Ni(s) Ni2+(aq) + 2e–
Pb2+(aq) + 2e– Pb(s)
The ionic half-equations show that electrons are donated by nickel atoms and accepted by lead
ions.
(i) Identify the reducing agent in the displacement reaction. Give a reason for your answer.
reducing agent .....................................................................................................................
reason..................................................................................................................................
[2]
(ii) What is the general term given to the type of reaction in which electrons are transferred from
one species to another?
....................................................................................................................................... [1]
(b) The ionic equation for another displacement reaction is shown. 0620/42/M/J/18/Q3
Pb(s) + 2Ag+(aq) 2Ag(s) + Pb2+(aq)
Write the two ionic half-equations for this reaction.
1 .................................................................................................................................................
2 ................................................................................................................................................. [2]
(c) When chlorine gas is passed through aqueous potassium bromide, a redox reaction
occurs.
The ionic equation is shown.
Cl 2 + 2Br – 2Cl – + Br2
(i) Write an ionic half-equation showing what happens to the chlorine molecules, Cl 2,
in this reaction.
....................................................................................................................................... [1]
(ii) Explain why the bromide ions, Br –, act as reducing agents in this reaction.
.......................................................................................................................................
[1]
2. (a) When aqueous iron(II) ions are warmed with aqueous hydrogen peroxide, iron(III) ions are formed.
(i) Construct an ionic equation for the oxidation of iron( II) ions to iron(III) ions.
……………………………………………………………………………………………………… [1]
(ii) Describe a chemical test that can be used to confirm that iron(II) ions have been oxidised to form
iron( III) ions.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..............................................................................................................................[2]
(b) Aqueous hydrogen peroxide was added to acidified aqueous potassium manganate(VII).
The purple solution turned colourless. Aqueous hydrogen peroxide was added to acidified
aqueous potassium iodide. The colourless solution turned brown.
What deductions can you make about hydrogen peroxide from these two observations?
Explain your answer.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
......................................................................................................................................[2]
(c) A few drops of aqueous K2FeO4 are added to a test-tube containing 3 cm3 of aqueous potassium iodide.
The solution in the test-tube changes from colourless to pale brown. Given this information, what can you
deduce about the chemical properties of K2FeO4?
.................................................................................................................................... [1]
(d) Magnesium reacts with aqueous copper(II) sulfate.
Mg(s) + CuSO4(aq) MgSO4(aq) + Cu(s)
(i) Explain by referring to the equation, why this is a redox reaction.
...........................................................................................................................................
…………………………………………………………………………………………[2]
(ii)Construct the ionic equation for this reaction.
.......................................................................................................................................[1]
(e) When chlorine gas is bubbled through an aqueous solution of potassium iodide, a redox
reaction takes place.
2I –
+ Cl 2 → I2 + 2Cl –
(i) State the colour change expected in this reaction.
start colour .........................................................................................................................
. end colour...........................................................................................................................
[2]
(ii) Identify the reducing agent in this reaction. Explain your answer.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(iii) In the presence of sulfuric acid, hydrogen peroxide reacts with iodide ions to form iodine and
water. This involves the reduction of hydrogen peroxide.
What is the meaning of the term reduction ?
.......................................................................................................................................... [1]
3. (a) Iron can be obtained by heating iron(III) oxide with zinc powder. 0620/41/O/N/19/Q3
Fe2O3 + 3Zn 2Fe + 3ZnO
(i) What can be deduced about the reactivity of zinc from this reaction?
....................................................................................................................................... [1]
(ii) The ionic equation for this reaction is shown.
2Fe3+ + 3Zn 2Fe + 3Zn2+
Identify the oxidising agent in this reaction. Explain your answer in terms of electron
transfer.
oxidising agent ....................................................................................................................
explanation .........................................................................................................................
............................................................................................................................................. [2]
(iii) Name an oxidising agent which can be used to oxidise ethanol to ethanoic acid.
....................................................................................................................................... [2]
(c) The gas hydrogen sulfide, H2S, is produced when concentrated sulfuric acid is added to solid
potassium iodide. 0620/41/O/N/18/Q4
The reaction involves oxidation.
(i) Define the term oxidation in terms of electron transfer.
....................................................................................................................................... [1]
4. (a) When magnesium is added to aqueous copper(II) sulfate a reaction occurs. 0620/41/O/N/17/Q3
The ionic equation for the reaction is shown.
Mg + Cu2+ Mg2+ + Cu
(i) Give one change you would observe during this reaction.
....................................................................................................................................... [1]
(ii) Explain why this is a redox reaction.
.............................................................................................................................................
....................................................................................................................................... [1]
(iii) Identify the oxidising agent in this reaction. Give a reason for your answer.
.............................................................................................................................................
....................................................................................................................................... [2]
(iv) A redox reaction occurs when magnesium is heated with iron(III) oxide.
Write a chemical equation for the reaction between magnesium and iron(III) oxide.
....................................................................................................................................... [2]
